ATSection: Linux Programmer's Manual (1)
Updated: Nov 1996
Index Return to Main Contents
NAMEat, batch, atq, atrm - queue, examine or delete jobs for later execution
SYNOPSISat [-V] [-q queue] [-f file] [-mldbv] TIME
at -c job [job...]
atq [-V] [-q queue]
atrm [-V] job [job...]
DESCRIPTIONat and batch read commands from standard input or a specified file which are to be executed at a later time, using /bin/sh.
- executes commands at a specified time.
- 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.
- deletes jobs, identified by their job number.
- 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 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 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 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.
- 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, 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.
- 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.
- Is an alias for atq.
- Is an alias for atrm.
- 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".
- cats the jobs listed on the command line to standard output.
SEE ALSOcron(1), nice(1), sh(1), umask(2), atd(8).
BUGSThe 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.
AUTHORAt was mostly written by Thomas Koenig, email@example.com.