AT(1) General Commands Manual AT(1)
at - execute commands at a later time
at [ -c ] [ -s ] [ -m ] time [ day ] [ file ]
At spools away a copy of the named file to be used as input to sh(1) or csh(1). If the -c flag (for (csh(1))) or the -s flag (for (sh(1)))
is specified, then that shell will be used to execute the job; if no shell is specified, the current environment shell is used. If no file
name is specified, at prompts for commands from standard input until a ^D is typed.
If the -m flag is specified, mail will be sent to the user after the job has been run. If errors occur during execution of the job, then a
copy of the error diagnostics will be sent to the user. If no errors occur, then a short message is sent informing the user that no errors
The format of the spool file is as follows: A four line header that includes the owner of the job, the name of the job, the shell used to
run the job, and whether mail will be set after the job is executed. The header is followed by a cd command to the current directory and a
umask command to set the modes on any files created by the job. Then at copies all relevant environment variables to the spool file. When
the script is run, it uses the user and group ID of the creator of the spool file.
The time is 1 to 4 digits, with an optional following `A', `P', `N' or `M' for AM, PM, noon or midnight. One and two digit numbers are
taken to be hours, three and four digits to be hours and minutes. If no letters follow the digits, a 24 hour clock time is understood.
The optional day is either (1) a month name followed by a day number, or (2) a day of the week; if the word `week' follows, invocation is
moved seven days further off. Names of months and days may be recognizably truncated. Examples of legitimate commands are
at 8am jan 24
at -c -m 1530 fr week
at -s -m 1200n week
At programs are executed by periodic execution of the command /usr/libexec/atrun from cron(8). The granularity of at depends upon the how
often atrun is executed.
Error output is lost unless redirected or the -m flag is requested, in which case a copy of the errors is sent to the user via mail(1).
/usr/spool/at spooling area
/usr/spool/at/yy.ddd.hhhh.* job file
/usr/spool/at/past directory where jobs are executed from
/usr/spool/at/lasttimedone last time atrun was run
/usr/libexec/atrun executor (run by cron(8))
atq(1), atrm(1), calendar(1), sleep(1), cron(8)
Complains about various syntax errors and times out of range.
Due to the granularity of the execution of /usr/libexec/atrun, there may be bugs in scheduling things almost exactly 24 hours into the
If the system crashes, mail is not sent to the user informing them that the job was not completed.
Sometimes old spool files are not removed from the directory /usr/spool/at/past. This is usually due to a system crash, and requires that
they be removed by hand.
4th Berkeley Distribution October 21, 1996 AT(1)
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AT(1) BSD General Commands Manual AT(1)
at, batch, atq, atrm -- queue, examine, or delete jobs for later execution
at [-q queue] [-f file] [-mldbv] time
at [-q queue] [-f file] [-mldbv] -t [[CC]YY]MMDDhhmm[.SS]
at -c job [job ...]
at -l [job ...]
at -l -q queue
at -r job [job ...]
atq [-q queue] [-v]
atrm job [job ...]
batch [-q queue] [-f file] [-mv] [time]
The at and batch utilities read commands from standard input or a specified file. The commands are executed at a later time, using sh(1).
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;
atrm deletes jobs;
batch executes commands when system load levels permit; in other words, when the load average drops below _LOADAVG_MX (1.5), or the value
specified in the invocation of atrun.
The at utility allows some moderately complex time specifications. It accepts times of the form HHMM or HH:MM to run a job at a specific
time of day. (If that time is already past, the next day is assumed.) As an alternative, the following keywords may be specified: midnight,
noon, or teatime (4pm) and time-of-day may be suffixed with AM or PM for running in the morning or the evening. The day on which the job is
to be run may also be specified by giving a date in the form month-name day with an optional year, or giving a date of the forms DD.MM.YYYY,
DD.MM.YY, MM/DD/YYYY, MM/DD/YY, MMDDYYYY, or MMDDYY. The specification of a date must follow the specification of the time of day. Time can
also be specified as: [now] + count time-units, where the time-units can be minutes, hours, days, weeks, months or years and at may be told
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, use at 4pm + 3 days, to run a job at 10:00am on July 31, use at 10am Jul 31 and to run
a job at 1am tomorrow, use at 1am tomorrow.
The at utility also supports the POSIX time format (see -t option).
For both at and batch, commands are read from standard input or the file specified with the -f option. The working directory, the environ-
ment (except for the variables TERM, TERMCAP, 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 sendmail(8). If at is executed from a su(1) shell, the owner of the login shell will receive the
The superuser may use these commands in any case. For other users, permission to use at is determined by the files _PERM_PATH/at.allow and
If the file _PERM_PATH/at.allow exists, only usernames mentioned in it are allowed to use at. In these two files, a user is considered to be
listed only if the user name has no blank or other characters before it on its line and a newline character immediately after the name, even
at the end of the file. Other lines are ignored and may be used for comments.
If _PERM_PATH/at.allow does not exist, _PERM_PATH/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.
Note that at is implemented through the launchd(8) daemon periodically invoking atrun(8), which is disabled by default. See atrun(8) for
information about enabling atrun.
-b Is an alias for batch.
-c Cat the jobs listed on the command line to standard output.
-d Is an alias for atrm (this option is deprecated; use -r instead).
Read the job from file rather than standard input.
-l With no arguments, list all jobs for the invoking user. If one or more job numbers are given, list only those jobs.
-m Send mail to the user when the job has completed even if there was no output.
Use the specified queue. A queue designation consists of a single letter; valid queue designations range from a to z and A to Z.
The _DEFAULT_AT_QUEUE queue (a) is the default for at and the _DEFAULT_BATCH_QUEUE queue (b) is the default 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 atq is given a specific queue, it will only show jobs pending in that queue.
-r Remove the specified jobs.
-t Specify the job time using the POSIX time format. The argument should be in the form [[CC]YY]MMDDhhmm[.SS] where each pair of let-
ters represents the following:
CC The first two digits of the year (the century).
YY The second two digits of the year.
MM The month of the year, from 1 to 12.
DD the day of the month, from 1 to 31.
hh The hour of the day, from 0 to 23.
mm The minute of the hour, from 0 to 59.
SS The second of the minute, from 0 to 61.
If the CC and YY letter pairs are not specified, the values default to the current year. If the SS letter pair is not specified, the
value defaults to 0.
-v For atq, shows completed but not yet deleted jobs in the queue; otherwise shows the time the job will be executed.
_ATJOB_DIR directory containing job files (/usr/lib/cron/jobs/)
_ATJOB_DIR/_LOCKFILE job-creation lock file (/usr/lib/cron/jobs/...)
_ATSPOOL_DIR directory containing output spool files (/usr/lib/cron/spool/)
_PERM_PATH/at.allow allow permission control (/usr/lib/cron/at.allow)
_PERM_PATH/at.deny deny permission control (/usr/lib/cron/at.deny)
/var/run/utmpx login records
nice(1), sh(1), umask(2), compat(5), atrun(8), cron(8), sendmail(8)
If the file /var/run/utmpx 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.
The at and batch utilities as presently implemented are not suitable when users are competing for resources. If this is the case, another
batch system such as nqs may be more suitable.
Specifying a date past 2038 may not work on some systems.
At was mostly written by Thomas Koenig <email@example.com>. The time parsing routines are by
David Parsons <firstname.lastname@example.org>, with minor enhancements by
Joe Halpin <email@example.com>.
January 13, 2002 BSD