AT(1) (User Environment Utilities) AT(1)
NAME
at, batch - execute commands at a later time
SYNOPSIS
at time [ date ] [ + increment ]
at -r job...
at -l [ job ... ]
batch
DESCRIPTION
at and batch read commands from standard input to be
executed at a later time. at allows you to specify when the
commands should be executed, while jobs queued with batch
will execute when system load level permits. at may be used
with the following options:
-r Removes jobs previously scheduled with at.
-l Reports all jobs scheduled for the invoking user.
Standard output and standard error output are mailed to the
user unless they are redirected elsewhere. The shell
environment variables, current directory, umask, and ulimit
are retained when the commands are executed. Open file
descriptors, traps, and priority are lost.
Users are permitted to use at if their name appears in the
file /usr/lib/cron/at.allow. If that file does not exist,
the file /usr/lib/cron/at.deny is checked to determine if
the user should be denied access to at. If neither file
exists, only root is allowed to submit a job. If at.deny is
empty, global usage is permitted. The allow/deny files
consist of one user name per line. These files can only be
modified by the superuser.
The time may be specified as 1, 2, or 4 digits. One and two
digit numbers are taken to be hours, four digits to be hours
and minutes. The time may alternately be specified as two
numbers separated by a colon, meaning hour:minute. A suffix
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AT(1) (User Environment Utilities) AT(1)
am or pm may be appended; otherwise a 24-hour clock time is
understood. The suffix zulu may be used to indicate GMT.
The special names noon, midnight, now, and next are also
recognized.
An optional date may be specified as either a month name
followed by a day number (and possibly year number preceded
by an optional comma) or a day of the week (fully spelled or
abbreviated to three characters). Two special ``days'',
today and tomorrow are recognized. If no date is given,
today is assumed if the given hour is greater than the
current hour and tomorrow is assumed if it is less. If the
given month is less than the current month (and no year is
given), next year is assumed.
The optional increment is simply a number suffixed by one of
the following: minutes, hours, days, weeks, months, or
years. (The singular form is also accepted.)
Thus legitimate commands include:
at 0815am Jan 24
at 8:15am Jan 24
at now + 1 day
at 5 pm Friday
at and batch write the job number and schedule time to
standard error.
batch submits a batch job. It is almost equivalent to
``at now'', but not quite. For one, it goes into a
different queue. For another, ``at now'' will respond with
the error message too late.
at -r removes jobs previously scheduled by at or batch. The
job number is the number given to you previously by the at
or batch command. You can also get job numbers by typing at
-l. You can only remove your own jobs unless you are the
super-user.
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AT(1) (User Environment Utilities) AT(1)
EXAMPLES
The at and batch commands read from standard input the
commands to be executed at a later time. sh(1) provides
different ways of specifying standard input. Within your
commands, it may be useful to redirect standard output.
This sequence can be used at a terminal:
batch
sort filename >outfile
<control-D> (hold down 'control' and depress 'D')
This sequence, which demonstrates redirecting standard error
to a pipe, is useful in a shell procedure (the sequence of
output redirection specifications is significant):
batch <<!
sort filename 2>&1 >outfile | mail loginid
!
To have a job reschedule itself, invoke at from within the
shell procedure, by including code similar to the following
within the shell file:
echo "sh shellfile" | at 1900 thursday next week
FILES
/usr/lib/cron main cron directory
/usr/lib/cron/at.allowlist of allowed users
/usr/lib/cron/at.denylist of denied users
/usr/lib/cron/queuescheduling information
/usr/spool/cron/atjobsspool area
SEE ALSO
kill(1), mail(1), nice(1), ps(1), sh(1), sort(1).
cron(1M) in the System Administrator's Reference Manual.
DIAGNOSTICS
Complains about various syntax errors and times out of
range.
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