If the syntax in your sudoers file is
If the syntax in your sudoers file is incorrect, sudo will not run. If you’re relying on sudo to provide access to the sudoers file and you corrupt the sudoers file, you can simultaneously lock yourself out of root-level activities on the system and be unable to correct your error. This is bad. Visudo(8) provides some protection against this sort of error. Much like vipw(8), visudo(8) locks the file so only one person can edit the configuration file at a time. It then opens the sudo configuration file in an editor (vi(1) by default, but it respects the $EDITOR environment variable). When you exit the editor, visudo parses the file and confirms that there are no sudo syntax errors. This is not a guarantee that the configuration will do what you want, merely a confirmation that the file is actually valid. Visudo(8) will accept a configuration file that says “nobody may do anything via sudo” if the rules are properly formatted. If visudo finds an error when you exit the editor, it will print out the line number and ask you what you want to do. # visudo >>> sudoers file: syntax error, line 44 <<< What now? Here, we've made an error on line 44. You have three choices: edit the file again, quit without saving any of the changes you made, or force visudo to write the sudoers file you created. If you press "e", visudo will send you back to the editor. You can go to the line it complained about, and try to find your error. If you enter "x", visudo will quit and revert the configuration file to what it was before you started editing. Your changes will be lost, but that may be all right. It's better to have the old, working configuration than to have a new, nonfunctional configuration. Entering "Q" forces visudo to accept the file, syntax error and all. If your configuration file has incorrect syntax, sudo(8) will not run. Essentially, you're telling visudo(8) to break sudo(8) until such time as you log in as root to fix the problem. This is almost certainly not what you want to do! /etc/sudoers The sudoers file tells sudo who may run which commands as which users. OpenBSD stores the sudoers file as /etc/sudoers. (If you're using this section as a reference for the sudo system on another operating system, finding the sudoers file is your problem.) Never edit this file directly, even if you think you know exactly what change you want to make; always use visudo(8). The various sample sudoers files you'll find on the Internet frequently look horrid and complicated, as they demonstrate all the nifty things sudo can do. At this stage you don't want to do nifty things just boring, simple things like give particular users access to run certain commands. The bare syntax is very simple, however. Each rule entry in sudoers has the following format: 1 username 2 host= 3 command The 1 username is the username of the user who may execute the command or an alias for the username. The 2 host is the host name of the system where this rule applies. Sudo is designed so you can use one sudoers file on all of your systems. This allows you to set per-host rules. The 3 command space lists the commands this rule applies to. You must have a full path to each command name, or sudo will not recognize it! (You wouldn't want people to be able to adjust their $PATH variable to access renamed versions of commands, now would you?) You can use ALL keyword in any of these fields to match all possible options. Page 151
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