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SUDO


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BSD mandoc

Sudo 1.8.6p3

 

NAME

sudo

sudoedit

– execute a command as another user

 

SYNOPSIS

sudo

-h | -K | -k | -V


sudo

-v

[-AknS

]

-words

[-g group name | #gid

]

-words

[-p prompt

]

-words

[-u user name | #uid

]


sudo

-l [l

]

[-AknS

]

-words

[-g group name | #gid

]

-words

[-p prompt

]

-words

[-U user name

]

-words

[-u user name | #uid

]

[command

]


sudo

[-AbEHnPS

]

-words

[-C fd

]

-words

[-g group name | #gid

]

-words

[-p prompt

]

-words

[-r role

]

-words

[-t type

]

-words

[-u user name | #uid

]

-words

[VAR = value

]

-words

-i | -s

[command

]


sudoedit

[-AnS

]

-words

[-C fd

]

-words

[-g group name | #gid

]

-words

[-p prompt

]

-words

[-u user name | #uid

]

-words

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
Sx 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
5

minutes.

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
5

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


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
/etc/sudo.conf

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


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.
Most interactive commands will fail to work properly in background
mode.

-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.
The security policy may restrict the user’s ability to use the
-C

option.
The
sudoers

policy only permits use of the
-C

option when the administrator has enabled the
closefrom_override

option.

-E


The
-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
-E

option is specified and the user does not have permission to preserve
the environment.

-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 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


Normally,
sudo

runs 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
sudo

to 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
-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 requests that the security policy set the
HOME

environment 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


The
-h ( help )

option causes
sudo

to print a short help message to the standard output and exit.

-i [command

]


The
-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
-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 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
-i

option affects the environment in which a command is run when the
sudoers

policy is in use.

-K


The
-K ( sure kill )

option is like
-k

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 [command

]


When used alone, the
-k ( kill )

option to
sudo

invalidates the user’s cached credentials.
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.
Not all security policies support credential caching.

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 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.

-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 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.
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 message and exit.

-P


The
-P ( preserve group vector )

option causes
sudo

to 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


The
-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:


%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 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

-r role


The
-r ( role )

option causes the new (SELinux) security context to have the role
specified by
role

-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 the
password database.
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.

-t type


The
-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 user


The
-U ( other user )

option is used in conjunction with the
-l

option 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
ALL

privilege on the current host to 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

#uid

When running commands as a
uid

many shells require that the
`#’

be escaped with a backslash
(`’

)

Security policies may restrict
uid s

to those listed in the password database.
The
sudoers

policy allows
uid s

that are not in the password database as long as the
targetpw

option is not set.
Other security policies may not support this.

-V


The
-V ( version )

option causes
sudo

to 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
-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


When given the
-v ( validate )

option,
sudo

will update the user’s cached credentials, authenticating the user’s
password if necessary.
For the
sudoers

plugin, this extends the
sudo

timeout for another
5

minutes (or whatever the timeout is set to by the security policy)
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 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
envionment 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
-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)

  • SELinux role and type

  • 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 method and exits.
If an I/O logging plugin is configured, 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.
 

Signal handling

Because 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 systyem.
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
Fn exec

family of functions instead of
Fn system

(which interposes a shell between the command and the calling process).
 

PLUGINS

Plugins are dynamically loaded based on the contents of the
/etc/sudo.conf

file.
If no
/etc/sudo.conf

file is present, or it contains no
Plugin

lines,
sudo

will use the traditional
sudoers

security policy and I/O logging, which corresponds to the following
/etc/sudo.conf

file.


#
# Default /etc/sudo.conf file
#
# Format:
# Plugin plugin_name plugin_path plugin_options …
# Path askpass /path/to/askpass
# Path noexec /path/to/sudo_noexec.so
# Debug sudo /var/log/sudo_debug [email protected]
# Set disable_coredump true
#
# The plugin_path is relative to /usr/libexec unless
# fully qualified.
# The plugin_name corresponds to a global symbol in the plugin
# that contains the plugin interface structure.
# The plugin_options are optional.
#
Plugin policy_plugin sudoers.so
Plugin io_plugin sudoers.so

A
Plugin

line consists of the
Plugin

keyword, followed by the
symbol_name

and the
path

to the shared object containing the plugin.
The
symbol_name

is the name of the
struct policy_plugin

or
struct io_plugin

in the plugin shared object.
The
path

may be fully qualified or relative.
If not fully qualified it is relative to the
/usr/libexec

directory.
Any additional parameters after the
path

are passed as arguments to the plugin’s
open

function.
Lines that don’t begin with
Plugin

Path

Debug

or
Set

are silently ignored.

For more information, see the
sudo_plugin8

manual.
 

PATHS

A
Path

line consists of the
Path

keyword, followed by the name of the path to set and its value.
E.g.


Path noexec /usr/libexec/sudo_noexec.so
Path askpass /usr/X11R6/bin/ssh-askpass

The following plugin-agnostic paths may be set in the
/etc/sudo.conf

file:


askpass

The fully qualified path to a helper program used to read the user’s
password when no terminal is available.
This may be the case when
sudo

is executed from a graphical (as opposed to text-based) application.
The program specified by
askpass

should display the argument passed to it as the prompt and write
the user’s password to the standard output.
The value of
askpass

may be overridden by the
SUDO_ASKPASS

environment variable.

noexec

The fully-qualified path to a shared library containing dummy
versions of the
Fn execv ,

Fn execve

and
Fn fexecve

library functions that just return an error.
This is used to implement the
noexec

functionality on systems that support
LD_PRELOAD

or its equivalent.
Defaults to
/usr/libexec/sudo_noexec.so


 

DEBUG FLAGS

sudo

versions 1.8.4 and higher support a flexible debugging framework
that can help track down what
sudo

is doing internally if there is a problem.

A
Debug

line consists of the
Debug

keyword, followed by the name of the program to debug
(sudo , visudo , sudoreplay

)

the debug file name and a comma-separated list of debug flags.
The debug flag syntax used by
sudo

and the
sudoers

plugin is
subsystem @ priority

but the plugin is free to use a different format so long as it does
not include a comma
(`,’

)

For instance:


Debug sudo /var/log/sudo_debug [email protected],[email protected]

would log all debugging statements at the
warn

level and higher in addition to those at the
info

level for the plugin subsystem.

Currently, only one
Debug

entry per program is supported.
The
sudo

Debug

entry is shared by the
sudo

front end,
sudoedit

and the plugins.
A future release may add support for per-plugin
Debug

lines and/or support for multiple debugging files for a single
program.

The priorities used by the
sudo

front end, in order of decreasing severity, are:
crit , err , warn , notice , diag , info , trace

and
debug

Each priority, when specified, also includes all priorities higher
than it.
For example, a priority of
notice

would include debug messages logged at
notice

and higher.

The following subsystems are used by the
sudo

front-end:


all


matches every subsystem
args


command line argument processing
conv


user conversation
edit


sudoedit
exec


command execution
main


sudo

main function

netif


network interface handling
pcomm


communication with the plugin
plugin


plugin configuration
pty


pseudo-tty related code
selinux


SELinux-specific handling
util


utility functions
utmp


utmp handling

 

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
/etc/sudo.conf

file as follows:


Set disable_coredump false

Note that by default, most operating systems disable core dumps
from setuid programs, which includes
sudo

To actually get a
sudo

core file you may need to enable core dumps for setuid processes.
On BSD and Linux systems this is accomplished via the sysctl command,
on Solaris the coreadm command can be used.
 

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

grep(1),

su(1),

stat(2),

passwd(5),

sudoers(5),

sudo_plugin8,

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
Sx 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.



 

Index



NAME

SYNOPSIS

DESCRIPTION

COMMAND EXECUTION


Process model

Signal handling


PLUGINS

PATHS

DEBUG FLAGS

EXIT VALUE

SECURITY NOTES

ENVIRONMENT

FILES

EXAMPLES

SEE ALSO

HISTORY

AUTHORS

CAVEATS

BUGS

SUPPORT

DISCLAIMER



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