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|at||executes commands at a specified time.|
|atq||lists the users pending jobs, unless the user is the superuser; in that case, everybodys 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.|
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.
The at daemon can be configured through the /etc/sysconfig/atd configuration file, which contains examples of settings.
|-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.|
|-c cats the jobs listed on the command line to standard output.|
|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) utilitys -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 users 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.|
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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