To verify that a username was added correctly to the /etc/cron.d/at.deny file, use the at -l command while logged in as the user. If the user smith cannot access the at command, the following message is displayed:
# su smith Password: $ at -l at: you are not authorized to use at. Sorry.
Likewise, if the user tries to submit an at job, the following message is displayed:
$ at 2:30pm at: you are not authorized to use at. Sorry.
This message confirms that the user is listed in the at.deny file.
If at command access is allowed, then the at -l command returns nothing.