at (5) - Linux Manuals

at: determine who can submit jobs via at or batch

Command to display at manual in Linux: $ man 5 at

at.allow, at.deny - determine who can submit jobs via at or batch

The /etc/at.allow and /etc/at.deny files determine which user can submit commands for later execution via at(1) or batch(1).

The format of the files is a list of usernames, one on each line. Whitespace is not permitted.

If the file /etc/at.allow exists, only usernames mentioned in it are allowed to use at.

If /etc/at.allow does not exist, /etc/at.deny is checked, every username not mentioned in it is then allowed to use at.

An empty /etc/at.deny means that every user may use at.

If neither exists, only the superuser is allowed to use at.