Linux and Unix visudo command
visudo edits the sudoers file, which is used by the sudo command.
visudo edits the sudoers file in a safe fashion, similar to the way that the vipw command safely edits the passwd file. 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. The default is /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 of the editor defined 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).
visudo [-chqsV] [-f sudoers]
|-c||Enable check-only mode. The existing sudoers file will be checked for syntax errors, owner and mode. A message will be printed to the standard output describing the status of sudoers unless the -q option was specified. If the check completes successfully, visudo will exit with a value of 0. If an error is encountered, visudo will exit with a value of 1.|
|-f sudoers||Specify an 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.|
The following environment variables are consulted, depending on the editor and env_editor settings in the sudoers file:
|VISUAL||The editor visudo will use to edit the sudoers file.|
|EDITOR||The editor visudo will use to edit the sudoers file, if the VISUAL variable is not set.|
|/etc/sudoers||List of who can run what.|