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SUDOERS(5) | File Formats Manual | SUDOERS(5) |
NAME¶
sudoers
—
default sudo security policy plugin
DESCRIPTION¶
The sudoers policy plugin determines a user'ssudo
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, please see
sudoers.ldap(5).
Configuring sudo.conf for sudoers¶
sudo
consults the
sudo.conf(5) file to determine which policy and
and I/O logging plugins to load. If no
sudo.conf(5) file is present, or if it contains
no Plugin
lines,
sudoers
will be used for 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_policy sudoers.so Plugin sudoers_io sudoers.so
sudo
1.8.5, it is possible to
specify optional arguments to the sudoers
plugin in the sudo.conf(5) file. These arguments,
if present, should be listed after the path to the plugin (i.e. after
sudoers.so). Multiple arguments may be
specified, separated by white space. For example:
Plugin sudoers_policy sudoers.so sudoers_mode=0400
- 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=uid
- 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=gid
- 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.
Authentication and logging¶
The sudoers security policy requires that most users authenticate themselves before they can usesudo
. 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
.
Note that mail will not be sent if an unauthorized user tries to run
sudo
with the
-l
or -v
option. This allows users to determine for themselves whether or not they are
allowed to use sudo
.
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 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 uid that was used to authenticate, the terminal session ID, 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
timeout option). By default,
sudoers uses a separate record for each tty,
which means that a user's login sessions are authenticated separately. The
tty_tickets option can be disabled to force the
use of a single time stamp for all of a user's sessions.
sudoers can log both successful and unsuccessful
attempts (as well as errors) to syslog(3), a log
file, or both. By default, sudoers will log via
syslog(3) but this is changeable via the
syslog and logfile
Defaults settings.
sudoers also supports logging a command's input and
output streams. I/O logging is not on by default but can be enabled using the
log_input and
log_output Defaults flags as well as the
LOG_INPUT
and LOG_OUTPUT
command tags.
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 option 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 new environment contains theTERM
,
PATH
,
HOME
,
MAIL
,
SHELL
,
LOGNAME
,
USER
,
USERNAME
and
SUDO_*
variables in addition to variables
from the invoking process permitted by the
env_check and
env_keep options. This is effectively a whitelist
for environment variables.
If, however, the env_reset option is disabled, any
variables not explicitly denied by the env_check
and env_delete options are inherited from the
invoking process. In this case, env_check and
env_delete behave like a blacklist. Since it is
not possible to blacklist all potentially dangerous environment variables, use
of the default env_reset behavior is encouraged.
In all cases, environment variables with a value beginning with
()
are removed as they could be interpreted as
bash functions. The list of environment variables
that sudo
allows or denies is contained in
the output of “sudo -V
” when run as
root.
Note that the dynamic linker on most operating systems will remove variables
that can control dynamic linking from the environment of setuid 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 sudo
's
-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.
Finally, if the env_file option is defined, any
variables present in that file will be set to their specified values as long
as 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 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.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. E.g.,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.
Aliases¶
There are four kinds of aliases:User_Alias
,
Runas_Alias
, Host_Alias
and
Cmnd_Alias
.
Alias ::= 'User_Alias' User_Alias (':' User_Alias)* | 'Runas_Alias' Runas_Alias (':' Runas_Alias)* | 'Host_Alias' Host_Alias (':' Host_Alias)* | 'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)* User_Alias ::= NAME '=' User_List Runas_Alias ::= NAME '=' Runas_List Host_Alias ::= NAME '=' Host_List Cmnd_Alias ::= NAME '=' Cmnd_List NAME ::= [A-Z]([A-Z][0-9]_)*
Alias_Type NAME = item1, item2, ...
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
(‘:
’). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
User_List ::= User | User ',' User_List User ::= '!'* user name | '!'* #uid | '!'* %group | '!'* %#gid | '!'* +netgroup | '!'* %:nonunix_group | '!'* %:#nonunix_gid | '!'* User_Alias
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_Alias
es. 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.
A user name
, uid
,
group
, gid
,
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"
\
’) 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 | '!'* #uid | '!'* %group | '!'* %#gid | '!'* %:nonunix_group | '!'* %:#nonunix_gid | '!'* +netgroup | '!'* Runas_Alias
Runas_List
is similar to a
User_List
except that instead of
User_Alias
es it can contain
Runas_Alias
es. Note that user names and groups are
matched as strings. In other words, two users (groups) with the same uid (gid)
are considered to be distinct. If you wish to match all user names with the
same uid (e.g. root and toor), you can use a uid instead (#0 in the example
given).
Host_List ::= Host | Host ',' Host_List Host ::= '!'* host name | '!'* ip_addr | '!'* network(/netmask)? | '!'* +netgroup | '!'* Host_Alias
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. If you do not specify a netmask along with the network number,
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, the corresponding netmask will be used. 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 host name
command on your machine returns
the fully qualified host name, you'll need to use the
fqdn option for wildcards to be useful. Note that
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 Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List command name ::= file name | file name args | file name '""' Cmnd ::= Digest_Spec? '!'* command name | '!'* directory | '!'* "sudoedit" | '!'* Cmnd_Alias
Cmnd_List
is a list of one or more command names,
directories, and other aliases. A command name is a fully qualified file name
which may include shell-style wildcards (see the
Wildcards section below). A
simple file name allows the user to run the command with any arguments he/she
wishes. However, you may also specify command line arguments (including
wildcards). Alternately, you can specify ""
to indicate that the command may only be run
without command line arguments. 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 a Cmnd
has associated command line arguments, then
the arguments in the Cmnd
must match exactly those
given by the user on the command line (or match the wildcards if there are
any). Note that the following characters must be escaped with a
‘\
’ if they are used in command
arguments: ‘,
’,
‘:
’,
‘=
’,
‘\
’. The built-in command
“sudoedit
” 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. Note that
“sudoedit
” is a command built into
sudo
itself and must be specified in
sudoers without a leading path.
If a command name
is prefixed with a
Digest_Spec
, the command will only match successfully
if it can be verified using the specified SHA-2 digest. This may be useful in
situations where the user invoking sudo
has
write access to the command or its parent directory. 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
$ openssl dgst -binary -sha224 /bin/ls | openssl base64 EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Defaults¶
Certain configuration options may be changed from their default values at run-time via one or moreDefault_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. Note that
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
!
’ 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
(‘\
’).
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: generic, host and user
Defaults first, then runas Defaults and finally command defaults.
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? SELinux_Spec? Tag_Spec* Cmnd Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')' SELinux_Spec ::= ('ROLE=role' | 'TYPE=type') Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' | 'SETENV:' | 'NOSETENV:' | 'FOLLOW:' | 'NOFOLLOW' | 'LOG_INPUT:' | 'NOLOG_INPUT:' | 'LOG_OUTPUT:' | 'NOLOG_OUTPUT:')
Runas_Spec¶
ARunas_Spec
determines the user and/or the group that a
command may be run as. A fully-specified Runas_Spec
consists of two Runas_List
s (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
sudo
's
-u
option. The second defines a list of
groups that can be specified via sudo
's
-g
option. If both
Runas_List
s are specified, the command may be run with
any combination of users and groups listed in their respective
Runas_List
s. If only the first is specified, the
command may be run as any user in the list but no
-g
option may be specified. 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_List
s are empty, the command may only be run as
the invoking user. If no Runas_Spec
is specified the
command may be run as root and no group may be
specified.
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
$ sudo -u operator /bin/ls
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
/bin/ls
with either the user or group set to
operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\ /usr/bin/lprm
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
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\ /usr/local/bin/minicom
$ sudo -g dialer /usr/bin/cu
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
SELinux_Spec¶
On systems with SELinux support, sudoers entries may optionally have an SELinux role and/or type associated with a command. 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.Tag_Spec¶
A command may have zero or more tags associated with it. There are ten possible tag values:NOPASSWD
, PASSWD
,
NOEXEC
, EXEC
,
SETENV
, NOSETENV
,
FOLLOW
, NOFOLLOW
,
LOG_INPUT
, NOLOG_INPUT
,
LOG_OUTPUT
and NOLOG_OUTPUT
.
Once a tag is set on a Cmnd
, subsequent
Cmnd
s 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
).
- NOPASSWD and PASSWD
-
By default,
sudo
requires that a user authenticate him or herself before running a command. This behavior can be modified via theNOPASSWD
tag. Like aRunas_Spec
, theNOPASSWD
tag sets a default for the commands that follow it in theCmnd_Spec_List
. Conversely, thePASSWD
tag can be used to reverse things. For example:ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
PASSWD
tag has no effect on users who are in the group specified by the exempt_group option. By default, if theNOPASSWD
tag is applied to any of the entries for a user on the current host, he or she will be able to run “sudo -l
” without a password. Additionally, a user may only run “sudo -v
” without a password if theNOPASSWD
tag is present for all a user's entries that pertain to the current host. This behavior may be overridden via the verifypw and listpw options. - NOEXEC and EXEC
-
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
NOEXEC
works and whether or not it will work on your system. - SETENV and NOSETENV
-
These tags override the value of the setenv
option on a per-command basis. Note that if
SETENV
has been set for a command, the user may disable the env_reset option 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. - FOLLOW and NOFOLLOW
- Starting with version 1.8.10p3-1+deb8u3,
sudoedit
will not follow symbolic links when opening files unless the sudoedit_follow option is enabled. The FOLLOW and NOFOLLOW 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 and NOLOG_INPUT
- These tags override the value of the log_input option on a per-command basis. For more information, see the description of log_input in the SUDOERS OPTIONS section below.
- LOG_OUTPUT and NOLOG_OUTPUT
- These tags override the value of the log_output option on a per-command basis. For more information, see the description of log_output in the SUDOERS OPTIONS section below.
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”).
Note that these are not regular expressions.
*
- Matches any set of zero or more characters.
?
- Matches any single character.
[...]
- 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 has special
meaning in sudoers, it must be escaped. For
example:
/bin/ls [[:alpha:]]*
/
’) will
not be matched by wildcards used in the path
name. This is to make a path like:
/usr/bin/*
?
’ or
‘*
’ can match multiple words. For
example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
$ sudo cat /var/log/messages.1
$ sudo cat /var/log/messages /etc/shadow
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 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.
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.
This 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 will be
/etc/sudoers and the per-machine one will
be /etc/sudoers.local. To include
/etc/sudoers.local from within
/etc/sudoers we would use the following
line in /etc/sudoers:
#include /etc/sudoers.local
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.
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
%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
sudo
to include the file
/etc/sudoers.xerxes.
The #includedir
directive can be used to create a
sudo.d directory that the system package
manager can drop sudoers rules into as part of
package installation. For example, given:
#includedir /etc/sudoers.d
sudo
will 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.
Note that 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.
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 uid). 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
.
You should not try to define your own alias
called ALL as the built-in alias will be used in
preference to your own. Please note that using
ALL can be dangerous since in a command context,
it allows the user to run any command on the
system.
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
!root
!
’ 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.
Boolean Flags:
- always_set_home
- If enabled,
sudo
will set theHOME
environment variable to the home directory of the target user (which is root unless the-u
option is used). This effectively means that the-H
option is always implied. Note thatHOME
is already set when the env_reset option is enabled, so always_set_home is only effective for configurations where either env_reset is disabled orHOME
is present in the env_keep list. 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. - closefrom_override
- If set, the user may use
sudo
's-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. - 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 substring match on the server. If netgroups are not needed, this option can be disabled to reduce the load on the LDAP server. This flag is on by default. - 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 pty (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 pty. 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, Mac OS X fails to restart thetcgetattr
() andtcsetattr
() system calls (this is a bug in Mac OS X). Furthermore, because this behavior depends on the command stopping with theSIGTTIN
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 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 theEDITOR
orVISUAL
environment variables before falling back on the default editor list. Note that this may create a security hole as it allows the user to run any arbitrary command as root without logging. A safer alternative is to place a colon-separated list of editors in theeditor
variable.visudo
will then only use theEDITOR
orVISUAL
if they match a value specified ineditor
. 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
,USERNAME
andSUDO_*
variables. Any variables in the caller's environment that match theenv_keep
andenv_check
lists are then added, followed by any variables present in the file specified by the env_file option (if any). The default contents of theenv_keep
andenv_check
lists are displayed whensudo
is run by root with the-V
option. If the secure_path option is set, 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 option 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 path names 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 option should not be used when sudoers contains rules that contain negated path names which include globbing characters. This flag is off by default. - 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 option is only effective when the “canonical” host name, as returned by thegetaddrinfo
() orgethostbyname
() 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 bysudoers
. 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.If the machine's hosts file entry is not formatted properly, the fqdn option will not be effective if it is queried before DNS. Beware that when using DNS for host name resolution, turning on fqdn requires192.168.1.1 xyzzy.sudo.ws xyzzy
sudoers
to make DNS lookups which renderssudo
unusable if DNS stops working (for example if the machine is disconnected from the network). Also note that 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_dot
- If set,
sudo
will ignore "." or "" (both denoting current directory) in thePATH
environment variable; thePATH
itself is not modified. This flag is off by default. - ignore_local_sudoers
- If set via LDAP, parsing of
/etc/sudoers will be skipped. This is
intended for Enterprises 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 option is
present, /etc/sudoers does not even
need to exist. Since this option tells
sudo
how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for thecn=defaults
section. 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_host
- If set, the host name will be logged in the (non-syslog)
sudo
log file. This flag is off by default. - log_input
- If set,
sudo
will run the command in a pseudo tty and log all user input. If the standard input is not connected to the user's tty, due to I/O redirection or because the command is part of a pipeline, that input is also captured and stored in a separate log file. Input 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 normalsudo
log line, prefixed with “TSID=
”. The iolog_file option may be used to control the format of the session ID. Note that 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 is all that is required. - log_output
- If set,
sudo
will run the command in a pseudo tty and log all output that is sent to the screen, similar to the script(1) command. If the standard output or standard error is not connected to the user's tty, due to I/O redirection or because the command is part of a pipeline, that output is also captured and stored in separate log files. Output 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 normalsudo
log line, prefixed with “TSID=
”. The iolog_file option may be used to control the format of the session ID. Output logs may be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs. - 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_always
- Send mail to the mailto user every time a
users 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 by sudoers and one of the 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.
- noexec
- If set, all commands run via
sudo
will behave as if theNOEXEC
tag has been set, unless overridden by aEXEC
tag. See the description of NOEXEC and EXEC below as well as the Preventing shell escapes section at the end of this manual. This flag is off by default. - pam_session
- On systems that use PAM for authentication,
sudo
will create a new PAM session for the command to be run in. 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 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 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
- The password prompt specified by passprompt will normally only be used if the password prompt provided by systems such as PAM matches the string “Password:”. If passprompt_override is set, passprompt will always be used. 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. Note that 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. - runaspw
- If set,
sudo
will prompt for the password of the user defined by the runas_default option (defaults toroot
) instead of the password of the invoking user when running a command or editing a file. This flag is off 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 root unless the-u
option is used). This effectively makes the-s
option imply-H
. Note thatHOME
is already set when the env_reset option is enabled, so set_home is only effective for configurations where either env_reset is disabled orHOME
is present in the env_keep list. This flag is off by default. - set_logname
- Normally,
sudo
will set theLOGNAME
,USER
andUSERNAME
environment variables to the name of the target user (usually root 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. Note that if the env_reset option has not been disabled, entries in the env_keep list will override the value of set_logname. This flag is on by default. - set_utmp
- When enabled,
sudo
will create an entry in the utmp (or utmpx) file when a pseudo-tty is allocated. A pseudo-tty is allocated bysudo
when the log_input, log_output or use_pty flags are 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 UIDs are set to the target user (root by default). This option changes that behavior such that the real UID is left as the invoking user's UID. In other words, this makessudo
act as a setuid wrapper. This can be useful on systems that disable some potentially dangerous functionality when a program is run setuid. 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 refuse to edit files located in a directory that is writable by the invoking user unless it is run by root. On many systems, this option requires that the parent directory of the file to be edited be readable by the target user. This flag is on by default. - 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 the FOLLOW and NOFOLLOW tags. This flag is off by default. This setting is only supported by version 1.8.10p3-1+deb8u3 or higher. - targetpw
- If set,
sudo
will prompt for the password of the user specified by the-u
option (defaults toroot
) instead of the password of the invoking user when running a command or editing a file. Note that this flag precludes the use of a uid 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 tty. If disabled, a single record is used for all login sessions. This flag is on by default. - umask_override
- If set,
sudo
will set the umask as specified by sudoers without modification. This makes it possible to specify a more permissive umask in sudoers 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. If set,sudo
will run the command in a pseudo-pty even if no I/O logging is being gone. A malicious program run undersudo
could conceivably fork a background process that retains to the user's terminal device after the main program has finished executing. Use of this option will make that impossible. This flag is off by default. - 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.
- closefrom
- Before it executes a command,
sudo
will close all open file descriptors other than standard input, standard output and standard error (ie: file descriptors 0-2). The closefrom option can be used to specify a different file descriptor at which to start closing. The default is3
. - passwd_tries
- The number of tries a user gets to enter his/her password before
sudo
logs the failure and exits. The default is3
.
- 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, or0
for no timeout. The timeout may include a fractional component if minute granularity is insufficient, for example2.5
. The default is0
. - timestamp_timeout
- Number of minutes that can elapse before
sudo
will ask for a passwd again. The timeout may include a fractional component if minute granularity is insufficient, for example2.5
. The default is15
. Set this to0
to always prompt for a password. If set to a value less than0
the user's time stamp will never expire. This can be used to allow users to create or delete their own time stamps via “sudo -v
” and “sudo -k
” respectively. - umask
- Umask to use when running the command. Negate this option or set it to
0777 to preserve the user's umask. The actual umask that is used will be
the union of the user's umask and the value of the
umask option, which defaults to
0022
. This guarantees thatsudo
never lowers the umask when running a command. Note: on systems that use PAM, the default PAM configuration may specify its own umask which will override the value set in sudoers.
- 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 editors allowed to be used withvisudo
.visudo
will choose the editor that matches the user'sEDITOR
environment variable if possible, or the first editor in the list that exists and is executable. The default is /usr/local/bin/vi. - 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
%
’ 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. Note that 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 moreX
s will have theX
s 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 moreX
s. - 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. - 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 ***
”. - maxseq
- The maximum sequence number that will be substituted for the
“
%{seq}
” escape in the I/O log file (see the iolog_dir description above 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 whichsudoers
will truncate and re-use any existing I/O log path names. This setting is only supported by version 1.8.7 or higher. - 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_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
”. 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
[sudo] password for %p:
”. 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 sudoers or via command line options. This option is only available whensudo
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 toroot
. - syslog_badpri
- Syslog priority to use when user authenticates unsuccessfully. Defaults to
alert
. The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning. - syslog_goodpri
- Syslog priority to use when user authenticates successfully. Defaults to
notice
. See syslog_badpri for the list of supported syslog priorities. - sudoers_locale
- Locale to use when parsing the sudoers file, logging commands, and sending
email. Note that changing the locale may affect how sudoers is
interpreted. Defaults to “
C
”. - timestampdir
- The directory in which
sudo
stores its time stamp files. This directory should be cleared when the system reboots. The default is /var/lib/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 sudoers or via command line options.
This option is only available when
sudo
is built with SELinux support.
- 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 surrounded by single or double quotes. Variables in this file are subject to othersudo
environment settings 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. - 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/lib/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 (""). 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
.
- 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 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
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.
- 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. 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. The address should be enclosed
in double quotes ("") to protect against
sudo
interpreting the@
sign. Defaults toroot
. - secure_path
- Path used for every command run from
sudo
. If you don't trust the people runningsudo
to have a sanePATH
environment variable you may want to use this. Another use is if you want to have the “root path” be separate from the “user path”. 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. - 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 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
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.
- 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
.
=
,+=
,-=
, and!
operators respectively. Regardless of whether theenv_reset
option is enabled or disabled, variables specified byenv_check
will be preserved in the environment if they pass the aforementioned check. The default 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 default list of environment variables to remove is displayed whensudo
is run by root with the-V
option. Note that many operating systems will remove potentially dangerous variables from the environment of any setuid 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 default list of variables to keep is displayed whensudo
is run by root with the-V
option.
GROUP PROVIDER PLUGINS¶
Thesudoers
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 Defaults setting. The argument to
group_plugin should consist of the plugin path,
either fully-qualified or relative to the
/usr/lib/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
() andgetgrid
(). 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
LOG FORMAT¶
sudoers
can log events using either
syslog(3) or a simple log file. In each case the
log format is almost identical.
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 ; PWD=cwd ; \ USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \ ENV=env_vars COMMAND=command
- 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. - 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.
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
sudo
's-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 sudoers 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 stat /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, please
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, please 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 /var/lib/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 /var/lib/sudo is not searchable by group or other. The default mode for /var/lib/sudo is 0711.
- unable to write to /var/lib/sudo/ts/username
- sudoers was unable to write to the user's time stamp file.
- /var/lib/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.
- /var/lib/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 syslog daemon, not sudoers itself. As such, they may vary in format on different systems. On most systems, syslog(3) has a relatively small log buffer. To prevent the command line arguments from being truncated,sudoers
will split up log messages that are
larger than 960 characters (not including the date, hostname, and the string
“sudo”). When a message is split, additional parts will include
the string “(command continued)” after the user name and before
the continued command line arguments.
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 and hostname fields are not present.
- If the log_year option is enabled, the date will also include the year.
- 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.
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
- /var/lib/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 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. Note that other programs use HOME to find # 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 WEBMASTERS = 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 = master, 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
sudo
to log via
syslog(3) using the
auth facility in all cases. We don't want to
subject the full time staff to the sudo
lecture, user millert need not give a password,
and we don't want to reset the LOGNAME
,
USER
or
USERNAME
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). Note that this will not
effectively constrain users with sudo
ALL privileges.
# Override built-in defaults Defaults syslog=auth Defaults>root !set_logname Defaults:FULLTIMERS !lecture Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec
root ALL = (ALL) ALL %wheel ALL = (ALL) ALL
FULLTIMERS ALL = NOPASSWD: ALL
PARTTIMERS ALL = ALL
NOPASSWD
tag).
jack CSNETS = ALL
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
128.138.0.0
).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/
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
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root %opers ALL = (: ADMINGRP) /usr/sbin/
Runas_Alias
(the adm and oper
groups).
The user pete is allowed to change anyone's
password except for root on the HPPA machines.
Note that this assumes passwd(1) does not take
multiple user names on the command line.
bob SPARC = (OP) ALL : SGI = (OP) ALL
Runas_Alias
(root and
operator.)
jim +biglab = ALL
sudo
knows that “biglab” is a
netgroup due to the ‘+
’ prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
fred ALL = (DB) NOPASSWD: ALL
Runas_Alias
(oracle or sybase)
without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
jen ALL, !SERVERS = ALL
Host_Alias
(master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
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/
matt valkyrie = KILL
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
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 nosuidnodev /dev/cd0a /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
!
’ 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 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
/usr/bin/passwd root
if
fast_glob is enabled by changing to
/usr/bin and running
./passwd root
instead.
Preventing shell escapes¶
Oncesudo
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 two 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. - noexec
- Many systems that support shared libraries have the ability to override
default library functions by pointing an environment variable (usually
LD_PRELOAD
) to an alternate shared library. On such systems,sudo
's noexec functionality can be used to prevent a program run bysudo
from executing any other programs. Note, however, that this applies only to native dynamically-linked executables. Statically-linked executables and foreign executables running under binary emulation are not affected. The noexec feature is known to work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, HP-UX 11.x and AIX 5.3 and above. It should be supported on most operating systems that support theLD_PRELOAD
environment variable. Check your operating system's manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see ifLD_PRELOAD
is supported. To enable noexec for a command, use theNOEXEC
tag as documented in the User Specification section above. Here is that example again:aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
sudoedit
(see below).
Secure editing¶
The sudoers plugin includessudoedit
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 sudoers without a leading path.
However, it may take command line arguments just as a normal command does. For
example, to allow user operator to edit the “message of the day”
file:
operator sudoedit /etc/motd
sudoedit
as
follows:
$ sudoedit /etc/motd
Time stamp file checks¶
sudoers will check the ownership of its time stamp directory (/var/lib/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 ofsudo
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
/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.
Since time stamp files live in the file system, they can outlive a user's login
session. As a result, a user may be able to login, run a command with
sudo
after authenticating, logout, login
again, and run sudo
without authenticating
so long as the record's time stamp is within 15
minutes (or whatever value the timeout is set to in
sudoers). When the
tty_tickets option is enabled, the time stamp
record includes the device number of the terminal the user authenticated with.
This provides per-tty granularity but time stamp records still may outlive the
user's session. 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. It also helps reduce the
chance that a user will be able to run sudo
without entering a password when logging out and back in again on the same
terminal.
DEBUGGING¶
Versions 1.8.4 and higher of thesudoers
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
andCmnd_Alias
processing- all
- matches every subsystem
- audit
- BSM and Linux audit code
- auth
- user authentication
- defaults
- sudoers Defaults settings
- env
- environment handling
- ldap
- LDAP-based sudoers
- logging
- logging support
- match
- matching of users, groups, hosts and netgroups in sudoers
- 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-tty related code
- rbtree
- redblack tree internals
- sssd
- SSSD-based sudoers
- util
- utility functions
Debug sudo /var/log/sudo_debug match@info,nss@info
SEE ALSO¶
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5), sudoers.ldap(5), sudo_plugin(8), sudo(8), visudo(8)CAVEATS¶
The sudoers file should always be edited by thevisudo
command which locks the file and
does grammatical checking. It is imperative that
sudoers be free of syntax errors since
sudo
will not run with a syntactically
incorrect sudoers file.
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 feel you have found a bug insudo
,
please submit a bug report at http://www.sudo.ws/sudo/bugs/
SUPPORT¶
Limited free support is available via the sudo-users mailing list, see http://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 file distributed with
sudo
or
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