executes commands at a specified time.

atq

lists the user's pending jobs, unless the user is the superuser; in that case, everybody's jobs are listed. The format of the output lines (one for each job) is: Job number, date, hour, queue, and username.

atrm

deletes jobs, identified by their job number.

batch

executes commands when system load levels permit; in other words, when the load average drops below 0.8, or the value specified in the invocation of atd.

For example, to run a job at 4pm three days from now, you would do at 4pm + 3 days, to run a job at 10:00am on July 31, you would do at 10am Jul 31 and to run a job at 1am tomorrow, you would do at 1am tomorrow.

The exact definition of the time specification can be found in /usr/share/doc/at-3.1.10/timespec.

For both at and batch, commands are read from standard input or the file specified with the -f option and executed. The working directory, the environment (except for the variables TERM, DISPLAY and _) and the umask are retained from the time of invocation. An at - or batch - command invoked from a su(1) shell will retain the current userid. The user will be mailed standard error and standard output from his commands, if any. Mail will be sent using the command /usr/sbin/sendmail. If at is executed from a su(1) shell, the owner of the login shell will receive the mail.

The superuser may use these commands in any case. For other users, permission to use at is determined by the files /etc/at.allow and /etc/at.deny.

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.

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

An empty /etc/at.deny means that every user is allowed use these commands, this is the default configuration.