VISUDO
Section: MAINTENANCE COMMANDS (8)
Updated: September 16, 2011
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NAME
visudo - edit the sudoers file
SYNOPSIS
visudo [
-chqsV] [
-f sudoers]
DESCRIPTION
visudo edits the
sudoers file in a safe fashion, analogous to
vipw(8).
visudo locks the
sudoers file against multiple
simultaneous edits, provides basic sanity checks, and checks
for parse errors. If the
sudoers file is currently being
edited you will receive a message to try again later.
There is a hard-coded list of one or more editors that visudo will
use set at compile-time that may be overridden via the editor sudoers
Default
variable. This list defaults to "/usr/local/bin/vi". Normally,
visudo does not honor the
VISUAL
or
EDITOR
environment
variables unless they contain an editor in the aforementioned editors
list. However, if visudo is configured with the --with-env-editor
option or the env_editor
Default
variable is set in sudoers,
visudo will use any the editor defines by
VISUAL
or
EDITOR
.
Note that this can be a security hole since it allows the user to
execute any program they wish simply by setting
VISUAL
or
EDITOR
.
visudo parses the sudoers file after the edit and will
not save the changes if there is a syntax error. Upon finding
an error, 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 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 visudo
believes there to be a parse error, so will sudo and no one
will be able to sudo again until the error is fixed.
If ``e'' is typed to edit the 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).
OPTIONS
visudo accepts the following command line options:
- -c
-
Enable check-only mode. The existing sudoers file will be
checked for syntax and a message will be printed to the
standard output detailing the status of sudoers.
If the syntax check completes successfully, visudo will
exit with a value of 0. If a syntax error is encountered,
visudo will exit with a value of 1.
- -f sudoers
-
Specify and alternate sudoers file location. With this option
visudo will edit (or check) the sudoers file of your choice,
instead of the default, /etc/sudoers. The lock file used
is the specified sudoers file with ``.tmp'' appended to it.
In check-only mode only, the argument to -f may be ``-'',
indicating that sudoers will be read from the standard input.
- -h
-
The -h (help) option causes visudo to print a short help message
to the standard output and exit.
- -q
-
Enable quiet mode. In this mode details about syntax errors
are not printed. This option is only useful when combined with
the -c option.
- -s
-
Enable strict checking of the sudoers file. If an alias is
used before it is defined, visudo will consider this a parse
error. Note that it is not possible to differentiate between an
alias and a host name or user name that consists solely of uppercase
letters, digits, and the underscore ('_') character.
- -V
-
The -V (version) option causes visudo to print its version number
and exit.
ENVIRONMENT
The following environment variables may be consulted depending on
the value of the
editor and
env_editor sudoers variables:
-
VISUAL
-
Invoked by visudo as the editor to use
-
EDITOR
-
Used by visudo if VISUAL is not set
FILES
- /etc/sudoers
-
List of who can run what
- /etc/sudoers.tmp
-
Lock file for visudo
DIAGNOSTICS
- sudoers file busy, try again later.
-
Someone else is currently editing the sudoers file.
- /etc/sudoers.tmp: Permission denied
-
You didn't run visudo as root.
- Can't find you in the passwd database
-
Your userid does not appear in the system passwd file.
- 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 host name listed that consists solely of
uppercase letters, digits, and the underscore ('_') character. In
the latter case, you can ignore the warnings (sudo will not
complain). In -s (strict) mode these are errors, not warnings.
- 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
-s (strict) mode this is an error, not a warning.
- Warning: cycle in {User,Runas,Host,Cmnd}_Alias
-
The specified {User,Runas,Host,Cmnd}_Alias includes a reference to
itself, either directly or through an alias it includes. This is
only a warning by default as sudo will ignore cycles when parsing
the sudoers file.
SEE ALSO
vi(1),
sudoers(5),
sudo(8),
vipw(8)
AUTHOR
Many people have worked on
sudo over the years; this version of
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.
CAVEATS
There is no easy way to prevent a user from gaining a root shell if
the editor used by
visudo allows shell escapes.
BUGS
If you feel you have found a bug in
visudo, 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
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
sudo or
http://www.sudo.ws/sudo/license.html
for complete details.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- ENVIRONMENT
-
- FILES
-
- DIAGNOSTICS
-
- SEE ALSO
-
- AUTHOR
-
- CAVEATS
-
- BUGS
-
- SUPPORT
-
- DISCLAIMER
-
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