|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;|
|batch||executes commands when system load levels permit; in other words, when the load average drops below 1.5, or the value specified in the invocation of atrun.|
The at utility allows some moderately complex time specifications. It accepts times of the form HHMM or HH:MM to run a job at a specific time of day. (If that time is already past, the next day is assumed.) As an alternative, the following keywords may be specified: midnight, noon, or teatime (4pm) and time-of-day may be suffixed with AM or PM for running in the morning or the evening. The day on which the job is to be run may also be specified by giving a date in the form month-name day with an optional year, or giving a date of the forms DD.MM.YYYY, DD.MM.YY, MM/DD/YYYY, MM/DD/YY, MMDDYYYY, or MMDDYY. The specification of a date must follow the specification of the time of day. Time can also be specified as: [now] + count time-units, where the time-units can be minutes, hours, days, weeks, months or years and at may be told 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, use at 4pm + 3 days, to run a job at 10:00am on July 31, use at 10am Jul 31 and to run a job at 1am tomorrow, use at 1am tomorrow.
The at utility also supports the POSIX time format (see -t option).
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, TERMCAP, 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 sendmail(8). 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 /var/at/at.allow and /var/at/at.deny.
If the file /var/at/at.allow exists, only usernames mentioned in it are allowed to use at. In these two files, a user is considered to be listed only if the user name has no blank or other characters before it on its line and a newline character immediately after the name, even at the end of the file. Other lines are ignored and may be used for comments.
If /var/at/at.allow does not exist, /var/at/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. This is the default configuration.
Note that at is implemented through the cron(8) daemon by calling atrun(8) every five minutes. This implies that the granularity of at might not be optimal for every deployment. If a finer granularity is needed, the system crontab at /etc/crontab needs to be changed.
-q queue Use the specified queue. A queue designation consists of a single letter; valid queue designations range from a to z and A to Z. The c queue is the default for at and the E queue for batch. Queues with higher letters run with increased niceness. 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 Read the job from file rather than standard input. -l With no arguments, list all jobs for the invoking user. If one or more job numbers are given, list only those jobs. -d Is an alias for atrm (this option is deprecated; use -r instead). -b Is an alias for batch. -v For atq, shows completed but not yet deleted jobs in the queue; otherwise shows the time the job will be executed. -c Cat the jobs listed on the command line to standard output. -r Remove the specified jobs. -t Specify the job time using the Px] time format. The argument should be in the form
.Sm off [[CCYY]] MM DD hh mm [.SS]
.Sm on where each pair of letters represents the following:
CC The first two digits of the year (the century). YY The second two digits of the year. MM The month of the year, from 1 to 12. DD the day of the month, from 1 to 31. hh The hour of the day, from 0 to 23. mm The minute of the hour, from 0 to 59. SS The second of the minute, from 0 to 61.
If the CC and YY letter pairs are not specified, the values default to the current year. If the SS letter pair is not specified, the value defaults to 0.
/var/at/jobs directory containing job files /var/at/spool directory containing output spool files /var/run/utx.active login records /var/at/at.allow allow permission control /var/at/at.deny deny permission control /var/at/jobs/.lockfile job-creation lock file
At was mostly written by
.An Thomas Koenig Aq email@example.com . The time parsing routines are by
.An David Parsons Aq firstname.lastname@example.org , with minor enhancements by
.An Joe Halpin Aq email@example.com .
If the file /var/run/utx.active 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.
The at and batch utilities as presently implemented are not suitable when users are competing for resources. If this is the case, another batch system such as nqs may be more suitable.
Specifying a date past 2038 may not work on some systems.