— execute a command as another user
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
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
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
Security policies may support credential caching to allow the user
sudo again for a period of time without
requiring authentication. The sudoers policy caches
5 minutes, unless overridden in
sudoers(5). By running
-v option, a user can update the cached
credentials without running a command.
When invoked as
-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:
- Normally, if
sudorequires 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_ASKPASSenvironment 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,
sudowill exit with an error.
-a(authentication type) option causes
sudoto use the specified authentication type when validating the user, as allowed by /etc/login.conf. The system administrator may specify a list of sudo-specific authentication methods by adding an “auth-sudo” entry in /etc/login.conf. This option is only available on systems that support BSD authentication.
-b(background) option tells
sudoto run the given command in the background. Note that if you use the
-boption you cannot use shell job control to manipulate the process. Most interactive commands will fail to work properly in background mode.
sudowill close all open file descriptors other than standard input, standard output and standard error. The
-C(close from) option allows the user to specify a starting point above the standard error (file descriptor three). Values less than three are not permitted. The security policy may restrict the user's ability to use the
-Coption. The sudoers policy only permits use of the
-Coption when the administrator has enabled the closefrom_override option.
-c(class) option causes
sudoto run the specified command with resources limited by the specified login class. The class argument can be either a class name as defined in /etc/login.conf, or a single ‘
-’ character. Specifying a class of
-indicates that the command should be run restricted by the default login capabilities for the user the command is run as. If the class argument specifies an existing user class, the command must be run as root, or the
sudocommand must be run from a shell that is already root. This option is only available on systems with BSD login classes.
-E(preserve environment) option indicates to the security policy that the user wishes to preserve their existing environment variables. The security policy may return an error if the
-Eoption is specified and the user does not have permission to preserve the environment.
-e(edit) option indicates that, instead of running a command, the user wishes to edit one or more files. In lieu of a command, 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
EDITORenvironment variables (in that order). If none of
EDITORare 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.
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,
sudois 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.
sudoruns a command with the primary group set to the one specified by the password database for the user the command is being run as (by default, root). The
-g(group) option causes
sudoto run the command with the primary group set to group instead. To specify a gid instead of a group name, use #gid. When running commands as a gid, many shells require that the ‘
#’ be escaped with a backslash (‘
\’). If no
-uoption is specified, the command will be run as the invoking user (not root). In either case, the primary group will be set to group.
-H(HOME) option requests that the security policy set the
HOMEenvironment variable to the home directory of the target user (root by default) as specified by the password database. Depending on the policy, this may be the default behavior.
-h(help) option causes
sudoto print a short help message to the standard output and exit.
-i(simulate initial login) option runs the shell specified by the password database entry of the target user 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
-coption. If no command is specified, an interactive shell is executed.
sudoattempts to change to that user's home directory before running the shell. The security policy shall initialize the environment to a minimal set of variables, similar to what is present when a user logs in. The Command Environment section in the sudoers(5) manual documents how the
-ioption affects the environment in which a command is run when the sudoers policy is in use.
-K(sure kill) option is like
-kexcept 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 alone, the
-k(kill) option to
sudoinvalidates the user's cached credentials. The next time
sudois run a password will be required. This option does not require a password and was added to allow a user to revoke
sudopermissions from a .logout file. Not all security policies support credential caching.
When used in conjunction with a command or an option that may require a password, the
-koption will cause
sudoto ignore the user's cached credentials. As a result,
sudowill prompt for a password (if one is required by the security policy) and will not update the user's cached credentials.
- If no command is specified, the
-l(list) option will list the allowed (and forbidden) commands for the invoking user (or the user specified by the
-Uoption) on the current host. 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,
sudowill exit with a status value of 1. If the
-loption is specified with an l argument (i.e.
-ll), or if
-lis specified multiple times, a longer list format is used.
-n(non-interactive) option prevents
sudofrom prompting the user for a password. If a password is required for the command to run,
sudowill display an error message and exit.
-P(preserve group vector) option causes
sudoto 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 in. The real and effective group IDs, however, are still set to match the target user.
-p(prompt) option allows you to override the default password prompt and use a custom one. The following percent (‘
%’) escapes are supported by the sudoers policy:
- 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))
- expanded to the local host name without the domain name
- expanded to the name of the user whose password is being requested (respects the rootpw, targetpw, and runaspw flags in sudoers(5))
- expanded to the login name of the user the command will be run as
(defaults to root unless the
-uoption is also specified)
- expanded to the invoking user's login name
- two consecutive ‘
%’ characters are collapsed into a single ‘
The prompt specified by the
-poption will override the system password prompt on systems that support PAM unless the passprompt_override flag is disabled in sudoers.
-r(role) option causes the new (SELinux) security context to have the role specified by role.
-S(stdin) option causes
sudoto read the password from the standard input instead of the terminal device. The password must be followed by a newline character.
-s(shell) option runs the shell specified by the
SHELLenvironment variable if it is set or the shell as specified in the password database. If a command is specified, it is passed to the shell for execution via the shell's
-coption. If no command is specified, an interactive shell is executed.
-t(type) option causes the new (SELinux) security context to have the type specified by type. If no type is specified, the default type is derived from the specified role.
-U(other user) option is used in conjunction with the
-loption to specify the user whose privileges should be listed. The security policy may restrict listing other users' privileges. The sudoers policy only allows root or a user with the
ALLprivilege on the current host to use this option.
-u(user) option causes
sudoto run the specified command as a user other than root. To specify a uid instead of a user name, #uid. When running commands as a uid, many shells require that the ‘
#’ be 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.
-V(version) option causes
sudoto print its version string and the version string of the security policy plugin and any I/O plugins. If the invoking user is already root the
-Voption will display the arguments passed to configure when
sudowas built and plugins may display more verbose information such as default options.
- When given the
sudowill update the user's cached credentials, authenticating the user's password if necessary. For the sudoers plugin, this extends the
sudotimeout for another
5minutes (or whatever the timeout is set to by the security policy) but does not run a command. Not all security policies support cached credentials.
--option indicates that
sudoshould 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 the same restrictions as
normal environment variables with one important exception. If the
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.
sudo executes a command, the security
policy specifies the execution environment for the command. Typically, the
real and effective uid and gid 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
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
- Solaris project
- Solaris privileges
- BSD login class
- scheduling priority (aka nice value)
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
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
sudo will execute the command directly
instead of calling fork(2) first.
Because the command is run as a child of the
relay signals it receives to the command. Unless the command is being run in
a new pty, the
are not relayed unless they are sent by a user process, not the kernel.
Otherwise, the command would receive
every time the user entered control-C. Some signals, such as
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
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
all non-system processes other than itself before rebooting the system. This
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
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
sudo may execute the command directly instead
of running it as a child process.
Plugins are dynamically loaded based on the contents of the
sudo.conf(5) file. If no sudo.conf(5)
file is present, or it contains no
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.
Upon successful execution of a program, the exit status from sudo will simply be the exit status of the program that was executed.
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
is on a machine that is currently unreachable.
sudo tries to be safe when executing
To prevent command spoofing,
checks "." and "" (both denoting current directory) last
when searching for a command in the user's
one or both are in the
PATH). Note, however, that
PATH environment variable is
not modified and is
passed unchanged to the program that
Please note that
normally only log the command it explicitly runs. If a user runs a command
sudo su or
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
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
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.
sudo utilizes the following environment
variables. The security policy has control over the actual content of the
- Default editor to use in
-e(sudoedit) mode if neither
-imode or when env_reset is enabled in sudoers, set to the mail spool of the target user.
- Set to the home directory of the target user if
-Hare specified, env_reset or always_set_home are set in sudoers, or when the
-soption is specified and set_home is set in sudoers.
- May be overridden by the security policy.
- Used to determine shell to run with
- Specifies the path to a helper program used to read the password if no
terminal is available or if the
-Aoption is specified.
- Set to the command run by sudo.
- Default editor to use in
- Set to the group ID of the user who invoked sudo.
- Used as the default password prompt.
- If set,
PS1will 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 target user (root unless the
-uoption is specified).
- Default editor to use in
-e(sudoedit) mode if
SUDO_EDITORis not set.
sudofront 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:
$ sudo -u yaz ls ~yaz
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 the HISTORY file in the
distribution (https://www.sudo.ws/sudo/history.html) for a brief history of
Many people have worked on
sudo over the
years; this version consists of code written primarily by:
See the CONTRIBUTORS file in the
distribution (https://www.sudo.ws/sudo/contributors.html) for an exhaustive
list of people who have contributed to
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
It is not meaningful to run the
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
If you feel you have found a bug in
please submit a bug report at https://www.sudo.ws/sudo/bugs/
Limited free support is available via the sudo-users mailing list, see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
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 https://www.sudo.ws/sudo/license.html for