Why a sudoers mistake is uniquely self-defeating

Most config file mistakes are inconvenient; a sudoers syntax error is different because `sudo` itself refuses to run at all when `/etc/sudoers` fails to parse — including for the very administrator trying to fix the mistake. That's precisely why `visudo` exists and locks the file during editing with built-in syntax checking before saving: a broken sudoers file edited directly with a plain text editor can strand every user who relies on `sudo`, including the one who just broke it, with no `sudo` available to fix it. Checking the syntax before it ever reaches the real file is cheap insurance against exactly that scenario.

Why aliases exist and how the naming convention signals intent

The four alias types (User_Alias, Runas_Alias, Host_Alias, Cmnd_Alias) let a sudoers file define a named group once and reference it by name across many rules, instead of repeating a list of users or commands on every line — genuinely useful once a sudoers file grows past a handful of rules. The uppercase-with-underscores naming convention for alias names isn't just a style choice sudoers happens to enforce; it's what makes a rule line instantly scannable as "this token here is an alias reference, not a literal username," which matters when reading an unfamiliar sudoers file and trying to understand who actually has what access.

Why this checks structure and stops there

This tool confirms a line has the shape sudoers syntax requires — an alias definition has a name and a value, a rule has a who/host before the `=` and commands after it — but it has no way to know whether "alice" is a real system user, whether a referenced Cmnd_Alias was actually defined elsewhere in the file, or whether a command path actually exists on the target system. Those checks require knowledge of the real target system that a text-only tool simply doesn't have. That's exactly why the guide above insists on running the real `visudo -c` on the actual target before deploying any change — this tool catches the mistakes visible from the text alone, and `visudo` catches everything else including the parts that would otherwise only surface once `sudo` itself starts failing.