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SUDO

SUDO

Section: MAINTENANCE COMMANDS (8) Updated: July 19, 2010
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NAME

sudo, sudoedit - execute a command as another user  

SYNOPSIS

sudo -h | -K | -k | -L | -V

sudo -v [-AknS] [-g group name|#gid] [-p prompt] [-u username|#uid]

sudo -l[l] [-AknS] [-g group name|#gid] [-p prompt] [-U user name] [-u user name|#uid] [command]

sudo [-AbEHnPS] [-C fd] [-g group name|#gid] [-p prompt] [-u user name|#uid] [VAR=value] [-i | -s] [command]

sudoedit [-AnS] [-C fd] [-g group name|#gid] [-p prompt] [-u user name|#uid] file ...  

DESCRIPTION

sudo allows a permitted user to execute a command as the superuser or another user, as specified in the sudoers file. The real and effective uid and gid are set to match those of the target user as specified in the passwd file and the group vector is initialized based on the group file (unless the -P option was specified). If the invoking user is root or if the target user is the same as the invoking user, no password is required. Otherwise, sudo requires that users authenticate themselves with a password by default (NOTE: in the default configuration this is the user's password, not the root password). Once a user has been authenticated, a time stamp is updated and the user may then use sudo without a password for a short period of time ( 15
minutes unless overridden in sudoers).

When invoked as sudoedit, the -e option (described below), is implied.

sudo determines who is an authorized user by consulting the file /etc/sudoers. By running sudo with the -v option, a user can update the time stamp without running a command. If a password is required, sudo will exit if the user's password is not entered within a configurable time limit. The default password prompt timeout is unlimited.

If a user who is not listed in the sudoers file tries to run a command via sudo, mail is sent to the proper authorities, as defined at configure time or in the sudoers file (defaults to root
). Note that the mail will not be sent if an unauthorized user tries to run sudo with the -l or -v option. This allows users to determine for themselves whether or not they are allowed to use sudo.

If sudo is run by root and the SUDO_USER
environment variable is set, sudo will use this value to determine who the actual user is. This can be used by a user to log commands through sudo even when a root shell has been invoked. It also allows the -e option to remain useful even when being run via a sudo-run script or program. Note however, that the sudoers lookup is still done for root, not the user specified by SUDO_USER
.

sudo can log both successful and unsuccessful attempts (as well as errors) to syslog(3), a log file, or both. By default sudo will log via syslog(3) but this is changeable at configure time or via the sudoers file.  

OPTIONS

sudo accepts the following command line options:
-A
Normally, if sudo requires a password, it will read it from the current 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, the value specified by the askpass option in sudoers(5) is used.
-b
The -b (background) option tells sudo to run the given command in the background. Note that if you use the -b option you cannot use shell job control to manipulate the process.
-C fd
Normally, sudo will 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. This option is only available if the administrator has enabled the closefrom_override option in sudoers(5).
-E
The -E (preserve environment) option will override the env_reset option in sudoers(5)). It is only available when either the matching command has the SETENV
tag or the setenv option is set in sudoers(5).
-e
The -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 sudoers file. If the user is authorized by sudoers 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 SUDO_EDITOR
, VISUAL
or EDITOR
environment variables is run to edit the temporary files. If none of SUDO_EDITOR
, VISUAL
or EDITOR
are set, the first program listed in the editor sudoers variable 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
Normally, sudo sets the primary group to the one specified by the passwd database for the user the command is being run as (by default, root). The -g (group) option causes sudo to run the specified command with the primary group set to group. 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 -u option 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
The -H (HOME) option sets the HOME
environment variable to the homedir of the target user (root by default) as specified in passwd(5). The default handling of the HOME
environment variable depends on sudoers(5) settings. By default, sudo will set HOME
if env_reset or always_set_home are set, or if set_home is set and the -s option is specified on the command line.
-h
The -h (help) option causes sudo to print a usage message and exit.
-i [command]
The -i (simulate initial login) option runs the shell specified in the passwd(5) 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. Otherwise, an interactive shell is executed. sudo attempts to change to that user's home directory before running the shell. It also initializes the environment, leaving DISPLAY and TERM unchanged, setting HOME, MAIL, SHELL, USER, LOGNAME, and PATH, as well as the contents of /etc/environment on Linux and AIX systems. All other environment variables are removed.
-K
The -K (sure kill) option is like -k except that it removes the user's time stamp entirely and may not be used in conjunction with a command or other option. This option does not require a password.
-k
When used by itself, the -k (kill) option to sudo invalidates the user's time stamp by setting the time on it to the Epoch. 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, the -k option will cause sudo to ignore the user's time stamp file. As a result, sudo will prompt for a password (if one is required by sudoers) and will not update the user's time stamp file.

-L
The -L (list defaults) option will list the parameters that may be set in a Defaults line along with a short description for each. This option will be removed from a future version of sudo.
-l[l] [command]
If no command is specified, the -l (list) option will list the allowed (and forbidden) commands for the invoking user (or the user specified by the -U option) on the current host. If a command is specified and is permitted by sudoers, 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. If the -l option is specified with an l argument (i.e. -ll), or if -l is specified multiple times, a longer list format is used.
-n
The -n (non-interactive) option prevents sudo from prompting the user for a password. If a password is required for the command to run, sudo will display an error messages and exit.
-P
The -P (preserve group vector) option causes sudo to preserve the invoking user's group vector unaltered. By default, sudo 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
The -p (prompt) option allows you to override the default password prompt and use a custom one. The following percent (` %
') escapes are supported:
%H
expanded to the local host name including the domain name (on if the machine's host name is fully qualified or the fqdn sudoers option is set)
%h
expanded to the local host name without the domain name
%p
expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)
%U
expanded to the login name of the user the command will be run as (defaults to root)
%u
expanded to the invoking user's login name
%%
two consecutive %
characters are collapsed into a single %
character

The prompt specified by the -p option will override the system password prompt on systems that support PAM unless the passprompt_override flag is disabled in sudoers.

-S
The -S (stdin) option causes sudo to read the password from the standard input instead of the terminal device. The password must be followed by a newline character.
-s [command]
The -s (shell) option runs the shell specified by the SHELL environment variable if it is set or the shell as specified in passwd(5). If a command is specified, it is passed to the shell for execution. Otherwise, an interactive shell is executed.
-U user
The -U (other user) option is used in conjunction with the -l option to specify the user whose privileges should be listed. Only root or a user with sudo ALL
on the current host may use this option.
-u user
The -u (user) option causes sudo to run the specified command as a user other than root. To specify a uid instead of a user name, use #uid. When running commands as a uid, many shells require that the '#' be escaped with a backslash ('\'). Note that if the targetpw Defaults option is set (see sudoers(5)) it is not possible to run commands with a uid not listed in the password database.
-V
The -V (version) option causes sudo to print the version number and exit. If the invoking user is already root the -V option will print out a list of the defaults sudo was compiled with as well as the machine's local network addresses.
-v
If given the -v (validate) option, sudo will update the user's time stamp, prompting for the user's password if necessary. This extends the sudo timeout for another 15
minutes (or whatever the timeout is set to in sudoers) but does not run a command.
--
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 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 overwise be forbidden. See sudoers(5) for more information.  

RETURN VALUES

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 quits with an exit 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 stderr. 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.

There are two distinct ways to deal with environment variables. By default, the env_reset sudoers option is enabled. This causes commands to be executed with a minimal environment containing TERM
, PATH
, HOME
, SHELL
, LOGNAME
, USER
and USERNAME
in addition to variables from the invoking process permitted by the env_check and env_keep sudoers options. There is effectively a whitelist for environment variables.

If, however, the env_reset option is disabled in sudoers, any variables not explicitly denied by the env_check and env_delete options are inherited from the invoking process. In this case, env_check and env_delete behave like a blacklist. Since it is not possible to blacklist all potentially dangerous environment variables, use of the default env_reset behavior is encouraged.

In all cases, environment variables with a value beginning with ()
are removed as they could be interpreted as bash functions. The list of environment variables that sudo allows or denies is contained in the output of sudo -V
when run as root.

Note that the dynamic linker on most operating systems will remove variables that can control dynamic linking from the environment of setuid executables, including sudo. Depending on the operating system this may include _RLD*
, DYLD_*
, LD_*
, LDR_*
, LIBPATH
, SHLIB_PATH
, and others. These type of variables are removed from the environment before sudo even begins execution and, as such, it is not possible for sudo to preserve them.

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.

sudo will check the ownership of its time stamp directory (/var/lib/sudo by default) and ignore the directory's contents if it is not owned by root or if it is writable by a user other than root. On systems that allow non-root users to give away files via chown(2), if the time stamp directory is located in a directory writable by anyone (e.g., /tmp), it is possible for a user to create the time stamp directory before sudo is run. However, because sudo checks the ownership and mode of the directory and its contents, the only damage that can be done is to ``hide'' files by putting them in the time stamp dir. This is unlikely to happen since once the time stamp dir is owned by root and inaccessible by any other user, the user placing files there would be unable to get them back out. To get around this issue you can use a directory that is not world-writable for the time stamps (/var/adm/sudo for instance) or create /var/lib/sudo with the appropriate owner (root) and permissions (0700) in the system startup files.

sudo will not honor time stamps set far in the future. Timestamps with a date greater than current_time + 2 * TIMEOUT
will be ignored and sudo will log and complain. This is done to keep a user from creating his/her own time stamp with a bogus date on systems that allow users to give away files.

On systems where the boot time is available, sudo will also not honor time stamps from before the machine booted.

Since time stamp files live in the file system, they can outlive a user's login session. As a result, a user may be able to login, run a command with sudo after authenticating, logout, login again, and run sudo without authenticating so long as the time stamp file's modification time is within 15
minutes (or whatever the timeout is set to in sudoers). When the tty_tickets option is enabled in sudoers, the time stamp has per-tty granularity but still may outlive the user's session. On Linux systems where the devpts filesystem is used, Solaris systems with the devices filesystem, as well as other systems that utilize a devfs filesystem that monotonically increase the inode number of devices as they are created (such as Mac OS X), sudo is able to determine when a tty-based time stamp file is stale and will ignore it. Administrators should not rely on this feature as it is not universally available.

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 will not be logged, nor will sudo's access control affect them. The same is true for commands that offer shell escapes (including most editors). 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).  

ENVIRONMENT

sudo utilizes the following environment variables:
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
Set to a sane value if the secure_path sudoers option is set.
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 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/sudoers
List of who can run what
/var/lib/sudo
Directory containing time stamps
/etc/environment
Initial environment for -i mode on Linux and AIX
 

EXAMPLES

Note: the following examples assume suitable sudoers(5) entries.

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 shutdown 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

grep(1), su(1), stat(2), passwd(5), sudoers(5), visudo(8)  

AUTHORS

Many people have worked on sudo over the years; this version consists of code written primarily by:


        Todd C. Miller

See the HISTORY file in the sudo distribution or visit http://www.sudo.ws/sudo/history.html for a short history of 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 sudo's noexec functionality. See the sudoers(5) manual for details.

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.

If users have sudo ALL
there is nothing to prevent them from creating their own program that gives them a root shell regardless of any '!' elements in the user specification.

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.


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
RETURN VALUES
SECURITY NOTES
ENVIRONMENT
FILES
EXAMPLES
SEE ALSO
AUTHORS
CAVEATS
BUGS
SUPPORT
DISCLAIMER

This document was created by man2html, using the manual pages.
Time: 22:02:27 GMT, April 16, 2011