NAME¶
sudo
,
sudoedit
—
execute a command as another user
SYNOPSIS¶
sudo |
-v
[-AknS ]
[-a
type ]
[-g
group ]
[-h
host ]
[-p
prompt ]
[-u
user ] |
sudo |
-l
[-AknS ]
[-a
type ]
[-g
group ]
[-h
host ]
[-p
prompt ]
[-U
user ]
[-u
user ]
[command ] |
sudo |
[ -AbEHnPS ]
[-a
type ]
[-C
num ]
[-c
class ]
[-g
group ]
[-h
host ]
[-p
prompt ]
[-r
role ]
[-t
type ]
[-u
user ]
[VAR=value ]
[-i |
-s ]
[command ] |
sudoedit |
[ -AknS ]
[-a
type ]
[-C
num ]
[-c
class ]
[-g
group ]
[-h
host ]
[-p
prompt ]
[-u
user ]
file ... |
DESCRIPTION¶
sudo
allows a permitted user to execute a
command as the superuser or another user, as
specified by the security policy.
sudo
supports a plugin architecture for
security policies and input/output logging. Third parties can develop and
distribute their own policy and I/O logging plugins to work seamlessly with
the
sudo
front end. The default security
policy is
sudoers, which is configured via the
file
/etc/sudoers, or via LDAP. See the
Plugins section for more
information.
The security policy determines what privileges, if any, a user has to run
sudo
. The policy may require that users
authenticate themselves with a password or another authentication mechanism.
If authentication is required,
sudo
will
exit if the user's password is not entered within a configurable time limit.
This limit is policy-specific; the default password prompt timeout for the
sudoers security policy is unlimited.
Security policies may support credential caching to allow the user to run
sudo
again for a period of time without
requiring authentication. The
sudoers policy
caches credentials for
15
minutes, unless overridden
in
sudoers(5). By running
sudo
with the
-v
option, a user can update the cached
credentials without running a
command.
When invoked as
sudoedit
, the
-e
option (described below), is implied.
Security policies may log successful and failed attempts to use
sudo
. If an I/O plugin is configured, the
running command's input and output may be logged as well.
The options are as follows:
-A
,
--askpass
- Normally, if
sudo
requires a password,
it will read it from the user's terminal. If the
-A
(askpass) option is specified, a (possibly
graphical) helper program is executed to read the user's password and
output the password to the standard output. If the
SUDO_ASKPASS
environment variable is
set, it specifies the path to the helper program. Otherwise, if
sudo.conf(5) contains a line specifying the
askpass program, that value will be used. For example:
# Path to askpass helper program
Path askpass /usr/X11R6/bin/ssh-askpass
If no askpass program is available, sudo
will exit with an error.
-b
,
--background
- Run the given command in the background. Note that it is not possible to
use shell job control to manipulate background processes started by
sudo
. Most interactive commands will
fail to work properly in background mode.
-C
num,
--close-from
=num
- Close all file descriptors greater than or equal to
num before executing a command. Values
less than three are not permitted. By default,
sudo
will close all open file
descriptors other than standard input, standard output and standard error
when executing a command. The security policy may restrict the user's
ability to use this option. The sudoers
policy only permits use of the -C
option when the administrator has enabled the
closefrom_override option.
-E
,
--preserve-env
- Indicates to the security policy that the user wishes to preserve their
existing environment variables. The security policy may return an error if
the user does not have permission to preserve the environment.
-e
,
--edit
- Edit one or more files instead of running a command. In lieu of a path
name, the string "sudoedit" is used when consulting the security
policy. If the user is authorized by the policy, the following steps are
taken:
- Temporary copies are made of the files to be edited with the owner set
to the invoking user.
- The editor specified by the policy is run to edit the temporary files.
The sudoers policy uses the
SUDO_EDITOR
,
VISUAL
and
EDITOR
environment variables (in
that order). If none of
SUDO_EDITOR
,
VISUAL
or
EDITOR
are set, the first program
listed in the editor
sudoers(5) option is used.
- If they have been modified, the temporary files are copied back to
their original location and the temporary versions are removed.
Unless explicitly allowed by the security policy, symbolic links will not be
opened. This helps prevent the editing of unauthorized files when the file
is located in a user-writable directory. Versions of
sudo
prior to 1.8.10p3-1+deb8u3 do not
have this restriction. Users are never allowed to edit device special
files.
If the specified file does not exist, it will be created. Note that unlike
most commands run by sudo, the editor is run
with the invoking user's environment unmodified. If, for some reason,
sudo
is unable to update a file with
its edited version, the user will receive a warning and the edited copy
will remain in a temporary file.
-g
group,
--group
=group
- Run the command with the primary group set to
group instead of the primary group
specified by the target user's password database entry. The
group may be either a group name or a
numeric group ID (GID) prefixed with the
‘
#
’ character (e.g.
#0
for GID 0). When running a command as a GID,
many shells require that the ‘#
’ be
escaped with a backslash (‘\
’). If
no -u
option is specified, the command
will be run as the invoking user. In either case, the primary group will
be set to group.
-H
,
--set-home
- Request that the security policy set the
HOME
environment variable to the home
directory specified by the target user's password database entry.
Depending on the policy, this may be the default behavior.
-h
,
--help
- Display a short help message to the standard output and exit.
-h
host,
--host
=host
- Run the command on the specified host if
the security policy plugin supports remote commands. Note that the
sudoers plugin does not currently support
running remote commands. This may also be used in conjunction with the
-l
option to list a user's privileges
for the remote host.
-i
,
--login
- Run the shell specified by the target user's password database entry as a
login shell. This means that login-specific resource files such as
.profile or
.login will be read by the shell. If a
command is specified, it is passed to the shell for execution via the
shell's
-c
option. If no command is
specified, an interactive shell is executed.
sudo
attempts to change to that user's
home directory before running the shell. The command is run with an
environment similar to the one a user would receive at log in. The
Command Environment section in the
sudoers(5) manual documents how the
-i
option affects the environment in
which a command is run when the sudoers
policy is in use.
-K
,
--remove-timestamp
- Similar to the
-k
option, except that
it removes the user's cached credentials entirely and may not be used in
conjunction with a command or other option. This option does not require a
password. Not all security policies support credential caching.
-k
,
--reset-timestamp
- When used without a command, invalidates the user's cached credentials. In
other words, the next time
sudo
is run
a password will be required. This option does not require a password and
was added to allow a user to revoke
sudo
permissions from a
.logout file.
When used in conjunction with a command or an option that may require a
password, this option will cause sudo
to ignore the user's cached credentials. As a result,
sudo
will prompt for a password (if one
is required by the security policy) and will not update the user's cached
credentials.
Not all security policies support credential caching.
-l
,
--list
- If no command is specified, list the
allowed (and forbidden) commands for the invoking user (or the user
specified by the
-U
option) on the
current host. A longer list format is used if this option is specified
multiple times and the security policy supports a verbose output format.
If a command is specified and is permitted
by the security policy, the fully-qualified path to the command is
displayed along with any command line arguments. If
command is specified but not allowed,
sudo
will exit with a status value of
1.
-n
,
--non-interactive
- Avoid prompting the user for input of any kind. If a password is required
for the command to run,
sudo
will
display an error message and exit.
-P
,
--preserve-groups
- Preserve the invoking user's group vector unaltered. By default, the
sudoers policy will initialize the group
vector to the list of groups the target user is a member of. The real and
effective group IDs, however, are still set to match the target user.
-p
prompt,
--prompt
=prompt
- Use a custom password prompt with optional escape sequences. The following
percent (‘
%
’) escape sequences are
supported by the sudoers policy:
%H
- expanded to the host name including the domain name (on if the
machine's host name is fully qualified or the
fqdn option is set in
sudoers(5))
%h
- expanded to the local host name without the domain name
%p
- expanded to the name of the user whose password is being requested
(respects the rootpw,
targetpw, and
runaspw flags in
sudoers(5))
%U
- expanded to the login name of the user the command will be run as
(defaults to root unless the
-u
option is also specified)
%u
- expanded to the invoking user's login name
%%
- two consecutive ‘
%
’ characters
are collapsed into a single ‘%
’
character
The custom prompt will override the system password prompt on systems that
support PAM unless the passprompt_override
flag is disabled in sudoers.
-r
role,
--role
=role
- Run the command with an SELinux security context that includes the
specified role.
-S
,
--stdin
- Write the prompt to the standard error and read the password from the
standard input instead of using the terminal device. The password must be
followed by a newline character.
-s
,
--shell
- Run the shell specified by the
SHELL
environment variable if it is set or the shell specified by the invoking
user's password database entry. If a command is specified, it is passed to
the shell for execution via the shell's
-c
option. If no command is specified,
an interactive shell is executed.
-t
type,
--type
=type
- Run the command with an SELinux security context that includes the
specified type. If no
type is specified, the default type is
derived from the role.
-U
user,
--other-user
=user
- Used in conjunction with the
-l
option
to list the privileges for user instead
of for the invoking user. The security policy may restrict listing other
users' privileges. The sudoers policy only
allows root or a user with the ALL
privilege on
the current host to use this option.
-u
user,
--user
=user
- Run the command as a user other than the default target user (usually
root ). The
user may be either a user name or a
numeric user ID (UID) prefixed with the
‘
#
’ character (e.g.
#0
for UID 0). When running commands as a UID,
many shells require that the ‘#
’ be
escaped with a backslash (‘\
’). Some
security policies may restrict UIDs to those listed in the password
database. The sudoers policy allows UIDs that
are not in the password database as long as the
targetpw option is not set. Other security
policies may not support this.
-V
,
--version
- Print the
sudo
version string as well
as the version string of the security policy plugin and any I/O plugins.
If the invoking user is already root the
-V
option will display the arguments
passed to configure when sudo
was built
and plugins may display more verbose information such as default
options.
-v
,
--validate
- Update the user's cached credentials, authenticating the user if
necessary. For the sudoers plugin, this
extends the
sudo
timeout for another
15
minutes by default, but does not run a command.
Not all security policies support cached credentials.
--
- The
--
option indicates that
sudo
should stop processing command
line arguments.
Environment variables to be set for the command may also be passed on the
command line in the form of
VAR=
value,
e.g.
LD_LIBRARY_PATH
=
/usr/local/pkg/lib.
Variables passed on the command line are subject to restrictions imposed by
the security policy plugin. The
sudoers policy
subjects variables passed on the command line to the same restrictions as
normal environment variables with one important exception. If the
setenv option is set in
sudoers, the command to be run has the
SETENV
tag set or the command matched is
ALL
, the user may set variables that would otherwise
be forbidden. See
sudoers(5) for more
information.
COMMAND EXECUTION¶
When
sudo
executes a command, the security
policy specifies the execution environment for the command. Typically, the
real and effective user and group and IDs are set to match those of the target
user, as specified in the password database, and the group vector is
initialized based on the group database (unless the
-P
option was specified).
The following parameters may be specified by security policy:
- real and effective user ID
- real and effective group ID
- supplementary group IDs
- the environment list
- current working directory
- file creation mode mask (umask)
- SELinux role and type
- scheduling priority (aka nice value)
Process model¶
When
sudo
runs a command, it calls
fork(2), sets up the execution environment as
described above, and calls the
execve system call
in the child process. The main
sudo
process
waits until the command has completed, then passes the command's exit status
to the security policy's close function and exits. If an I/O logging plugin is
configured or if the security policy explicitly requests it, a new
pseudo-terminal (“pty”) is created and a second
sudo
process is used to relay job control
signals between the user's existing pty and the new pty the command is being
run in. This extra process makes it possible to, for example, suspend and
resume the command. Without it, the command would be in what POSIX terms an
“orphaned process group” and it would not receive any job
control signals. As a special case, if the policy plugin does not define a
close function and no pty is required,
sudo
will execute the command directly instead of calling
fork(2) first. The
sudoers policy plugin will only define a close
function when I/O logging is enabled, a pty is required, or the
pam_session or
pam_setcred options are enabled. Note that
pam_session and
pam_setcred are enabled by default on systems
using PAM.
Signal handling¶
When the command is run as a child of the
sudo
process,
sudo
will relay signals it receives to the
command. Unless the command is being run in a new pty, the
SIGHUP
,
SIGINT
and
SIGQUIT
signals are not relayed unless they
are sent by a user process, not the kernel. Otherwise, the command would
receive
SIGINT
twice every time the user
entered control-C. Some signals, such as
SIGSTOP
and
SIGKILL
, cannot be caught and thus will not
be relayed to the command. As a general rule,
SIGTSTP
should be used instead of
SIGSTOP
when you wish to suspend a command
being run by
sudo
.
As a special case,
sudo
will not relay
signals that were sent by the command it is running. This prevents the command
from accidentally killing itself. On some systems, the
reboot(8) command sends
SIGTERM
to all non-system processes other
than itself before rebooting the system. This prevents
sudo
from relaying the
SIGTERM
signal it received back to
reboot(8), which might then exit before the
system was actually rebooted, leaving it in a half-dead state similar to
single user mode. Note, however, that this check only applies to the command
run by
sudo
and not any other processes
that the command may create. As a result, running a script that calls
reboot(8) or
shutdown(8) via
sudo
may cause the system to end up in this
undefined state unless the
reboot(8) or
shutdown(8) are run using the
exec
() family of functions instead of
system
() (which interposes a shell between
the command and the calling process).
If no I/O logging plugins are loaded and the policy plugin has not defined a
close
() function, set a command timeout or
required that the command be run in a new pty,
sudo
may execute the command directly
instead of running it as a child process.
Plugins¶
Plugins may be specified via
Plugin
directives in the
sudo.conf(5) file. They may be loaded as dynamic
shared objects (on systems that support them), or compiled directly into the
sudo
binary. If no
sudo.conf(5) file is present, or it contains no
Plugin
lines,
sudo
will use the traditional
sudoers security policy
and I/O logging. See the
sudo.conf(5) manual for
details of the
/etc/sudo.conf file and the
sudo_plugin(8) manual for more information about
the
sudo
plugin architecture.
EXIT VALUE¶
Upon successful execution of a program, the exit status from
sudo will simply be the exit status of the
program that was executed.
Otherwise,
sudo
exits with a value of 1 if
there is a configuration/permission problem or if
sudo
cannot execute the given command. In
the latter case the error string is printed to the standard error. If
sudo
cannot
stat(2) one or more entries in the user's
PATH
, an error is printed on stderr. (If
the directory does not exist or if it is not really a directory, the entry is
ignored and no error is printed.) This should not happen under normal
circumstances. The most common reason for
stat(2)
to return “permission denied” is if you are running an
automounter and one of the directories in your
PATH
is on a machine that is currently
unreachable.
SECURITY NOTES¶
sudo
tries to be safe when executing external
commands.
To prevent command spoofing,
sudo
checks
"." and "" (both denoting current directory) last when
searching for a command in the user's
PATH
(if one or both are in the
PATH
). Note,
however, that the actual
PATH
environment
variable is
not modified and is passed unchanged
to the program that
sudo
executes.
Please note that
sudo
will normally only log
the command it explicitly runs. If a user runs a command such as
sudo su
or
sudo sh
, subsequent
commands run from that shell are not subject to
sudo
's security policy. The same is true
for commands that offer shell escapes (including most editors). If I/O logging
is enabled, subsequent commands will have their input and/or output logged,
but there will not be traditional logs for those commands. Because of this,
care must be taken when giving users access to commands via
sudo
to verify that the command does not
inadvertently give the user an effective root shell. For more information,
please see the
PREVENTING SHELL ESCAPES section
in
sudoers(5).
To prevent the disclosure of potentially sensitive information,
sudo
disables core dumps by default while
it is executing (they are re-enabled for the command that is run). To aid in
debugging
sudo
crashes, you may wish to
re-enable core dumps by setting “disable_coredump” to false in
the
sudo.conf(5) file as follows:
Set disable_coredump false
See the
sudo.conf(5) manual for more information.
ENVIRONMENT¶
sudo
utilizes the following environment
variables. The security policy has control over the actual content of the
command's environment.
EDITOR
- Default editor to use in
-e
(sudoedit)
mode if neither SUDO_EDITOR
nor
VISUAL
is set.
MAIL
- In
-i
mode or when
env_reset is enabled in
sudoers, set to the mail spool of the target
user.
HOME
- Set to the home directory of the target user if
-i
or
-H
are specified,
env_reset or
always_set_home are set in
sudoers, or when the
-s
option is specified and
set_home is set in
sudoers.
PATH
- May be overridden by the security policy.
SHELL
- Used to determine shell to run with
-s
option.
SUDO_ASKPASS
- Specifies the path to a helper program used to read the password if no
terminal is available or if the
-A
option is specified.
SUDO_COMMAND
- Set to the command run by sudo.
SUDO_EDITOR
- Default editor to use in
-e
(sudoedit)
mode.
SUDO_GID
- Set to the group ID of the user who invoked sudo.
SUDO_PROMPT
- Used as the default password prompt.
SUDO_PS1
- If set,
PS1
will be set to its value
for the program being run.
SUDO_UID
- Set to the user ID of the user who invoked sudo.
SUDO_USER
- Set to the login name of the user who invoked sudo.
USER
- Set to the target user (root unless the
-u
option is specified).
VISUAL
- Default editor to use in
-e
(sudoedit)
mode if SUDO_EDITOR
is not set.
FILES¶
- /etc/sudo.conf
sudo
front end configuration
EXAMPLES¶
Note: the following examples assume a properly configured security policy.
To get a file listing of an unreadable directory:
$ sudo ls /usr/local/protected
To list the home directory of user yaz on a machine where the file system
holding ~yaz is not exported as root:
To edit the
index.html file as user www:
$ sudo -u www vi ~www/htdocs/index.html
To view system logs only accessible to root and users in the adm group:
$ sudo -g adm view /var/log/syslog
To run an editor as jim with a different primary group:
$ sudo -u jim -g audio vi ~jim/sound.txt
To shut down a machine:
$ sudo shutdown -r +15 "quick reboot"
To make a usage listing of the directories in the /home partition. Note that
this runs the commands in a sub-shell to make the
cd
and file redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
SEE ALSO¶
su(1),
stat(2),
passwd(5),
sudo.conf(5),
sudoers(5),
sudo_plugin(8),
sudoreplay(8),
visudo(8)
HISTORY¶
See the HISTORY file in the
sudo
distribution
(
http://www.sudo.ws/sudo/history.html) for a brief history of sudo.
AUTHORS¶
Many people have worked on
sudo
over the
years; this version consists of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS file in the
sudo
distribution (
http://www.sudo.ws/sudo/contributors.html) for an exhaustive
list of people who have contributed to
sudo
.
CAVEATS¶
There is no easy way to prevent a user from gaining a root shell if that user is
allowed to run arbitrary commands via
sudo
.
Also, many programs (such as editors) allow the user to run commands via shell
escapes, thus avoiding
sudo
's checks.
However, on most systems it is possible to prevent shell escapes with the
sudoers(5) plugin's
noexec functionality.
It is not meaningful to run the
cd
command directly via
sudo, e.g.,
$ sudo cd /usr/local/protected
since when the command exits the parent process (your shell) will still be the
same. Please see the
EXAMPLES
section for more information.
Running shell scripts via
sudo
can expose the
same kernel bugs that make setuid shell scripts unsafe on some operating
systems (if your OS has a /dev/fd/ directory, setuid shell scripts are
generally safe).
BUGS¶
If you feel you have found a bug in
sudo
,
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
http://www.sudo.ws/sudo/license.html for complete details.