Provided by: sudo-ldap_1.8.9p5-1ubuntu1.4_amd64 
NAME
sudo, sudoedit — execute a command as another user
SYNOPSIS
sudo -h | -K | -k | -V
sudo -v [-AknS] [-g group] [-h host] [-p prompt] [-u user]
sudo -l [-AknS] [-g group] [-h host] [-p prompt] [-U user] [-u user] [command]
sudo [-AbEHnPS] [-C num] [-g group] [-h host] [-p prompt] [-u user] [VAR=value] [-i | -s]
[command]
sudoedit [-AknS] [-C num] [-g group] [-h host] [-p prompt] [-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.
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 unlimited.
Security policies may support credential caching to allow the user to run sudo again for a
period of time without requiring authentication. The sudoers policy caches credentials for
15 minutes, unless overridden in sudoers(5). 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, --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.
-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.
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.
-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 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. 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 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 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 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 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.
-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 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)
• scheduling priority (aka nice value)
Process model
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 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 sudo process 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,
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. Unless the command is being run in a new pty, the SIGHUP, SIGINT and
SIGQUIT signals are not relayed unless they are sent by a user process, not the kernel.
Otherwise, the command would receive SIGINT twice every time the user entered 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(8) manual for more information about
the sudo plugin architecture.
EXIT VALUE
Upon successful execution of a program, the exit status from sudo will simply be the exit
status of the program that was executed.
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 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 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.
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). 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 In -i mode or when env_reset is enabled in sudoers, set to the mail spool
of the target user.
HOME Set to the home directory of the target user if -i or -H are specified,
env_reset or always_set_home are set in sudoers, or when the -s option is
specified and set_home is set in sudoers.
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 target user (root unless the -u option is specified).
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:
$ 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"
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 sudo distribution (http://www.sudo.ws/sudo/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
(http://www.sudo.ws/sudo/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 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
http://www.sudo.ws/sudo/bugs/
SUPPORT
Limited free support is available via the sudo-users mailing list, see
http://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
http://www.sudo.ws/sudo/license.html for complete details.