|-A -, --askpass|
requires a password, it will read it from the users terminal.
option is specified, a (possibly graphical) helper program is
executed to read the users password and output the password to the
environment variable is set, it specifies the path to the helper
contains a line specifying the askpass program, that value will be
# 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 -, --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 users ability to use this option. The sudoers policy only permits use of the -C option when the administrator has enabled the closefrom_override option.|
|-c class,--login-class-= class|
|Run the command with resource limits and scheduling priority of the specified login class. The class argument can be either a class name as defined in /etc/login.conf, or a single - character. If class is -, the default login class of the target user will be used. Otherwise, the command must be run as the superuser (user ID 0), or sudo must be run from a shell that is already running as the superuser. If the command is being run as a login shell, additional /etc/login.conf settings, such as the umask and environment variables, will be applied, if present. This option is only available on systems with BSD login classes.|
|-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.|
|-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
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. Note that unlike most commands run by sudo, the editor is run with the invoking users 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 users 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.|
|-H -, --set-home|
|Request that the security policy set the HOME environment variable to the home directory specified by the target users 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 users privileges for the remote host.|
|-i -, --login|
|Run the shell specified by the target users 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 shells -c option. If no command is specified, an interactive shell is executed. sudo attempts to change to that users 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.|
|-K -, --remove-timestamp|
|Similar to the -k option, except that it removes the users 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 users cached credentials.
In other words, the next time
is run a password will be required.
This option does not require a password and was added to allow a
user to revoke
permissions from a
When used in conjunction with a command or an option that may require a password, this option will cause sudo to ignore the users cached credentials. As a result, sudo will prompt for a password (if one is required by the security policy) and will not update the users cached credentials.
Not all security policies support credential caching.
|-l -, --list|
list the allowed (and forbidden) commands for the
invoking user (or the user specified by the
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 command is specified but not allowed, 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 users 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 machines 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 users login name|
|%%||two consecutive % characters are collapsed into a single % character|
The custom prompt will override the system password prompt on systems that support PAM unless the passprompt_override flag is disabled in sudoers.
|-S -, --stdin|
|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.|
|-s -, --shell|
|Run the shell specified by the SHELL environment variable if it is set or the shell specified by the invoking users password database entry. If a command is specified, it is passed to the shell for execution via the shells -c option. If no command is specified, an interactive shell is executed.|
|-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.|
|-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 users cached credentials, authenticating the user if necessary. For the sudoers plugin, this extends the sudo timeout for another 5 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.
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)
- BSD login class
- scheduling priority (aka nice value)
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 commands exit status to the security policys 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 users 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 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 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 /usr/local/etc/sudo.conf file and the sudo_plugin(8) manual for more information about the sudo plugin architecture.
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.
Otherwise, 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 users 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 users 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 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: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 commands environment.
EDITOR Default editor 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 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. 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. USERNAME Same as USER. VISUAL Default editor to use in -e (sudoedit) mode if SUDO_EDITOR is not set.
/usr/local/etc/sudo.conf sudo front end configuration
Note: the following examples assume a properly configured security policy.
To get a file listing of an unreadable directory:$ sudo ls /usr/local/protected
To list the home directory of user yaz on a machine where the file system holding ~yaz is not exported as root:$ sudo -u yaz ls ~yaz
To edit the index.html file as user www:$ sudo -u www vi ~www/htdocs/index.html
To view system logs only accessible to root and users in the adm group:$ sudo -g adm view /var/log/syslog
To run an editor as jim with a different primary group:$ sudo -u jim -g audio vi ~jim/sound.txt
To shut down a machine:$ sudo shutdown -r +15 "quick reboot"
To make a usage listing of the directories in the /home partition. Note that this runs the commands in a sub-shell to make the cd and file redirection work.$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
su(1), stat(2), login_cap(3), passwd(5), sudo.conf(5), sudoers(5), sudo_plugin(8), sudoreplay(8), visudo(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:
.An 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.
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) plugins 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 https://bugzilla.sudo.ws/
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 complete details.