sudo,
sudoedit
—
execute a command as another user
| 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]
[-T
timeout]
[-u
user]
[VAR=value]
[-i |
-s]
[command] |
| sudoedit |
[-AknS]
[-a
type]
[-C
num]
[-c
class]
[-g
group]
[-h
host]
[-p
prompt]
[-T
timeout]
[-u
user]
file ... |
sudo allows a permitted user to execute a
command as the superuser or another user, as
specified by the security policy. The invoking user's real
(
not effective) user ID is used to determine the
user name with which to query the security policy.
sudo supports a plugin architecture for security
policies and input/output logging. Third parties can develop and distribute
their own policy and I/O logging plugins to work seamlessly with the
sudo front end. The default security policy is
sudoers, which is configured via the file
/etc/sudoers, or via LDAP. See the
Plugins section for more
information.
The security policy determines what privileges, if any, a user has to run
sudo. The policy may require that users
authenticate themselves with a password or another authentication mechanism.
If authentication is required,
sudo will exit if
the user's password is not entered within a configurable time limit. This
limit is policy-specific; the default password prompt timeout for the
sudoers security policy is
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,
--askpass
- Normally, if sudo requires a
password, it will read it from the user's terminal. If the
-A (askpass)
option is specified, a (possibly graphical) helper program is executed to
read the user's password and output the password to the standard output.
If the
SUDO_ASKPASS environment
variable is set, it specifies the path to the helper program. Otherwise,
if sudo.conf(5) contains a line specifying
the askpass program, that value will be used. For example:
# Path to askpass helper program
Path askpass /usr/X11R6/bin/ssh-askpass
If no askpass program is available, sudo will
exit with an error.
-
-
- -a
type,
--auth-type=type
- Use the specified BSD authentication
type when validating the user, if allowed
by /etc/login.conf. The system administrator
may specify a list of sudo-specific authentication methods by adding an
“auth-sudo” entry in
/etc/login.conf. This option is only
available on systems that support BSD authentication.
-
-
- -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.
-
-
- -c
class,
--login-class=class
- Run the command with resource limits and scheduling
priority of the specified login class.
The class argument can be either a class
name as defined in /etc/login.conf, or a
single ‘
-’ character. If
class is -,
the default login class of the target user will be used. Otherwise, the
command must be run as the superuser (user ID 0), or
sudo must be run from a shell that is already
running as the superuser. If the command is being run as a login shell,
additional /etc/login.conf settings, such as
the umask and environment variables, will be applied, if present. This
option is only available on systems with BSD login classes.
-
-
- -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.
-
-
- --preserve-env=list
- Indicates to the security policy that the user wishes to
add the comma-separated list of environment variables to those preserved
from the user's environment. 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.
To help prevent the editing of unauthorized files, the following
restrictions are enforced unless explicitly allowed by the security
policy:
- Symbolic links may not be edited (version 1.8.15 and
higher).
- Symbolic links along the path to be edited are not
followed when the parent directory is writable by the invoking user
unless that user is root (version 1.8.16 and higher).
- Files located in a directory that is writable by the
invoking user may not be edited unless that user is root (version
1.8.16 and higher).
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 default prompt specified by either the
security policy or the SUDO_PROMPT
environment variable. On systems that use PAM, the custom prompt will also
override the prompt specified by a PAM module 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.
-
-
- -T
timeout,
--command-timeout=timeout
- Used to set a timeout for the command. If the timeout
expires before the command has exited, the command will be terminated. The
security policy may restrict the ability to set command timeouts. The
sudoers policy requires that user-specified
timeouts be explicitly enabled.
-
-
- -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
5 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.
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
- Solaris project
- Solaris privileges
- BSD login class
- scheduling priority (aka nice value)
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.
When the command is run as a child of the
sudo
process,
sudo will relay signals it receives to
the command. The
SIGINT and
SIGQUIT signals are only relayed when the
command is being run in a new pty or when the signal was sent by a user
process, not the kernel. This prevents the command from receiving
SIGINT twice each time the user enters
control-C. Some signals, such as
SIGSTOP
and
SIGKILL, cannot be caught and thus will
not be relayed to the command. As a general rule,
SIGTSTP should be used instead of
SIGSTOP when you wish to suspend a command
being run by
sudo.
As a special case,
sudo will not relay signals that
were sent by the command it is running. This prevents the command from
accidentally killing itself. On some systems, the
reboot(8) command sends
SIGTERM to all non-system processes other
than itself before rebooting the system. This prevents
sudo from relaying the
SIGTERM signal it received back to
reboot(8), which might then exit before the
system was actually rebooted, leaving it in a half-dead state similar to
single user mode. Note, however, that this check only applies to the command
run by
sudo and not any other processes that the
command may create. As a result, running a script that calls
reboot(8) or
shutdown(8) via
sudo
may cause the system to end up in this undefined state unless the
reboot(8) or
shutdown(8) are run using the
exec() family of functions instead of
system() (which interposes a shell between the
command and the calling process).
If no I/O logging plugins are loaded and the policy plugin has not defined a
close() function, set a command timeout or
required that the command be run in a new pty,
sudo may execute the command directly instead of
running it as a child process.
Plugins may be specified via
Plugin directives in the
sudo.conf(5) file. They may be loaded as dynamic
shared objects (on systems that support them), or compiled directly into the
sudo binary. If no
sudo.conf(5) file is present, or it contains no
Plugin lines,
sudo will
use the traditional
sudoers security policy and
I/O logging. See the
sudo.conf(5) manual for
details of the
/etc/sudo.conf file and the
sudo_plugin(5) manual for more information about
the
sudo plugin architecture.
Upon successful execution of a command, the exit status from
sudo will be the exit status of the program that
was executed. If the command terminated due to receipt of a signal,
sudo will send itself the signal that terminated
the command.
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 to the standard
error. (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.
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.
Users should
never be granted
sudo privileges to execute files that are
writable by the user or that reside in a directory that is writable by the
user. If the user can modify or replace the command there is no way to limit
what additional commands they can run.
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). This historical
practice dates from a time when most operating systems allowed setuid
processes to dump core by default. To aid in debugging
sudo crashes, you may wish to re-enable core
dumps by setting “disable_coredump” to false in the
sudo.conf(5) file as follows:
Set disable_coredump false
See the
sudo.conf(5) manual for more information.
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- Set to the mail spool of the target user when the
-i option is specified or when
env_reset is enabled in
sudoers (unless
MAIL is present in the
env_keep list).
-
-
HOME- Set to the home directory of the target user when the
-i or -H options
are specified, when the -s option is
specified and set_home is set in
sudoers, when
always_set_home is enabled in
sudoers, or when
env_reset is enabled in
sudoers and HOME
is not present in the env_keep list.
-
-
LOGNAME- Set to the login name of the target user when the
-i option is specified, when the
set_logname option is enabled in
sudoers or when the
env_reset option is enabled in
sudoers (unless
LOGNAME is present in the
env_keep list).
-
-
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 unless the
-p option was specified.
-
-
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 same value as
LOGNAME, described above.
-
-
USERNAME- Same as
USER.
-
-
VISUAL- Default editor to use in -e
(sudoedit) mode if
SUDO_EDITOR is not
set.
-
-
- /etc/sudo.conf
- sudo front end
configuration
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:
To edit the
index.html file as user www:
$ sudoedit -u www ~www/htdocs/index.html
To view system logs only accessible to root and users in the adm group:
$ sudo -g adm more /var/log/syslog
To run an editor as jim with a different primary group:
$ sudoedit -u jim -g audio ~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"
su(1),
stat(2),
login_cap(3),
passwd(5),
sudo.conf(5),
sudoers(5),
sudo_plugin(5),
sudoreplay(8),
visudo(8)
See the HISTORY file in the
sudo distribution
(
https://www.sudo.ws/history.html) for a brief history of sudo.
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
(
https://www.sudo.ws/contributors.html) for an exhaustive list of people who
have contributed to
sudo.
There is no easy way to prevent a user from gaining a root shell if that user is
allowed to run arbitrary commands via
sudo. Also,
many programs (such as editors) allow the user to run commands via shell
escapes, thus avoiding
sudo's checks. However, on
most systems it is possible to prevent shell escapes with the
sudoers(5) plugin's
noexec functionality.
It is not meaningful to run the
cd command directly via
sudo, e.g.,
$ sudo cd /usr/local/protected
since when the command exits the parent process (your shell) will still be the
same. Please see the
EXAMPLES
section for more information.
Running shell scripts via
sudo can expose the same
kernel bugs that make setuid shell scripts unsafe on some operating systems
(if your OS has a /dev/fd/ directory, setuid shell scripts are generally
safe).
If you feel you have found a bug in
sudo, please
submit a bug report at
https://bugzilla.sudo.ws/
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the
archives.
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
https://www.sudo.ws/license.html for
complete details.