| SUDO(8) | Maintenance Commands and Procedures | SUDO(8) |
sudo, sudoedit —
sudo |
-h | -K |
-k | -V |
sudo |
-v [-ABknS]
[-g group]
[-h host]
[-p prompt]
[-u user] |
sudo |
-l [-ABknS]
[-g group]
[-h host]
[-p prompt]
[-U user]
[-u user]
[command] |
sudo |
[-ABbEHnPS] [-C
num] [-D
directory] [-g
group] [-h
host] [-p
prompt] [-R
directory] [-T
timeout] [-u
user]
[VAR=value]
[-i | -s]
[command] |
sudoedit |
[-ABknS] [-C
num] [-D
directory] [-g
group] [-h
host] [-p
prompt] [-R
directory] [-T
timeout] [-u
user] file ... |
sudo allows a permitted user to execute a
command 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 security policy.
sudo supports a plugin architecture for
security policies, auditing, and input/output logging. Third parties can
develop and distribute their own 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 5
minutes.
Security policies may support credential caching to allow the user
to run sudo again for a period of time without
requiring authentication. By default, the sudoers policy
caches credentials on a per-terminal basis for 5
minutes. See the timestamp_type and
timestamp_timeout options in
sudoers(5) for more information. By
running sudo with the -v
option, a user can update the cached credentials without running a
command.
On systems where sudo is the primary
method of gaining superuser privileges, it is imperative to avoid syntax
errors in the security policy configuration files. For the default security
policy, sudoers(5), changes to the
configuration files should be made using the
visudo(8) utility which will ensure
that no syntax errors are introduced.
When invoked as sudoedit, the
-e option (described below), is implied.
Security policies and audit plugins may log successful and failed
attempts to run 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,
--askpasssudo 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,
--bell-b,
--backgroundsudo. Most interactive commands will fail to work
properly in background mode.-C
num,
--close-from=numsudo 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.-D
directory,
--chdir=directory-E,
--preserve-env--preserve-env=list-e,
--editSUDO_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.To help prevent the editing of unauthorized files, the following restrictions are enforced unless explicitly allowed by the security policy:
Users are never allowed to edit device special files.
If the specified file does not exist, it will be created.
Unlike most commands run by sudo, the editor is run
with the invoking user's environment unmodified. If the temporary file
becomes empty after editing, the user will be prompted before it is
installed. 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#’ 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. The sudoers policy permits
any of the target user's groups to be specified via the
-g option as long as the
-P option is not in use.-H,
--set-homeHOME
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-h
host,
--host=host-l option to list a user's privileges for the
remote host.-i,
--login-c option. The command and any arguments are
concatenated, separated by spaces, after escaping each character
(including white space) with a backslash
(‘\’) except for alphanumerics,
underscores, hyphens, and dollar signs. 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. Most shells behave differently when a command is specified as compared
to an interactive session; consult the shell's manual for details. 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-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-timestampsudo 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-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 a
command is specified but not allowed by the
policy, sudo will exit with a status value of
1.
-n,
--non-interactivesudo will display an error
message and exit.-P,
--preserve-groups-p
prompt,
--prompt=prompt%’) escape sequences are
supported by the sudoers policy:
%H%h%p%U-u option is also
specified)%u%%%’ characters
are collapsed into a single ‘%’
characterThe custom prompt will override the default prompt specified
by either the security policy or the SUDO_PROMPT
environment variable. On systems that use PAM, the custom prompt will
also override the prompt specified by a PAM module unless the
passprompt_override flag is disabled in
sudoers.
-R
directory,
--chroot=directory-S,
--stdin-s,
--shellSHELL 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 as a simple command using the -c option. The
command and any arguments are concatenated, separated by spaces, after
escaping each character (including white space) with a backslash
(‘\’) except for alphanumerics,
underscores, hyphens, and dollar signs. If no command is specified, an
interactive shell is executed. Most shells behave differently when a
command is specified as compared to an interactive session; consult the
shell's manual for details.-U
user,
--other-user=user-l option to list the
privileges for user instead of for the invoking
user. The security policy may restrict listing other users' privileges.
When using the sudoers policy, only root or a user with
the ability to run any command as either root or the specified
user on the current host may use this option.-T
timeout,
--command-timeout=timeout-u
user,
--user=user#’ 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,
--versionsudo version string as well as the
version string of any configured plugins. If the invoking user is already
root, the -V option will display the arguments
passed to configure when sudo was built; plugins
may display additional information such as default options.-v,
--validatesudo timeout for another 5
minutes by default, but does not run a command. Not all security policies
support cached credentials.---- option indicates that
sudo should stop processing command line
arguments.Options that take a value may only be specified once unless
otherwise indicated in the description. This is to help guard against
problems caused by poorly written scripts that invoke
sudo with user-controlled input.
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.
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:
sudo can run a command.
If an I/O logging plugin is configured or if the security policy
explicitly requests it, a new pseudo-terminal (“pty”) is
allocated and fork(2) is used to create
a second sudo process, referred to as the
monitor. The monitor creates a new
terminal session with itself as the leader and the pty as its controlling
terminal, calls fork(2), sets up the
execution environment as described above, and then uses the
execve(2) system call to run the
command in the child process. The monitor exists to relay
job control signals between the user's existing terminal and the pty the
command is being run in. This makes it possible to suspend and resume the
command. Without the monitor, the command would be in what POSIX terms an
“orphaned process group” and it would not receive any job
control signals from the kernel. When the command exits or is terminated by
a signal, the monitor passes the command's exit status to
the main sudo process and exits. After receiving the
command's exit status, the main sudo passes the
command's exit status to the security policy's close function and exits.
If no pty is used, sudo calls
fork(2), sets up the execution
environment as described above, and uses the
execve(2) system call to run the
command 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. As a special case, if the
policy plugin does not define a close function, 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, an SELinux role is
specified, the command has an associated timeout, or the
pam_session or pam_setcred options are
enabled. Both pam_session and
pam_setcred are enabled by default on systems using
PAM.
On systems that use PAM, the security policy's close function is responsible for closing the PAM session. It may also log the command's exit status.
sudo process,
sudo will relay signals it receives to the command.
The SIGINT and SIGQUIT signals
are 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
receiving SIGINT twice each time the user enters
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.
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 if
it doesn't contain any Plugin lines,
sudo will use
sudoers(5) for the policy, auditing,
and I/O logging plugins. See the
sudo.conf(5) manual for details of
the /etc/sudo.conf file and the
sudo_plugin(5) manual for more
information about the sudo plugin architecture.
sudo will be the exit status of the program that was
executed. If the command terminated due to receipt of a signal,
sudo will send itself the same signal that terminated
the command.
If the -l option was specified without a
command, sudo will exit with a value of 0 if the
user is allowed to run sudo and they authenticated
successfully (as required by the security policy). If a command is specified
with the -l option, the exit value will only be 0 if
the command is permitted by the security policy, otherwise it will be 1.
If there is an authentication failure, a configuration/permission
problem, or if the given command cannot be executed,
sudo exits with a value of 1. 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 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
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.
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). Depending on the security
policy, the user's PATH environment variable may be
modified, replaced, or passed unchanged to the program that
sudo executes.
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.
By default, sudo will 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 information on
ways to address this, 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). This historical
practice dates from a time when most operating systems allowed set-user-ID
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.
sudo utilizes the following environment variables. The
security policy has control over the actual content of the command's
environment.
EDITOR-e (sudoedit) mode if
neither SUDO_EDITOR nor
VISUAL is set.MAIL-i option is specified, or when
env_reset is enabled in sudoers
(unless MAIL is present in the
env_keep list).HOME-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
env_keep list.LOGNAME-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
env_keep list).PATHSHELL-s
option.SUDO_ASKPASS-A option is
specified.SUDO_COMMANDSUDO_EDITOR-e (sudoedit) mode.SUDO_GIDSUDO_PROMPT-p
option was specified.SUDO_PS1PS1 will be set to its value for the
program being run.SUDO_UIDSUDO_USERUSERLOGNAME, described
above.VISUAL-e (sudoedit) mode if
SUDO_EDITOR is not set.sudo front-end configurationTo 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:
$ 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.
The commands are run in a sub-shell to allow the cd
command and file redirection to work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
sudo include:
editing
files in a writable directory is not permittedsudoedit does not permit editing a
file when any of the parent directories are writable by the invoking user.
This avoids a race condition that could allow the user to overwrite an
arbitrary file. See the sudoedit_checkdir option in
sudoers(5) for more
information.editing
symbolic links is not permittedsudoedit does not follow symbolic
links when opening files. See the sudoedit_follow option
in sudoers(5) for more
information.effective
uid is not 0, is sudo installed setuid root?sudo was not run with root privileges. The
sudo binary must be owned by the root user and
have the set-user-ID bit set. Also, it must not be located on a file
system mounted with the ‘nosuid’ option or on an NFS file
system that maps uid 0 to an unprivileged uid.effective
uid is not 0, is sudo on a file system with the 'nosuid' option set or an
NFS file system without root privileges?sudo was not run with root privileges. The
sudo binary has the proper owner and permissions
but it still did not run with root privileges. The most common reason for
this is that the file system the sudo binary is
located on is mounted with the ‘nosuid’ option or it is an
NFS file system that maps uid 0 to an unprivileged uid.fatal
error, unable to load pluginsinvalid
environment variable name-E option contained an equal sign
(‘=’). The arguments to the
-E option should be environment variable names
without an associated value.no
password was providedsudo tried to read the password, it did not
receive any characters. This may happen if no terminal is available (or
the -S option is specified) and the standard input
has been redirected from /dev/null.a
terminal is required to read the passwordsudo needs to read the password but there is no
mechanism available for it to do so. A terminal is not present to read the
password from, sudo has not been configured to
read from the standard input, the -S option was
not used, and no askpass helper has been specified either via the
sudo.conf(5) file or the
SUDO_ASKPASS environment variable.no
writable temporary directory foundsudoedit was unable to find a usable temporary
directory in which to store its intermediate files.The
“no new privileges” flag is set, which prevents sudo from
running as root.sudo was run by a process that has the Linux
“no new privileges” flag is set. This causes the set-user-ID
bit to be ignored when running an executable, which will prevent
sudo from functioning. The most likely cause for
this is running sudo within a container that sets
this flag. Check the documentation to see if it is possible to configure
the container such that the flag is not set.sudo
must be owned by uid 0 and have the setuid bit setsudo was not run with root privileges. The
sudo binary does not have the correct owner or
permissions. It must be owned by the root user and have the set-user-ID
bit set.sudoedit
is not supported on this platformsudoedit on systems
that support setting the effective user-ID.timed
out reading passwordyou
do not exist in the passwd databaseyou
may not specify environment variables in edit modesudo distribution
(https://www.sudo.ws/about/history/) for a brief history of sudo.
sudo over the years; this
version consists of code written primarily by:
See the CONTRIBUTORS.md file in the sudo
distribution (https://www.sudo.ws/about/contributors/) for an exhaustive
list of people who have contributed to sudo.
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. See the EXAMPLES section for more information.
Running shell scripts via sudo can expose
the same kernel bugs that make set-user-ID shell scripts unsafe on some
operating systems (if your OS has a /dev/fd/ directory, set-user-ID shell
scripts are generally safe).
sudo, you can
submit a bug report at https://bugzilla.sudo.ws/
sudo is provided “AS IS” and any express
or implied warranties, including, but not limited to, the implied warranties
of merchantability and fitness for a particular purpose are disclaimed. See
the LICENSE.md file distributed with sudo or
https://www.sudo.ws/about/license/ for complete details.
| February 16, 2022 | Sudo 1.9.11p3 |