at

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, job class.

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 atrun.

At allows fairly complex time specifications, extending the POSIX.2 standard. It accepts times of the form HH:MM to run a job at a specific time of day. (If that time is already past, the next day is assumed.) You may also specify midnight, noon, or teatime (4pm) and you can have a time-of-day suffixed with AM or PM for running in the morning or the evening. You can also say what day the job will be run, by giving a date in the form month-name day with an optional year, or giving a date of the form MMDDYY or MM/DD/YY or DD.MM.YY. The specification of a date must follow the specification of the time of day. You can also give times like now + count time-units, where the time-units can be minutes, hours, days, or weeks and you can tell at to run the job today by suffixing the time with today and to run the job tomorrow by suffixing the time with tomorrow.

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-3.1.8/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.

-V

prints the version number to standard error.

-q queue

uses the specified queue. A queue designation consists of a single letter; valid queue designations range from a to z. and A to Z. The a queue is the default for at and the b queue for batch. Queues with higher letters run with increased niceness. The special queue "=" is reserved for jobs which are currently running. If a job is submitted to a queue designated with an uppercase letter, it is treated as if it had been submitted to batch at that time. If atq is given a specific queue, it will only show jobs pending in that queue.

-m

Send mail to the user when the job has completed even if there was no output.

-f file

Reads the job from file rather than standard input.

-l

Is an alias for atq.

-d

Is an alias for atrm.

-v

Shows the time the job will be executed. Times displayed will be in the format "1997-02-20 14:50" unless the environment variable POSIXLY_CORRECT is set; then, it will be "Thu Feb 20 14:50:00 1997".

-c

cats the jobs listed on the command line to standard output.

-t time_arg

Submit the job to be run at the time specified by the time_arg option argument, which must have the same format as specified for the touch(1) utility's -t time option argument ([[CC]YY]MMDDhhmm).

SHELL

The value of the SHELL environment variable at the time of at invocation will determine which shell is used to execute the at job commands. If SHELL is unset when at is invoked, the user's login shell will be used; otherwise, if SHELL is set when at is invoked, it must contain the path of a shell interpreter executable that will be used to run the commands at the specified time. at will record the values of environment variables present at time of at invocation. When the commands are run at the specified time, at will restore these variables to their recorded values . These variables are excluded from this processing and are never set by at when the commands are run : TERM, DISPLAY, SHELLOPTS, _, PPID, BASH_VERSINFO, EUID, UID, GROUPS. If the user submitting the at job is not the super-user, variables that alter the behaviour of the loader such as LD_LIBRARY_PATH , cannot be recorded and restored by at .

If the file /var/run/utmp is not available or corrupted, or if the user is not logged on at the time at is invoked, the mail is sent to the userid found in the environment variable LOGNAME. If that is undefined or empty, the current userid is assumed.

At and batch as presently implemented are not suitable when users are competing for resources. If this is the case for your site, you might want to consider another batch system, such as nqs.