sudo/sudo.pod

=cut
$Sudo$
=pod

=head1 NAME

sudo - execute a command as the superuser

=head1 SYNOPSIS

B<sudo> B<-V> | B<-h> | B<-l> | B<-v> | B<-k> | B<-s> | B<-H> |
[ B<-b> ] | [ B<-r> realm ] | [ B<-p> prompt ] [ B<-u> username/#uid] I<command>

=head1 DESCRIPTION

B<sudo> allows a permitted user to execute a I<command>
as the superuser (real and effective uid and gid are set
to C<0> and root's group as set in the passwd file respectively).

B<sudo> determines who is an authorized user by consulting the
file I</etc/sudoers>.  By giving B<sudo> the C<-v> flag a user
can update the time stamp without running a I<command.>
The password prompt itself will also time out if the user's password is
not entered with N minutes (again, this is defined at installation
time and defaults to 5 minutes).

If an unauthorized user executes B<sudo>, mail will be sent from the
user to the local authorities (defined at installation time).

B<sudo> was designed to log via the 4.3 BSD syslog(3) facility but
can log to a file instead if so desired (or to both syslog and a file).

=head1 OPTIONS

B<sudo> accepts the following command line options:

=over 4

=item -V

The C<-V> (I<version>) option causes B<sudo> to print the
version number and exit.

=item -l

The C<-l> (I<list>) option will list out the allowed and
forbidden commands for the user on the current host.

=item -h

The C<-h> (I<help>) option causes B<sudo> to print the version
of B<sudo> and a usage message before exiting.

=item -v

If given the C<-v> (I<validate>) option, B<sudo> will update the
user's timestamp file, prompting for the user's password if necessary.
This extends the B<sudo> timeout to for another N minutes
(where N is defined at installation time and defaults to 5
minutes) but does not run a command.

=item -k

The C<-k> (I<kill>) option to B<sudo> removes the user's timestamp
file, thus requiring the user's password the next time B<sudo> is run.
This option does not require a password and was added to
allow a user to revoke B<sudo> permissions from a .logout file.

=item -b

The C<-b> (I<background>) option tells B<sudo> to run the given
command in the background.  Note that if you use the C<-b>
option you cannot use shell job control to manipulate the command.

=item -r

The C<-r> (I<realm>) option is only available if B<sudo> was configured
with B<Kerberos> version 5 support.  It allows the user to specify a
B<Kerberos> realm other than the system default to use when authenticating
the user via B<Kerberos>.

=item -p

The C<-p> (I<prompt>) option allows you to override the default
password prompt and use a custom one.  If the password prompt
contains the C<%u> escape, C<%u> will be replaced by the user's
login name.  Similarly, C<%h> will be replaced by the local
hostname.

=item -u

The C<-u> (I<user>) option causes sudo to run the specified command
as a user other than I<root>.  To specify a I<uid> instead of a
I<username>, use "#uid".

=item -s

The C<-s> (I<shell>) option runs the shell specified by the I<SHELL>
environment variable if it is set or the shell as specified
in passwd(5).

=item -H

The C<-H> (I<HOME>) option sets the I<HOME> environment variable
to the homedir of the target user (root by default) as specified
in passwd(5).

=item --

The C<--> flag indicates that B<sudo> should stop processing command
line arguments.  It is most useful in conjunction with the C<-s> flag.

=back

=head1 RETURN VALUES

B<sudo> quits with an exit value of 1 if there is a
configuration/permission problem or if B<sudo> cannot execute the
given command.  In the latter case the error string is printed to
stderr via perror(3).  If B<sudo> cannot stat(2) one or more entries
in the user's PATH the error is printed on stderr via perror(3).
(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(3) 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.

=head1 SECURITY NOTES

B<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 B<sudo> runs.  To combat this the
C<LD_*>, C<_RLD_*>, C<SHLIB_PATH> (HP-UX only), and C<LIBPATH> (AIX
only) environment variables are removed from the environment passed
on to all commands executed.  B<sudo> will also remove the C<IFS>,
C<ENV>, C<BASH_ENV>, C<KRB_CONF> and C<KRB5_CONFIG> variables as
they too can pose a threat.

To prevent command spoofing, B<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 I<not> modified and is passed
unchanged to the program that B<sudo> executes.

For security reasons, if your OS supports shared libraries, B<sudo>
should always be statically linked unless the dynamic loader disables
user-defined library search paths for setuid programs.  (Most modern
dynamic loaders do this.)

B<sudo> will check the ownership of its timestamp directory
(F</var/run/sudo> or F</tmp/.odus> by default) and ignore the
directory's contents if it is not owned by root and only read,
writable, and executable by root.  On systems that allow users to
give files away to root (via chown), if the timestamp directory is
located in a directory writable by anyone (ie: F</tmp>), it is
possible for a user to create the timestamp directory before B<sudo>
is run.  However, because B<sudo> checks the ownership and mode of
the directory, 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 (F</var/adm/sudo> for
instance).

C<sudo> will not honor timestamp files set far in the future.
Timestamp files with a date greater than current_time + 2 * C<TIMEOUT>
will be ignored and sudo complain about a "preposterous stampfile
date".  This is done to keep a user from creating his/her own
timestamp file with a bogus date.

=head1 FILES

 /etc/sudoers		file of authorized users.

=head1 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 mode, set to homedir of root (or runas user)
			if built with the SHELL_SETS_HOME option
 SUDO_PROMPT		Replaces 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

=head1 AUTHORS

Many people have worked on B<sudo> over the years, this
version consists of code written primarily by:

	Jeff Nieusma
	David Hieb
	Todd Miller
	Chris Jepeway

See the HISTORY file in the B<sudo> distribution for more details.

Please send all bugs, comments, and changes to sudo-bugs@courtesan.com.

=head1 DISCLAIMER

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
675 Mass Ave, Cambridge, MA 02139, USA.

=head1 CAVEATS

There is no easy way to prevent a user from gaining a root shell if
that user has access to commands allow 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 B<sudo> can expose the same kernel bugs
that make setuid shell scripts unsafe on some operating systems.

=head1 SEE ALSO

sudoers(5), visudo(8), su(1).