I tried it run reboot at 5AM, so I create file "reboot" and put in it one line "reboot"; then run "sudo at 5AM -f reboot". At morning I saw in syslog line: Apr 4 05:00:00 [atd] Job 1 a00001013b0bb8 - groupid 0 does not match file gid 25 But directory /var/spool/at/atjobs was empty. I query again job - and saw in this directory file, that is owned by root and has attributes 700.
it looks to me, at is refusing to run the command because the file in which you put it hast the wrong permissions. is that correct? if yes, then there is no bug. that is how at is supposed to work. its a security feature, i suppose... try $ echo 'reboot' | sudo at 5AM or make sure the file 'reboot' is owned by root.