From Linux Man Pages
at, batch, atq, atrm - queue, examine or delete jobs for later execution
SYNOPSIS
at [-V] [-q queue] [-f file] [-mldrbvt] TIME
at -c job [job...]
atq [-V] [-q queue]
atrm [-V] job [job...]
batch [-V] [-q queue] [-f file] [-mv] [TIME]
DESCRIPTION
at and batch read commands from standard input or a specified file which are to be executed at a later time,
using /bin/sh.
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/timespec.
For both at and batch, commands are read from standard input or the file specified with the -f option and exe-
cuted. 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 cur-
rent 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.
OPTIONS
-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, -r Are aliases 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 1996".
-c cats the jobs listed on the command line to standard output.
-t time_arg
Specify the time to run in a format compatible with the touch -t time command.
FILES
/var/spool/atjobs
/var/spool/atspool
/proc/loadavg
/var/run/utmp
/etc/at.allow
/etc/at.deny
RELATED
cron(1), nice(1), sh(1), umask(2), atd(8).
BUGS
The correct operation of batch for Linux depends on the presence of a proc- type directory mounted on
/proc.
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.
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