at(1) at(1)
NAME
at, batch - execute commands at a later time
SYNOPSIS
at time [date] [+increment]
at -l[job ...]
at -rjob ...
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 -r removes
jobs previously scheduled with at. The -l flag option
reports all jobs scheduled for the invoking user.
Standard output and standard error output are mailed to the
user via mail(1) 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. The
allow/deny files consist of one user name per line.
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
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
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at(1) at(1)
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 similar to at now, but
goes into a different queue, and will respond more promptly
with any error messages.
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 remove only your own jobs unless you are the
super-user.
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
nroff filename > outfile
<CONTROL-d> (hold down CONTROL and press 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 <<!
nroff 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
If the machine is down at the scheduled time, the job is not
run.
FILES
/usr/bin/at
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/usr/bin/batch
/usr/lib/cron main cron directory
/usr/lib/cron/at.allow list of allowed users
/usr/lib/cron/at.deny list of denied users
/usr/lib/cron/queue scheduling information
/usr/spool/cron/atjobs spool area
SEE ALSO
kill(1), mail(1), nice(1), ps(1), sh(1), cron(1M).
DIAGNOSTICS
Complaints about various syntax errors and times out of
range.
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