queue, examine or delete jobs for later
commands from standard input or a specified file which are to be executed at a
later time, via the user's shell as specified by the
environment variable. If
is not set, the shell in the user's
password database entry is used instead. If all else fails,
will be used.
The related programs are as follows:
- Executes commands at a specified time.
- 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
The options are as follows:
- An alias for batch.
- Prints the jobs listed on the command line to standard
- Reads the job from file
rather than standard input.
- Displays the queue of jobs which are currently awaiting
execution. If a job argument is
specified, only the specified jobs will be displayed. Unless the user is
the superuser, only the user's own jobs will be displayed.
- Send mail to the user when the job has completed, even if
there was no output.
- 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
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 the user specified the
-l option and at
is given a specific queue, only jobs pending in that queue will be
- Remove the specified job(s) from the
- Specify the job time. The argument should be of the form
where the parts of the argument represent the following:
- Year. If yy is specified, but cc is not, a value for yy
between 69 and 99 results in a cc value of 19. Otherwise, a cc value
of 20 is used.
- Month: a number from 1 to 12.
- Day: a number from 1 to 31.
- Hour: a number from 0 to 23.
- Minute: a number from 0 to 59.
- Second: a number from 0 to 60 (permitting a leap
second), preceded by a period. The default is 0.
allows some moderately complex
specifications. It accepts times of
the form HHMM
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
(4pm) and you can have a time-of-day
suffixed with AM
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
with an optional
, or giving a date of the form
The year may be given as two or four digits. If the year is given as two digits,
it is taken to occur as soon as possible in the future, which may be in the
next century -- unless it's last year, in which case it's considered to be a
The specification of a date must follow the specification of the time of day.
You can also give times like
, where the time-units can be
, or years
(the singular forms are also accepted). You can tell
to run the job today by suffixing the time
and to run the job tomorrow by
suffixing the time with tomorrow
keyword may be used as an alias for
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
. To run a job at
1am tomorrow, you would do at 1am tomorrow
run a job at midnight in one week's time, you would do
at midnight next week
utility also supports the time format used
For both at
commands are read from standard input (or the file specified with the
option) and executed. The working directory,
the environment (except for the variables
), and the
are retained from the time of
invocation. An at
command invoked from a
shell will retain the current
user ID. The user will be mailed standard error and standard output from his
commands, if any. If at
is executed from a
shell, the owner of the login
shell will receive the mail.
For non-root users, permission to run at
determined by the files /var/cron/at.allow
: these files must be readable by group
crontab (if they exist).
If the file /var/cron/at.allow
usernames mentioned in it are allowed to use at
does not exist,
is checked. Every username not
mentioned in it is then allowed to use at
neither exists, only the superuser is allowed to run
An empty /var/cron/at.deny
means that every user is
allowed to use these commands. This is the default configuration.
- directory containing job files
- allow permission control
- deny permission control
utility exits with one of the following
- Jobs were successfully submitted, removed, or listed.
- An error occurred.
utilities are compliant with the IEEE Std
] and the
], as well as the
keyword, are extensions to that
IEEE Std 1003.1-2008
jobs are submitted to the queue
“with no time constraints”; this implementation permits a
The at.allow/deny mechanism is marked by IEEE Std
as being an X/Open System
was mostly written by
The time parsing routines are by David
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