> В vlock 2.2.2 из Debian testing опция -n есть, и sudo нужен
> как раз для неё.
> -na решает эти проблемы.

Ясненько.

$ vlock --help
vlock: locks virtual consoles, saving your current session.
Usage: vlock [options]
       Where [options] are any of:
-c or --current: lock only this virtual console, allowing user to
       switch to other virtual consoles.
-a or --all: lock all virtual consoles by preventing other users
       from switching virtual consoles.
-v or --version: Print the version number of vlock and exit.
-h or --help: Print this help message and exit

Fedora 16.