| SUDO(8) | System Manager's Manual | SUDO(8) |
sudo, sudoedit - execute a command as another user
sudo
-h | -K | -k | -V
sudo -v [-ABkNnS]
[-g group] [-h host]
[-p prompt] [-u user]
sudo -l [-ABkNnS]
[-g group] [-h host]
[-p prompt] [-U user]
[-u user]
[command [arg ...]]
sudo [-ABbEHnPS] [-C num]
[-D directory] [-g group]
[-h host] [-p prompt]
[-R directory] [-T timeout]
[-u user] [VAR=value]
[-i | -s]
[command [arg ...]]
sudoedit [-ABkNnS] [-C num] [-D directory] [-g group] [-h host] [-p prompt] [-R directory] [-T timeout] [-u user] file ...
sudo allows a permitted user to execute a command as the superuser or another user, as specified by the security policy. The invoking user's real (not effective) user-ID is used to determine the user name with which to query the security policy.
sudo supports a plugin architecture for security policies, auditing, and input/output logging. Third parties can develop and distribute their own plugins to work seamlessly with the sudo front-end. The default security policy is sudoers, which is configured via the file /private/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 5 minutes. See the timestamp_type and timestamp_timeout options in sudoers(5) for more information. By running sudo with the -v option, a user can update the cached credentials without running a command.
On systems where sudo is the primary method of gaining superuser privileges, it is imperative to avoid syntax errors in the security policy configuration files. For the default security policy, sudoers(5), changes to the configuration files should be made using the visudo(8) utility which will ensure that no syntax errors are introduced.
When invoked as sudoedit, the -e option (described below), is implied.
Security policies and audit plugins may log successful and failed attempts to run sudo. If an I/O plugin is configured, the running command's input and output may be logged as well.
The options are as follows:
# Path to askpass helper program Path askpass /usr/X11R6/bin/ssh-askpass
If no askpass program is available, sudo will exit with an error.
To help prevent the editing of unauthorized files, the following restrictions are enforced unless explicitly allowed by the security policy:
Users are never allowed to edit device special files.
If the specified file does not exist, it will be created. Unlike most commands run by sudo, the editor is run with the invoking user's environment unmodified. If the temporary file becomes empty after editing, the user will be prompted before it is installed. If, for some reason, sudo is unable to update a file with its edited version, the user will receive a warning and the edited copy will remain in a temporary file.
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.
If a command is specified and is permitted by the security policy for the invoking user (or the, user specified by the -U option) on the current host, the fully-qualified path to the command is displayed along with any args. If -l is specified more than once (and the security policy supports it), the matching rule is displayed in a verbose format along with the command. If a command is specified but not allowed by the policy, sudo will exit with a status value of 1.
sudo -Nnv
Not all security policies support credential caching.
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.
This option is deprecated and will be removed in a future version of sudo.
Options that take a value may only be specified once unless otherwise indicated in the description. This is to help guard against problems caused by poorly written scripts that invoke sudo with user-controlled input.
Environment variables to be set for the command may also be passed as options to sudo in the form VAR=value, for example LD_LIBRARY_PATH=/usr/local/pkg/lib. Environment variables may be subject to restrictions imposed by the security policy plugin. The sudoers policy subjects environment variables passed as options to the same restrictions as existing environment variables with one important difference. 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:
There are two distinct ways sudo can run a command.
If an I/O logging plugin is configured to log terminal I/O, 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) again, 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 terminal and the pty the command is being run in. This makes it possible to suspend and resume the command normally. 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 process passes the command's exit status to the security policy's close function, as well as the close function of any configured audit plugin, and exits. This mode is the default for sudo versions 1.9.14 and above when using the sudoers policy.
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, as well as the close function of any configured audit plugins, and exits. As a special case, if the policy plugin does not define a close function, sudo will execute the command directly instead of calling fork(2) first. The sudoers policy plugin will only define a close function when I/O logging is enabled, a pty is required, an SELinux role is specified, the command has an associated timeout, or the pam_session or pam_setcred options are enabled. Both pam_session and pam_setcred are enabled by default on systems using PAM. This mode is the default for sudo versions prior to 1.9.14 when using the sudoers policy.
On systems that use PAM, the security policy's close function is responsible for closing the PAM session. It may also log the command's exit status.
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) utility 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).
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 if it doesn't contain any Plugin lines, sudo will use sudoers(5) for the policy, auditing, and I/O logging plugins. See the sudo.conf(5) manual for details of the /private/etc/sudo.conf file and the sudo_plugin(5) 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 same signal that terminated the command.
If the -l option was specified without a command, sudo will exit with a value of 0 if the user is allowed to run sudo and they authenticated successfully (as required by the security policy). If a command is specified with the -l option, the exit value will only be 0 if the command is permitted by the security policy, otherwise it will be 1.
If there is an authentication failure, a configuration/permission problem, or if the given command cannot be executed, sudo exits with a value of 1. In the latter case, the error string is printed to the standard error. If sudo cannot stat(2) one or more entries in the user's PATH, an error is printed to the standard error. (If the directory does not exist or if it is not really a directory, the entry is ignored and no error is printed.) This should not happen under normal circumstances. The most common reason for stat(2) to return “permission denied” is if you are running an automounter and one of the directories in your PATH is on a machine that is currently unreachable.
sudo tries to be safe when executing external commands.
To prevent command spoofing, sudo checks "." and "" (both denoting current directory) last when searching for a command in the user's PATH (if one or both are in the PATH). Depending on the security policy, the user's PATH environment variable may be modified, replaced, or passed unchanged to the program that sudo executes.
Users should never be granted sudo privileges to execute files that are writable by the user or that reside in a directory that is writable by the user. If the user can modify or replace the command there is no way to limit what additional commands they can run.
By default, sudo will only log the command it explicitly runs. If a user runs a command such as ‘sudo su’ or ‘sudo sh’, subsequent commands run from that shell are not subject to sudo's security policy. The same is true for commands that offer shell escapes (including most editors). If I/O logging is enabled, subsequent commands will have their input and/or output logged, but there will not be traditional logs for those commands. Because of this, care must be taken when giving users access to commands via sudo to verify that the command does not inadvertently give the user an effective root shell. For information on ways to address this, see the Preventing shell escapes section in sudoers(5).
To prevent the disclosure of potentially sensitive information, sudo disables core dumps by default while it is executing (they are re-enabled for the command that is run). This historical practice dates from a time when most operating systems allowed set-user-ID processes to dump core by default. To aid in debugging sudo crashes, you may wish to re-enable core dumps by setting “disable_coredump” to false in the sudo.conf(5) file as follows:
Set disable_coredump false
See the sudo.conf(5) manual for more information.
sudo utilizes the following environment variables. The security policy has control over the actual content of the command's environment.
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. The commands are run in a sub-shell to allow the ‘cd’ command and file redirection to work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
Error messages produced by sudo include:
editing files in a writable directory is not permitted
editing symbolic links is not permitted
effective uid is not 0, is sudo installed setuid root?
effective uid is not 0, is sudo on a file system with the 'nosuid' option set or an NFS file system without root privileges?
fatal error, unable to load plugins
invalid environment variable name
no password was provided
a terminal is required to read the password
no writable temporary directory found
The “no new privileges” flag is set, which prevents sudo from running as root.
sudo must be owned by uid 0 and have the setuid bit set
sudoedit is not supported on this platform
timed out reading password
you do not exist in the passwd database
you may not specify environment variables in edit mode
su(1), stat(2), login_cap(3), passwd(5), sudo.conf(5), sudo_plugin(5), sudoers(5), sudoers_timestamp(5), sudoreplay(8), visudo(8)
See the HISTORY.md file in the sudo distribution (https://www.sudo.ws/about/history/) for a brief history of sudo.
Many people have worked on sudo over the years; this version consists of code written primarily by:
See the CONTRIBUTORS.md file in the sudo distribution (https://www.sudo.ws/about/contributors/) for an exhaustive list of people who have contributed to sudo.
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. The -D option can be used to run a command in a specific directory.
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).
If you believe you have found a bug in sudo, you can either file a bug report in the sudo bug database, https://bugzilla.sudo.ws/, or open an issue at https://github.com/sudo-project/sudo/issues. If you would prefer to use email, messages may be sent to the sudo-workers mailing list, https://www.sudo.ws/mailman/listinfo/sudo-workers (public) or <sudo@sudo.ws> (private).
Please do not report security vulnerabilities through public GitHub issues, Bugzilla or mailing lists. Instead, report them via email to <Todd.Miller@sudo.ws>. You may encrypt your message with PGP if you would like, using the key found at https://www.sudo.ws/dist/PGPKEYS.
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.md file distributed with sudo or https://www.sudo.ws/about/license/ for complete details.
| January 16, 2023 | Sudo 1.9.13p2 |