Linux Commands Examples

A great documentation place for Linux commands

at

rm queue, examine or delete jobs for later execution


see also : batch - atq - atrm - atd - cron - nice - sh

Synopsis

at [-V] [-q queue] [-f file] [-mMlv] timespec...
at
[-V] [-q queue] [-f file] [-mMkv] [-t time]
at -c
job [job...]
atq
[-V] [-q queue]
at
[-rd] job [job...]
atrm
[-V] job [job...]
batch
at -b


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examples

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Linux at command with seconds precision

Use cron to run a script that calls the sleep command for the sub-miniute precision bit of it? So

sleep 10 ; foo.sh 

should run foo.sh 10 seconds after the command is called.

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Getting zenity and at to work properly

Check your /var/log/messages, chances are you'll have some "Cannot open display" errors from your X Server.

You need to provide utilities like at and cron access to your X Display by name. Edit your ~/.bashrc to include the following:

xhost local:USERNAME > /dev/null

Substitute your username for the USERNAME value above. This will provide the at utility with the name of your X Display so it can attempt to fork zenity on it.

Modify your zenity command to include the --display switch:

echo "zenity --info --display=:0.0" | at now + 1 min 
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How can at execute a command from the command line

at read the command from standard input (or a file if you specify it with -f).

This should work:

echo 'find /path -name "pattern" > output.lst' | at now +X minutes

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How to list all 'at' jobs without root privileges?

This may not be the answer you want, but strictly speaking, you could boot a Live CD and use that to look at the files in /var/spool/at (or equivalent).

The privacy and security provisions of Unix/Linux does not allow you to do what you want. The at files are stored by default with "other" read privilege set to off.

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'at' command output on Mac

That is because you're echoing the output of $ at 08.00 into at_output.txt.

Try this instead.

$ at 08:00
./VM-run.sh > at_output.txt
^D

Then you'll get a confirmation like this.

job 1 at Sat Sep 24 08:00:00 2011

Edit: Alternatively for shell scripts, you can restructure the command like this.

#!/bin/bash
./VM-run.sh > at_output.txt | at 08:00

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Have the at command return the job id of the task just submitted

Assuming that the job you want to run is in a file called test.sh, the following will return the id:

 $ at now -f test.sh 2>&1 | grep job | awk '{print $2}'
 8

The 2>&1 redirects stderr to stdout so you can manipulate it. The grep gets the job line. The awk returns the second field in the line found by grep, which contains the job id.

So it get it into a variable, you can do:

$ TEST=`at now -f test.sh 2>&1 | grep job | awk '{print $2}'`
$ echo $TEST
9

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Linux 'at' command history

On my system I can find the list at /var/log/cron/*. You might look for something similar.

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How configure email the at/batch results is sent to?

I don't see a way of doing that in the at invocation, but you could probably do something like this with the command you're calling via at:

 $ at 16:00
 at> some-command [arguments, &c.] 2>&1 | sendmail [-f <from-address>] <recipient>
 at> ^D

When the command runs, it will hand off its output to sendmail for delivery to the specified recipient, and in the quick test I've just run, this does work.

Of course, if you're already redirecting the output from some-command to go somewhere else, you might be out of luck -- but, then, you could always tee(1) the output, or add a final line to the at job calling sendmail to push out the message.

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Puzzle of atrm vs at -d

Program code can know what the name of the executable was that launched it. It's possible that the at program does something like this:

if (my name is 'atrm') then
   add '-d' parmeter
end
do stuff like regular 'at' program.

description

at and batch read commands from standard input or a specified file which are to be executed at a later time, using /bin/sh.

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. The format of the output lines (one for each job) is: Job number, date, hour, queue, and username.

atrm

deletes jobs, identified by their job number.

batch

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 atd.

At allows fairly complex time specifications, extending the POSIX.2 standard. It accepts times of the form 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 midnight, noon, or teatime (4pm) and you can have a time-of-day suffixed with AM or 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 MMDD[CC]YY, MM/DD/[CC]YY, DD.MM.[CC]YY or [CC]YY-MM-DD. The specification of a date must follow the specification of the time of day. You can also give times like now + count time-units, where the time-units can be minutes, hours, days, or weeks and you can tell at 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, you would do at 4pm + 3 days, to run a job at 10:00am on July 31, you would do at 10am Jul 31 and to run a job at 1am tomorrow, you would do at 1am tomorrow.

The definition of the time specification can be found in /usr/share/doc/at/timespec.

For both at and 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 BASH_VERSINFO, DISPLAY, EUID, GROUPS, SHELLOPTS, TERM, UID, and _) and the umask are retained from the time of invocation.

As at is currently implemented as a setuid program, other environment variables (e.g. LD_LIBRARY_PATH or LD_PRELOAD) are also not exported. This may change in the future. As a workaround, set these variables explicitly in your job.

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 /usr/sbin/sendmail. If at is executed from a su(1) shell, the owner of the login shell will receive the mail.

The superuser may use these commands in any case. For other users, permission to use at is determined by the files /etc/at.allow and /etc/at.deny. See at.allow(5) for details.

options

-V

prints the version number to standard error and exit successfully.

-q queue

uses the specified queue. A queue designation consists of a single letter; valid queue designations range from a to z and A to Z. The a queue is the default for at and the b queue for batch. Queues with higher letters run with increased niceness. The special queue "=" is reserved for jobs which are currently running.

If a job is submitted to a queue designated with an uppercase letter, the job is treated as if it were submitted to batch at the time of the job. Once the time is reached, the batch processing rules with respect to load average apply. If atq is given a specific queue, it will only show jobs pending in that queue.

-m

Send mail to the user when the job has completed even if there was no output.

-M

Never send mail to the user.

-f file

Reads the job from file rather than standard input.

-t time

run the job at time, given in the format [[CC]YY]MMDDhhmm[.ss]

-l

Is an alias for atq.

-r

Is an alias for atrm.

-d

Is an alias for atrm.

-b

is an alias for batch.

-v

Shows the time the job will be executed before reading the job.

Times displayed will be in the format "Thu Feb 20 14:50:00 1997".

-c

cats the jobs listed on the command line to standard output.

files

/var/spool/cron/atjobs
/var/spool/cron/atspool
/proc/loadavg
/var/run/utmp
/etc/at.allow
/etc/at.deny


bugs

The correct operation of batch for Linux depends on the presence of a proc- type directory mounted on /proc.

If the file /var/run/utmp 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.

At and batch as 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 nqs.


see also

at.allow, at.deny, atd , cron , nice , sh , umask.


author

At was mostly written by Thomas Koenig, ig25[:at:]rz[:dot:]uni-karlsruhe.de.

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