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Manual Pages for UNIX Operating System command usage for man sudo

MAINTENANCE COMMANDS SUDO(1m)

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 (5 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 5 minutes.

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.

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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(4) 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(4).

-E The -E (preserve environment) option will

override the env_reset option in sudoers(4)).

It is only available when either the matching command has the SETENV tag or the setenv option

is set in sudoers(4).

-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 1.7.4 Last change: July 19, 2010 2 MAINTENANCE COMMANDS SUDO(1m)

"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(4). The default handling of the HOME environment

variable depends on sudoers(4) 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

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-i [command]

The -i (simulate initial login) option runs the

shell specified in the passwd(4) entry of the target user as a login shell. This means that

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 1.7.4 Last change: July 19, 2010 4 MAINTENANCE COMMANDS SUDO(1m)

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

1.7.4 Last change: July 19, 2010 5 MAINTENANCE COMMANDS SUDO(1m) 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(4). 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(4)) 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 5 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 1.7.4 Last change: July 19, 2010 6 MAINTENANCE COMMANDS SUDO(1m)

sudoers(4) 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

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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/run/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/run/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 5

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

1.7.4 Last change: July 19, 2010 8 MAINTENANCE COMMANDS SUDO(1m) 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(4).

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 1.7.4 Last change: July 19, 2010 9 MAINTENANCE COMMANDS SUDO(1m)

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/run/sudo Directory containing time stamps

/etc/environment Initial environment for -i mode on

Linux and AIX

EXAMPLES

Note: the following examples assume suitable sudoers(4)

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

1.7.4 Last change: July 19, 2010 10 MAINTENANCE COMMANDS SUDO(1m) to make the cd and file redirection work.

$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"

grep(1), su(1), stat(2), passwd(4), sudoers(5), visudo(1m)

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(4) 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. 1.7.4 Last change: July 19, 2010 11 MAINTENANCE COMMANDS SUDO(1m) 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.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

_______________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | security/sudo |

|____________________|__________________|_

| Interface Stability| Uncommitted |

|____________________|_________________|

NOTES

sudo does not create audit(2) records; for a Role Based

administration solution that performs auditing of all actions, please refer to rbac(5).

Source for sudo is available on http://opensolaris.org.

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