execute a command as another user
[-i | -s]
allows a permitted user to execute a
as the superuser or another user, as specified
by the security policy. The invoking user's real (not
effective) user ID is used to determine the user name with which to query the
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
front end. The default security policy is
, which is configured via the file
, or via LDAP. See the
section for more information.
The security policy determines what privileges, if any, a user has to run
. 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
security policy is unlimited.
Security policies may support credential caching to allow the user to run
again for a period of time without requiring
authentication. The sudoers
policy caches credentials for
minutes, unless overridden in
. By running sudo
option, a user can update the cached credentials without
running a command
When invoked as sudoedit
, the -e
(described below), is implied.
Security policies may log successful and failed attempts to use
. If an I/O plugin is configured, the running command's
input and output may be logged as well.
The options are as follows:
- 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:
If no askpass program is available, sudo will exit with an
# Path to askpass helper program
Path askpass /usr/X11R6/bin/ssh-askpass
- 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.
- 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
- 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
- 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:
To help prevent the editing of unauthorized files, the following
restrictions are enforced unless explicitly allowed by the security
- 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
EDITOR environment variables (in that
order). If none of
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
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
- Symbolic links may not be edited (version 1.8.15 and
- Symbolic links along the path to be edited are not
followed when the parent directory is writable by the invoking user
unless that user is root (version 1.8.16 and higher).
- Files located in a directory that is writable by the
invoking user may not be edited unless that user is root (version
1.8.16 and higher).
- 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 ‘
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
- 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.
- Display a short help message to the standard output and
- 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
- 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.
- 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.
- 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
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.
- 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.
- 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.
- 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.
- Use a custom password prompt with optional escape
sequences. The following percent (‘
escape sequences are supported by the sudoers policy:
The custom prompt will override the system password prompt on systems that
support PAM unless the passprompt_override flag is
disabled in sudoers.
- 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
- expanded to the local host name without the domain
- expanded to the name of the user whose password is
being requested (respects the rootpw,
targetpw, and runaspw flags in
- expanded to the login name of the user the command will
be run as (defaults to root unless the -u option is
- expanded to the invoking user's login name
- two consecutive ‘
characters are collapsed into a single
- Run the command with an SELinux security context that
includes the specified role.
- 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.
- 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.
- Run the command with an SELinux security context that
includes the specified type. If no
type is specified, the default type is derived from
- 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.
- Used to set a timeout for the command. If the timeout
expires before the command has exited, the command will be terminated. The
security policy may restrict the ability to set command timeouts. The
sudoers policy requires that user-specified timeouts be
- 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 ‘
escaped with a backslash (‘
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.
- 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
- Update the user's cached credentials, authenticating the
user if necessary. For the sudoers plugin, this extends
the sudo timeout for another
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
Variables passed on the command line are subject to restrictions imposed by
the security policy plugin. The sudoers
variables passed on the command line to the same restrictions as normal
environment variables with one important exception. If the
option is set in sudoers
command to be run has the
tag set or the
command matched is
, the user may set variables
that would otherwise be forbidden. See sudoers(5)
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)
runs a command, it calls fork(2)
sets up the execution environment as described above, and calls the
system call in the child process. The main
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)
policy plugin will only define a close function when
I/O logging is enabled, a pty is required, or the
enabled. Note that pam_session
are enabled by default on systems using PAM.
When the command is run as a child of the sudo
will relay signals it receives to the command. The
only relayed when the command is being run in a new pty or when the signal was
sent by a user process, not the kernel. This prevents the command from
twice each time the user enters
control-C. Some signals, such as
, cannot be caught and thus will not be relayed
to the command. As a general rule,
used instead of
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)
to all non-system processes other than itself
before rebooting the system. This prevents sudo
signal it received back to
, 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
and not any other processes that the command may
create. As a result, running a script that calls reboot(8)
may cause the
system to end up in this undefined state unless the
are run using the
() family of functions instead of
() (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
() 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 may be specified via
directives in the
file. They may be loaded as dynamic shared
objects (on systems that support them), or compiled directly into the
binary. If no sudo.conf(5)
present, or it contains no
will use the traditional sudoers
security policy and I/O logging. See the sudo.conf(5)
for details of the /etc/sudo.conf
file and the
manual for more information about the
Upon successful execution of a command, the exit status from
will be the exit status of the program that was
executed. If the command terminated due to receipt of a signal,
will send itself the signal that terminated the
exits with a value of 1 if there is a
configuration/permission problem or if sudo
the given command. In the latter case, the error string is printed to the
standard error. If sudo
or more entries in the user's
, an error is
printed to the standard error. (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
to return “permission denied” is if you
are running an automounter and one of the directories in your
is on a machine that is currently unreachable.
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
(if one or both are in the
). Note, however, that the actual
environment variable is not
modified and is passed unchanged to the program that sudo
Users should never
be granted sudo
privileges to execute files that are writable by the user or that reside in a
directory that is writable by the user. If the user can modify or replace the
command there is no way to limit what additional commands they can run.
Please note that sudo
will normally only log the command it
explicitly runs. If a user runs a command such as
, 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
to verify that the command does not inadvertently give
the user an effective root shell. For more information, please see the
Preventing shell escapes
To prevent the disclosure of potentially sensitive information,
disables core dumps by default while it is executing
(they are re-enabled for the command that is run). This historical practice
dates from a time when most operating systems allowed setuid processes to dump
core by default. 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.
utilizes the following environment variables. The
security policy has control over the actual content of the command's
- Default editor to use in -e (sudoedit)
mode if neither
VISUAL is set.
- Set to the mail spool of the target user when the
-i option is specified or when
env_reset is enabled in sudoers
MAIL is present in the
- Set to the home directory of the target user when the
-i or -H options are specified, when
the -s option is specified and
set_home is set in sudoers, when
always_set_home is enabled in sudoers,
or when env_reset is enabled in
sudoers and HOME is not present in the
- Set to the login name of the target user when the
-i option is specified, when the
set_logname option is enabled in
sudoers or when the env_reset option
is enabled in sudoers (unless
LOGNAME is present in the
- May be overridden by the security policy.
- Used to determine shell to run with -s
- Specifies the path to a helper program used to read the
password if no terminal is available or if the -A option
- Set to the command run by sudo.
- Default editor to use in -e (sudoedit)
- Set to the group ID of the user who invoked sudo.
- Used as the default password prompt.
- If set,
PS1 will be set to its
value for the program being run.
- Set to the user ID of the user who invoked sudo.
- Set to the login name of the user who invoked sudo.
- Set to the same value as
- Same as
- Default editor to use in -e (sudoedit)
SUDO_EDITOR is not set.
- sudo front end configuration
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:
$ sudoedit -u www ~www/htdocs/index.html
To view system logs only accessible to root and users in the adm group:
$ sudo -g adm more /var/log/syslog
To run an editor as jim with a different primary group:
$ sudoedit -u jim -g audio ~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
and file redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
See the HISTORY file in the sudo
for a brief history of sudo.
Many people have worked on sudo
over the years; this version
consists of code written primarily by:
See the CONTRIBUTORS file in the sudo
for an exhaustive list of people who
have contributed to sudo
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)
It is not meaningful to run the
command directly via
$ sudo cd /usr/local/protected
since when the command exits the parent process (your shell) will still be the
same. Please see the EXAMPLES
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).
If you feel you have found a bug in sudo
, please submit a bug
report at https://bugzilla.sudo.ws/
Limited free support is available via the sudo-users mailing list, see
to subscribe or search the
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
for complete details.