Linux and Unix at, batch, atq, atrm command
Schedules a command to be ran at a particular time, such as a print job late at night.
at [-V] [-q queue] [-f file] [-mMlv] timespec...
at [-V] [-q queue] [-f file] [-mMkv] [-t time]
at -c job [job...]
atq [-V] [-q queue]
at [-rd] job [job...]
atrm [-V] job [job...]
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, 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 1.5, or the value specified in the invocation of atd.
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 MMDD[CC]YY, MM/DD/[CC]YY, DD.MM.[CC]YY or [CC]YY-MM-DD. 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 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 executed. The working directory, the environment (except for the variables BASH_VERSINFO, DISPLAY, EUID, GROUPS, SHELLOPTS, TERM, UID, and _) and the umask are retained from the time of invocation.
As at is currently implemented as a setuid program, other environment variables (e.g. LD_LIBRARY_PATH or LD_PRELOAD) are also not exported. This may change in the future. As a workaround, set these variables explicitly in your job.
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 always use these commands. For other users, permission to use at is determined by the files /etc/at.allow and /etc/at.deny. See at.allow for details.
|-V||prints the version number to standard error and exit successfully.|
|-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, the job is treated as if it were submitted to batch at the time of the job. Once the time is reached, the batch processing rules with respect to load average apply. 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.|
|-M||Never send mail to the user.|
|-f file||Reads the job from file rather than standard input.|
|-t time||run the job at time, given in the format [[CC]YY]MMDDhhmm[.ss]|
|-l||Is an alias for atq.|
|-r||Is an alias for atrm.|
|-d||Is an alias for atrm.|
|-b||is an alias for batch.|
|-v||Shows the time the job will be executed before reading the job. Times displayed will be in the format "Thu Feb 20 14:50:00 1997".|
|-c||cats the jobs listed on the command line to standard output.|
at -m 01:35 < atjob
Run the commands listed in the 'atjob' file at 1:35AM; in addition, all output that is generated from job will be mailed to the user running the task. When this command has been successfully entered you should receive a prompt similar to the below example:
commands will be executed using /bin/csh job 1072250520.a at Wed Dec 24 00:22:00 2003
This command will list each of the scheduled jobs in a format like the following:
1072250520.a Wed Dec 24 00:22:00 2003
at -r 1072250520.a
Deletes the job listed above, 1072250520.a.
Deletes job 23.
Note: Performing just the at command at the prompt will give you an error "Garbled Time", this is a standard error message if no switch or time setting is given.