Provided by: sudo_1.8.31-1ubuntu1.5_amd64 
NAME
sudo, sudoedit — execute a command as another user
SYNOPSIS
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] [-g group] [-h host] [-p prompt] [-r role] [-t type] [-T timeout] [-u user]
[VAR=value] [-i | -s] [command]
sudoedit [-ABknS] [-C num] [-g group] [-h host] [-p prompt] [-T timeout] [-u user] file ...
DESCRIPTION
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 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.
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 0 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 15 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.
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, --askpass
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:
# 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 Ring the bell as part of the password promp when a terminal is present. This option has no
effect if an askpass program is used.
-b, --background
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.
-C num, --close-from=num
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.
-E, --preserve-env
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 environment.
--preserve-env=list
Indicates to the security policy that the user wishes to add the comma-separated list of
environment variables to those preserved from the user's environment. The security policy
may return an error if the user does not have permission to preserve the environment.
-e, --edit 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:
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.
To help prevent the editing of unauthorized files, the following restrictions are enforced
unless explicitly allowed by the security policy:
• 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.
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, --group=group
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 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-home
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.
-h, --help Display a short help message to the standard output and exit.
-h host, --host=host
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.
-i, --login
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, .bash_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. Note that 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
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.
-k, --reset-timestamp
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
credentials.
Not all security policies support credential caching.
-l, --list 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 a command is specified
but not allowed by the policy, sudo will exit with a status value of 1.
-n, --non-interactive
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.
-P, --preserve-groups
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.
-p prompt, --prompt=prompt
Use a custom password prompt with optional escape sequences. The following percent (‘%’)
escape sequences are supported by the sudoers policy:
%H 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))
%h expanded to the local host name without the domain name
%p expanded to the name of the user whose password is being requested (respects the rootpw,
targetpw, and runaspw flags in sudoers(5))
%U expanded to the login name of the user the command will be run as (defaults to root
unless the -u option is also specified)
%u expanded to the invoking user's login name
%% two consecutive ‘%’ characters are collapsed into a single ‘%’ character
The 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 role, --role=role
Run the command with an SELinux security context that includes the specified role.
-S, --stdin
Write the prompt to the standard error and read the password from the standard input instead
of using the terminal device.
-s, --shell
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. Note that most shells behave differently when a command is
specified as compared to an interactive session; consult the shell's manual for details.
-t type, --type=type
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.
-U user, --other-user=user
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.
-T timeout, --command-timeout=timeout
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 explicitly enabled.
-u user, --user=user
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.
-V, --version
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 options.
-v, --validate
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 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
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.
COMMAND EXECUTION
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).
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)
Process model
There are two distinct ways 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, 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.
Signal handling
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 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.
Plugins
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(5) manual for more information about the sudo plugin architecture.
EXIT VALUE
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 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.
SECURITY NOTES
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). Note, however, that the actual PATH
environment variable is not modified and is 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.
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 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.
ENVIRONMENT
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 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 env_keep list).
HOME 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.
LOGNAME 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).
PATH May be overridden by the security policy.
SHELL Used to determine shell to run with -s option.
SUDO_ASKPASS Specifies the path to a helper program used to read the password if no terminal is
available or if the -A option is specified.
SUDO_COMMAND Set to the command run by sudo.
SUDO_EDITOR Default editor to use in -e (sudoedit) mode.
SUDO_GID Set to the group-ID of the user who invoked sudo.
SUDO_PROMPT Used as the default password prompt unless the -p option was specified.
SUDO_PS1 If set, PS1 will be set to its value for the program being run.
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 same value as LOGNAME, described above.
VISUAL Default editor to use in -e (sudoedit) mode if SUDO_EDITOR is not set.
FILES
/etc/sudo.conf sudo front end configuration
EXAMPLES
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:
$ 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 cd and file redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
DIAGNOSTICS
Error messages produced by sudo include:
editing files in a writable directory is not permitted
By default, sudoedit 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 permitted
By default, sudoedit 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 plugins
An error occurred while loading or initializing the plugins specified in sudo.conf(5).
invalid environment variable name
One or more environment variable names specified via the -E option contained an equal sign (‘=’).
The arguments to the -E option should be environment variable names without an associated value.
no password was provided
When sudo 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 password
sudo 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 found
sudoedit was unable to find a usable temporary directory in which to store its intermediate files.
sudo must be owned by uid 0 and have the setuid bit set
sudo 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 platform
It is only possible to run sudoedit on systems that support setting the effective user-ID.
timed out reading password
The user did not enter a password before the password timeout (5 minutes by default) expired.
you do not exist in the passwd database
Your user-ID does not appear in the system passwd database.
you may not specify environment variables in edit mode
It is only possible to specify environment variables when running a command. When editing a file,
the editor is run with the user's environment unmodified.
SEE ALSO
su(1), stat(2), login_cap(3), passwd(5), sudo.conf(5), sudo_plugin(5), sudoers(5), sudoers_timestamp(5),
sudoreplay(8), visudo(8)
HISTORY
See the HISTORY file in the sudo distribution (https://www.sudo.ws/history.html) for a brief history of
sudo.
AUTHORS
Many people have worked on sudo over the years; this version consists of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS file in the sudo distribution (https://www.sudo.ws/contributors.html) for an
exhaustive list of people who have contributed to sudo.
CAVEATS
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 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 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).
BUGS
If you feel you have found a bug in sudo, please submit a bug report at https://bugzilla.sudo.ws/
SUPPORT
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.
DISCLAIMER
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 complete details.
Sudo 1.8.31 October 20, 2019 SUDO(8)