SUDO
Section: Maintenance Commands (8)
Index
Return to Main Contents
BSD mandoc
Sudo 1.8.10p3
NAME
sudo
sudoedit
- execute a command as another user
SYNOPSIS
sudo
-
h | K | k | V
sudo
-
v
[-
AknS
]
[-
a type
]
[-
g group
]
[-
h host
]
[-
p prompt
]
[-
u user
]
sudo
-
l
[-
AknS
]
[-
a type
]
[-
g group
]
[-
h host
]
[-
p prompt
]
[-
U user
]
[-
u user
]
[
command
]
sudo
[-
AbEHnPS
]
[-
a type
]
[-
C num
]
[-
c class
]
[-
g group
]
[-
h host
]
[-
p prompt
]
[-
r role
]
[-
t type
]
[-
u user
]
[
VAR = value
]
[-
i | s
]
[
command
]
sudoedit
[-
AknS
]
[-
a type
]
[-
C num
]
[-
c class
]
[-
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
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
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.conf5
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:
-
Temporary copies are made of the files to be edited with the owner
set to the invoking user.
-
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.
-
If they have been modified, the temporary files are copied back to
their original location and the temporary versions are removed.
Unless explicitly allowed by the security policy, symbolic links
will not be opened.
This helps prevent the editing of unauthorized files when the file
is located in a user-writable directory.
Versions of
sudo
prior to 1.8.10p3-1+deb8u3 do not have this restriction.
Users are never allowed to edit device special files.
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
- -r role , --role = role
-
Run the command with an SELinux security context that includes
the specified
role
- -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.
- -t type , --type = type
-
Run the command with an SELinux security context that includes
the specified
type
If no
type
is specified, the default type is derived from the role.
- -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)
-
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 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
Fn exec
family of functions instead of
Fn 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
Fn 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.conf5
file.
They may be loaded as dynamic shared objects (on systems that support them),
or compiled directly into the
sudo
binary.
If no
sudo.conf5
file is present, or it contains no
Plugin
lines,
sudo
will use the traditional
sudoers
security policy and I/O logging.
See the
sudo.conf5
manual for details of the
/etc/sudo.conf
file and the
sudo_plugin8
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.conf5
file as follows:
Set disable_coredump false
See the
sudo.conf5
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.conf5,
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
-
- EXIT VALUE
-
- SECURITY NOTES
-
- ENVIRONMENT
-
- FILES
-
- EXAMPLES
-
- SEE ALSO
-
- HISTORY
-
- AUTHORS
-
- CAVEATS
-
- BUGS
-
- SUPPORT
-
- DISCLAIMER
-