at(1) manual page
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at, batch - execute commands at a later time
at [-c|-k|-s] [-m]
[-f file] [-q queuename] -t time
at [-c|-k|-s] [-m] [-f file] [-q queuename] timespec...
at -l [-q queuename] [at_job_id...]
at -r at_job_id...
batch
SUNWcsu
SUNWesu
The at utility reads commands from standard input and groups them together
as an at-job, to be executed at a later time.
The at-job will be executed
in a separate invocation of the shell, running in a separate process group
with no controlling terminal, except that the environment variables, current
working directory, file creation mask (see umask(1)
), and system resource
limits (for sh and ksh only, see ulimit(1)
) in effect when the at utility
is executed will be retained and used when the at-job is executed.
When the
at-job is submitted, the at_job_id and scheduled time are written to standard
error. The at_job_id is an identifier that will be a string consisting solely
of alphanumeric characters and the period character. The at_job_id is assigned
by the system when the job is scheduled such that it uniquely identifies
a particular job.
User notification and the processing of the job’s standard
output and standard error are described under the -m option.
Users are permitted
to use at and batch (see below) 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 a process with the super-user privileges is allowed to submit a job.
If only at.deny exists and is empty, global usage is permitted. The at.allow
and at.deny files consist of one user name per line.
The batch utility
reads commands to be executed at a later time. It is the equivalent of the
command: at -q b -m now
where queue b is a special at queue, specifically
for batch jobs. Batch jobs will be submitted to the batch queue for immediate
execution.
The following options are supported. If the -c, -k, or -s
options are not specified, the SHELL
environment variable by default determines
which shell to use.
- -c
- C shell. csh(1)
is used to execute the at-job.
- -k
- Korn
shell. ksh(1)
is used to execute the at-job.
- -s
- Bourne shell. sh(1)
is used
to execute the at-job.
- -f file
- Specify the path of a file to be used as the
source of the at-job, instead of standard input.
- -l
- (The letter ell.) Report
all jobs scheduled for the invoking user if no at_job_id operands are specified.
If at_job_ids are specified, report only information for these jobs.
- -m
- Send
mail to the invoking user after the at-job has run, announcing its completion.
Standard output and standard error produced by the at-job will be mailed
to the user as well, unless redirected elsewhere. Mail will be sent even
if the job produces no output.
If -m is not used, the job’s standard output
and standard error will be provided to the user by means of mail, unless
they are redirected elsewhere; if there is no such output to provide, the
user is not notified of the job’s completion.
- -q queuename
- Specify in which queue to schedule a job for submission. When
used with the -l option, limit the search to that particular queue. Values
for queuename are limited to the lower case letters a through z. By default,
at-jobs will be scheduled in queue a. In contrast, queue b is reserved for
batch jobs. Since queue c is reserved for cron jobs, it can not be used
with the -q option.
- -r at_job_id
- Remove the jobs with the specified at_job_id
operands that were previously scheduled by the at utility.
- -t time
- Submit
the job to be run at the time specified by the time option-argument, which
must have the format as specified by the touch(1)
utility.
The following
operands are supported:
- at_job_id
- The name reported by a previous invocation
of the at utility at the time the job was scheduled.
- timespec
- Submit the
job to be run at the date and time specified. All of the timespec operands
are interpreted as if they were separated by space characters and concatenated.
The date and time are interpreted as being in the timezone of the user
(as determined by the TZ
variable), unless a timezone name appears as
part of time, below.
In the "C" locale, the following describes the three
parts of the time specification string. All of the values from the LC_TIME
categories in the "C" locale are recognized in a case-insensitive manner.
- time
- The time can be specified as one, two or four digits. One- and two-digit
numbers are taken to be hours, four-digit numbers to be hours and minutes.
The time can alternatively be specified as two numbers separated by a colon,
meaning hour:minute. An AM/PM indication (one of the values from the am_pm
keywords in the LC_TIME
locale category) can follow the time; otherwise,
a 24-hour clock time is understood. A timezone name can follow to further
qualify the time; see TZ
on the environ(5)
manual page. The time field
can also be one of the following tokens in the "C" locale:
- midnight
- Indicates
the time 12:00 am (00:00).
- noon
- Indicates the time 12:00 pm.
- now
- Indicate
the current day and time. Invoking at now will submit an at-job for potentially
immediate execution (that is, subject only to unspecified scheduling delays).
- date
- An optional date can be specified as either a month name (one of the
values from the mon or abmon keywords in the LC_TIME
locale category)
followed by a day number (and possibly year number preceded by a comma)
or a day of the week (one of the values from the day or abday keywords
in the LC_TIME
locale category). Two special days are recognized in the
"C" locale:
- today
- Indicates the current day.
- tomorrow
- Indicates the day
following the current day.
If no date is given, today is assumed if the
given time is greater than the current time, 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.
- increment
- The optional increment is a number
preceded by a plus sign (+) and suffixed by one of the following: minutes,
hours, days, weeks, months, or years. (The singular forms will be also accepted.)
The keyword next is equivalent to an increment number of + 1. For example,
the following are equivalent commands:
at 2pm + 1 week
at 2pm next week
The format of the at command line shown here is guaranteed only for
the "C" locale. Other locales are not supported for midnight, noon, now,
mon, abmon, day, abday, today, tomorrow, minutes, hours, days, weeks, months,
years, and next.
Since the commands run in a separate shell invocation,
running in a separate process group with no controlling terminal, open
file descriptors, traps and priority inherited from the invoking environment
are lost.
.- This sequence can be used at a terminal:
$ at -m 0730 tomorrow
sort < file >outfile
<EOT>
- 2.This sequence, which demonstrates redirecting standarderror to a pipe,
is useful in a command procedure (the sequence ofoutput redirection specifications
is significant):$ at now + 1 hour <<!diff file1 file2 2>&1 >outfile | mailx mygroup!3.
- To have a job reschedule itself, at can be invoked from within the at-job.
For example, this "daily-processing" script named my.daily will run every
day (although crontab is a more appropriate vehicle for such work):
# my.daily runs every day
at now tomorrow < my.daily
daily-processing
.- The spacing of the three portions of the "C" locale timespec is quite flexible
as long as there are no ambiguities. Examples of various times and operand
presentations include:
at 0815am Jan 24
at 8 :15amjan24
at now "+ 1day"
at 5 pm FRIday
at ’17
utc+
30minutes’
.- This sequence can be used at a terminal:
$ batch
sort <file >outfile
<EOT>
.- This sequence, which demonstrates redirecting standard error to a pipe,
is useful in a command procedure (the sequence of output redirection specifications
is significant):
$ batch <<!
diff file1 file2 2>&1 >outfile | mailx mygroup
!
See environ(5)
for descriptions of the following environment
variables that affect the execution of at and batch: LC_CTYPE,
LC_MESSAGES,
NLSPATH,
and LC_TIME.
- SHELL
- Determine a name of a command interpreter to be used to invoke
the at-job. If the variable is unset or NULL
, sh will be used. If it is set
to a value other than sh, the implementation will use that shell; a warning
diagnostic will be printed telling which shell will be used.
- TZ
- Determine
the timezone. The job will be submitted for execution at the time specified
by timespec or -t time relative to the timezone specified by the TZ
variable.
If timespec specifies a timezone, it will override TZ
. If timespec does
not specify a timezone and TZ
is unset or NULL
, an unspecified default
timezone will be used.
- DATEMSK
- If the environment variable DATEMSK
is
set, at will use its value as the full path name of a template file
containing format strings. The strings consist of format specifiers and
text characters that are used to provide a richer set of allowable date
formats in different languages by appropriate settings of the environment
variable LANG
or LC_TIME.
The list of allowable format specifiers
is located in the getdate(3C)
manual page. The formats described in the
OPERANDS section for the time and date arguments, the special names noon,
midnight, now, next, today, tomorrow, and the increment argument are not
recognized when DATEMSK
is set.
The following exit statuses
are returned:
- The at utility successfully submitted, removed or listed
a job or jobs.
- >0
- An error occurred, and the job will not be scheduled.
- /usr/lib/cron/at.allow
- names of users, one per line, who are authorized
access to the at and batch utilities
- /usr/lib/cron/at.deny
- names of users,
one per line, who are denied access to the at and batch utilities
crontab(1)
, csh(1)
, date(1)
, ksh(1)
, sh(1)
, touch(1)
, ulimit(1)
, umask(1)
,
getdate(3C)
, environ(5)
Regardless of queue used, cron has a limit
of 100 jobs in execution at any time.
There can be delays in cron at job
execution. In some cases, these delays can compound to the point that cron
job processing appears to be hung. All jobs will be executed eventually.
When the delays are excessive, the only workaround is to kill and restart
cron.
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