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sudoallows a permitted user to execute a command as the superuser or another user, as specified by 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
5minutes. 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
5minutes, 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:
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.
-a(authentication type) option causes
sudoto use the specified authentication type when validating the user, as allowed by /etc/login.conf. The system administrator may specify a list of sudo-specific authentication methods by adding an “auth-sudo” entry in /etc/login.conf. This option is only available on systems that support BSD authentication.
-b(background) option tells
sudoto run the given command in the background. Note that if you use the
-boption you cannot use shell job control to manipulate the process. Most interactive commands will fail to work properly in background mode.
sudowill close all open file descriptors other than standard input, standard output and standard error. The
-C(close from) option allows the user to specify a starting point above the standard error (file descriptor three). Values less than three are not permitted. The security policy may restrict the user's ability to use the
-Coption. The sudoers policy only permits use of the
-Coption when the administrator has enabled the closefrom_override option.
-c(class) option causes
sudoto run the specified command with resources limited by the specified login class. The class argument can be either a class name as defined in /etc/login.conf, or a single ‘
-’ character. Specifying a class of
-indicates that the command should be run restricted by the default login capabilities for the user the command is run as. If the class argument specifies an existing user class, the command must be run as root, or the
sudocommand must be run from a shell that is already root. This option is only available on systems with BSD login classes.
-E(preserve environment) 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
-Eoption is specified and the user does not have permission to preserve the environment.
-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 policy, the following steps are taken:
EDITORenvironment variables (in that order). If none of
EDITORare set, the first program listed in the editor sudoers(5) option is used.
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.
sudoruns 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
sudoto 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
-uoption 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(HOME) option requests that the security policy set the
HOMEenvironment 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 behavior.
-h(help) option causes
sudoto print a short help message to the standard output and exit.
-i(simulate initial login) option runs the shell specified by the password database entry of the target user 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 shell's
-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 security policy shall initialize the environment to a minimal 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
-ioption affects the environment in which a command is run when the sudoers policy is in use.
-K(sure kill) option is like
-kexcept 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(kill) option to
sudoinvalidates the user's cached credentials. 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. Not all security policies support credential caching. When used in conjunction with a command or an option that may require a password, the
-koption 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.
-l(list) option will list the allowed (and forbidden) commands for the invoking user (or the user specified by the
-Uoption) 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 specified but not allowed,
sudowill exit with a status value of 1. If the
-loption is specified with an l argument (i.e.
-ll), or if
-lis specified multiple times, a longer list format is used.
-n(non-interactive) option prevents
sudofrom prompting the user for a password. If a password is required for the command to run,
sudowill display an error message and exit.
-P(preserve group vector) option causes
sudoto 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) option allows you to override the default password prompt and use a custom one. The following percent (‘
%’) escapes are supported by the sudoers policy:
-uoption is also specified)
%’ characters are collapsed into a single ‘
-poption will override the system password prompt on systems that support PAM unless the passprompt_override flag is disabled in sudoers.
-r(role) option causes the new (SELinux) security context to have the role specified by role.
-S(stdin) option causes
sudoto read the password from the standard input instead of the terminal device. The password must be followed by a newline character.
-s(shell) option runs the shell specified by the
SHELLenvironment 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
-coption. If no command is specified, an interactive shell is executed.
-t(type) option causes the new (SELinux) security context to have the type specified by type. If no type is specified, the default type is derived from the specified role.
-U(other user) option is used in conjunction with the
-loption to specify the user whose privileges should be listed. 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.
-u(user) option causes
sudoto 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(version) option causes
sudoto 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
-Voption will display the arguments passed to configure when
sudowas built and plugins may display more verbose information such as default options.
sudowill update the user's cached credentials, authenticating the user's password if necessary. For the sudoers plugin, this extends the
sudotimeout for another
5minutes (or whatever the timeout is set to by the security policy) but does not run a command. Not all security policies support cached credentials.
--option indicates that
sudoshould stop processing command line arguments.
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 uid and gid 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:
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.
sudowill relay signals it receives to the command. Unless the command is being run in a new pty, the
SIGQUITsignals are not relayed unless they are sent by a user process, not the kernel. Otherwise, the command would receive
SIGINTtwice every time the user entered 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. sudo.conf(5) file. 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
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 on stderr. (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. 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). 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.
-e(sudoedit) mode if neither
-imode or when env_reset is enabled in sudoers, set to the mail spool of the target user.
-Hare specified, env_reset or always_set_home are set in sudoers, or when the
-soption is specified and set_home is set in sudoers.
-Aoption is specified.
PS1will be set to its value for the program being run.
-uoption is specified).
-e(sudoedit) mode if
SUDO_EDITORis not set.
sudofront end configuration
$ sudo ls /usr/local/protected
$ sudo -u yaz ls ~yaz
$ sudo -u www vi ~www/htdocs/index.html
$ sudo -g adm view /var/log/syslog
$ sudo -u jim -g audio vi ~jim/sound.txt
$ sudo shutdown -r +15 "quick reboot"
cdand file redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
sudodistribution (https://www.sudo.ws/sudo/history.html) for a brief history of sudo.
sudoover the years; this version consists of code written primarily by:
sudodistribution (https://www.sudo.ws/sudo/contributors.html) for an exhaustive list of people who have contributed to
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).
sudo, please submit a bug report at https://www.sudo.ws/sudo/bugs/ 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/sudo/license.html for complete details.