|SUDO(8)||System Manager's Manual||SUDO(8)|
execute a command as another user
] file ...
sudoallows 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.
sudosupports 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
sudofront 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,
sudowill 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. Security policies may support credential caching to allow the user to run
sudoagain for a period of time without requiring authentication. The sudoers policy caches credentials for
15minutes, unless overridden in sudoers(5). By running
-voption, a user can update the cached credentials without running a command. When invoked as
-eoption (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:
- Normally, if
sudorequires 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_ASKPASSenvironment 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
sudowill exit with an error.
- 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,
sudowill 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
-Coption 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 environment.
- 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
- Temporary copies are made of the files to be edited with the owner set to the invoking user.
- The editor specified by the policy is run to edit the temporary files.
The sudoers policy uses the
EDITORenvironment variables (in that order). If none of
EDITORare 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.
- 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).
sudois 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.
#0for GID 0). When running a command as a GID, many shells require that the ‘
#’ be escaped with a backslash (‘
\’). If no
-uoption is specified, the command will be run as the invoking user. In either case, the primary group will be set to group.
- Request that the security policy set the
HOMEenvironment variable to the home directory specified by the target user's password database entry. Depending on the policy, this may be the default behavior.
- 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
-loption 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
.login will be read by the shell. If a
command is specified, it is passed to the shell for execution via the
-coption. If no command is specified, an interactive shell is executed.
sudoattempts 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
-ioption affects the environment in which a command is run when the sudoers policy is in use.
- Similar to the
-koption, 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.
- When used without a command, invalidates the user's cached credentials. In
other words, the next time
sudois run a password will be required. This option does not require a password and was added to allow a user to revoke
sudopermissions from a .logout file. When used in conjunction with a command or an option that may require a password, this option will cause
sudoto ignore the user's cached credentials. As a result,
sudowill 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 no command is specified, list the
allowed (and forbidden) commands for the invoking user (or the user
specified by the
-Uoption) 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,
sudowill 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,
sudowill display an error message and exit.
- 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.
- Use a custom password prompt with optional escape sequences. The following
%’) escape sequences are supported by the sudoers policy:
- 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 in sudoers(5))
- expanded to the login name of the user the command will be run as
(defaults to root unless the
-uoption is also specified)
- expanded to the invoking user's login name
- two consecutive ‘
%’ characters are collapsed into a single ‘
- Run the command with an SELinux security context that includes the specified role.
- 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
SHELLenvironment 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
-coption. If no command is specified, an interactive shell is executed.
- 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
-loption 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
ALLprivilege on the current host to use this option.
- Run the command as a user other than the default target user (usually
user may be either a user name or a
numeric user ID (UID) prefixed with the
#’ character (e.g.
#0for 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
sudoversion 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
-Voption will display the arguments passed to configure when
sudowas built and plugins may display more verbose information such as default options.
- Update the user's cached credentials, authenticating the user if
necessary. For the sudoers plugin, this
sudotimeout for another
15minutes by default, but does not run a command. Not all security policies support cached credentials.
--option indicates that
sudoshould stop processing command line arguments.
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
SETENVtag set or the command matched is
ALL, the user may set variables that would otherwise be forbidden. See sudoers(5) for more information.
sudoexecutes 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
-Poption 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)
sudoruns 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
sudoprocess 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
sudoprocess 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,
sudowill 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
sudowill relay signals it receives to the command. The
SIGQUITsignals 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
SIGINTtwice each time the user enters control-C. Some signals, such as
SIGKILL, cannot be caught and thus will not be relayed to the command. As a general rule,
SIGTSTPshould be used instead of
SIGSTOPwhen you wish to suspend a command being run by
sudo. As a special case,
sudowill 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
SIGTERMto all non-system processes other than itself before rebooting the system. This prevents
sudofrom relaying the
SIGTERMsignal 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
sudoand not any other processes that the command may create. As a result, running a script that calls reboot(8) or shutdown(8) via
sudomay 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,
sudomay execute the command directly instead of running it as a child process.
Plugins¶Plugins may be specified via
Plugindirectives in the sudo.conf(5) file. They may be loaded as dynamic shared objects (on systems that support them), or compiled directly into the
sudobinary. If no sudo.conf(5) file is present, or it contains no
sudowill 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
EXIT VALUE¶Upon successful execution of a command, the exit status from
sudowill be the exit status of the program that was executed. If the command terminated due to receipt of a signal,
sudowill send itself the signal that terminated the command. Otherwise,
sudoexits with a value of 1 if there is a configuration/permission problem or if
sudocannot execute the given command. In the latter case, the error string is printed to the standard error. If
sudocannot 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
PATHis on a machine that is currently unreachable.
sudotries to be safe when executing external commands. To prevent command spoofing,
sudochecks "." 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
PATHenvironment variable is not modified and is passed unchanged to the program that
sudoexecutes. Users should never be granted
sudoprivileges 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
sudowill normally only log the command it explicitly runs. If a user runs a command such as
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
sudoto 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,
sudodisables 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
sudocrashes, 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
sudoutilizes the following environment variables. The security policy has control over the actual content of the command's environment.
- Default editor to use in
-e(sudoedit) mode if neither
- Set to the mail spool of the target user when the
-ioption is specified or when env_reset is enabled in sudoers (unless
- Set to the home directory of the target user when the
-Hoptions are specified, when the
-soption 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
-ioption is specified, when the set_logname option is enabled in sudoers or when the env_reset option is enabled in sudoers (unless
LOGNAMEis present in the env_keep list).
- May be overridden by the security policy.
- Used to determine shell to run with
- Specifies the path to a helper program used to read the password if no
terminal is available or if the
-Aoption is specified.
- Set to the command run by sudo.
- Default editor to use in
- Set to the group ID of the user who invoked sudo.
- Used as the default password prompt.
- If set,
PS1will 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.
- Same as
- Default editor to use in
-e(sudoedit) mode if
SUDO_EDITORis not set.
sudofront 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
$ sudo -u yaz ls ~yaz
$ sudoedit -u www ~www/htdocs/index.html
$ sudo -g adm more /var/log/syslog
$ sudoedit -u jim -g audio ~jim/sound.txt
$ sudo shutdown -r +15 "quick reboot"
cdand file redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
SEE ALSO¶su(1), stat(2), passwd(5), sudo.conf(5), sudoers(5), sudo_plugin(8), sudoreplay(8), visudo(8)
HISTORY¶See the HISTORY file in the
sudodistribution (https://www.sudo.ws/history.html) for a brief history of sudo.
AUTHORS¶Many people have worked on
sudoover the years; this version consists of code written primarily by:
Todd C. MillerSee the CONTRIBUTORS file in the
sudodistribution (https://www.sudo.ws/contributors.html) for an exhaustive list of people who have contributed to
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
cdcommand directly via sudo, e.g.,
$ sudo cd /usr/local/protected
sudocan 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).
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.
sudois 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
sudoor https://www.sudo.ws/license.html for complete details.
|January 19, 2016||Sudo 1.8.19p1|