|-l||Specifies a limiting load factor, over which batch jobs should not be run, instead of the compile-time choice of 0.8. For an SMP system with n CPUs, you will probably want to set this higher than n-1.|
|-b||Specifiy the minimum interval in seconds between the start of two batch jobs (60 default).|
|-d||Debug; print error messages to standard error instead of using syslog(3) .|
|-s||Process the at/batch queue only once. This is primarily of use for compatibility with old versions of at; atd -s is equivalent to the old atrun command. A script invoking atd -s is installed as /usr/sbin/atrun for backward compatibility.|
|-n||Dont fork option.|
/var/spool/at/spool The directory for storing output; this should be mode 700, owner root.
/etc/at.allow, /etc/at.deny determine who can use the at system.