sudo
sudo(8) MAINTENANCE COMMANDS sudo(8)
NAME
sudo - execute a command as another user
SYNOPSIS
sudo -V | -h | -l | -L | -v | -k | -K | -s | [ -H ] [-P ] [-S ] [ -b ]
| [ -p prompt ] [ -c class|- ] [ -a auth_type ] [ -u username|#uid ]
command
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 (the group vector is also initialized when the target
user is not root). By default, sudo requires that users authenticate
themselves with a password (NOTE: by default this is the user's pass-
word, not the root password). Once a user has been authenticated, a
timestamp is updated and the user may then use sudo without a password
for a short period of time (5 minutes unless overridden in sudoers).
sudo determines who is an authorized user by consulting the file
/etc/sudoers. By giving sudo the -v flag a user can update the time
stamp without running a command. The password prompt itself will also
time out if the user's password is not entered within 5 minutes (unless
overridden via sudoers).
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 config-
ure time or 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 flags. This allows users to determine for themselves whether or
not they are allowed to use sudo.
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 sudo-
ers file.
OPTIONS
sudo accepts the following command line options:
-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.
-l The -l (list) option will list out the allowed (and forbidden) com-
mands for the user on the current host.
-L The -L (list defaults) option will list out the parameters that may
be set in a Defaults line along with a short description for each.
This option is useful in conjunction with grep(1).
-h The -h (help) option causes sudo to print a usage message and exit.
-v If given the -v (validate) option, sudo will update the user's
timestamp, 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.
-k The -k (kill) option to sudo invalidates the user's timestamp 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.
-K The -K (sure kill) option to sudo removes the user's timestamp
entirely. Likewise, this option does not require a password.
-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.
-p The -p (prompt) option allows you to override the default password
prompt and use a custom one. If the password prompt contains the
%u escape, %u will be replaced with the user's login name. Simi-
larly, %h will be replaced with the local hostname.
-c The -c (class) option causes sudo to run the specified command with
resources limited by the specified login class. The class argument
can be either a class name as defined in /etc/login.conf, or a sin-
gle '-' character. Specifying a class of - indicates that the com-
mand should be run restricted by the default login capabilities for
the user the command is run as. If the class argument specifies an
existing user class, the command must be run as root, or the sudo
command must be run from a shell that is already root. This option
is only available on systems with BSD login classes where sudo has
been configured with the --with-logincap option.
-a The -a (authentication type) option causes sudo to use the speci-
fied authentication type when validating the user, as 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 where sudo has been configured with the
--with-bsdauth option.
-u The -u (user) option causes sudo to run the specified command as a
user other than root. To specify a uid instead of a username, use
#uid.
-s The -s (shell) option runs the shell specified by the SHELL envi-
ronment variable if it is set or the shell as specified in
passwd(5).
-H The -H (HOME) option sets the HOME environment variable to the
homedir of the target user (root by default) as specified in
passwd(5). By default, sudo does not modify HOME.
-P The -P (preserve group vector) option causes sudo to preserve the
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.
-S The -S (stdin) option causes sudo to read the password from stan-
dard input instead of the terminal device.
-- The -- flag indicates that sudo should stop processing command line
arguments. It is most useful in conjunction with the -s flag.
RETURN VALUES
Upon successful execution of a program, the return value from sudo will
simply be the return value of the program that was executed.
Otherwise, sudo quits with an exit value of 1 if there is a configura-
tion/permission problem or if sudo cannot execute the given command.
In the latter case the error string is printed to stderr. If sudo can-
not 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 auto-
mounter 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. Variables that
control how dynamic loading and binding is done can be used to subvert
the program that sudo runs. To combat this the LD_*, _RLD_*,
SHLIB_PATH (HP-UX only), and LIBPATH (AIX only) environment variables
are removed from the environment passed on to all commands executed.
sudo will also remove the IFS, ENV, BASH_ENV, KRB_CONF, KRBCONFDIR,
KRBTKFILE, KRB5_CONFIG, LOCALDOMAIN, RES_OPTIONS, HOSTALIASES, NLSPATH,
PATH_LOCALE, TERMINFO, TERMINFO_DIRS and TERMPATH variables as they too
can pose a threat. If the TERMCAP variable is set and is a pathname,
it too is ignored. Additionally, if the LC_* or LANGUAGE variables
contain the / or % characters, they are ignored. If sudo has been com-
piled with SecurID support, the VAR_ACE, USR_ACE and DLC_ACE variables
are cleared as well. The list of environment variables that sudo
clears is contained in the output of sudo -V when run as root.
To prevent command spoofing, sudo checks "." and "" (both denoting cur-
rent 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.
For security reasons, if your OS supports shared libraries and does not
disable user-defined library search paths for setuid programs (most
do), you should either use a linker option that disables this behavior
or link sudo statically.
sudo will check the ownership of its timestamp directory (/var/run/sudo
by default) and ignore the directory's contents if it is not owned by
root and only writable by root. On systems that allow non-root users
to give away files via chown(2), if the timestamp directory is located
in a directory writable by anyone (e.g.: /tmp), it is possible for a
user to create the timestamp 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 timestamp dir. This is unlikely to happen since
once the timestamp 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 timestamps (/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 timestamps 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 timestamp with a bogus date on systems that allow users to
give away files.
Please note that sudo will 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 inadvertantly give the user an effective root shell.
EXAMPLES
Note: the following examples assume suitable sudoers(5) entries.
To get a file listing of an unreadable directory:
% sudo ls /usr/local/protected
To list the home directory of user yazza on a machine where the
filesystem holding ~yazza is not exported as root:
% sudo -u yazza ls ~yazza
To edit the index.html file as user www:
% sudo -u www vi ~www/htdocs/index.html
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 to make the cd and file
redirection work.
% sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
ENVIRONMENT
sudo utilizes the following environment variables:
PATH Set to a sane value if SECURE_PATH is set
SHELL Used to determine shell to run with -s option
USER Set to the target user (root unless the -u option
is specified)
HOME In -s or -H mode (or if sudo was configured with
the --enable-shell-sets-home option), set to
homedir of the target user.
SUDO_PROMPT Used as the default password prompt
SUDO_COMMAND Set to the command run by sudo
SUDO_USER Set to the login of the user who invoked sudo
SUDO_UID Set to the uid of the user who invoked sudo
SUDO_GID Set to the gid of the user who invoked sudo
SUDO_PS1 If set, PS1 will be set to its value
FILES
/etc/sudoers List of who can run what
/var/run/sudo Directory containing timestamps
AUTHORS
Many people have worked on sudo over the years; this version consists
of code written primarily by:
Todd Miller
Chris Jepeway
See the HISTORY file in the sudo distribution or visit
http://www.sudo.ws/sudo/history.html for a short history of sudo.
BUGS
If you feel you have found a bug in sudo, please submit a bug report at
http://www.sudo.ws/sudo/bugs/
DISCLAIMER
Sudo is provided ``AS IS'' and any express or implied warranties,
including, but not limited to, the implied warranties of merchantabil-
ity and fitness for a particular purpose are disclaimed. See the
LICENSE file distributed with sudo for complete details.
CAVEATS
There is no easy way to prevent a user from gaining a root shell if
that user has access to commands allowing shell escapes.
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
supports the /dev/fd/ directory, setuid shell scripts are generally
safe).
SEE ALSO
stat(2), login_cap(3), sudoers(5), passwd(5), visudo(8), grep(1),
su(1).
3rd Berkeley Distribution 1.6.6 sudo(8)
