SUDOERS(5) | File Formats Manual | SUDOERS(5) |
NAME¶
sudoers
— default
sudo security policy plugin
DESCRIPTION¶
The sudoers
policy plugin determines a
user's sudo
privileges. It is the default
sudo
policy plugin. The policy is driven by the
/etc/sudoers file or, optionally, in LDAP. The
policy format is described in detail in the
SUDOERS FILE FORMAT section.
For information on storing sudoers
policy
information in LDAP, see sudoers.ldap(5).
Configuring sudo.conf for sudoers¶
sudo
consults the
sudo.conf(5) file to determine which plugins to load. If
no sudo.conf(5) file is present, or if it contains no
Plugin lines, sudoers
will be used
for auditing, policy decisions and I/O logging. To explicitly configure
sudo.conf(5) to use the sudoers
plugin, the following configuration can be used.
Plugin sudoers_audit sudoers.so Plugin sudoers_policy sudoers.so Plugin sudoers_io sudoers.so
Starting with sudo
1.8.5, it is possible
to specify optional arguments to the sudoers
plugin
in the sudo.conf(5) file. Plugin arguments, if any, should
be listed after the path to the plugin (i.e., after
sudoers.so). The arguments are only effective for
the plugin that opens (and parses) the sudoers file.
For sudo
version 1.9.1
and higher, this is the
sudoers_audit
plugin. For older versions, it is the
sudoers_policy
plugin. Multiple arguments may be specified, separated by white space. For
example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false
The following plugin arguments are supported:
- error_recovery=bool
- The
error_recovery
argument can be used to control whether
sudoers
should attempt to recover from syntax errors in the sudoers file. If set to true (the default),sudoers
will try to recover from a syntax error by discarding the portion of the line that contains the error until the end of the line. A value of false will disable error recovery. Prior to version 1.9.3, no error recovery was performed. - ldap_conf=pathname
- The ldap_conf argument can be used to override the default path to the ldap.conf file.
- ldap_secret=pathname
- The ldap_secret argument can be used to override the default path to the ldap.secret file.
- sudoers_file=pathname
- The sudoers_file argument can be used to override the default path to the sudoers file.
- sudoers_uid=user-ID
- The sudoers_uid argument can be used to override the default owner of the sudoers file. It should be specified as a numeric user-ID.
- sudoers_gid=group-ID
- The sudoers_gid argument can be used to override the default group of the sudoers file. It must be specified as a numeric group-ID (not a group name).
- sudoers_mode=mode
- The sudoers_mode argument can be used to override the default file mode for the sudoers file. It should be specified as an octal value.
For more information on configuring sudo.conf(5), refer to its manual.
User Authentication¶
The sudoers
security policy requires that
most users authenticate themselves before they can use
sudo
. A password is not required if the invoking
user is root, if the target user is the same as the
invoking user, or if the policy has disabled authentication for the user or
command. Unlike su(1), when
sudoers
requires authentication, it validates the
invoking user's credentials, not the target user's (or
root's) credentials. This can be
changed via the rootpw, targetpw and
runaspw flags, described later.
If a user who is not listed in the policy tries to run a command
via sudo
, mail is sent to the proper authorities.
The address used for such mail is configurable via the
mailto Defaults entry (described later) and defaults to
root.
No mail will be sent if an unauthorized user tries to run
sudo
with the -l
or
-v
option unless there is an authentication error
and either the mail_always or
mail_badpass flags are enabled. This allows users to
determine for themselves whether or not they are allowed to use
sudo
. By default, all attempts to run
sudo
(successful or not) are logged, regardless of
whether or not mail is sent.
If sudo
is run by root
and the SUDO_USER
environment variable is set, the
sudoers
policy will use this value to determine who
the actual user is. This can be used by a user to log commands through sudo
even when a root shell has been invoked. It also allows
the -e
option to remain useful even when invoked via
a sudo-run script or program. Note, however, that the
sudoers file lookup is still done for
root, not the user specified by
SUDO_USER
.
sudoers
uses per-user time stamp files for
credential caching. Once a user has been authenticated, a record is written
containing the user-ID that was used to authenticate, the terminal session
ID, the start time of the session leader (or parent process) and a time
stamp (using a monotonic clock if one is available). The user may then use
sudo
without a password for a short period of time
(15 minutes unless overridden by the timestamp_timeout
option). By default, sudoers
uses a separate record
for each terminal, which means that a user's login sessions are
authenticated separately. The timestamp_type option can be
used to select the type of time stamp record sudoers
will use.
Logging¶
By default, sudoers
logs both successful
and unsuccessful attempts (as well as errors). The
log_allowed
and
log_denied
flags can be used to control this behavior. Messages can be logged to
syslog(3), a log file, or both. The default is to log to
syslog(3) but this is configurable via the
syslog and logfile settings. See
EVENT LOGGING for a description of
the log file format.
sudoers
is also capable of running a
command in a pseudo-terminal and logging input and/or output. The standard
input, standard output, and standard error can be logged even when not
associated with a terminal. For more information about I/O logging, see the
I/O LOGGING section.
Starting with version 1.9, the log_servers
setting may be used to send event and I/O log data to a remote server
running sudo_logsrvd
or another service that
implements the protocol described by
sudo_logsrv.proto(5).
Command environment¶
Since environment variables can influence program behavior,
sudoers
provides a means to restrict which variables
from the user's environment are inherited by the command to be run. There
are two distinct ways sudoers
can deal with
environment variables.
By default, the env_reset flag is enabled. This
causes commands to be executed with a new, minimal environment. On AIX (and
Linux systems without PAM), the environment is initialized with the contents
of the /etc/environment file. The
HOME
, MAIL
,
SHELL
, LOGNAME
and
USER
environment variables are initialized based on
the target user and the SUDO_*
variables are set
based on the invoking user. Additional variables, such as
DISPLAY
, PATH
and
TERM
, are preserved from the invoking user's
environment if permitted by the env_check, or
env_keep options. A few environment variables are treated
specially. If the PATH
and
TERM
variables are not preserved from the user's
environment, they will be set to default values. The
LOGNAME
and USER
are handled
as a single entity. If one of them is preserved (or removed) from the user's
environment, the other will be as well. If LOGNAME
and USER
are to be preserved but only one of them is
present in the user's environment, the other will be set to the same value.
This avoids an inconsistent environment where one of the variables
describing the user name is set to the invoking user and one is set to the
target user. Environment variables with a value beginning with
‘()
’ are removed unless both the name
and value parts are matched by env_keep or
env_check, as they may be interpreted as functions by the
bash shell. Prior to version 1.8.11, such variables were
always removed.
If, however, the env_reset flag is disabled, any
variables not explicitly denied by the env_check and
env_delete options are allowed and their values are
inherited from the invoking process. Prior to version 1.8.21, environment
variables with a value beginning with
‘()
’ were always removed. Beginning
with version 1.8.21, a pattern in env_delete is used to
match bash shell functions instead. Since it is not
possible to block all potentially dangerous environment variables, use of
the default env_reset behavior is encouraged.
Environment variables specified by env_check,
env_delete, or env_keep may include one
or more ‘*
’ characters which will
match zero or more characters. No other wildcard characters are
supported.
By default, environment variables are matched by name. However, if
the pattern includes an equal sign
(‘=
’), both the variables name and
value must match. For example, a bash shell function could
be matched as follows:
env_keep += "BASH_FUNC_my_func%%=()*"
Without the ‘=()*
’ suffix,
this would not match, as bash shell functions are not
preserved by default.
The complete list of environment variables that are preserved or
removed, as modified by global Defaults parameters in
sudoers, is displayed when sudo
is
run by root with the -V
option.
The list of environment variables to remove varies based on the operating
system sudo
is running on.
Other sudoers
options
may influence the command environment, such as
always_set_home,
secure_path, set_logname, and
set_home.
On systems that support PAM where the
pam_env module is
enabled for sudo
, variables in the PAM environment
may be merged in to the environment. If a variable in the PAM environment is
already present in the user's environment, the value will only be overridden
if the variable was not preserved by sudoers
. When
env_reset is enabled, variables preserved from the
invoking user's environment by the env_keep list take
precedence over those in the PAM environment. When
env_reset is disabled, variables present the invoking
user's environment take precedence over those in the PAM environment unless
they match a pattern in the env_delete list.
The dynamic linker on most operating systems will remove variables
that can control dynamic linking from the environment of set-user-ID
executables, including sudo
. Depending on the
operating system this may include _RLD*
,
DYLD_*
, LD_*
,
LDR_*
, LIBPATH
,
SHLIB_PATH
, and others. These type of variables are
removed from the environment before sudo
even begins
execution and, as such, it is not possible for sudo
to preserve them.
As a special case, if the -i
option
(initial login) is specified, sudoers
will
initialize the environment regardless of the value of
env_reset. The DISPLAY
,
PATH
and TERM
variables
remain unchanged; HOME
,
MAIL
, SHELL
,
USER
, and LOGNAME
are set
based on the target user. On AIX (and Linux systems without PAM), the
contents of /etc/environment are also included. All
other environment variables are removed unless permitted by
env_keep or env_check, described
above.
Finally, the restricted_env_file and env_file files are applied, if present. The variables in restricted_env_file are applied first and are subject to the same restrictions as the invoking user's environment, as detailed above. The variables in env_file are applied last and are not subject to these restrictions. In both cases, variables present in the files will only be set to their specified values if they would not conflict with an existing environment variable.
SUDOERS FILE FORMAT¶
The sudoers file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).
The sudoers file grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.
Resource limits¶
By default, sudoers
uses the operating
system's native method of setting resource limits for the target user. On
Linux systems, resource limits are usually set by the
pam_limits.so PAM module. On some BSD systems, the
/etc/login.conf file specifies resource limits for
the user. On AIX systems, resource limits are configured in the
/etc/security/limits file. If there is no system
mechanism to set per-user resource limits, the command will run with the
same limits as the invoking user. The one exception to this is the core dump
file size, which is set by sudoers
to 0 by default.
Disabling core dumps by default makes it possible to avoid potential
security problems where the core file is treated as trusted input.
Resource limits may also be set in the
sudoers file itself, in which case they override those set
by the system. See the
rlimit_as,
rlimit_core,
rlimit_cpu,
rlimit_data,
rlimit_fsize,
rlimit_locks,
rlimit_memlock,
rlimit_nofile,
rlimit_nproc,
rlimit_rss,
rlimit_stack
options described below. Resource limits in sudoers
may be specified in one of the following formats:
- “value”
- Both the soft and hard resource limits are set to the same value. The special value “infinity” can be used to indicate that the value is unlimited.
- “soft,hard”
- Two comma-separated values. The soft limit is set to the first value and
the hard limit is set to the second. Both values must either be enclosed
in a set of double quotes, or the comma must be escaped with a backslash
(‘
\
’). The special value “infinity” may be used in place of either value. - “default”
- The default resource limit for the user will be used. This may be a
user-specific value (see above) or the value of the resource limit when
sudo
was invoked for systems that don't support per-user limits. - “user”
- The invoking user's resource limits will be preserved when running the command.
For example, to restore the historic core dump file size behavior, a line like the following may be used.
Defaults
rlimit_core=default
Resource limits in sudoers
are only
supported by version 1.8.7 or higher.
Quick guide to EBNF¶
EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up of production rules. For example:
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with “wildcard” characters, which have different meanings.
- ?
- Means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or not at all.
- *
- Means that the preceding symbol (or group of symbols) may appear zero or more times.
- +
- Means that the preceding symbol (or group of symbols) may appear one or more times.
Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name).
Aliases¶
There are four kinds of aliases: User_Alias,
Runas_Alias, Host_Alias and
Cmnd_Alias. Beginning with sudo
1.9.0,
Cmd_Alias
may be used in place of Cmnd_Alias if desired.
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* | 'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* | 'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* | 'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* | 'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* User_Alias ::= NAME User_Alias_Spec ::= User_Alias '=' User_List Runas_Alias ::= NAME Runas_Alias_Spec ::= Runas_Alias '=' Runas_List Host_Alias ::= NAME Host_Alias_Spec ::= Host_Alias '=' Host_List Cmnd_Alias ::= NAME Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where
Alias_Type is
one of User_Alias, Runas_Alias,
Host_Alias, or Cmnd_Alias. A
NAME
is a string of uppercase letters, numbers, and
underscore characters (‘_
’). A
NAME
must start
with an uppercase letter. It is possible to put several alias definitions of
the same type on a single line, joined by a colon
(‘:
’). For example:
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is possible to use the same name for aliases of different types, but this is not recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User | User ',' User_List User ::= '!'* user name | '!'* #user-ID | '!'* %group | '!'* %#group-ID | '!'* +netgroup | '!'* %:nonunix_group | '!'* %:#nonunix_gid | '!'* User_Alias
A User_List is made up of one or more user
names, user-IDs (prefixed with ‘#
’),
system group names and IDs (prefixed with
‘%
’ and
‘%#
’ respectively), netgroups
(prefixed with ‘+
’), non-Unix group
names and IDs (prefixed with ‘%:
’ and
‘%:#
’ respectively), and
User_Aliases. Each list item may be prefixed with zero or
more ‘!
’ operators. An odd number of
‘!
’ operators negate the value of the
item; an even number just cancel each other out. User netgroups are matched
using the user and domain members only; the host member is not used when
matching.
A user name, user-ID, group, group-ID, netgroup, nonunix_group or nonunix_gid may be enclosed in double quotes to avoid the need for escaping special characters. Alternately, special characters may be specified in escaped hex mode, e.g., \x20 for space. When using double quotes, any prefix characters must be included inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the underlying group provider plugin. For instance, the QAS AD plugin supports the following formats:
- Group in the same domain: "%:Group Name"
- Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
- Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
See GROUP PROVIDER PLUGINS for more information.
Quotes around group names are optional. Unquoted strings must use
a backslash (‘\
’) to escape spaces and
special characters. See
Other
special characters and reserved words for a list of characters that need
to be escaped.
Runas_List ::= Runas_Member | Runas_Member ',' Runas_List Runas_Member ::= '!'* user name | '!'* #user-ID | '!'* %group | '!'* %#group-ID | '!'* %:nonunix_group | '!'* %:#nonunix_gid | '!'* +netgroup | '!'* Runas_Alias | '!'* ALL
A Runas_List is similar to a User_List except that instead of User_Aliases it can contain Runas_Aliases. User names and groups are matched as strings. In other words, two users (groups) with the same user (group) ID are considered to be distinct. If you wish to match all user names with the same user-ID (e.g., root and toor), you can use a user-ID instead of a name (#0 in the example given). The user-ID or group-ID specified in a Runas_Member need not be listed in the password or group database.
Host_List ::= Host | Host ',' Host_List Host ::= '!'* host name | '!'* ip_addr | '!'* network(/netmask)? | '!'* +netgroup | '!'* Host_Alias | '!'* ALL
A Host_List is made up of one or more host
names, IP addresses, network numbers, netgroups (prefixed with
‘+
’), and other aliases. Again, the
value of an item may be negated with the
‘!
’ operator. Host netgroups are
matched using the host (both qualified and unqualified) and domain members
only; the user member is not used when matching. If you specify a network
number without a netmask, sudo
will query each of
the local host's network interfaces and, if the network number corresponds
to one of the hosts's network interfaces, will use the netmask of that
interface. The netmask may be specified either in standard IP address
notation (e.g., 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation
(number of bits, e.g., 24 or 64). A host name may include shell-style
wildcards (see the Wildcards section
below), but unless the hostname command on your machine
returns the fully qualified host name, you'll need to use the
fqdn flag for wildcards to be useful.
sudo
only inspects actual network interfaces; this
means that IP address 127.0.0.1 (localhost) will never match. Also, the host
name “localhost” will only match if that is the actual host
name, which is usually only the case for non-networked systems.
digest ::= [A-Fa-f0-9]+ | [A-Za-z0-9\+/=]+ Digest_Spec ::= "sha224" ':' digest | "sha256" ':' digest | "sha384" ':' digest | "sha512" ':' digest Digest_List ::= Digest_Spec | Digest_Spec ',' Digest_List Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List command name ::= regex | file name command ::= command name | command name args | command name regex | command name '""' | ALL Edit_Spec ::= "sudoedit" file name+ | "sudoedit" regex | "sudoedit" List_Spec ::= "list" Cmnd ::= Digest_List? '!'* command | '!'* directory | '!'* Edit_Spec | '!'* List_Spec | '!'* Cmnd_Alias
A Cmnd_List is a list of one or more
commands, directories, or aliases. A command is a fully qualified file name,
which may include shell-style wildcards (see the
Wildcards section below), or a regular
expression that starts with ‘^
’ and
ends with ‘$
’ (see the
Regular expressions section
below). A directory is a fully qualified path name ending in a
‘/
’. When you specify a directory in a
Cmnd_List, the user will be able to run any file within
that directory (but not in any sub-directories therein). If no command line
arguments are specified, the user may run the command with any arguments
they choose. Command line arguments can include wildcards or be a regular
expression that starts with ‘^
’ and
ends with ‘$
’. If the command line
arguments consist of ‘""
’,
the command may only be run with
no arguments.
If a Cmnd has associated command line arguments,
the arguments in the Cmnd must match those given by the
user on the command line. If the arguments in a Cmnd begin
with the ‘^
’ character, they will be
interpreted as a regular expression and matched accordingly. Otherwise,
shell-style wildcards are used when matching. Unless a regular expression is
specified, the following characters must be escaped with a
‘\
’ if they are used in command
arguments: ‘,
’,
‘:
’,
‘=
’,
‘\
’. To prevent arguments in a
Cmnd that begin with a
‘^
’ character from being interpreted
as a regular expression, the ‘^
’ must
be escaped with a ‘\
’.
There are two commands built into sudo
itself: “list” and “sudoedit”. Unlike other
commands, these two must be specified in the sudoers file
without a leading path.
The “list” built-in can be used to permit a user to
list another user's privileges with sudo
's
-U
option. For example, “sudo -l -U
otheruser”. A user with the “list” privilege is able to
list another user's privileges even if they don't have permission to run
commands as that user. By default, only root or a user with the ability to
run any command as either root or the specified user
on the current host may use the -U
option. No
command line arguments may be specified with the “list”
built-in.
The “sudoedit” built-in is used to permit a user to
run sudo
with the -e
option
(or as sudoedit
). It may take command line arguments
just as a normal command does. Unlike other commands,
“sudoedit” is built into sudo
itself
and must be specified in the sudoers file
without a leading path. If a leading path is present, for
example /usr/bin/sudoedit, the path name will be
silently converted to “sudoedit”. A fully-qualified path for
sudoedit
is treated as an error by
visudo
.
A command may be preceded by a Digest_List, a comma-separated list of one or more Digest_Spec entries. If a Digest_List is present, the command will only match successfully if it can be verified using one of the SHA-2 digests in the list. Starting with version 1.9.0, the ALL reserved word can be used in conjunction with a Digest_List. The following digest formats are supported: sha224, sha256, sha384, and sha512. The string may be specified in either hex or base64 format (base64 is more compact). There are several utilities capable of generating SHA-2 digests in hex format such as openssl, shasum, sha224sum, sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64 EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself
(directly or via a sudo
command), it may be possible
for the user to replace the command after the digest check has been
performed but before the command is executed. A similar race condition
exists on systems that lack the fexecve(2) system call
when the directory in which the command is located is writable by the user.
See the description of the fdexec setting for more
information on how sudo
executes commands that have
an associated digest.
Command digests are only supported by version 1.8.7 or higher.
Defaults¶
Certain configuration options may be changed from their default values at run-time via one or more Default_Entry lines. These may affect all users on any host, all users on a specific host, a specific user, a specific command, or commands being run as a specific user. Per-command entries may not include command line arguments. If you need to specify arguments, define a Cmnd_Alias and reference that instead.
Default_Type ::= 'Defaults' | 'Defaults' '@' Host_List | 'Defaults' ':' User_List | 'Defaults' '!' Cmnd_List | 'Defaults' '>' Runas_List Default_Entry ::= Default_Type Parameter_List Parameter_List ::= Parameter | Parameter ',' Parameter_List Parameter ::= Parameter '=' Value | Parameter '+=' Value | Parameter '-=' Value | '!'* Parameter
Parameters may be
flags,
integer
values,
strings,
or
lists.
Flags are implicitly boolean and can be turned off via the
‘!
’ operator. Some integer, string and
list parameters may also be used in a boolean context to disable them.
Values may be enclosed in double quotes ("") when they contain
multiple words. Special characters may be escaped with a backslash
(‘\
’).
To include a literal backslash character in a command line
argument you must escape the backslash twice. For example, to match
‘\n
’ as part of a command line
argument, you must use ‘\\\\n
’ in the
sudoers file. This is due to there being two levels of
escaping, one in the sudoers parser itself and another
when command line arguments are matched by the fnmatch(3)
or regexec(3) function.
Lists have two additional assignment operators,
‘+=
’ and
‘-=
’. These operators are used to add
to and delete from a list respectively. It is not an error to use the
‘-=
’ operator to remove an element
that does not exist in a list.
Defaults entries are parsed in the following order: global, host, user, and runas Defaults first, then command defaults. If there are multiple Defaults settings of the same type, the last matching setting is used. The following Defaults settings are parsed before all others since they may affect subsequent entries: fqdn, group_plugin, runas_default, sudoers_locale.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User specification¶
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \ (':' Host_List '=' Cmnd_Spec_List)* Cmnd_Spec_List ::= Cmnd_Spec | Cmnd_Spec ',' Cmnd_Spec_List Cmnd_Spec ::= Runas_Spec? Option_Spec* (Tag_Spec ':')* Cmnd Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')' Option_Spec ::= (SELinux_Spec | Date_Spec | Timeout_Spec | Chdir_Spec | Chroot_Spec) SELinux_Spec ::= ('ROLE=role' | 'TYPE=type') Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp') Timeout_Spec ::= 'TIMEOUT=timeout' Chdir_Spec ::= 'CWD=directory' Chroot_Spec ::= 'CHROOT=directory' Tag_Spec ::= ('EXEC' | 'NOEXEC' | 'FOLLOW' | 'NOFOLLOW' | 'LOG_INPUT' | 'NOLOG_INPUT' | 'LOG_OUTPUT' | 'NOLOG_OUTPUT' | 'MAIL' | 'NOMAIL' | 'INTERCEPT' | 'NOINTERCEPT' | 'PASSWD' | 'NOPASSWD' | 'SETENV' | 'NOSETENV')
A user specification determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as root (unless runas_default has been set to a different value) but this can also be changed on a per-command basis.
The basic structure of a user specification is “who where = (as_whom) what”. Let's break that down into its constituent parts:
Runas_Spec¶
A Runas_Spec determines the user and/or the
group that a command may be run as. A fully-specified
Runas_Spec consists of two Runas_Lists
(as defined above) separated by a colon
(‘:
’) and enclosed in a set of
parentheses. The first Runas_List indicates which users
the command may be run as via the -u
option. The
second defines a list of groups that may be specified via the
-g
option (in addition to any of the target user's
groups). If both Runas_Lists are specified, the command
may be run with any combination of users and groups listed in their
respective Runas_Lists. If only the first is specified,
the command may be run as any user in the list and, optionally, with any
group the target user belongs to. If the first Runas_List
is empty but the second is specified, the command may be run as the invoking
user with the group set to any listed in the Runas_List.
If both Runas_Lists are empty, the command may only be run
as the invoking user and the group, if specified, must be one that the
invoking user is a member of. If no Runas_Spec is
specified, the command may only be run as the
runas_default user (root by default) and
the group, if specified, must be one that the
runas_default user is a member of.
A Runas_Spec sets the default for the commands that follow it. What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the host boulder—but only as operator. For example:
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\ /usr/bin/lprm
While the group portion of the Runas_Spec permits the user to run as command with that group, it does not force the user to do so. If no group is specified on the command line, the command will run with the group listed in the target user's password database entry. The following would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls $ sudo -u operator -g operator /bin/ls $ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\ /usr/local/bin/minicom
In this example only the group will be set, the command still runs as user tcm. For example:
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a
Runas_Spec, in which case the user may select any
combination of users and groups via the -u
and
-g
options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally setting the group to operator or system.
Option_Spec¶
A Cmnd may have zero or more options associated with it. Options may consist of SELinux roles and/or types, start and/or end dates and command timeouts. Once an option is set for a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit that option unless it is overridden by another option. Option names are reserved words in sudoers. This means that none of the valid option names (see below) can be used when declaring an alias.
SELinux_Spec¶
On systems with SELinux support, sudoers file entries may optionally have an SELinux role and/or type associated with a command. This can be used to implement a form of role-based access control (RBAC). If a role or type is specified with the command it will override any default values specified in sudoers. A role or type specified on the command line, however, will supersede the values in sudoers.
Date_Spec¶
sudoers
rules can be specified with a
start and end date via the NOTBEFORE
and
NOTAFTER
settings. The time stamp must be specified
in “Generalized Time” as defined by RFC 4517. The format is
effectively ‘yyyymmddHHMMSSZ
’ where
the minutes and seconds are optional. The
‘Z
’ suffix indicates that the time
stamp is in Coordinated Universal Time (UTC). It is also possible to specify
a timezone offset from UTC in hours and minutes instead of a
‘Z
’. For example,
‘-0500
’ would correspond to Eastern
Standard time in the US. As an extension, if no
‘Z
’ or timezone offset is specified,
local time will be used.
The following are all valid time stamps:
20170214083000Z 2017021408Z 20160315220000-0500 20151201235900
Timeout_Spec¶
A command may have a timeout associated with it. If the timeout
expires before the command has exited, the command will be terminated. The
timeout may be specified in combinations of days, hours, minutes, and
seconds with a single-letter case-insensitive suffix that indicates the unit
of time. For example, a timeout of 7 days, 8 hours, 30 minutes, and 10
seconds would be written as
‘7d8h30m10s
’. If a number is specified
without a unit, seconds are assumed. Any of the days, minutes, hours, or
seconds may be omitted. The order must be from largest to smallest unit and
a unit may not be specified more than once.
The following are all
valid timeout
values: ‘7d8h30m10s
’,
‘14d
’,
‘8h30m
’,
‘600s
’,
‘3600
’. The following are
invalid
timeout values: ‘12m2w1d
’,
‘30s10m4h
’,
‘1d2d3h
’.
This setting is only supported by version 1.8.20 or higher.
Chdir_Spec¶
The working directory that the command will be run in can be
specified using the CWD
setting. The
directory must be a fully-qualified path name
beginning with a ‘/’ or ‘~’ character, or the
special value “*”. A value of “*” indicates that
the user may specify the working directory by running
sudo
with the -D
option. By
default, commands are run from the invoking user's current working
directory, unless the -i
option is given. Path names
of the form ~user/path/name are interpreted as being
relative to the named user's home directory. If the user name is omitted,
the path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Chroot_Spec¶
The root directory that the command will be run in can be
specified using the CHROOT
setting. The
directory must be a fully-qualified path name
beginning with a ‘/’ or ‘~’ character, or the
special value “*”. A value of “*” indicates that
the user may specify the root directory by running
sudo
with the -R
option.
This setting can be used to run the command in a chroot(2)
“sandbox” similar to the chroot(8) utility.
Path names of the form ~user/path/name are
interpreted as being relative to the named user's home directory. If the
user name is omitted, the path will be relative to the runas user's home
directory.
This setting is only supported by version 1.9.3 or higher.
Tag_Spec¶
A command may have zero or more tags associated with it. The
following tag values are supported: EXEC
,
NOEXEC
, FOLLOW
,
NOFOLLOW
, LOG_INPUT
,
NOLOG_INPUT
, LOG_OUTPUT
,
NOLOG_OUTPUT
, MAIL
,
NOMAIL
, INTERCEPT
,
NOINTERCEPT
, PASSWD
,
NOPASSWD
, SETENV
, and
NOSETENV
. Once a tag is set on a
Cmnd, subsequent Cmnds in the
Cmnd_Spec_List, inherit the tag unless it is overridden by
the opposite tag (in other words, PASSWD
overrides
NOPASSWD
and NOEXEC
overrides EXEC
).
EXEC
andNOEXEC
-
If
sudo
has been compiled with noexec support and the underlying operating system supports it, theNOEXEC
tag can be used to prevent a dynamically-linked executable from running further commands itself.In the following example, user aaron may run /usr/bin/more and /usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the Preventing shell escapes section below for more details on how
NOEXEC
works and whether or not it will work on your system. FOLLOW
andNOFOLLOW
-
Starting with version 1.8.15,
sudoedit
will not open a file that is a symbolic link unless the sudoedit_follow flag is enabled. TheFOLLOW
andNOFOLLOW
tags override the value of sudoedit_follow and can be used to permit (or deny) the editing of symbolic links on a per-command basis. These tags are only effective for the sudoedit command and are ignored for all other commands. LOG_INPUT
andNOLOG_INPUT
-
These tags override the value of the log_input flag on a per-command basis. For more information, see I/O LOGGING.
LOG_OUTPUT
andNOLOG_OUTPUT
-
These tags override the value of the log_output flag on a per-command basis. For more information, see I/O LOGGING.
MAIL
andNOMAIL
-
These tags provide fine-grained control over whether mail will be sent when a user runs a command by overriding the value of the mail_all_cmnds flag on a per-command basis. They have no effect when
sudo
is run with the-l
or-v
options. ANOMAIL
tag will also override the mail_always and mail_no_perms options. For more information, see the descriptions of mail_all_cmnds, mail_always, and mail_no_perms in the SUDOERS OPTIONS section below. PASSWD
andNOPASSWD
-
By default,
sudo
requires that a user authenticate before running a command. This behavior can be modified via theNOPASSWD
tag. Like a Runas_Spec, theNOPASSWD
tag sets a default for the commands that follow it in the Cmnd_Spec_List. Conversely, thePASSWD
tag can be used to reverse things. For example:ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as root on the machine “rushmore” without authenticating himself. If we only want ray to be able to run /bin/kill without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the
PASSWD
tag has no effect on users who are in the group specified by the exempt_group setting.By default, if the
NOPASSWD
tag is applied to any of a user's entries for the current host, the user will be able to run ‘sudo -l
’ without a password. Additionally, a user may only run ‘sudo -v
’ without a password if all of the user's entries for the current host have theNOPASSWD
tag. This behavior may be overridden via the verifypw and listpw options. SETENV
andNOSETENV
-
These tags override the value of the setenv flag on a per-command basis. If
SETENV
has been set for a command, the user may disable the env_reset flag from the command line via the-E
option. Additionally, environment variables set on the command line are not subject to the restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner. If the command matched is ALL, theSETENV
tag is implied for that command; this default may be overridden by use of theNOSETENV
tag. INTERCEPT
andNOINTERCEPT
-
If
sudo
has been compiled with intercept support and the underlying operating system supports it, theINTERCEPT
tag can be used to cause programs spawned by a command to be validated against sudoers and logged just like they would be if run throughsudo
directly. This is useful in conjunction with commands that allow shell escapes such as editors, shells, and paginators. There is additional overhead due to the policy check that may add latency when running commands such as shell scripts that execute a large number of sub-commands. For interactive commands, such as a shell or editor, the overhead is not usually noticeable.In the following example, user chuck may run any command on the machine “research” in intercept mode.
chuck research = INTERCEPT: ALL
See the Preventing shell escapes section below for more details on how
INTERCEPT
works and whether or not it will work on your system.
Wildcards¶
sudo
allows shell-style
wildcards (aka meta or glob characters) to be used in host
names, path names, and command line arguments in the
sudoers file. Wildcard matching is done via the
glob(3) and fnmatch(3) functions as
specified by IEEE Std 1003.1
(“POSIX.1”).
- *
- Matches any set of zero or more characters (including white space).
- ?
- Matches any single character (including white space).
- [...]
- Matches any character in the specified range.
- [!...]
- Matches any character not in the specified range.
- \x
- For any character ‘x’, evaluates to ‘x’. This
is used to escape special characters such as:
‘
*
’, ‘?
’, ‘[
’, and ‘]
’.
Character classes may be used if your system's
glob(3) and fnmatch(3) functions support
them. However, because the ‘:
’
character has special meaning in sudoers, it must be
escaped. For example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
A forward slash (‘/
’) will
not be matched by wildcards used in the file name portion
of the command. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get matched by wildcards since command line arguments may contain arbitrary strings and not just path names.
Wildcards can match any character, including white space. In most cases, it is safer to use a regular expression to match command line arguments. For more information, see Wildcards in command arguments below.
Exceptions to wildcard rules¶
The following exceptions apply to the above rules:
- ""
- If the empty string ‘
""
’ is the only command line argument in the sudoers file entry it means that command is not allowed to be run with any arguments. - sudoedit
- Command line arguments to the sudoedit built-in command
should always be path names, so a forward slash
(‘
/
’) will not be matched by a wildcard.
Regular expressions¶
Starting with version 1.9.10, it is possible to use regular
expressions for path names and command line arguments. Regular expressions
are more expressive than shell-style wildcards and are
usually safer because they provide a greater degree of control when
matching. The type of regular expressions supported by
sudoers
are POSIX extended regular expressions,
similar to those used by the egrep(1) utility. They are
usually documented in the regex(7) or
re_format(7) manual, depending on the system. As an
extension, if the regular expression begins with “(?i)”, it
will be matched in a case-insensitive manner.
In sudoers, regular expressions must start with
a ‘^
’ character and end with a
‘$
’. This makes it explicit what is,
or is not, a regular expression. Either the path name, the command line
arguments or both may be regular expressions. Because the path name and
arguments are matched separately, it is even possible to use wildcards for
the path name and regular expressions for the arguments. It is not possible
to use a single regular expression to match both the command and its
arguments. Regular expressions in sudoers are limited to
1024 characters.
There is no need to escape sudoers special
characters in a regular expression other than the pound sign
(‘#
’).
In the following example, user john can run the passwd(1) command as root on any host but is not allowed to change root's password. This kind of rule is impossible to express safely using wildcards.
john ALL = /usr/bin/passwd ^[a-zA-Z0-9_]+$,\ !/usr/bin/passwd root
It is also possible to use a regular expression in conjunction
with sudoedit
rules. The following rule would give
user bob the ability to edit the /etc/motd,
/etc/issue, and /etc/hosts
files only.
bob ALL = sudoedit ^/etc/(motd|issue|hosts)$
Regular expressions may also be used to match the command itself. In this example, a regular expression is used to allow user sid to run the /usr/sbin/groupadd, /usr/sbin/groupmod, /usr/sbin/groupdel, /usr/sbin/useradd, /usr/sbin/usermod, and /usr/sbin/userdel commands as root.
sid ALL = ^/usr/sbin/(group|user)(add|mod|del)$
One disadvantage of using a regular expression to
match the command name is that it is not possible to match relative paths
such as ./useradd or
../sbin/useradd. This has security implications when
a regular expression is used for the command name in conjunction with the
negation operator, ‘!
’, as such rules
can be trivially bypassed. Because of this, using a negated regular
expression for the command name is
strongly
discouraged. This does not apply to negated commands that only use a
regular expression to match the command arguments. See
Regular
expressions in command names below for more information.
Including other files from within sudoers¶
It is possible to include other sudoers files from within the sudoers file currently being parsed using the @include and @includedir directives. For compatibility with sudo versions prior to 1.9.1, #include and #includedir are also accepted.
An include file can be used, for example, to keep a site-wide sudoers file in addition to a local, per-machine file. For the sake of this example the site-wide sudoers file will be /etc/sudoers and the per-machine one will be /etc/sudoers.local. To include /etc/sudoers.local from within /etc/sudoers one would use the following line in /etc/sudoers:
@include /etc/sudoers.local
When sudo
reaches this line it will
suspend processing of the current file
(/etc/sudoers) and switch to
/etc/sudoers.local. Upon reaching the end of
/etc/sudoers.local, the rest of
/etc/sudoers will be processed. Files that are
included may themselves include other files. A hard limit of 128 nested
include files is enforced to prevent include file loops.
Starting with version 1.9.1, the path to the include file may
contain white space if it is escaped with a backslash
(‘\
’). Alternately, the entire path
may be enclosed in double quotes (""), in which case no escaping
is necessary. To include a literal backslash in the path,
‘\\
’ should be used.
If the path to the include file is not fully-qualified (does not
begin with a ‘/
’), it must be located
in the same directory as the sudoers file it was included from. For example,
if /etc/sudoers contains the line:
@include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the
‘%h
’ escape, signifying the short form
of the host name. In other words, if the machine's host name is
“xerxes”, then
@include /etc/sudoers.%h
will cause sudo
to include the file
/etc/sudoers.xerxes.
The @includedir directive can be used to create a sudoers.d directory that the system package manager can drop sudoers file rules into as part of package installation. For example, given:
@includedir /etc/sudoers.d
sudo
will suspend processing of the
current file and read each file in /etc/sudoers.d,
skipping file names that end in ‘~
’ or
contain a ‘.
’ character to avoid
causing problems with package manager or editor temporary/backup files.
Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed before /etc/sudoers.d/10_second. Be aware that because the sorting is lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second. Using a consistent number of leading zeroes in the file names can be used to avoid such problems. After parsing the files in the directory, control returns to the file that contained the @includedir directive.
Unlike files included via @include,
visudo
will not edit the files in a
@includedir directory unless one of them contains a syntax
error. It is still possible to run visudo
with the
-f
flag to edit the files directly, but this will
not catch the redefinition of an alias that is also
present in a different file.
Other special characters and reserved words¶
The pound sign (‘#
’) is used
to indicate a comment (unless it is part of a #include directive or unless
it occurs in the context of a user name and is followed by one or more
digits, in which case it is treated as a user-ID). Both the comment
character and any text after it, up to the end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever one might otherwise use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias. Attempting to define an alias named ALL will result in a syntax error. Using ALL can be dangerous since in a command context, it allows the user to run any command on the system.
The following option names permitted in an
Option_Spec are also considered reserved words:
CHROOT
, ROLE
,
TYPE
, TIMEOUT
,
CWD
, NOTBEFORE
and
NOTAFTER
. Attempting to define an
alias with the same name as one of the options will result
in a syntax error.
An exclamation point (‘!
’)
can be used as a logical not operator in a list or
alias as well as in front of a Cmnd.
This allows one to exclude certain values. For the
‘!
’ operator to be effective, there
must be something for it to exclude. For example, to match all users except
for root one would use:
ALL, !root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This is different from a true “negation” operator.
Note, however, that using a
‘!
’ in conjunction with the built-in
ALL alias to allow a user to run “all but a
few” commands rarely works as intended (see
SECURITY NOTES below).
Long lines can be continued with a backslash
(‘\
’) as the last character on the
line.
White space between elements in a list as well as special
syntactic characters in a User Specification
(‘=
’,
‘:
’,
‘(
’,
‘)
’) is optional.
The following characters must be escaped with a backslash
(‘\
’) when used as part of a word
(e.g., a user name or host name): ‘!
’,
‘=
’,
‘:
’,
‘,
’,
‘(
’,
‘)
’,
‘\
’.
SUDOERS OPTIONS¶
sudo
's behavior can be modified by
Default_Entry lines, as explained earlier. A list of all
supported Defaults parameters, grouped by type, are listed below.
- always_query_group_plugin
- If a group_plugin is configured, use it to resolve
groups of the form ‘
%group
’ as long as there is not also a system group of the same name. Normally, only groups of the form ‘%:group
’ are passed to the group_plugin. This flag is off by default. - always_set_home
- If enabled,
sudo
will set theHOME
environment variable to the home directory of the target user (which is the runas_default user unless the-u
option is used). This flag is largely obsolete and has no effect unless the env_reset flag has been disabled orHOME
is present in the env_keep list, both of which are strongly discouraged. This flag is off by default. - authenticate
- If set, users must authenticate themselves via a password (or other means
of authentication) before they may run commands. This default may be
overridden via the
PASSWD
andNOPASSWD
tags. This flag is on by default. - case_insensitive_group
- If enabled, group names in sudoers will be matched in a case insensitive manner. This may be necessary when users are stored in LDAP or AD. This flag is on by default.
- case_insensitive_user
- If enabled, user names in sudoers will be matched in a case insensitive manner. This may be necessary when groups are stored in LDAP or AD. This flag is on by default.
- closefrom_override
- If set, the user may use the
-C
option which overrides the default starting point at whichsudo
begins closing open file descriptors. This flag is off by default. - compress_io
- If set, and
sudo
is configured to log a command's input or output, the I/O logs will be compressed using zlib. This flag is on by default whensudo
is compiled with zlib support. - exec_background
- By default,
sudo
runs a command as the foreground process as long assudo
itself is running in the foreground. When the exec_background flag is enabled and the command is being run in a pseudo-terminal (due to I/O logging or the use_pty flag), the command will be run as a background process. Attempts to read from the controlling terminal (or to change terminal settings) will result in the command being suspended with theSIGTTIN
signal (orSIGTTOU
in the case of terminal settings). If this happens whensudo
is a foreground process, the command will be granted the controlling terminal and resumed in the foreground with no user intervention required. The advantage of initially running the command in the background is thatsudo
need not read from the terminal unless the command explicitly requests it. Otherwise, any terminal input must be passed to the command, whether it has required it or not (the kernel buffers terminals so it is not possible to tell whether the command really wants the input). This is different from historic sudo behavior or when the command is not being run in a pseudo-terminal.For this to work seamlessly, the operating system must support the automatic restarting of system calls. Unfortunately, not all operating systems do this by default, and even those that do may have bugs. For example, macOS fails to restart the tcgetattr(3) and tcsetattr(3) functions (this is a bug in macOS). Furthermore, because this behavior depends on the command stopping with the
SIGTTIN
orSIGTTOU
signals, programs that catch these signals and suspend themselves with a different signal (usuallySIGTOP
) will not be automatically foregrounded. Some versions of the linux su(1) command behave this way. This flag is off by default.This setting is only supported by version 1.8.7 or higher. It has no effect unless I/O logging is enabled or the use_pty flag is enabled.
- env_editor
- If set,
visudo
will use the value of theSUDO_EDITOR
,VISUAL
orEDITOR
environment variables before falling back on the default editor list.visudo
is typically run as root so this flag may allow a user withvisudo
privileges to run arbitrary commands as root without logging. An alternative is to place a colon-separated list of “safe” editors int the editor setting.visudo
will then only useSUDO_EDITOR
,VISUAL
orEDITOR
if they match a value specified in editor. If the env_reset flag is enabled, theSUDO_EDITOR
,VISUAL
and/orEDITOR
environment variables must be present in the env_keep list for the env_editor flag to function whenvisudo
is invoked viasudo
. This flag is on by default. - env_reset
- If set,
sudo
will run the command in a minimal environment containing theTERM
,PATH
,HOME
,MAIL
,SHELL
,LOGNAME
,USER
andSUDO_*
variables. Any variables in the caller's environment or in the file specified by the restricted_env_file setting that match the env_keep and env_check lists are then added, followed by any variables present in the file specified by the env_file setting (if any). The contents of the env_keep and env_check lists, as modified by global Defaults parameters in sudoers, are displayed whensudo
is run by root with the-V
option. If the secure_path setting is enabled, its value will be used for thePATH
environment variable. This flag is on by default. - fast_glob
- Normally,
sudo
uses the glob(3) function to do shell-style globbing when matching path names. However, since it accesses the file system, glob(3) can take a long time to complete for some patterns, especially when the pattern references a network file system that is mounted on demand (auto mounted). The fast_glob flag causessudo
to use the fnmatch(3) function, which does not access the file system to do its matching. The disadvantage of fast_glob is that it is unable to match relative paths such as ./ls or ../bin/ls. This has security implications when path names that include globbing characters are used with the negation operator, ‘!
’, as such rules can be trivially bypassed. As such, this flag should not be used when the sudoers file contains rules that contain negated path names which include globbing characters. This flag is off by default. - log_passwords
- Most programs that require a user's password will disable echo before
reading the password to avoid displaying the plaintext password on the
screen. However, if terminal input is being logged (see
I/O LOGGING), the password will
still be present in the I/O log. If the log_passwords
option is disabled,
sudoers
will attempt to prevent passwords from being logged. It does this by using the regular expressions in passprompt_regex to match a password prompt in the terminal output buffer. When a match is found, input characters in the I/O log will be replaced with ‘*
’ until either a line feed or carriage return is found in the terminal input or a new terminal output buffer is received. If, however, a program displays characters as the user types (such assudo
when pwfeedback is set), only the first character of the password will be replaced in the I/O log. This option has no effect unless log_input or log_ttyin are also set. This flag is on by default.This setting is only supported by version 1.9.10 or higher.
- fqdn
- Set this flag if you want to put fully qualified host names in the
sudoers file when the local host name (as returned by
the ‘
hostname
’ command) does not contain the domain name. In other words, instead of myhost you would use myhost.mydomain.edu. You may still use the short form if you wish (and even mix the two). This flag is only effective when the “canonical” host name, as returned by the getaddrinfo(3) or gethostbyname(3) function, is a fully-qualified domain name. This is usually the case when the system is configured to use DNS for host name resolution.If the system is configured to use the /etc/hosts file in preference to DNS, the “canonical” host name may not be fully-qualified. The order that sources are queried for host name resolution is usually specified in the /etc/nsswitch.conf, /etc/netsvc.conf, /etc/host.conf, or, in some cases, /etc/resolv.conf file. In the /etc/hosts file, the first host name of the entry is considered to be the “canonical” name; subsequent names are aliases that are not used by
sudoers
. For example, the following hosts file line for the machine “xyzzy” has the fully-qualified domain name as the “canonical” host name, and the short version as an alias.192.168.1.1 xyzzy.sudo.ws xyzzy
If the machine's hosts file entry is not formatted properly, the fqdn flag will not be effective if it is queried before DNS.
Beware that when using DNS for host name resolution, turning on fqdn requires
sudoers
to make DNS lookups which renderssudo
unusable if DNS stops working (for example if the machine is disconnected from the network). Just like with the hosts file, you must use the “canonical” name as DNS knows it. That is, you may not use a host alias (CNAME entry) due to performance issues and the fact that there is no way to get all aliases from DNS.This flag is on by default.
- ignore_audit_errors
- Allow commands to be run even if
sudoers
cannot write to the audit log. If enabled, an audit log write failure is not treated as a fatal error. If disabled, a command may only be run after the audit event is successfully written. This flag is only effective on systems for whichsudoers
supports audit logging, including FreeBSD, Linux, macOS, and Solaris. This flag is on by default. - ignore_dot
- If set,
sudo
will ignore "." or "" (both denoting the current directory) in thePATH
environment variable; thePATH
itself is not modified. This flag is off by default. - ignore_iolog_errors
- Allow commands to be run even if
sudoers
cannot write to the I/O log (local or remote). If enabled, an I/O log write failure is not treated as a fatal error. If disabled, the command will be terminated if the I/O log cannot be written to. This flag is off by default. - ignore_logfile_errors
- Allow commands to be run even if
sudoers
cannot write to the log file. If enabled, a log file write failure is not treated as a fatal error. If disabled, a command may only be run after the log file entry is successfully written. This flag only has an effect whensudoers
is configured to use file-based logging via the logfile setting. This flag is on by default. - ignore_local_sudoers
- If set via LDAP, parsing of /etc/sudoers will be
skipped. This is intended for sites that wish to prevent the usage of
local sudoers files so that only LDAP is used. This thwarts the efforts of
rogue operators who would attempt to add roles to
/etc/sudoers. When this flag is enabled,
/etc/sudoers does not even need to exist. Since
this flag tells
sudo
how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for the ‘cn=defaults
’ section. This flag is off by default. - ignore_unknown_defaults
- If set,
sudo
will not produce a warning if it encounters an unknown Defaults entry in the sudoers file or an unknown sudoOption in LDAP. This flag is off by default. - insults
- If set,
sudo
will insult users when they enter an incorrect password. This flag is off by default. - log_allowed
- If set,
sudoers
will log commands allowed by the policy to the system audit log (where supported) as well as to syslog and/or a log file. This flag is on by default.This setting is only supported by version 1.8.29 or higher.
- log_denied
- If set,
sudoers
will log commands denied by the policy to the system audit log (where supported) as well as to syslog and/or a log file. This flag is on by default.This setting is only supported by version 1.8.29 or higher.
- log_exit_status
- If set,
sudoers
will log the exit value of commands that are run to syslog and/or a log file. If a command was terminated by a signal, the signal name is logged as well. This flag is off by default.This setting is only supported by version 1.9.8 or higher.
- log_host
- If set, the host name will be included in log entries written to the file configured by the logfile setting. This flag is off by default.
- log_input
- If set,
sudo
will run the command in a pseudo-terminal (ifsudo
was run from a terminal) and log all user input. If the standard input is not connected to the user's terminal, due to I/O redirection or because the command is part of a pipeline, that input is also logged. For more information about I/O logging, see the I/O LOGGING section. This flag is off by default. - log_output
- If set,
sudo
will run the command in a pseudo-terminal (ifsudo
was run from a terminal) and log all output that is sent to the user's terminal, the standard output or the standard error. If the standard output or standard error is not connected to the user's terminal, due to I/O redirection or because the command is part of a pipeline, that output is also logged. For more information about I/O logging, see the I/O LOGGING section. This flag is off by default. - log_server_keepalive
- If set,
sudo
will enable the TCP keepalive socket option on the connection to the log server. This enables the periodic transmission of keepalive messages to the server. If the server does not respond to a message, the connection will be closed and the running command will be terminated unless the ignore_iolog_errors flag (I/O logging enabled) or the ignore_log_errors flag (I/O logging disabled) is set. This flag is on by default.This setting is only supported by version 1.9.0 or higher.
- log_server_verify
- If set, the server certificate received during the TLS handshake must be
valid and it must contain either the server name (from
log_servers) or its IP address. If either of these
conditions is not met, the TLS handshake will fail. This flag is
on by default.
This setting is only supported by version 1.9.0 or higher.
- log_stderr
- If set,
sudo
will log the standard error if it is not connected to the user's terminal. This can be used to log output to a pipe or redirected to a file. This flag is off by default but is enabled when either the log_output flag or theLOG_OUTPUT
command tag is set. - log_stdin
- If set,
sudo
will log the standard input if it is not connected to the user's terminal. This can be used to log input from a pipe or redirected from a file. This flag is off by default but is enabled when either the log_input flag or theLOG_INPUT
command tag is set. - log_stdout
- If set,
sudo
will log the standard output if it is not connected to the user's terminal. This can be used to log output to a pipe or redirected to a file. This flag is off by default but is enabled when either the log_output flag or theLOG_OUTPUT
command tag is set. - log_subcmds
- If set,
sudoers
will log when a command spawns a child process and executes a program using the execve(2), execl(3), execle(3), execlp(3), execv(3), execvp(3), execvpe(3), or system(3) library functions. For example, if a shell is run bysudo
, the individual commands run via the shell will be logged. This flag is off by default.The log_subcmds flag uses the same underlying mechanism as the intercept setting. See Preventing shell escapes for more information on what systems support this option and its limitations. This setting is only supported by version 1.9.8 or higher and is incompatible with SELinux RBAC support unless the system supports seccomp(2) filter mode.
- log_ttyin
- If set,
sudo
will run the command in a pseudo-terminal and log user keystrokes sent to the user's terminal, if one is present. This flag is off by default but is enabled when either the log_input flag or theLOG_INPUT
command tag is set. If no terminal is present, for example when running a remote command using ssh(1), this flag will have no effect. - log_ttyout
- If set,
sudo
will run the command in a pseudo-terminal and log all output displayed on the user's terminal, if one is present. This flag is off by default but is enabled when either the log_output flag or theLOG_OUTPUT
command tag is set. If no terminal is present, for example when running a remote command using ssh(1), this flag will have no effect. - log_year
- If set, the four-digit year will be logged in the (non-syslog)
sudo
log file. This flag is off by default. - long_otp_prompt
- When validating with a One Time Password (OTP) scheme such as S/Key or OPIE, a two-line prompt is used to make it easier to cut and paste the challenge to a local window. It's not as pretty as the default but some people find it more convenient. This flag is off by default.
- mail_all_cmnds
- Send mail to the mailto user every time a user attempts
to run a command via
sudo
(this includessudoedit
). No mail will be sent if the user runssudo
with the-l
or-v
option unless there is an authentication error and the mail_badpass flag is also set. This flag is off by default. - mail_always
- Send mail to the mailto user every time a user runs
sudo
. This flag is off by default. - mail_badpass
- Send mail to the mailto user if the user running
sudo
does not enter the correct password. If the command the user is attempting to run is not permitted bysudoers
and one of the mail_all_cmnds, mail_always, mail_no_host, mail_no_perms or mail_no_user flags are set, this flag will have no effect. This flag is off by default. - mail_no_host
- If set, mail will be sent to the mailto user if the invoking user exists in the sudoers file, but is not allowed to run commands on the current host. This flag is off by default.
- mail_no_perms
- If set, mail will be sent to the mailto user if the
invoking user is allowed to use
sudo
but the command they are trying is not listed in their sudoers file entry or is explicitly denied. This flag is off by default. - mail_no_user
- If set, mail will be sent to the mailto user if the invoking user is not in the sudoers file. This flag is on by default.
- match_group_by_gid
- By default,
sudoers
will look up each group the user is a member of by group-ID to determine the group name (this is only done once). The resulting list of the user's group names is used when matching groups listed in the sudoers file. This works well on systems where the number of groups listed in the sudoers file is larger than the number of groups a typical user belongs to. On systems where group lookups are slow, where users may belong to a large number of groups, or where the number of groups listed in the sudoers file is relatively small, it may be prohibitively expensive and running commands viasudo
may take longer than normal. On such systems it may be faster to use the match_group_by_gid flag to avoid resolving the user's group-IDs to group names. In this case,sudoers
must look up any group name listed in the sudoers file and use the group-ID instead of the group name when determining whether the user is a member of the group.If match_group_by_gid is enabled, group database lookups performed by
sudoers
will be keyed by group name as opposed to group-ID. On systems where there are multiple sources for the group database, it is possible to have conflicting group names or group-IDs in the local /etc/group file and the remote group database. On such systems, enabling or disabling match_group_by_gid can be used to choose whether group database queries are performed by name (enabled) or ID (disabled), which may aid in working around group entry conflicts.The match_group_by_gid flag has no effect when sudoers data is stored in LDAP. This flag is off by default.
This setting is only supported by version 1.8.18 or higher.
- intercept
- If set, all commands run via
sudo
will behave as if theINTERCEPT
tag has been set, unless overridden by anNOINTERCEPT
tag. See the description ofINTERCEPT and NOINTERCEPT
above as well as the Preventing shell escapes section at the end of this manual. This flag is off by default.This setting is only supported by version 1.9.8 or higher and is incompatible with SELinux RBAC support unless the system supports seccomp(2) filter mode.
- intercept_allow_setid
- On most systems, the dynamic loader will ignore
LD_PRELOAD
(or the equivalent) when running set-user-ID and set-group-ID programs, effectively disabling intercept mode. To prevent this from happening,sudoers
will not permit a set-user-ID or set-group-ID program to be run in intercept mode unless intercept_allow_setid is enable. This flag has no effect unless the intercept flag is enabled or theINTERCEPT
tag has been set for the command. This flag is on by default when the intercept_type option is set to trace, otherwise it default to off.This setting is only supported by version 1.9.8 or higher.
- intercept_authenticate
- If set, commands run by an intercepted process must be authenticated when
the user's time stamp is not current. For example, if a shell is run with
intercept enabled, as soon as the invoking user's time
stamp is out of date, subsequent commands will need to be authenticated.
This flag has no effect unless the intercept flag is
enabled or the
INTERCEPT
tag has been set for the command. This flag is off by default.This setting is only supported by version 1.9.8 or higher.
- intercept_verify
- If set,
sudo
will attempt to verify that a command run in intercept mode has the expected path name, command line arguments and environment.The process will be stopped after execve(2) has completed but before the new command has had a chance to run. To verify the command,
sudo
will read the command's path from /proc/PID/exe, the command line arguments and environment from the process's memory, and compare them against the arguments that were passed to execve(2). In the event of a mismatch, the command will be sent aSIGKILL
signal and terminated.This can help prevent a time of check versus time of use issue with intercept mode where the execve(2) arguments could be altered after the
sudoers
policy check. The checks can only be performed if the proc(5) file system is available. This flag has no effect unless the intercept flag is enabled or theINTERCEPT
tag has been set for the command and the intercept_type option is set to trace. This flag is on by default.This setting is only supported by version 1.9.12 or higher.
- netgroup_tuple
- If set, netgroup lookups will be performed using the full netgroup tuple:
host name, user name, and domain (if one is set). Historically,
sudo
only matched the user name and domain for netgroups used in a User_List and only matched the host name and domain for netgroups used in a Host_List. This flag is off by default. - noexec
- If set, all commands run via
sudo
will behave as if theNOEXEC
tag has been set, unless overridden by anEXEC
tag. See the description ofEXEC and NOEXEC
above as well as the Preventing shell escapes section at the end of this manual. This flag is off by default. - noninteractive_auth
- If set, authentication will be attempted even in non-interactive mode
(when
sudo
's-n
option is specified). This allows authentication methods that don't require user interaction to succeed. Authentication methods that require input from the user's terminal will still fail. If disabled, authentication will not be attempted in non-interactive mode. This flag is off by default.This setting is only supported by version 1.9.10 or higher.
- pam_acct_mgmt
- On systems that use PAM for authentication,
sudo
will perform PAM account validation for the invoking user by default. The actual checks performed depend on which PAM modules are configured. If enabled, account validation will be performed regardless of whether or not a password is required. This flag is on by default.This setting is only supported by version 1.8.28 or higher.
- pam_rhost
- On systems that use PAM for authentication,
sudo
will set the PAM remote host value to the name of the local host when the pam_rhost flag is enabled. On Linux systems, enabling pam_rhost may result in DNS lookups of the local host name when PAM is initialized. On Solaris versions prior to Solaris 8, pam_rhost must be enabled if pam_ruser is also enabled to avoid a crash in the Solaris PAM implementation.This flag is off by default on systems other than Solaris.
This setting is only supported by version 1.9.0 or higher.
- pam_ruser
- On systems that use PAM for authentication,
sudo
will set the PAM remote user value to the name of the user that invoked sudo when the pam_ruser flag is enabled. This flag is on by default.This setting is only supported by version 1.9.0 or higher.
- pam_session
- On systems that use PAM for authentication,
sudo
will create a new PAM session for the command to be run in. Unlesssudo
is given the-i
or-s
options, PAM session modules are run with the “silent” flag enabled. This prevents last login information from being displayed for every command on some systems. Disabling pam_session may be needed on older PAM implementations or on operating systems where opening a PAM session changes the utmp or wtmp files. If PAM session support is disabled, resource limits may not be updated for the command being run. If pam_session, pam_setcred, and use_pty are disabled, log_servers has not been set and I/O logging has not been configured,sudo
will execute the command directly instead of running it as a child process. This flag is on by default.This setting is only supported by version 1.8.7 or higher.
- pam_setcred
- On systems that use PAM for authentication,
sudo
will attempt to establish credentials for the target user by default, if supported by the underlying authentication system. One example of a credential is a Kerberos ticket. If pam_session, pam_setcred, and use_pty are disabled, log_servers has not been set and I/O logging has not been configured,sudo
will execute the command directly instead of running it as a child process. This flag is on by default.This setting is only supported by version 1.8.8 or higher.
- passprompt_override
- If set, the prompt specified by passprompt or the
SUDO_PROMPT
environment variable will always be used and will replace the prompt provided by a PAM module or other authentication method. This flag is off by default. - path_info
- Normally,
sudo
will tell the user when a command could not be found in theirPATH
environment variable. Some sites may wish to disable this as it could be used to gather information on the location of executables that the normal user does not have access to. The disadvantage is that if the executable is simply not in the user'sPATH
,sudo
will tell the user that they are not allowed to run it, which can be confusing. This flag is on by default. - preserve_groups
- By default,
sudo
will initialize the group vector to the list of groups the target user is in. When preserve_groups is set, the user's existing group vector is left unaltered. The real and effective group-IDs, however, are still set to match the target user. This flag is off by default. - pwfeedback
- By default,
sudo
reads the password like most other Unix programs, by turning off echo until the user hits the return (or enter) key. Some users become confused by this as it appears to them thatsudo
has hung at this point. When pwfeedback is set,sudo
will provide visual feedback when the user presses a key. This does have a security impact as an onlooker may be able to determine the length of the password being entered. This flag is off by default. - requiretty
- If set,
sudo
will only run when the user is logged in to a real tty. When this flag is set,sudo
can only be run from a login session and not via other means such as cron(8) or cgi-bin scripts. This flag is off by default. - root_sudo
- If set, root is allowed to run
sudo
too. Disabling this prevents users from “chaining”sudo
commands to get a root shell by doing something like ‘sudo sudo /bin/sh
’. Note, however, that turning off root_sudo will also prevent root from runningsudoedit
. Disabling root_sudo provides no real additional security; it exists purely for historical reasons. This flag is on by default. - rootpw
- If set,
sudo
will prompt for the root password instead of the password of the invoking user when running a command or editing a file. This flag is off by default. - runas_allow_unknown_id
- If enabled, allow matching of runas user and group IDs that are not
present in the password or group databases. In addition to explicitly
matching unknown user or group IDs in a Runas_List, this
option also allows the ALL alias to match unknown IDs.
This flag is off by default.
This setting is only supported by version 1.8.30 or higher. Older versions of
sudo
always allowed matching of unknown user and group IDs. - runas_check_shell
- If enabled,
sudo
will only run commands as a user whose shell appears in the /etc/shells file, even if the invoking user's Runas_List would otherwise permit it. If no /etc/shells file is present, a system-dependent list of built-in default shells is used. On many operating systems, system users such as “bin”, do not have a valid shell and this flag can be used to prevent commands from being run as those users. This flag is off by default.This setting is only supported by version 1.8.30 or higher.
- runaspw
- If set,
sudo
will prompt for the password of the user defined by the runas_default option (defaults to root) instead of the password of the invoking user when running a command or editing a file. This flag is off by default. - selinux
- If enabled, the user may specify an SELinux role and/or type to use when running the command, as permitted by the SELinux policy. If SELinux is disabled on the system, this flag has no effect. This flag is on by default.
- set_home
- If enabled and
sudo
is invoked with the-s
option, theHOME
environment variable will be set to the home directory of the target user (which is the runas_default user unless the-u
option is used). This flag is largely obsolete and has no effect unless the env_reset flag has been disabled orHOME
is present in the env_keep list, both of which are strongly discouraged. This flag is off by default. - set_logname
- Normally,
sudo
will set theLOGNAME
andUSER
environment variables to the name of the target user (the user specified by runas_default unless the-u
option is given). However, since some programs (including the RCS revision control system) useLOGNAME
to determine the real identity of the user, it may be desirable to change this behavior. This can be done by negating the set_logname option. The set_logname option will have no effect if the env_reset option has not been disabled and the env_keep list containsLOGNAME
orUSER
. This flag is on by default. - set_utmp
- When enabled,
sudo
will create an entry in the utmp (or utmpx) file when a pseudo-terminal is allocated. A pseudo-terminal is allocated bysudo
when it is running in a terminal and one or more of the log_input, log_output, log_stdin, log_stdout, log_stderr, log_ttyin, log_ttyout, or use_pty flags is enabled. By default, the new entry will be a copy of the user's existing utmp entry (if any), with the tty, time, type, and pid fields updated. This flag is on by default. - setenv
- Allow the user to disable the env_reset option from the
command line via the
-E
option. Additionally, environment variables set via the command line are not subject to the restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner. This flag is off by default. - shell_noargs
- If set and
sudo
is invoked with no arguments it acts as if the-s
option had been given. That is, it runs a shell as root (the shell is determined by theSHELL
environment variable if it is set, falling back on the shell listed in the invoking user's /etc/passwd entry if not). This flag is off by default. - stay_setuid
- Normally, when
sudo
executes a command the real and effective user-IDs are set to the target user (root by default). This option changes that behavior such that the real user-ID is left as the invoking user's user-ID. In other words, this makessudo
act as a set-user-ID wrapper. This can be useful on systems that disable some potentially dangerous functionality when a program is run set-user-ID. This option is only effective on systems that support either the setreuid(2) or setresuid(2) system call. This flag is off by default. - sudoedit_checkdir
- If set,
sudoedit
will check all directory components of the path to be edited for writability by the invoking user. Symbolic links will not be followed in writable directories andsudoedit
will refuse to edit a file located in a writable directory. These restrictions are not enforced whensudoedit
is run by root. On some systems, if all directory components of the path to be edited are not readable by the target user,sudoedit
will be unable to edit the file. This flag is on by default.This setting was first introduced in version 1.8.15 but initially suffered from a race condition. The check for symbolic links in writable intermediate directories was added in version 1.8.16.
- sudoedit_follow
- By default,
sudoedit
will not follow symbolic links when opening files. The sudoedit_follow option can be enabled to allowsudoedit
to open symbolic links. It may be overridden on a per-command basis by theFOLLOW
andNOFOLLOW
tags. This flag is off by default.This setting is only supported by version 1.8.15 or higher.
- syslog_pid
- When logging via syslog(3), include the process ID in
the log entry. This flag is off by default.
This setting is only supported by version 1.8.21 or higher.
- targetpw
- If set,
sudo
will prompt for the password of the user specified by the-u
option (defaults to the value of runas_default) instead of the password of the invoking user when running a command or editing a file. This flag precludes the use of a user-ID not listed in the passwd database as an argument to the-u
option. This flag is off by default. - tty_tickets
- If set, users must authenticate on a per-tty basis. With this flag
enabled,
sudo
will use a separate record in the time stamp file for each terminal. If disabled, a single record is used for all login sessions.This option has been superseded by the timestamp_type option.
- umask_override
- If set,
sudo
will set the umask as specified in the sudoers file without modification. This makes it possible to specify a umask in the sudoers file that is more permissive than the user's own umask and matches historical behavior. If umask_override is not set,sudo
will set the umask to be the union of the user's umask and what is specified in sudoers. This flag is off by default. - use_netgroups
- If set, netgroups (prefixed with
‘
+
’), may be used in place of a user or host. For LDAP-based sudoers, netgroup support requires an expensive sub-string match on the server unless the NETGROUP_BASE directive is present in the /etc/ldap.conf file. If netgroups are not needed, this option can be disabled to reduce the load on the LDAP server. This flag is on by default. - use_pty
- If set, and
sudo
is running in a terminal, the command will be run in a pseudo-terminal (even if no I/O logging is being done). If thesudo
process is not attached to a terminal, use_pty has no effect.A malicious program run under
sudo
may be capable of injecting commands into the user's terminal or running a background process that retains access to the user's terminal device even after the main program has finished executing. By running the command in a separate pseudo-terminal, this attack is no longer possible. This flag is off by default. - user_command_timeouts
- If set, the user may specify a timeout on the command line. If the timeout
expires before the command has exited, the command will be terminated. If
a timeout is specified both in the sudoers file
and on the command line, the smaller of the two timeouts will be used. See
the Timeout_Spec section for a description of the
timeout syntax. This flag is off by default.
This setting is only supported by version 1.8.20 or higher.
- utmp_runas
- If set,
sudo
will store the name of the runas user when updating the utmp (or utmpx) file. By default,sudo
stores the name of the invoking user. This flag is off by default. - visiblepw
- By default,
sudo
will refuse to run if the user must enter a password but it is not possible to disable echo on the terminal. If the visiblepw flag is set,sudo
will prompt for a password even when it would be visible on the screen. This makes it possible to run things like ‘ssh somehost sudo ls
’ since by default, ssh(1) does not allocate a tty when running a command. This flag is off by default.
Integers:
- closefrom
- Before it executes a command,
sudo
will close all open file descriptors other than standard input, standard output, and standard error (file descriptors 0-2). The closefrom option can be used to specify a different file descriptor at which to start closing. The default is 3. - command_timeout
- The maximum amount of time a command is allowed to run before it is
terminated. See the Timeout_Spec section for a
description of the timeout syntax.
This setting is only supported by version 1.8.20 or higher.
- log_server_timeout
- The maximum amount of time to wait when connecting to a log server or
waiting for a server response. See the Timeout_Spec
section for a description of the timeout syntax. The default value is 30
seconds.
This setting is only supported by version 1.9.0 or higher.
- maxseq
- The maximum sequence number that will be substituted for the
‘
%{seq}
’ escape in the I/O log file (see the iolog_dir description below for more information). While the value substituted for ‘%{seq}
’ is in base 36, maxseq itself should be expressed in decimal. Values larger than 2176782336 (which corresponds to the base 36 sequence number “ZZZZZZ”) will be silently truncated to 2176782336. The default value is 2176782336.Once the local sequence number reaches the value of maxseq, it will “roll over” to zero, after which
sudoers
will truncate and re-use any existing I/O log path names.This setting is only supported by version 1.8.7 or higher.
- passwd_tries
- The number of tries a user gets to enter his/her password before
sudo
logs the failure and exits. The default is 3. - syslog_maxlen
- On many systems, syslog(3) has a relatively small log
buffer. IETF RFC 5424 states that syslog servers must support messages of
at least 480 bytes and should support messages up to 2048 bytes. By
default,
sudoers
creates log messages up to 980 bytes which corresponds to the historic BSD syslog implementation which used a 1024 byte buffer to store the message, date, hostname, and program name. To prevent syslog messages from being truncated,sudoers
will split up log messages that are larger than syslog_maxlen bytes. When a message is split, additional parts will include the string “(command continued)” after the user name and before the continued command line arguments.This setting is only supported by version 1.8.19 or higher.
Integers that can be used in a boolean context:
- loglinelen
- Number of characters per line for the file log. This value is used to decide when to wrap lines for nicer log files. This has no effect on the syslog log file, only the file log. The default is 80 (use 0 or negate the option to disable word wrap).
- passwd_timeout
- Number of minutes before the
sudo
password prompt times out, or 0 for no timeout. The timeout may include a fractional component if minute granularity is insufficient, for example 2.5. The default is 0. - timestamp_timeout
- Number of minutes that can elapse before
sudo
will ask for a password again. The timeout may include a fractional component if minute granularity is insufficient, for example 2.5. The default is 15. Set this to 0 to always prompt for a password. If set to a value less than 0 the user's time stamp will not expire until the system is rebooted. This can be used to allow users to create or delete their own time stamps via ‘sudo -v
’ and ‘sudo -k
’ respectively. - umask
- File mode creation mask to use when running the command. Negate this
option or set it to 0777 to prevent
sudoers
from changing the umask. Unless the umask_override flag is set, the actual umask will be the union of the user's umask and the value of the umask setting, which defaults to 0022. This guarantees thatsudo
never lowers the umask when running a command.If umask is explicitly set in sudoers, it will override any umask setting in PAM or login.conf. If umask is not set in sudoers, the umask specified by PAM or login.conf will take precedence. The umask setting in PAM is not used for
sudoedit
, which does not create a new PAM session.
Strings:
- authfail_message
- Message that is displayed after a user fails to authenticate. The message
may include the ‘
%d
’ escape which will expand to the number of failed password attempts. If set, it overrides the default message, “%d incorrect password attempt(s)”. - badpass_message
- Message that is displayed if a user enters an incorrect password. The default is “Sorry, try again.” unless insults are enabled.
- editor
- A colon (‘
:
’) separated list of editor path names used bysudoedit
andvisudo
. Forsudoedit
, this list is used to find an editor when none of theSUDO_EDITOR
,VISUAL
orEDITOR
environment variables are set to an editor that exists and is executable. Forvisudo
, it is used as a white list of allowed editors;visudo
will choose the editor that matches the user'sSUDO_EDITOR
,VISUAL
orEDITOR
environment variable if possible, or the first editor in the list that exists and is executable if not. Unless invoked assudoedit
,sudo
does not preserve theSUDO_EDITOR
,VISUAL
orEDITOR
environment variables unless they are present in the env_keep list or the env_reset option is disabled. The default is /usr/bin/editor. - intercept_type
- The underlying mechanism used by the intercept and
log_subcmds options. It has the following possible
values:
- dso
- Preload a dynamic shared object (shared library) that intercepts the
execve(2), execl(3),
execle(3), execlp(3),
execv(3), execvp(3),
execvpe(3), and system(3) library
functions. A value of dso is incompatible with
sudo
's SELinux RBAC support. - trace
- Use ptrace(2) to intercept the execve(2) system call. This is only supported on Linux systems where seccomp(2) filtering is enabled. If the /proc/sys/kernel/seccomp/actions_avail file is missing or does not contain a “trap” element, setting intercept_type to trace will have no effect and dso will be used instead.
The default is to use trace if it is supported by the system and dso if it is not.
- iolog_dir
- The top-level directory to use when constructing the path name for the
input/output log directory. Only used if the log_input
or log_output options are enabled or when the
LOG_INPUT
orLOG_OUTPUT
tags are present for a command. The session sequence number, if any, is stored in the directory. The default is /var/log/sudo-io.The following percent (‘
%
’) escape sequences are supported:- %{seq}
- expanded to a monotonically increasing base-36 sequence number, such as 0100A5, where every two digits are used to form a new directory, e.g., 01/00/A5
- %{user}
- expanded to the invoking user's login name
- %{group}
- expanded to the name of the invoking user's real group-ID
- %{runas_user}
- expanded to the login name of the user the command will be run as (e.g., root)
- %{runas_group}
- expanded to the group name of the user the command will be run as (e.g., wheel)
- %{hostname}
- expanded to the local host name without the domain name
- %{command}
- expanded to the base name of the command being run
In addition, any escape sequences supported by the system's strftime(3) function will be expanded.
To include a literal ‘
%
’ character, the string ‘%%
’ should be used. - iolog_file
- The path name, relative to iolog_dir, in which to store
input/output logs when the log_input or
log_output options are enabled or when the
LOG_INPUT
orLOG_OUTPUT
tags are present for a command. iolog_file may contain directory components. The default is ‘%{seq}
’.See the iolog_dir option above for a list of supported percent (‘
%
’) escape sequences.In addition to the escape sequences, path names that end in six or more Xs will have the Xs replaced with a unique combination of digits and letters, similar to the mktemp(3) function.
If the path created by concatenating iolog_dir and iolog_file already exists, the existing I/O log file will be truncated and overwritten unless iolog_file ends in six or more Xs.
- iolog_flush
- If set,
sudo
will flush I/O log data to disk after each write instead of buffering it. This makes it possible to view the logs in real-time as the program is executing but may significantly reduce the effectiveness of I/O log compression. This flag is off by default.This setting is only supported by version 1.8.20 or higher.
- iolog_group
- The group name to look up when setting the group-ID on new I/O log files
and directories. If iolog_group is not set, the primary
group-ID of the user specified by iolog_user is used. If
neither iolog_group nor iolog_user are
set, I/O log files and directories are created with group-ID 0.
This setting is only supported by version 1.8.19 or higher.
- iolog_mode
- The file mode to use when creating I/O log files. Mode bits for read and
write permissions for owner, group, or other are honored, everything else
is ignored. The file permissions will always include the owner read and
write bits, even if they are not present in the specified mode. When
creating I/O log directories, search (execute) bits are added to match the
read and write bits specified by
iolog_mode.
Defaults to 0600 (read and write by user only).
This setting is only supported by version 1.8.19 or higher.
- iolog_user
- The user name to look up when setting the user and group-IDs on new I/O
log files and directories. If iolog_group is set, it
will be used instead of the user's primary group-ID. By default, I/O log
files and directories are created with user and group-ID 0.
This setting can be useful when the I/O logs are stored on a Network File System (NFS) share. Having a dedicated user own the I/O log files means that
sudoers
does not write to the log files as user-ID 0, which is usually not permitted by NFS.This setting is only supported by version 1.8.19 or higher.
- lecture_status_dir
- The directory in which
sudo
stores per-user lecture status files. Once a user has received the lecture, a zero-length file is created in this directory so thatsudo
will not lecture the user again. This directory should not be cleared when the system reboots. The default is /var/lib/sudo/lectured. - log_server_cabundle
- The path to a certificate authority bundle file, in PEM format, to use
instead of the system's default certificate authority database when
authenticating the log server. The default is to use the system's default
certificate authority database. This setting has no effect unless
log_servers is set and the remote log server is secured
with TLS.
This setting is only supported by version 1.9.0 or higher.
- log_server_peer_cert
- The path to the
sudo
client's certificate file, in PEM format. This setting is required when the remote log server is secured with TLS and client certificate validation is enabled. Forsudo_logsrvd
, client certificate validation is controlled by the tls_checkpeer option, which defaults to false.This setting is only supported by version 1.9.0 or higher.
- log_server_peer_key
- The path to the
sudo
client's private key file, in PEM format. This setting is required when the remote log server is secured with TLS and client certificate validation is enabled. Forsudo_logsrvd
, client certificate validation is controlled by the tls_checkpeer flag, which defaults to false.This setting is only supported by version 1.9.0 or higher.
- mailsub
- Subject of the mail sent to the mailto user. The escape
‘
%h
’ will expand to the host name of the machine. Default is “*** SECURITY information for %h ***”. - noexec_file
- As of
sudo
version 1.8.1 this option is no longer supported. The path to the noexec file should now be set in the sudo.conf(5) file. - pam_askpass_service
- On systems that use PAM for authentication, this is the service name used
when the
-A
option is specified. The default value is either ‘sudo
’ or ‘sudo-i
’, depending on whether or not the-i
option is also specified. See the description of pam_service for more information.This setting is only supported by version 1.9.9 or higher.
- pam_login_service
- On systems that use PAM for authentication, this is the service name used
when the
-i
option is specified. The default value is ‘sudo-i
’. See the description of pam_service for more information.This setting is only supported by version 1.8.8 or higher.
- pam_service
- On systems that use PAM for authentication, the service name specifies the
PAM policy to apply. This usually corresponds to an entry in the
pam.conf file or a file in the
/etc/pam.d directory. The default value is
‘
sudo
’.This setting is only supported by version 1.8.8 or higher.
- passprompt
- The default prompt to use when asking for a password; can be overridden
via the
-p
option or theSUDO_PROMPT
environment variable. The following percent (‘%
’) escape sequences are supported:- %H
- expanded to the local host name including the domain name (only if the machine's host name is fully qualified or the fqdn option is set)
- %h
- expanded to the local host name without the domain name
- %p
- expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)
- %U
- expanded to the login name of the user the command will be run as (defaults to root)
- %u
- expanded to the invoking user's login name
- %%
- two consecutive ‘
%
’ characters are collapsed into a single ‘%
’ character
On systems that use PAM for authentication, passprompt will only be used if the prompt provided by the PAM module matches the string “Password: ” or “username's Password: ”. This ensures that the passprompt setting does not interfere with challenge-response style authentication. The passprompt_override flag can be used to change this behavior.
The default value is ‘
[sudo] password for %p:
’. - role
- The default SELinux role to use when constructing a new security context
to run the command. The default role may be overridden on a per-command
basis in the sudoers file or via command line options.
This option is only available when
sudo
is built with SELinux support. - runas_default
- The default user to run commands as if the
-u
option is not specified on the command line. This defaults to root. - sudoers_locale
- Locale to use when parsing the sudoers file, logging commands, and sending
email. Changing the locale may affect how sudoers is interpreted. Defaults
to ‘
C
’. - timestamp_type
sudoers
uses per-user time stamp files for credential caching. The timestamp_type option can be used to specify the type of time stamp record used. It has the following possible values:- global
- A single time stamp record is used for all of a user's login sessions,
regardless of the terminal or parent process ID. An additional record
is used to serialize password prompts when
sudo
is used multiple times in a pipeline, but this does not affect authentication. - ppid
- A single time stamp record is used for all processes with the same
parent process ID (usually the shell). Commands run from the same
shell (or other common parent process) will not require a password for
timestamp_timeout minutes (15 by default). Commands
run via
sudo
with a different parent process ID, for example from a shell script, will be authenticated separately. - tty
- One time stamp record is used for each terminal, which means that a user's login sessions are authenticated separately. If no terminal is present, the behavior is the same as ppid. Commands run from the same terminal will not require a password for timestamp_timeout minutes (15 by default).
- kernel
- The time stamp is stored in the kernel as an attribute of the terminal device. If no terminal is present, the behavior is the same as ppid. Negative timestamp_timeout values are not supported and positive values are limited to a maximum of 60 minutes. This is currently only supported on OpenBSD.
The default value is tty.
This setting is only supported by version 1.8.21 or higher.
- timestampdir
- The directory in which
sudo
stores its time stamp files. This directory should be cleared when the system reboots. The default is /run/sudo/ts. - timestampowner
- The owner of the lecture status directory, time stamp directory and all files stored therein. The default is root.
- type
- The default SELinux type to use when constructing a new security context
to run the command. The default type may be overridden on a per-command
basis in the sudoers file or via command line options.
This option is only available when
sudo
is built with SELinux support.
Strings that can be used in a boolean context:
- admin_flag
- The
admin_flag
option specifies the path to a file that is created the first time a user
that is a member of the sudo or
admin
groups runs
sudo
. Only available ifsudo
is configured with the--enable-admin-flag
option. The default value is ~/.sudo_as_admin_successful. - env_file
- The env_file option specifies the fully qualified path
to a file containing variables to be set in the environment of the program
being run. Entries in this file should either be of the form
‘
VARIABLE=value
’ or ‘export VARIABLE=value
’. The value may optionally be enclosed in single or double quotes. Variables in this file are only added if the variable does not already exist in the environment. This file is considered to be part of the security policy, its contents are not subject to othersudo
environment restrictions such as env_keep and env_check. - exempt_group
- Users in this group are exempt from password and PATH requirements. The
group name specified should not include a
‘
%
’ prefix. This is not set by default. - fdexec
- Determines whether
sudo
will execute a command by its path or by an open file descriptor. It has the following possible values:- always
- Always execute by file descriptor.
- never
- Never execute by file descriptor.
- digest_only
- Only execute by file descriptor if the command has an associated digest in the sudoers file.
The default value is digest_only. This avoids a time of check versus time of use race condition when the command is located in a directory writable by the invoking user.
fdexec will change the first element of the argument vector for scripts ($0 in the shell) due to the way the kernel runs script interpreters. Instead of being a normal path, it will refer to a file descriptor. For example, /dev/fd/4 on Solaris and /proc/self/fd/4 on Linux. A workaround is to use the
SUDO_COMMAND
environment variable instead.The fdexec setting is only used when the command is matched by path name. It has no effect if the command is matched by the built-in ALL alias.
This setting is only supported by version 1.8.20 or higher. If the operating system does not support the fexecve(2) system call, this setting has no effect.
- group_plugin
- A string containing a
sudoers
group plugin with optional arguments. The string should consist of the plugin path, either fully-qualified or relative to the /usr/libexec/sudo directory, followed by any configuration arguments the plugin requires. These arguments (if any) will be passed to the plugin's initialization function. If arguments are present, the string must be enclosed in double quotes ("").On 64-bit systems, if the plugin is present but cannot be loaded,
sudoers
will look for a 64-bit version and, if it exists, load that as a fallback. The exact rules for this vary by system. On Solaris, if the plugin is stored in a directory ending in “lib”,sudoers
will create a fallback path by appending “/64” to the directory name; /usr/lib/group_plugin.so becomes /usr/lib/64/group_plugin.so. On Linux, a directory ending in “lib” will be transformed to “lib64” as the fallback path; /usr/lib/group_plugin.so becomes /usr/lib64/group_plugin.so. On all other systems, the fallback path is generated by adding a “64” before the file extension; group_plugin.so becomes group_plugin64.so.For more information see GROUP PROVIDER PLUGINS.
- lecture
- This option controls when a short lecture will be printed along with the
password prompt. It has the following possible values:
- always
- Always lecture the user.
- never
- Never lecture the user.
- once
- Only lecture the user the first time they run
sudo
.
If no value is specified, a value of once is implied. Negating the option results in a value of never being used. The default value is never.
- lecture_file
- Path to a file containing an alternate
sudo
lecture that will be used in place of the standard lecture if the named file exists. By default,sudo
uses a built-in lecture. - listpw
- This option controls when a password will be required when a user runs
sudo
with the-l
option. It has the following possible values:- all
- All the user's sudoers file entries for the current
host must have the
NOPASSWD
flag set to avoid entering a password. - always
- The user must always enter a password to use the
-l
option. - any
- At least one of the user's sudoers file entries for
the current host must have the
NOPASSWD
flag set to avoid entering a password. - never
- The user need never enter a password to use the
-l
option.
If no value is specified, a value of any is implied. Negating the option results in a value of never being used. The default value is any.
- log_format
- The event log format. Supported log formats are:
- json
- Logs in JSON format. JSON log entries contain the full user details as well as the execution environment if the command was allowed. Due to limitations of the protocol, JSON events sent via syslog may be truncated.
- sudo
- Traditional sudo-style logs, see EVENT LOGGING for a description of the log file format.
This setting affects logs sent via syslog(3) as well as the file specified by the logfile setting, if any. The default value is sudo.
- logfile
- Path to the
sudo
log file (not the syslog log file). Setting a path turns on logging to a file; negating this option turns it off. By default,sudo
logs via syslog. - mailerflags
- Flags to use when invoking mailer. Defaults to
-t
. - mailerpath
- Path to mail program used to send warning mail (negate to prevent
sudo
from sending mail). Defaults to the path to sendmail found at configure time. - mailfrom
- Address to use for the “from” address when sending warning
and error mail. The address should be enclosed in double quotes
("") to protect against
sudo
interpreting the ‘@
’ sign. Defaults to the name of the user runningsudo
. - mailto
- Address to send warning and error mail to (negate to prevent
sudo
from sending mail). The address should be enclosed in double quotes ("") to protect againstsudo
interpreting the ‘@
’ sign. Defaults to root. - rlimit_as
- The maximum size to which the process's address space may grow (in bytes), if supported by the operating system. See Resource limits for more information.
- rlimit_core
- The largest size core dump file that may be created (in bytes). See Resource limits for more information. Defaults to 0 (no core dump created).
- rlimit_cpu
- The maximum amount of CPU time that the process may use (in seconds). See Resource limits for more information.
- rlimit_data
- The maximum size of the data segment for the process (in bytes). See Resource limits for more information.
- rlimit_fsize
- The largest size file that the process may create (in bytes). See Resource limits for more information.
- rlimit_locks
- The maximum number of locks that the process may establish, if supported by the operating system. See Resource limits for more information.
- rlimit_memlock
- The maximum size that the process may lock in memory (in bytes), if supported by the operating system. See Resource limits for more information.
- rlimit_nofile
- The maximum number of files that the process may have open. See Resource limits for more information.
- rlimit_nproc
- The maximum number of processes that the user may run simultaneously. See Resource limits for more information.
- rlimit_rss
- The maximum size to which the process's resident set size may grow (in bytes). See Resource limits for more information.
- rlimit_stack
- The maximum size to which the process's stack may grow (in bytes). See Resource limits for more information.
- restricted_env_file
- The restricted_env_file option specifies the fully
qualified path to a file containing variables to be set in the environment
of the program being run. Entries in this file should either be of the
form ‘
VARIABLE=value
’ or ‘export VARIABLE=value
’. The value may optionally be enclosed in single or double quotes. Variables in this file are only added if the variable does not already exist in the environment. Unlike env_file, the file's contents are not trusted and are processed in a manner similar to that of the invoking user's environment. If env_reset is enabled, variables in the file will only be added if they are matched by either the env_check or env_keep list. If env_reset is disabled, variables in the file are added as long as they are not matched by the env_delete list. In either case, the contents of restricted_env_file are processed before the contents of env_file. - runchroot
- If set,
sudo
will use this value for the root directory when running a command. The special value “*” will allow the user to specify the root directory viasudo
's-R
option. See the Chroot_Spec section for more details.It is only possible to use runchroot as a command-specific Defaults setting if the command exists with the same path both inside and outside the chroot jail. This restriction does not apply to global, host, or user-based Defaults settings or to a Cmnd_Spec that includes a Chroot_Spec.
This setting is only supported by version 1.9.3 or higher.
- runcwd
- If set,
sudo
will use this value for the working directory when running a command. The special value “*” will allow the user to specify the working directory viasudo
's-D
option. See the Chdir_Spec section for more details.This setting is only supported by version 1.9.3 or higher.
- secure_path
- If set,
sudo
will use this value in place of the user'sPATH
environment variable. This option can be used to reset thePATH
to a known good value that contains directories for system administrator commands such as /usr/sbin.Users in the group specified by the exempt_group option are not affected by secure_path. This option is not set by default.
- syslog
- Syslog facility if syslog is being used for logging (negate to disable
syslog logging). Defaults to authpriv.
The following syslog facilities are supported: authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
- syslog_badpri
- Syslog priority to use when the user is not allowed to run a command or
when authentication is unsuccessful. Defaults to alert.
The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, warning, and none. Negating the option or setting it to a value of none will disable logging of unsuccessful commands.
- syslog_goodpri
- Syslog priority to use when the user is allowed to run a command and
authentication is successful. Defaults to notice.
See syslog_badpri for the list of supported syslog priorities. Negating the option or setting it to a value of none will disable logging of successful commands.
- verifypw
- This option controls when a password will be required when a user runs
sudo
with the-v
option. It has the following possible values:- all
- All the user's sudoers file entries for the current
host must have the
NOPASSWD
flag set to avoid entering a password. - always
- The user must always enter a password to use the
-v
option. - any
- At least one of the user's sudoers file entries for
the current host must have the
NOPASSWD
flag set to avoid entering a password. - never
- The user need never enter a password to use the
-v
option.
If no value is specified, a value of all is implied. Negating the option results in a value of never being used. The default value is all.
Lists that can be used in a boolean context:
- env_check
- Environment variables to be removed from the user's environment unless
they are considered “safe”. For all variables except
TZ
, “safe” means that the variable's value does not contain any ‘%
’ or ‘/
’ characters. This can be used to guard against printf-style format vulnerabilities in poorly-written programs. TheTZ
variable is considered unsafe if any of the following are true:- It consists of a fully-qualified path name, optionally prefixed with a
colon (‘
:
’), that does not match the location of the zoneinfo directory. - It contains a .. path element.
- It contains white space or non-printable characters.
- It is longer than the value of
PATH_MAX
.
The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the ‘
=
’, ‘+=
’, ‘-=
’, and ‘!
’ operators respectively. Regardless of whether the env_reset option is enabled or disabled, variables specified by env_check will be preserved in the environment if they pass the aforementioned check. The global list of environment variables to check is displayed whensudo
is run by root with the-V
option. - It consists of a fully-qualified path name, optionally prefixed with a
colon (‘
- env_delete
- Environment variables to be removed from the user's environment when the
env_reset option is not in effect. The argument may be a
double-quoted, space-separated list or a single value without
double-quotes. The list can be replaced, added to, deleted from, or
disabled by using the ‘
=
’, ‘+=
’, ‘-=
’, and ‘!
’ operators respectively. The global list of environment variables to remove is displayed whensudo
is run by root with the-V
option. Many operating systems will remove potentially dangerous variables from the environment of any set-user-ID process (such assudo
). - env_keep
- Environment variables to be preserved in the user's environment when the
env_reset option is in effect. This allows fine-grained
control over the environment
sudo
-spawned processes will receive. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the ‘=
’, ‘+=
’, ‘-=
’, and ‘!
’ operators respectively. The global list of variables to keep is displayed whensudo
is run by root with the-V
option.Preserving the
HOME
environment variable has security implications since many programs use it when searching for configuration or data files. AddingHOME
to env_keep may enable a user to run unrestricted commands viasudo
and is strongly discouraged. Users wishing to edit files withsudo
should runsudoedit
(orsudo
-e
) to get their accustomed editor configuration instead of invoking the editor directly. - log_servers
- A list of one or more servers to use for remote event and I/O log storage,
separated by white space. Log servers must be running
sudo_logsrvd
or another service that implements the protocol described by sudo_logsrv.proto(5).Server addresses should be of the form “host[:port][(tls)]”. The host portion may be a host name, an IPv4 address, or an IPv6 address in square brackets.
If the optional tls flag is present, the connection will be secured with Transport Layer Security (TLS) version 1.2 or 1.3. Versions of TLS prior to 1.2 are not supported.
If a port is specified, it may either be a port number or a well-known service name as defined by the system service name database. If no port is specified, port 30343 will be used for plaintext connections and port 30344 will be used for TLS connections.
When log_servers is set, event log data will be logged both locally (see the syslog and log_file settings) as well as remotely, but I/O log data will only be logged remotely. If multiple hosts are specified, they will be attempted in reverse order. If no log servers are available, the user will not be able to run a command unless either the ignore_iolog_errors flag (I/O logging enabled) or the ignore_log_errors flag (I/O logging disabled) is set. Likewise, if the connection to the log server is interrupted while
sudo
is running, the command will be terminated unless the ignore_iolog_errors flag (I/O logging enabled) or the ignore_log_errors flag (I/O logging disabled) is set.This setting is only supported by version 1.9.0 or higher.
- passprompt_regex
- A list of POSIX extended regular expressions used to match password
prompts in the terminal output. As an extension, if the regular expression
begins with “(?i)”, it will be matched in a case-insensitive
manner. Each regular expression is limited to 1024 characters. This option
is only used when log_passwords has been disabled. The
default value is “[Pp]assword[: ]*”
This setting is only supported by version 1.9.10 or higher.
GROUP PROVIDER PLUGINS¶
The sudoers
plugin supports its own plugin
interface to allow non-Unix group lookups which can query a group source
other than the standard Unix group database. This can be used to implement
support for the nonunix_group syntax described
earlier.
Group provider plugins are specified via the group_plugin setting. The argument to group_plugin should consist of the plugin path, either fully-qualified or relative to the /usr/libexec/sudo directory, followed by any configuration options the plugin requires. These options (if specified) will be passed to the plugin's initialization function. If options are present, the string must be enclosed in double quotes ("").
The following group provider plugins are installed by default:
- group_file
- The
group_file
plugin supports an alternate group file that uses the same syntax as the
/etc/group file. The path to the group file should
be specified as an option to the plugin. For example, if the group file to
be used is /etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"
- system_group
- The
system_group
plugin supports group lookups via the standard C library functions
getgrnam(3) and getgrid(3). This
plugin can be used in instances where the user belongs to groups not
present in the user's supplemental group vector. This plugin takes no
options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in sudo_plugin(5).
EVENT LOGGING¶
sudoers
can log events in either JSON or
sudo format, this section describes the
sudo log format. Depending on sudoers
configuration, sudoers
can log events via
syslog(3), to a local log file, or both. The log format is
almost identical in both cases. Any control characters present in the log
data are formatted in octal with a leading
‘#
’ character. For example, a
horizontal tab is stored as ‘#011
’ and
an embedded carriage return is stored as
‘#015
’. In addition, space characters
in the command path are stored as
‘#040
’. Command line arguments that
contain spaces are enclosed in single quotes (''). This makes it possible to
distinguish multiple command line arguments from a single argument that
contains spaces. Literal single quotes and backslash characters
(‘\
’) in command line arguments are
escaped with a backslash.
Accepted command log entries¶
Commands that sudo runs are logged using the following format (split into multiple lines for readability):
date hostname progname: username : TTY=ttyname ; CHROOT=chroot ; \ PWD=cwd ; USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \ ENV=env_vars COMMAND=command
Where the fields are as follows:
- date
- The date the command was run. Typically, this is in the format “MMM, DD, HH:MM:SS”. If logging via syslog(3), the actual date format is controlled by the syslog daemon. If logging to a file and the log_year option is enabled, the date will also include the year.
- hostname
- The name of the host
sudo
was run on. This field is only present when logging via syslog(3). - progname
- The name of the program, usually sudo or sudoedit. This field is only present when logging via syslog(3).
- username
- The login name of the user who ran
sudo
. - ttyname
- The short name of the terminal (e.g., “console”,
“tty01”, or “pts/0”)
sudo
was run on, or “unknown” if there was no terminal present. - chroot
- The root directory that the command was run in, if one was specified.
- cwd
- The current working directory that
sudo
was run in. - runasuser
- The user the command was run as.
- runasgroup
- The group the command was run as if one was specified on the command line.
- logid
- An I/O log identifier that can be used to replay the command's output. This is only present when the log_input or log_output option is enabled.
- env_vars
- A list of environment variables specified on the command line, if specified.
- command
- The actual command that was executed, including any command line arguments.
Messages are logged using the locale specified by
sudoers_locale, which defaults to the
‘C
’ locale.
Denied command log entries¶
If the user is not allowed to run the command, the reason for the denial will follow the user name. Possible reasons include:
- user NOT in sudoers
- The user is not listed in the sudoers file.
- user NOT authorized on host
- The user is listed in the sudoers file but is not allowed to run commands on the host.
- command not allowed
- The user is listed in the sudoers file for the host but they are not allowed to run the specified command.
- 3 incorrect password attempts
- The user failed to enter their password after 3 tries. The actual number of tries will vary based on the number of failed attempts and the value of the passwd_tries option.
- a password is required
- The
-n
option was specified but a password was required. - sorry, you are not allowed to set the following environment variables
- The user specified environment variables on the command line that were not allowed by sudoers.
Error log entries¶
If an error occurs, sudoers
will log a
message and, in most cases, send a message to the administrator via email.
Possible errors include:
- parse error in /etc/sudoers near line N
sudoers
encountered an error when parsing the specified file. In some cases, the actual error may be one line above or below the line number listed, depending on the type of error.- problem with defaults entries
- The sudoers file contains one or more unknown Defaults
settings. This does not prevent
sudo
from running, but the sudoers file should be checked usingvisudo
. - timestamp owner (username): No such user
- The time stamp directory owner, as specified by the timestampowner setting, could not be found in the password database.
- unable to open/read /etc/sudoers
- The sudoers file could not be opened for reading. This
can happen when the sudoers file is located on a remote
file system that maps user-ID 0 to a different value. Normally,
sudoers
tries to open the sudoers file using group permissions to avoid this problem. Consider either changing the ownership of /etc/sudoers or adding an argument like “sudoers_uid=N” (where ‘N’ is the user-ID that owns the sudoers file) to the end of thesudoers
Plugin line in the sudo.conf(5) file. - unable to open /etc/sudoers
- The /etc/sudoers file is missing.
- /etc/sudoers is not a regular file
- The /etc/sudoers file exists but is not a regular file or symbolic link.
- /etc/sudoers is owned by uid N, should be 0
- The sudoers file has the wrong owner. If you wish to
change the sudoers file owner, add
“sudoers_uid=N” (where ‘N’ is the user-ID that
owns the sudoers file) to the
sudoers
Plugin line in the sudo.conf(5) file. - /etc/sudoers is world writable
- The permissions on the sudoers file allow all users to
write to it. The sudoers file must not be
world-writable, the default file mode is 0440 (readable by owner and
group, writable by none). The default mode may be changed via the
“sudoers_mode” option to the
sudoers
Plugin line in the sudo.conf(5) file. - /etc/sudoers is owned by gid N, should be 1
- The sudoers file has the wrong group ownership. If you
wish to change the sudoers file group ownership, add
“sudoers_gid=N” (where ‘N’ is the group-ID
that owns the sudoers file) to the
sudoers
Plugin line in the sudo.conf(5) file. - unable to open /run/sudo/ts/username
sudoers
was unable to read or create the user's time stamp file. This can happen when timestampowner is set to a user other than root and the mode on /run/sudo is not searchable by group or other. The default mode for /run/sudo is 0711.- unable to write to /run/sudo/ts/username
sudoers
was unable to write to the user's time stamp file.- /run/sudo/ts is owned by uid X, should be Y
- The time stamp directory is owned by a user other than
timestampowner. This can occur when the value of
timestampowner has been changed.
sudoers
will ignore the time stamp directory until the owner is corrected. - /run/sudo/ts is group writable
- The time stamp directory is group-writable; it should be writable only by
timestampowner. The default mode for the time stamp
directory is 0700.
sudoers
will ignore the time stamp directory until the mode is corrected.
Notes on logging via syslog¶
By default, sudoers
logs messages via
syslog(3). The
date,
hostname, and progname fields are added
by the system's syslog(3) function, not
sudoers
itself. As such, they may vary in format on
different systems.
The maximum size of syslog messages varies from system to system. The syslog_maxlen setting can be used to change the maximum syslog message size from the default value of 980 bytes. For more information, see the description of syslog_maxlen.
Notes on logging to a file¶
If the logfile option is set,
sudoers
will log to a local file, such as
/var/log/sudo. When logging to a file,
sudoers
uses a format similar to
syslog(3), with a few important differences:
- The progname field is not present.
- The hostname is only logged if the log_host option is enabled.
- The date does not include the year unless the log_year option is enabled.
- Lines that are longer than loglinelen characters (80 by
default) are word-wrapped and continued on the next line with a four
character indent. This makes entries easier to read for a human being, but
makes it more difficult to use grep(1) on the log files.
If the loglinelen option is set to 0 (or negated with a
‘
!
’), word wrap will be disabled.
I/O LOGGING¶
When I/O logging is enabled, sudo
will
runs the command in a pseudo-terminal, logging user input and/or output,
depending on which sudoers
flags are enabled. There
are five distinct types of I/O that can be logged, each with a corresponding
sudoers
flag.
Type | Flag | Description |
terminal input | log_ttyin | keystrokes entered by the user |
terminal output | log_ttyout | command output displayed to the screen |
standard input | log_stdin | input from a pipe or a file |
standard output | log_stdout | output to a pipe or a file |
standard error | log_stderr | output to a pipe or a file |
In addition to flags described the above, the
log_input flag and LOG_INPUT
command tag set both log_ttyin and
log_stdin. The log_output flag and
LOG_OUTPUT
command tag set
log_ttyout, log_stdout, and
log_stderr.
To capture terminal input and output, sudo
run the command in a pseudo-terminal, logging the input and output before
passing it on to the user. To capture the standard input, standard output or
standard error, sudo
uses a pipe to interpose itself
between the input or output stream, logging the I/O before passing it to the
other end of the pipe.
I/O can be logged either to the local machine or to a remote log
server. For local logs, I/O is logged to the directory specified by the
iolog_dir option (/var/log/sudo-io
by default) using a unique session ID that is included in the
sudo
log line, prefixed with
‘TSID=
’. The
iolog_file option may be used to control the format of the
session ID. For remote logs, the log_servers setting is
used to specify one or more log servers running
sudo_logsrvd
or another server that implements the
protocol described by sudo_logsrv.proto(5).
I/O logging pitfals¶
When logging standard input, anything sent to the standard input
will be consumed, regardless of whether or not the command run via
sudo
is actively reading the standard input. This
may have unexpected results when using sudo
in a
shell script that expects to process the standard input. For example, given
the following shell script:
#!/bin/sh sudo echo testing echo done
It will behave as expected when the script is passed to the shell as a an argument:
$ sh test.sh testing done
However, if the script is passed to the shell on the standard
input, the ‘sudo echo testing
’ command
will consume the rest of the script. This means that the
‘echo done
’ statement is never
executed.
$ sh -s < test.sh testing
There are several ways to work around this problem:
- Redirect the standard input from /dev/null when
running a command via
sudo
that does not need to read the standard input.sudo echo testing < /dev/null
- Pass the script to the shell by path name instead of via the standard
input.
sh test.sh
- Disable logging the standard input for commands that do not need to read
the standard input.
Defaults!/bin/echo !log_stdin
Depending on the command, it may not be desirable to log the standard input or standard output. For example, I/O logging of commands that send or receive large amount of data via the standard output or standard input such as rsync(1) and tar(1) could fill up the log file system with superfluous data. It is possible to disable logging of the standard input and standard output for such commands as follows:
Cmnd_Alias COPY_CMDS = /usr/bin/tar, /usr/bin/cpio, /usr/bin/rsync # Log input and output but omit stdin and stdout when copying files. Defaults log_input, log_output Defaults!COPY_CMDS !log_stdin, !log_stdout
However, be aware that using the
log_input flag or the LOG_INPUT
command tag will also enable log_stdin. Likewise, the
log_ouput flag
or the LOG_OUTPUT
command tag will enable
log_stdout and
log_stderr.
Careful ordering of rules may be necessary to achieve the results that you
expect.
I/O log format¶
For both local and remote I/O logs, each log is stored in a separate directory that contains the following files:
- log
- A text file containing information about the command. The first line
consists of the following colon-delimited fields: the time the command was
run, the name of the user who ran
sudo
, the name of the target user, the name of the target group (optional), the terminal thatsudo
was run from, and the number of lines and columns of the terminal. The second and third lines contain the working directory the command was run from and the path name of the command itself (with arguments if present). - log.json
- A JSON-formatted file containing information about the command. This is
similar to the log file but contains additional
information and is easily extensible. The log.json
file will be used by sudoreplay(8) in preference to the
log file if it exists. The file may contain the
following elements:
- timestamp
- A JSON object containing time the command was run. It consists of two values, seconds and nanoseconds.
- columns
- The number of columns of the terminal the command ran on, or zero if no terminal was present.
- command
- The fully-qualified path of the command that was run.
- lines
- The number of lines of the terminal the command ran on, or zero if no terminal was present.
- runargv
- A JSON array representing the command's argument vector as passed to the execve(2) system call.
- runenv
- A JSON array representing the command's environment as passed to the execve(2) system call.
- rungid
- The group ID the command ran as. This element is only present when the user specifies a group on the command line.
- rungroup
- The name of the group the command ran as. This element is only present when the user specifies a group on the command line.
- runuid
- The user ID the command ran as.
- runuser
- The name of the user the command ran as.
- submitcwd
- The current working directory at the time
sudo
was run. - submithost
- The name of the host the command was run on.
- submituser
- The name of the user who ran the command via
sudo
. - ttyname
- The path name of the terminal the user invoked
sudo
from. If the command was run in a pseudo-terminal, ttyname will be different from the terminal the command actually ran in.
- timing
- Timing information used to replay the session. Each line consists of the
I/O log entry type and amount of time since the last entry, followed by
type-specific data. The I/O log entry types and their corresponding
type-specific data are:
- 0
- standard input, number of bytes in the entry
- 1
- standard output, number of bytes in the entry
- 2
- standard error, number of bytes in the entry
- 3
- terminal input, number of bytes in the entry
- 4
- terminal output, number of bytes in the entry
- 5
- window change, new number lines and columns
- 6
- bug compatibility for
sudo
1.8.7 terminal output - 7
- command suspend or resume, signal received
- ttyin
- Raw input from the user's terminal, exactly as it was received. This file
is only present if the log_input or
log_ttyin flags are set and
sudo
was run from a terminal. No post-processing is performed. For manual viewing, you may wish to convert carriage return characters in the log to line feeds. For example: ‘gunzip -c ttyin | tr "\r" "\n"
’ - stdin
- The standard input when no terminal is present, or input redirected from a pipe or file. This file is only present if the log_input or log_stdin flags are set and the standard input is not connected to a terminal.
- ttyout
- Output from the pseudo-terminal (what the command writes to the screen).
Terminal-specific post-processing is performed before the data is logged.
This means that, for example, line feeds are usually converted to line
feed/carriage return pairs and tabs may be expanded to spaces. This file
is only present if the log_output or
log_ttyout flags are set and
sudo
was run from a terminal. - stdout
- The standard output when no terminal is present, or output redirected to a pipe or file. This file is only present if the log_output or log_stdout flags are set and the standard output is not connected to a terminal.
- stderr
- The standard error when no terminal is present, or output redirected to a pipe or file. This file is only present if the log_output or log_stderr flags are set and the standard error is not connected to a terminal.
All files other than log
are compressed in gzip format unless the
compress_io
flag has been disabled. Due to buffering, it is not normally possible to
display the I/O logs in real-time as the program is executing. The I/O log
data will not be complete until the program run by
sudo
has exited or has been terminated by a signal.
The
iolog_flush
flag can be used to disable buffering, in which case I/O log data is written
to disk as soon as it is available. The output portion of an I/O log file
can be viewed with the sudoreplay(8) utility, which can
also be used to list or search the available logs.
User input may contain sensitive information such as passwords
(even if they are not echoed to the screen), which will be stored in the log
file unencrypted. In most cases, logging the command output via
log_output or LOG_OUTPUT
is all
that is required. When logging input, consider disabling the
log_passwords flag.
Since each session's I/O logs are stored in a separate directory,
traditional log rotation utilities cannot be used to limit the number of I/O
logs. The simplest way to limit the number of I/O is by setting the
maxseq option to the maximum number of logs you wish to
store. Once the I/O log sequence number reaches maxseq, it
will be reset to zero and sudoers
will truncate and
re-use any existing I/O logs.
FILES¶
- /etc/sudo.conf
- Sudo front-end configuration
- /etc/sudoers
- List of who can run what
- /etc/group
- Local groups file
- /etc/netgroup
- List of network groups
- /var/log/sudo-io
- I/O log files
- /run/sudo/ts
- Directory containing time stamps for the
sudoers
security policy - /var/lib/sudo/lectured
- Directory containing lecture status files for the
sudoers
security policy - /etc/environment
- Initial environment for
-i
mode on AIX and Linux systems
EXAMPLES¶
Below are example sudoers file entries. Admittedly, some of these are a bit contrived. First, we allow a few environment variables to pass and then define our aliases:
# Run X applications through sudo; HOME is used to find the # .Xauthority file. Other programs use HOME to locate configuration # files and this may lead to privilege escalation! Defaults env_keep += "DISPLAY HOME" # User alias specification User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBADMIN = will, wendy, wim # Runas alias specification Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase Runas_Alias ADMINGRP = adm, oper # Host alias specification Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 128.138.0.0/255.255.0.0 Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0 Host_Alias SERVERS = primary, mail, www, ns Host_Alias CDROM = orion, perseus, hercules # Cmnd alias specification Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore,\ sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \ /home/operator/bin/start_backups Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\ /usr/local/bin/tcsh, /usr/bin/rsh,\ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want
sudo
to log via syslog(3) using
the auth facility in all cases and for commands to be run
with the target user's home directory as the working directory. We don't
want to subject the full time staff to the sudo
lecture and we want to allow them to run commands in a
chroot(2) “sandbox” via the
-R
option. User millert need not
provide a password and we don't want to reset the
LOGNAME
or USER
environment
variables when running commands as root. Additionally, on
the machines in the SERVERS
Host_Alias, we keep an additional local log file and make
sure we log the year in each log line since the log entries will be kept
around for several years. Lastly, we disable shell escapes for the commands
in the PAGERS Cmnd_Alias
(/usr/bin/more, /usr/bin/pg
and /usr/bin/less). This will not effectively
constrain users with sudo
ALL
privileges.
# Override built-in defaults Defaults syslog=auth,runcwd=~ Defaults>root !set_logname Defaults:FULLTIMERS !lecture,runchroot=* Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec
The User specification is the part that actually determines who may run what.
root ALL = (ALL) ALL %wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins
bostley,
jwfox,
and
crawl)
may run any command on any host but they must authenticate themselves first
(since the entry lacks the NOPASSWD
tag).
jack CSNETS = ALL
The user
jack may run any
command on the machines in the CSNETS
alias (the
networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those
networks, only 128.138.204.0 has an explicit netmask (in CIDR notation)
indicating it is a class C network. For the other networks in
CSNETS
, the local machine's netmask will be used
during matching.
lisa CUNETS = ALL
The user
lisa may run any
command on any host in the CUNETS
alias (the class B
network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to
simple maintenance. Here, those are commands related to backups, killing
processes, the printing system, shutting down the system, and any commands
in the directory /usr/oper/bin/. One command in the
DUMPS
Cmnd_Alias includes a sha224 digest,
/home/operator/bin/start_backups. This is because
the directory containing the script is writable by the operator user. If the
script is modified (resulting in a digest mismatch) it will no longer be
possible to run it via sudo
.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root* %opers ALL = (: ADMINGRP) /usr/sbin/
Users in the
opers group may run
commands in /usr/sbin/ as themselves with any group
in the ADMINGRP
Runas_Alias (the
adm and
oper
groups).
The user
pete is allowed to
change anyone's password except for root on the
HPPA
machines. Because command line arguments are
matched as a single, concatenated string, the
‘*
’ wildcard will match
multiple
words. This example assumes that passwd(1) does not take
multiple user names on the command line. On systems with GNU
getopt(3), options to passwd(1) may be
specified after the user argument. As a result, this rule will also
allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user
bob may run anything
on the SPARC
and SGI
machines as any user listed in the OP
Runas_Alias (root and
operator.)
jim +biglab = ALL
The user
jim may run any
command on machines in the
biglab
netgroup. sudo
knows that “biglab” is
a netgroup due to the ‘+
’ prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as well as add and remove users, so they are allowed to run those commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user
fred can run
commands as any user in the DB
Runas_Alias
(oracle
or
sybase)
without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA
machines, user
john may su to anyone except root but he
is not allowed to specify any options to the su(1)
command.
jen ALL, !SERVERS = ALL
The user
jen may run any
command on any machine except for those in the
SERVERS
Host_Alias (primary, mail,
www, and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS
Host_Alias,
jill may run any
commands in the directory /usr/bin/ except for those
commands belonging to the SU
and
SHELLS
Cmnd_Aliases.
While not specifically mentioned in the rule, the commands in the
PAGERS
Cmnd_Alias all reside in
/usr/bin and have the noexec
option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory /usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung processes.
WEBADMIN www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBADMIN
User_Alias (will, wendy, and wim), may run any command as
user www (which owns the web pages) or simply su(1) to
www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM Host_Alias (orion, perseus, hercules) without entering a password. This is a bit tedious for users to type, so it is a prime candidate for encapsulating in a shell script.
SECURITY NOTES¶
Limitations of the ‘!’ operator¶
It is generally not effective to “subtract” commands
from ALL using the
‘!
’ operator. A user can trivially
circumvent this by copying the desired command to a different name and then
executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent
bill from running
the commands listed in SU
or
SHELLS
since he can simply copy those commands to a
different name, or use a shell escape from an editor or other program.
Therefore, these kind of restrictions should be considered advisory at best
(and reinforced by policy).
In general, if a user has sudo ALL there is
nothing to prevent them from creating their own program that gives them a
root shell (or making their own copy of a shell)
regardless of any ‘!
’ elements in the
user specification.
Security implications of fast_glob¶
If the fast_glob option is in use, it is not possible to reliably negate commands where the path name includes globbing (aka wildcard) characters. This is because the C library's fnmatch(3) function cannot resolve relative paths. While this is typically only an inconvenience for rules that grant privileges, it can result in a security issue for rules that subtract or revoke privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\ /usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run
‘/usr/bin/passwd root
’ if
fast_glob is enabled by changing to
/usr/bin and running
‘./passwd root
’ instead.
Another potential issue is that when sudo
executes the command, it must use the command or path specified by the user
instead of a path listed in the sudoers file. This may
lead to a time of check versus time of use race condition.
Wildcards in command arguments¶
Command line arguments are matched as a single, concatenated
string. This mean a wildcard character such as
‘?
’ or
‘*
’ will match across word boundaries,
which may be unexpected. For example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. A safer alternative is to use a regular expression for matching command line arguments. The above example can be rewritten as a regular expression:
%operator ALL = /bin/cat ^/var/log/messages[^[:space:]]*$
The regular expression will only match a single file with a name that begins with /var/log/messages and does not include any white space in the name. It is often better to do command line processing outside of the sudoers file in a scripting language for anything non-trivial.
Regular expressions in command names¶
Using a regular expression to match a command name has the same security implications as using the fast_glob option:
- It is not possible to reliably negate commands when the path name is a regular expression.
- When
sudo
executes the command, it must use the command or path specified by the user instead of a path listed in the sudoers file. This may lead to a time of check versus time of use race condition.
These issues do not apply to rules where only the command line options are matched using a regular expression.
Preventing shell escapes¶
Once sudo
executes a program, that program
is free to do whatever it pleases, including run other programs. This can be
a security issue since it is not uncommon for a program to allow shell
escapes, which lets a user bypass sudo
's access
control and logging. Common programs that permit shell escapes include
shells (obviously), editors, paginators, mail, and terminal programs.
There are four basic approaches to this problem:
- restrict
- Avoid giving users access to commands that allow the user to run arbitrary
commands. Many editors have a restricted mode where shell escapes are
disabled, though
sudoedit
is a better solution to running editors viasudo
. Due to the large number of programs that offer shell escapes, restricting users to the set of programs that do not is often unworkable. - intercept
- On most systems,
sudo
's intercept functionality can be used to transparently intercept an attempt to run a new command, allow or deny it based on sudoers rules, and log the result. For example, this can be used to restrict the commands run from within a privileged shell or editor.There are two underlying mechanisms that may be used to implement intercept mode: dso and trace. The intercept_type setting can be used to select between them.
The first mechanism, dso, overrides the standard C library functions that are used to execute a command. It does this by setting an environment variable (usually
LD_PRELOAD
) to the path of a dynamic shared object, or shared library, containing custom versions of the execve(2), execl(3), execle(3), execlp(3), execv(3), execvp(3), execvpe(3), and system(3) library functions that connect back tosudo
for a policy decision. Note, however, that this applies only to dynamically-linked executables. It is not possible to intercept commands for statically-linked executables or executables that run under binary emulation this way. Because most dynamic loaders ignoreLD_PRELOAD
(or the equivalent) when running set-user-ID and set-group-ID programs,sudoers
will not permit such programs to be run in intercept mode by default. The dso mechanism is incompatible withsudo
's SELinux RBAC support (but see below). SELinux disablesLD_PRELOAD
by default and interferes with file descriptor inheritance, whichsudo
relies on.The second mechanism, trace, is available on Linux systems that support seccomp(2) filtering. It uses ptrace(2) and seccomp(2) to intercept the execve(2) system call instead of pre-loading a dynamic shared object. Both static and dynamic executables are supported and it is compatible with
sudo
's SELinux RBAC mode. Functions utilizing the execveat(2) system call, such as fexecve(3), are not currently intercepted.The intercept feature is known to work on Solaris, *BSD, Linux, macOS, HP-UX 11.x and AIX 5.3 and above. It should be supported on most operating systems that support the
LD_PRELOAD
environment variable or an equivalent. It is not possible to intercept shell built-in commands or restrict the ability to read or write sensitive files from within a shell.To enable intercept mode on a per-command basis, use the
INTERCEPT
tag as documented in the User Specification section above. Here is that example again:chuck research = INTERCEPT: ALL
This allows user chuck to run any command on the machine “research” in intercept mode. Any commands run via shell escapes will be validated and logged by
sudo
. If you are unsure whether or not your system is capable of supporting intercept, you can always just try it out and check whether or not external commands run via a shell are logged when intercept is enabled.There is an inherent race condition between when a command is checked against
sudoers
rules and when it is actually executed. If a user is allowed to run arbitrary commands, they may be able to change the execve(2) arguments in the program after thesudoers
policy check has completed but before the new command is executed. Starting with version 1.9.12, the trace method will verify that the command and its arguments have not changed after execve(2) has completed but before execution of the new program has had a chance to run. This is not the case with the dso method. See the description of the intercept_verify setting for more information. - log
- There are two separate but related ways to log additional commands. The first is to enable I/O logging using the log_output flag. This will log the command's output but will not create an event log entry when the additional command is run. The second is to enable the log_subcmds flag in sudoers which will create an event log entry every time a new command is run. If I/O logging is also enabled, the log entry will include a time offset into the I/O log to indicate when the command was run. This offset can be passed to the sudoreplay(8) utility to replay the I/O log at the exact moment when the command was run. The log_subcmds flag uses the same mechanism as intercept (see above) and has the same limitations.
- noexec
sudo
's noexec functionality can be used to prevent a program run bysudo
from executing any other programs. On most systems, it uses the sameLD_PRELOAD
mechanism as intercept (see above) and thus the same caveats apply. The noexec functionality is capable of blocking execution of commands run via the execve(2), execl(3), execle(3), execlp(3), exect(3), execv(3), execveat(3), execvP(3), execvp(3), execvpe(3), fexecve(3), popen(3), posix_spawn(3), posix_spawnp(3), system(3), and wordexp(3) functions. On Linux, a seccomp(2) filter is used to implement noexec. On Solaris 10 and higher, noexec uses Solaris privileges instead of theLD_PRELOAD
environment variable.To enable noexec for a command, use the
NOEXEC
tag as documented in the User Specification section above. Here is that example again:aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. This will prevent those two commands from executing other commands (such as a shell). If you are unsure whether or not your system is capable of supporting noexec you can always just try it out and check whether shell escapes work when noexec is enabled.
Restricting shell escapes is not a panacea. Programs running as
root are still capable of many potentially hazardous
operations (such as changing or overwriting files) that could lead to
unintended privilege escalation. In the specific case of an editor, a safer
approach is to give the user permission to run
sudoedit
(see below).
Secure editing¶
The sudoers
plugin includes
sudoedit
support which allows users to securely edit
files with the editor of their choice. As sudoedit
is a built-in command, it must be specified in the sudoers
file without a leading path. However, it may take command line arguments
just as a normal command does. Wildcards used in sudoedit
command line arguments are expected to be path names, so a forward slash
(‘/
’) will not be matched by a
wildcard.
Unlike other sudo
commands, the editor is
run with the permissions of the invoking user and with the environment
unmodified. More information may be found in the description of the
-e
option in sudo(8).
For example, to allow user operator to edit the “message of the day” file on any machine:
operator ALL = sudoedit /etc/motd
The operator user then runs sudoedit
as
follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy of /etc/motd. After the file has been edited, /etc/motd will be updated with the contents of the temporary copy.
Users should never be
granted sudoedit
permission to edit a file that
resides in a directory the user has write access to, either directly or via
a wildcard. If the user has write access to the directory it is possible to
replace the legitimate file with a link to another file, allowing the
editing of arbitrary files. To prevent this, starting with version 1.8.16,
symbolic links will not be followed in writable directories and
sudoedit
will refuse to edit a file located in a
writable directory unless the
sudoedit_checkdir
option has been disabled or the invoking user is root.
Additionally, in version 1.8.15 and higher, sudoedit
will refuse to open a symbolic link unless either the
sudoedit_follow option is enabled or the
sudoedit command is prefixed with the
FOLLOW
tag in the sudoers
file.
Time stamp file checks¶
sudoers
will check the ownership of its
time stamp directory (/run/sudo/ts by default) and
ignore the directory's contents if it is not owned by root
or if it is writable by a user other than root. Older
versions of sudo
stored time stamp files in
/tmp; this is no longer recommended as it may be
possible for a user to create the time stamp themselves on systems that
allow unprivileged users to change the ownership of files they create.
While the time stamp directory
should be cleared
at reboot time, not all systems contain a /run or
/var/run directory. To avoid potential problems,
sudoers
will ignore time stamp files that date from
before the machine booted on systems where the boot time is available.
Some systems with graphical desktop environments allow
unprivileged users to change the system clock. Since
sudoers
relies on the system clock for time stamp
validation, it may be possible on such systems for a user to run
sudo
for longer than
timestamp_timeout by setting the clock back. To combat
this, sudoers
uses a monotonic clock (which never
moves backwards) for its time stamps if the system supports it.
sudoers
will not honor time stamps set far
in the future. Time stamps with a date greater than current_time + 2 *
TIMEOUT
will be ignored and
sudoers
will log and complain.
If the timestamp_type option is set to “tty”, the time stamp record includes the device number of the terminal the user authenticated with. This provides per-terminal granularity but time stamp records may still outlive the user's session.
Unless the timestamp_type option is set to “global”, the time stamp record also includes the session ID of the process that last authenticated. This prevents processes in different terminal sessions from using the same time stamp record. On systems where a process's start time can be queried, the start time of the session leader is recorded in the time stamp record. If no terminal is present or the timestamp_type option is set to “ppid”, the start time of the parent process is used instead. In most cases this will prevent a time stamp record from being re-used without the user entering a password when logging out and back in again.
DEBUGGING¶
Versions 1.8.4 and higher of the sudoers
plugin support a flexible debugging framework that can help track down what
the plugin is doing internally if there is a problem. This can be configured
in the sudo.conf(5) file.
The sudoers
plugin uses the
same debug flag format as the sudo
front-end:
subsystem@priority.
The priorities used by sudoers
,
in order of decreasing severity, are: crit,
err,
warn,
notice,
diag,
info, trace, and
debug. Each priority, when specified, also includes all
priorities higher than it. For example, a priority of
notice would include debug messages logged at
notice and higher.
The following subsystems are used by the
sudoers
plugin:
- alias
- User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias processing
- all
- matches every subsystem
- audit
- BSM and Linux audit code
- auth
- user authentication
- defaults
- sudoers file Defaults settings
- env
- environment handling
- ldap
- LDAP-based sudoers
- logging
- logging support
- match
- matching of users, groups, hosts, and netgroups in the sudoers file
- netif
- network interface handling
- nss
- network service switch handling in
sudoers
- parser
- sudoers file parsing
- perms
- permission setting
- plugin
- The equivalent of main for the plugin.
- pty
- pseudo-terminal related code
- rbtree
- redblack tree internals
- sssd
- SSSD-based sudoers
- util
- utility functions
For example:
Debug sudoers.so /var/log/sudoers_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
SEE ALSO¶
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5), sudo_plugin(5), sudoers.ldap(5), sudoers_timestamp(5), sudo(8), visudo(8)
AUTHORS¶
Many people have worked on sudo
over the
years; this version consists of code written primarily by:
See the CONTRIBUTORS.md file in the sudo
distribution (https://www.sudo.ws/about/contributors/) for an exhaustive
list of people who have contributed to sudo
.
CAVEATS¶
The sudoers file should
always
be edited by the visudo
utility which locks the file
and checks for syntax errors. If sudoers contains syntax
errors, sudo
may refuse to run, which is a serious
problem if sudo
is your only method of obtaining
superuser privileges. Recent versions of sudoers
will attempt to recover after a syntax error by ignoring the rest of the
line after encountering an error. Older versions of
sudo
will not run if sudoers
contains a syntax error.
When using netgroups of machines (as opposed to users), if you store fully qualified host name in the netgroup (as is usually the case), you either need to have the machine's host name be fully qualified as returned by the hostname command or use the fqdn option in sudoers.
BUGS¶
If you believe you have found a bug in
sudo
, you can submit a bug report at
https://bugzilla.sudo.ws/
SUPPORT¶
Limited free support is available via the sudo-users mailing list, see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
DISCLAIMER¶
sudo
is provided “AS IS” and
any express or implied warranties, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose
are disclaimed. See the LICENSE.md file distributed with
sudo
or https://www.sudo.ws/about/license/ for
complete details.
January 16, 2023 | Sudo 1.9.13p3 |