sudo (1) - Linux Manuals
sudo: execute a command as another user
NAME
sudo, sudoedit - execute a command as another user
SYNOPSIS
sudo -h | -K | -k | -L | -V
sudo -v [-AknS]
[-g
sudo -l[l] [-AknS]
[-g
sudo [-AbEHnPS]
[-C
sudoedit [-AnS]
[-C
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
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
If sudo is run by root and the
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.
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.
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.
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.
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
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
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
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
()
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*
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
sudo will check the ownership of its time stamp directory
(/var/db/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/db/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
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
Please note that sudo will normally only log the command it
explicitly runs. If a user runs a command such as
sudo su
To get a file listing of an unreadable directory:
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:
To view system logs only accessible to root and users in the adm group:
To run an editor as jim with a different primary group:
To shutdown a machine:
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
See the HISTORY file in the sudo distribution or visit
http://www.sudo.ws/sudo/history.html for a short history
of sudo.
It is not meaningful to run the
cd
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
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).
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).
minutes.
). 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.
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
.
OPTIONS
sudo accepts the following command line options:
environment variable is set, it specifies the
path to the helper program. Otherwise, the value specified by the
askpass option in sudoers(5) is used.
tag
or the setenv option is set in sudoers(5).
,
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.
environment variable
to the homedir of the target user (root by default) as specified
in passwd(5). The default handling of the
HOME
environment
variable depends on sudoers(5) settings. By default, sudo
will set
HOME
if env_reset or always_set_home are set, or
if set_home is set and the -s option is specified on the
command line.
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.
')
escapes are supported:
characters are collapsed into a single
%
character
on the current host may use this
option.
minutes
(or whatever the timeout is set to in sudoers) but does not run
a command.
tag
set or the command matched is
ALL
, the user may set variables
that would overwise be forbidden. See sudoers(5) for more information.
RETURN VALUES
Upon successful execution of a program, the exit status from sudo
will simply be the exit status of the program that was executed.
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.
,
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.
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.
,
DYLD_*
,
LD_*
,
LDR_*
,
LIBPATH
,
SHLIB_PATH
, and others. These type of variables are
removed from the environment before sudo even begins execution
and, as such, it is not possible for sudo to preserve them.
environment variable is not modified and is passed
unchanged to the program that sudo executes.
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.
minutes (or
whatever the timeout is set to in sudoers). When the tty_tickets
option is enabled in sudoers, the time stamp has per-tty granularity
but still may outlive the user's session. On Linux systems where
the devpts filesystem is used, Solaris systems with the devices
filesystem, as well as other systems that utilize a devfs filesystem
that monotonically increase the inode number of devices as they are
created (such as Mac OS X), sudo is able to determine when a
tty-based time stamp file is stale and will ignore it. Administrators
should not rely on this feature as it is not universally available.
or
sudo sh
, subsequent commands run from that shell will not be
logged, nor will sudo's access control affect them. The same
is true for commands that offer shell escapes (including most
editors). Because of this, care must be taken when giving users
access to commands via sudo to verify that the command does not
inadvertently give the user an effective root shell. For more
information, please see the
PREVENTING SHELL ESCAPES
section in
sudoers(5).
ENVIRONMENT
sudo utilizes the following environment variables:
nor
VISUAL
is set
option
option is specified.
will be set to its value for the program being run
is not set
FILES
EXAMPLES
Note: the following examples assume suitable sudoers(5) entries.
$ sudo ls /usr/local/protected
$ sudo -u yaz ls ~yaz
$ sudo -u www vi ~www/htdocs/index.html
$ sudo -g adm view /var/log/syslog
$ sudo -u jim -g audio vi ~jim/sound.txt
$ sudo shutdown -r +15 "quick reboot"
and file redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
AUTHORS
Many people have worked on sudo over the years; this
version consists of code written primarily by:
Todd C. Miller
CAVEATS
There is no easy way to prevent a user from gaining a root shell
if that user is allowed to run arbitrary commands via sudo.
Also, many programs (such as editors) allow the user to run commands
via shell escapes, thus avoiding sudo's checks. However, on
most systems it is possible to prevent shell escapes with sudo's
noexec functionality. See the sudoers(5) manual
for details.
command directly via sudo, e.g.,
$ sudo cd /usr/local/protected
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.
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.