sudo/sudo.pod

=cut
Copyright (c) 1994-1996,1998-1999 Todd C. Miller <Todd.Miller@courtesan.com>
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.

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   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.

3. The name of the author may not be used to endorse or promote products
   derived from this software without specific prior written permission
   from the author.

4. Products derived from this software may not be called "Sudo" nor
   may "Sudo" appear in their names without specific prior written
   permission from the author.

THIS SOFTWARE 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.  IN NO EVENT SHALL
THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

$Sudo$
=pod

=head1 NAME

sudo - execute a command as another user

=head1 SYNOPSIS

B<sudo> B<-V> | B<-h> | B<-l> | B<-L> | B<-v> | B<-k> | B<-K> | B<-s> | B<-H> |
[ B<-b> ] | [ 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 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).

B<sudo> determines who is an authorized user by consulting the
file F</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 configure
time and defaults to 5 minutes).

If a user that is not listed in the I<sudoers> file tries to run
a command via B<sudo>, mail is sent to the proper authorities,
as defined at configure time (defaults to root).  Note that the
mail will not be sent if an unauthorized user tries to run sudo
with the C<-l> or C<-v> flags.  This allows users to determine
for themselves whether or not they are allowed to use B<sudo>.

B<sudo> can log both successful an unsuccessful attempts (as well
as errors) to syslog(3), a log file, or both.  By default B<sudo>
will log via syslog(3) but this is changeable at configure time.

=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 -L

The C<-L> (I<list> defaults) option will list out the parameters
that may be set in a I<Defaults> line along with a short description
for each.  This option is useful in conjunction with grep(1).

=item -h

The C<-h> (I<help>) option causes B<sudo> to print a usage message and exit.

=item -v

If given the C<-v> (I<validate>) option, B<sudo> will update the
user's timestamp, 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> invalidates the user's timestamp
by setting the time on it to the epoch.  The next time B<sudo> is
run a password will be required.  This option does not require a password
and was added to allow a user to revoke B<sudo> permissions from a .logout
file.

=item -K

The C<-K> (sure I<kill>) option to B<sudo> removes the user's timestamp
entirely.  This option does not require a password.

=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 -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 with the user's
login name.  Similarly, C<%h> will be replaced with 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).  By default, B<sudo> does not modify I<HOME>.

=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.  If B<sudo> cannot stat(2) one or more entries in the user's
C<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 C<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>, C<KRB5_CONFIG>, C<LOCALDOMAIN>,
C<RES_OPTIONS> and C<HOSTALIASES> 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 C<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 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 B<sudo> statically.

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 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 (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 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 (F</var/adm/sudo> for
instance) or create /tmp/.odus with the appropriate owner (root)
and permissions (0700) in the system startup files.

B<sudo> will not honor timestamps set far in the future.
Timestamps with a date greater than current_time + 2 * C<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 system that allow users to give away files.

=head1 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 F<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 C<cd> and file redirection work.

 % sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"

=head1 ENVIRONMENT

B<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

=head1 FILES

 /etc/sudoers		List of who can run what
 /var/run/sudo		Directory containing timestamps

B<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

=head1 FILES

 /etc/sudoers		List of who can run what
 /var/run/sudo		Directory containing timestamps
 /tmp/.odus		Same as above if no /var/run exists

=head1 AUTHORS

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

	Todd Miller
	Chris Jepeway

See the HISTORY file in the B<sudo> distribution for a short history
of B<sudo>.

=head1 BUGS

Please send all bugs, comments, and changes to sudo-bugs@courtesan.com.
Be sure to include the version of B<sudo> you are using and the platform
you are running it on.

=head1 DISCLAIMER

B<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 B<sudo> for complete details.

=head1 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 C<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
(if your OS supports the /dev/fd/ directory, setuid shell scripts
are generally safe).

=head1 SEE ALSO

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