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
SHELL environment variable. If
SHELL 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 cron(8).
The options are as follows:
- An alias for
- Prints the jobs listed on the command line to standard output.
- Reads the job from file rather than standard input.
- Displays the queue of jobs which are currently awaiting execution. If a user argument is specified, only jobs belonging to that user 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
c queue is the default for
atand 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
atis given a specific queue, only jobs pending in that queue will be shown.
- 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.
at allows some moderately complex
timespec 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.) You may also specify
teatime (4pm) and
you can have a time-of-day suffixed with
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
mmddccyy, or mmddyy.
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 typo.
The specification of a date must follow the specification of the
time of day. You can also give times like [
+ count time-units, where the
time-units can be
years (the singular forms are also accepted). You
at to run the job today by suffixing the
today and to run the job tomorrow by
suffixing the time with
next 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. To run a job
at midnight in one week's time, you would do
at utility also supports the time
format used by touch(1) (see the
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
_), and the
umask are retained from the time of invocation. An
batch command invoked
from a su(1) 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 is determined by the files
Note: these files
must be readable by group crontab (if they exist).
If the file /var/cron/at.allow exists,
only usernames mentioned in it are allowed to use
at. If /var/cron/at.allow
does not exist, /var/cron/at.deny is checked. Every
username not mentioned in it is then allowed to use
at. If neither exists, only the superuser is allowed
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
at utility exits with one of the
- Jobs were successfully submitted, removed, or listed.
- An error occurred.
atq(1), atrm(1), nice(1), sh(1), touch(1), umask(2), cron(8)
utilities are compliant with the IEEE Std 1003.1-2008
(“POSIX.1”) specification, except behaviour for the
-l flag differs.
at flags [
batch flags [
as well as the
teatime keyword, are extensions to
IEEE Std 1003.1-2008
(“POSIX.1”) states that
jobs are submitted to the queue "with no time constraints"; this
implementation permits a timespec argument.
The at.allow/deny mechanism is marked by IEEE Std 1003.1-2008 (“POSIX.1”) as being an X/Open System Interfaces option.
at was mostly written by
The time parsing routines are by David Parsons
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