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sudo -v [-AknS] [-g group name | #gid] [-p prompt] [-u user name | #uid]
sudo -l[l] [-AknS] [-g group name | #gid] [-p prompt] [-U user name]
[-u user name | #uid] [command]
sudo [-AbEHnPS] [-C fd] [-g group name | #gid] [-p prompt] [-r role]
[-t type] [-u user name | #uid] [VAR=value] -i | -s [command]
sudoedit [-AnS] [-C fd] [-g group name | #gid] [-p prompt]
[-u user name | #uid] file ...
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/out-
put 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 5 minutes.
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 5 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 Normally, if sudo requires a password, it will read it from
the user's terminal. If the -A (askpass) option is speci-
fied, a (possibly graphical) helper program is executed to
read the user's password and output the password to the stan-
dard output. If the SUDO_ASKPASS environment variable is
set, it specifies the path to the helper program. Otherwise,
if /etc/sudo.conf contains a line specifying the askpass pro-
gram, 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
sudoers policy only permits use of the -C option when the
administrator has enabled the closefrom_override option.
-E The -E (preserve environment) option indicates to the secu-
rity policy that the user wishes to preserve their existing
environment variables. The security policy may return an
error if the -E option is specified and the user does not
have permission to preserve the environment.
-e The -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 pol-
icy, the following steps are taken:
1. Temporary copies are made of the files to be edited with
the owner set to the invoking user.
2. 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.
3. 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, 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 Normally, sudo runs 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 sudo to 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 -u option 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 The -H (HOME) option requests that the security policy set
the HOME environment 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
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 -i option affects the environment in which
a command is run when the sudoers policy is in use.
-K The -K (sure kill) option is like -k 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
When used alone, the -k (kill) option to sudo invalidates the
user's cached credentials. The next time sudo is run a pass-
word will be required. This option does not require a pass-
word and was added to allow a user to revoke sudo permissions
from a .logout file. Not all security policies support cre-
When used in conjunction with a command or an option that may
require a password, the -k 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.
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 -U option) 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 speci-
fied but not allowed, sudo will exit with a status value of
1. If the -l option is specified with an l argument (i.e.
-ll), or if -l is specified multiple times, a longer list
format is used.
-n The -n (non-interactive) option prevents sudo from prompting
the user for a password. If a password is required for the
command to run, sudo will display an error message and exit.
-P The -P (preserve group vector) option causes sudo to 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 The -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:
%H expanded to the host name including the domain name (on
%% two consecutive '%' characters are collapsed into a sin-
gle '%' character
The prompt specified by the -p option will override the sys-
tem password prompt on systems that support PAM unless the
passprompt_override flag is disabled in sudoers.
-r role The -r (role) option causes the new (SELinux) security con-
text to have the role specified by role.
-S The -S (stdin) option causes sudo to read the password from
the standard input instead of the terminal device. The pass-
word must be followed by a newline character.
The -s (shell) option runs the shell specified by the SHELL
environment 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 -c option.
If no command is specified, an interactive shell is executed.
-t type The -t (type) option causes the new (SELinux) security con-
text to have the type specified by type. If no type is spec-
ified, the default type is derived from the specified role.
-U user The -U (other user) option is used in conjunction with the -l
option to specify the user whose privileges should be listed.
The security policy may restrict listing other users' privi-
leges. The sudoers policy only allows root or a user with
the ALL privilege on the current host to use this option.
-u user The -u (user) option causes sudo to 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 The -V (version) option causes sudo to 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 -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 When given the -v (validate) option, sudo will update the
user's cached credentials, authenticating the user's password
if necessary. For the sudoers plugin, this extends the sudo
timeout for another 5 minutes (or whatever the timeout is set
When sudo executes a command, the security policy specifies the execution
envionment for the command. Typically, the real and effective uid and
gid are set to match those of the target user, as specified in the pass-
word 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)
When sudo runs a command, it calls fork(2), sets up the execution envi-
ronment 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
method and exits. If an I/O logging plugin is configured, 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.
Because 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 com-
mand it is running. This prevents the command from accidentally killing
itself. On some systems, the reboot(8) command sends SIGTERM to all non-
tains no Plugin lines, sudo will use the traditional sudoers security
policy and I/O logging, which corresponds to the following /etc/sudo.conf
# Default /etc/sudo.conf file
# Plugin plugin_name plugin_path plugin_options ...
# Path askpass /path/to/askpass
# Path noexec /path/to/sudo_noexec.so
# Debug sudo /var/log/sudo_debug all@warn
# Set disable_coredump true
# The plugin_path is relative to /usr/libexec unless
# fully qualified.
# The plugin_name corresponds to a global symbol in the plugin
# that contains the plugin interface structure.
# The plugin_options are optional.
Plugin policy_plugin sudoers.so
Plugin io_plugin sudoers.so
A Plugin line consists of the Plugin keyword, followed by the symbol_name
and the path to the shared object containing the plugin. The symbol_name
is the name of the struct policy_plugin or struct io_plugin in the plugin
shared object. The path may be fully qualified or relative. If not
fully qualified it is relative to the /usr/libexec directory. Any addi-
tional parameters after the path are passed as arguments to the plugin's
open function. Lines that don't begin with Plugin, Path, Debug, or Set
are silently ignored.
For more information, see the sudo_plugin(8) manual.
A Path line consists of the Path keyword, followed by the name of the
path to set and its value. E.g.
Path noexec /usr/libexec/sudo_noexec.so
Path askpass /usr/X11R6/bin/ssh-askpass
The following plugin-agnostic paths may be set in the /etc/sudo.conf
askpass The fully qualified path to a helper program used to read the
user's password when no terminal is available. This may be the
case when sudo is executed from a graphical (as opposed to
text-based) application. The program specified by askpass
should display the argument passed to it as the prompt and
write the user's password to the standard output. The value of
askpass may be overridden by the SUDO_ASKPASS environment vari-
comma-separated list of debug flags. The debug flag syntax used by sudo
and the sudoers plugin is subsystem@priority but the plugin is free to
use a different format so long as it does not include a comma (',').
Debug sudo /var/log/sudo_debug all@warn,plugin@info
would log all debugging statements at the warn level and higher in addi-
tion to those at the info level for the plugin subsystem.
Currently, only one Debug entry per program is supported. The sudo Debug
entry is shared by the sudo front end, sudoedit and the plugins. A
future release may add support for per-plugin Debug lines and/or support
for multiple debugging files for a single program.
The priorities used by the sudo front end, in order of decreasing sever-
ity, are: crit, err, warn, notice, diag, info, trace and debug. Each
priority, when specified, also includes all priorities higher than it.
For example, a priority of notice would include debug messages logged at
notice and higher.
The following subsystems are used by the sudo front-end:
all matches every subsystem
args command line argument processing
conv user conversation
exec command execution
main sudo main function
netif network interface handling
pcomm communication with the plugin
plugin plugin configuration
pty pseudo-tty related code
selinux SELinux-specific handling
util utility functions
utmp utmp handling
Upon successful execution of a program, the exit status from sudo will
sudo tries to be safe when executing external commands.
To prevent command spoofing, sudo checks "." and "" (both denoting cur-
rent 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 envi-
ronment 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 inadver-
tently 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 dis-
ables 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 /etc/sudo.conf file as follows:
Set disable_coredump false
Note that by default, most operating systems disable core dumps from
setuid programs, which includes sudo. To actually get a sudo core file
you may need to enable core dumps for setuid processes. On BSD and Linux
systems this is accomplished via the sysctl command, on Solaris the core-
adm command can be used.
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_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
VISUAL Default editor to use in -e (sudoedit) mode if
SUDO_EDITOR is not set.
/etc/sudo.conf sudo front end configuration
Note: the following examples assume a properly configured security pol-
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 redi-
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
grep(1), su(1), stat(2), passwd(5), sudoers(5), sudo_plugin(8),
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 pre-
vent 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).
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
http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the
sudo is provided "AS IS" and any express or implied warranties, includ-
ing, 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 com-
Sudo 1.8.6p3 July 10, 2012 Sudo 1.8.6p3