Periodic Command Scheduler. It run commands scheduled by the 'at' program at their scheduled times.
It is a task scheduling tool. Jobs are stored in /var/spool/at
Now lets see the manual of atd service.Manual atd:NAME
atd - run jobs queued for later executionSYNOPSIS
atd [-l load_avg] [-b batch_interval] [-d] [-s]DESCRIPTION
atd runs jobs queued by at(1).OPTIONS
-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.WARNING
atd won't work if its spool directory is mounted via NFS even if no_root_squash is set.FILES
/var/spool/at The directory for storing jobs; this should be mode 700, owner root.
/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.SEE ALSO
at(1), atrun(1), cron(8), crontab(1), syslog(3), at.deny(5), at.allow(5).BUGS
The functionality of atd should be merged into cron(8).