Copyright (c) 1996,1998-2005, 2007-2008
	Todd C. Miller <Todd.Miller@courtesan.com>

Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Sponsored in part by the Defense Advanced Research Projects
Agency (DARPA) and Air Force Research Laboratory, Air Force
Materiel Command, USAF, under agreement number F39502-99-1-0512.

$Sudo: visudo.pod,v 1.55 2008/11/15 18:34:01 millert Exp $
=pod

=head1 NAME

visudo - edit the sudoers file

=head1 SYNOPSIS

B<visudo> [B<-c>] [B<-q>] [B<-s>] [B<-V>] [B<-f> I<sudoers>]

=head1 DESCRIPTION

B<visudo> edits the I<sudoers> file in a safe fashion, analogous to
L<vipw(8)>.  B<visudo> locks the I<sudoers> file against multiple
simultaneous edits, provides basic sanity checks, and checks
for parse errors.  If the I<sudoers> file is currently being
edited you will receive a message to try again later.

There is a hard-coded list of editors that B<visudo> will use set
at compile-time that may be overridden via the I<editor> I<sudoers>
C<Default> variable.  This list defaults to the path to L<vi(1)> on
your system, as determined by the I<configure> script.  Normally,
B<visudo> does not honor the C<VISUAL> or C<EDITOR> environment
variables unless they contain an editor in the aforementioned editors
list.  However, if B<visudo> is configured with the I<--with-enveditor>
option or the I<env_editor> C<Default> variable is set in I<sudoers>,
B<visudo> will use any the editor defines by C<VISUAL> or C<EDITOR>.
Note that this can be a security hole since it allows the user to
execute any program they wish simply by setting C<VISUAL> or C<EDITOR>.

B<visudo> parses the I<sudoers> file after the edit and will
not save the changes if there is a syntax error.  Upon finding
an error, B<visudo> will print a message stating the line number(s)
where the error occurred and the user will receive the
"What now?" prompt.  At this point the user may enter "e"
to re-edit the I<sudoers> file, "x" to exit without
saving the changes, or "Q" to quit and save changes.  The
"Q" option should be used with extreme care because if B<visudo>
believes there to be a parse error, so will B<sudo> and no one
will be able to B<sudo> again until the error is fixed.
If "e" is typed to edit the  I<sudoers> file after a parse error
has been detected, the cursor will be placed on the line where the
error occurred (if the editor supports this feature).

=head1 OPTIONS

B<visudo> accepts the following command line options:

=over 12

=item -c

Enable B<check-only> mode.  The existing I<sudoers> file will be
checked for syntax and a message will be printed to the
standard output detailing the status of I<sudoers>.
If the syntax check completes successfully, B<visudo> will
exit with a value of 0.  If a syntax error is encountered,
B<visudo> will exit with a value of 1.

=item -f I<sudoers>

Specify and alternate I<sudoers> file location.  With this option
B<visudo> will edit (or check) the I<sudoers> file of your choice,
instead of the default, F<@sysconfdir@/sudoers>.  The lock file used
is the specified I<sudoers> file with ".tmp" appended to it.

=item -q

Enable B<quiet> mode.  In this mode details about syntax errors
are not printed.  This option is only useful when combined with
the B<-c> option.

=item -s

Enable B<strict> checking of the I<sudoers> file.  If an alias is
used before it is defined, B<visudo> will consider this a parse
error.  Note that it is not possible to differentiate between an
alias and a hostname or username that consists solely of uppercase
letters, digits, and the underscore ('_') character.

=item -V

The B<-V> (version) option causes B<visudo> to print its version number
and exit.

=back

=head1 ENVIRONMENT

The following environment variables may be consulted depending on
the value of the I<editor> and I<env_editor> I<sudoers> variables:

=over 16

=item C<VISUAL>

Invoked by visudo as the editor to use

=item C<EDITOR>

Used by visudo if VISUAL is not set

=back

=head1 FILES

=over 24

=item F<@sysconfdir@/sudoers>

List of who can run what

=item F<@sysconfdir@/sudoers.tmp>

Lock file for visudo

=back

=head1 DIAGNOSTICS

=over 4

=item sudoers file busy, try again later.

Someone else is currently editing the I<sudoers> file.

=item @sysconfdir@/sudoers.tmp: Permission denied

You didn't run B<visudo> as root.

=item Can't find you in the passwd database

Your userid does not appear in the system passwd file.

=item Warning: {User,Runas,Host,Cmnd}_Alias referenced but not defined

Either you are trying to use an undeclare {User,Runas,Host,Cmnd}_Alias
or you have a user or hostname listed that consists solely of
uppercase letters, digits, and the underscore ('_') character.  In
the latter case, you can ignore the warnings (B<sudo> will not
complain).  In B<-s> (strict) mode these are errors, not warnings.

=item Warning: unused {User,Runas,Host,Cmnd}_Alias

The specified {User,Runas,Host,Cmnd}_Alias was defined but never
used.  You may wish to comment out or remove the unused alias.  In
B<-s> (strict) mode this is an error, not a warning.

=back

=head1 SEE ALSO

L<vi(1)>, L<sudoers(5)>, L<sudo(8)>, L<vipw(8)>

=head1 AUTHOR

Many people have worked on I<sudo> over the years; this version of
B<visudo> was written by:

 Todd Miller

See the HISTORY file in the sudo distribution or visit
http://www.sudo.ws/sudo/history.html for more details.

=head1 CAVEATS

There is no easy way to prevent a user from gaining a root shell if 
the editor used by B<visudo> allows shell escapes.

=head1 BUGS

If you feel you have found a bug in B<visudo>, please submit a bug report
at http://www.sudo.ws/sudo/bugs/

=head1 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.

=head1 DISCLAIMER

B<visudo> 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> or http://www.sudo.ws/sudo/license.html
for complete details.