SUDO(8) BSD System Manager’s Manual SUDO(8)
— execute a command as another user
sudo −h |
−K | −k | −V
sudo −v [−AknS]
sudo −l [−AknS]
[−u user] [command]
[−u user] [VAR=value]
[−i | −s]
[−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
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.
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.
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
When invoked as
sudoedit, the −e option (described
below), is implied.
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
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
# Path to
askpass helper program
Path askpass /usr/X11R6/bin/ssh-askpass
If no askpass
program is available, sudo will exit with an
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 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 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:
Temporary copies are made of
the files to be edited with the owner set to the invoking
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.
To help prevent
the editing of unauthorized files, the following
restrictions are enforced unless explicitly allowed by the
Symbolic links may not be
edited (version 1.8.15 and higher).
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).
Users are never
allowed to edit device special files.
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.
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
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
Display a short
help message to the standard output and exit.
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.
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
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
security policies support credential caching.
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.
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
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
Use a custom password prompt
with optional escape sequences. The following percent
(’%’) escape sequences are supported by the
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
expanded to the
login name of the user the command will be run as (defaults
to root unless the −u option is also
expanded to the
invoking user’s login name
’%’ characters are collapsed into a single
prompt will override the system password prompt on systems
that support PAM unless the passprompt_override flag
is disabled in sudoers.
Run the command with an SELinux
security context that includes the specified
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
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.
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
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.
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 15 minutes by default, but does not run a
command. Not all security policies support cached
−− option indicates that sudo
should stop processing command line arguments.
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
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).
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
SELinux role and type
scheduling priority (aka nice
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.
When the command is run as a child of the 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
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
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
Upon successful execution of a
command, the exit status from 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 signal that terminated the command.
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 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.
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.
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 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). 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:
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
to use in −e (sudoedit) mode if neither
SUDO_EDITOR nor 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 (unless 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 env_keep list.
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 env_keep list).
overridden by the security policy.
determine shell to run with −s option.
path to a helper program used to read the password if no
terminal is available or if the −A option is
Set to the
command run by sudo.
to use in −e (sudoedit) mode.
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 LOGNAME, described above.
to use in −e (sudoedit) mode if SUDO_EDITOR is
front end configuration
Note: the following examples
assume a properly configured security policy.
To get a file
listing of an unreadable directory:
$ sudo ls
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
To edit the
index.html file as user www:
$ sudo -u www
To view system
logs only accessible to root and users in the adm group:
$ sudo -g adm
To run an editor
as jim with a different primary group:
$ sudo -u jim
-g audio vi ~jim/sound.txt
To shut down a
$ 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"
su(1), stat(2), passwd(5),
sudo.conf(5), sudoers(5), sudo_plugin(8), sudoreplay(8),
See the HISTORY file in the
sudo distribution (https://www.sudo.ws/history.html)
for a brief history of sudo.
Many people have worked on
sudo over the years; this version consists of code
written primarily by:
CONTRIBUTORS file in the sudo distribution
(https://www.sudo.ws/contributors.html) 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) plugin’s noexec
It is not
meaningful to run the cd command directly via sudo,
$ sudo cd
since when the
command exits the parent process (your shell) will still be
the same. Please see the EXAMPLES section for more
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
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/license.html for
January 19, 2016 Sudo 1.8.16