"at","atq","atrm","batch" Command

Learn all about 'at','atq','atrm','batch' command

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'at','atq','atrm','batch' read commands from standard input or a specified file which are to be executed at a later time, using the shell set by the user's environment variable SHELL, the user's login shell, or ultimately /bin/sh. It executes commands at a specified time. Here, user will come to know about 'atq', 'atrm' and 'batch' commands which are aliases of 'at' command.

'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). /usr/share/doc/at/timespec contains the exact definition of the time specification.

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.

If the file /etc/at.allow exists, only usernames mentioned in it are allowed to use at.

If /etc/at.allow does not exist, /etc/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.

An empty /etc/at.deny means that every user is allowed to use these commands, this is the default configuration.

Following command will display help.

root:~# man at

Example-1

When you give something wrong in time format, you will get the error Garbled time

When correct time is given, it will display the terminal where user can write commands. To come out of terminal press ctrl + d

root:~# at
Garbled time

root:~# date
Wed Jun  7 06:41:21 UTC 2017
root:~# at 6:45
warning: commands will be executed using /bin/sh
at> echo "Hello World"
at> sleep 600
at> 
job 1 at Wed Jun  7 06:45:00 2017
root:~# at 6:46
warning: commands will be executed using /bin/sh
at> echo "Second Hello"
at> sleep 300
at> 
job 2 at Wed Jun  7 06:46:00 2017

Example-2

To Trigger jobs from file use following command:

root:~#cat myjobs.txt
/home/parthshah/calculatenumbers.sh
/path/to/a/shell-script
/path/to/any/command/or/script

root:~# at -f myjobs.txt now + 2 hour

2 hours from now, it will execute all the jobs from the myjobs.txt.

By Default, queue name of 'a' will be used but following example will show how to use different queue name.

root:~# at -q h 10:00
warning: commands will be executed using /bin/sh
at> echo Hello
at> sleep 30
at> 
job 4 at Wed Jun  7 10:00:00 2017
root:~# atq
4    Wed Jun  7 10:00:00 2017 h root

Example-3

To list current entries, use following command. Here 1 and 2 represents job id number.

root:~# atq
2    Wed Jun  7 06:46:00 2017 a root
1    Wed Jun  7 06:45:00 2017 a root

To remove any entry use following command.

root:~# atrm 1
root:~# atq
2    Wed Jun  7 06:46:00 2017 a root

if schedule job is running then it will show following:

root:~# atq
2    Wed Jun  7 06:46:00 2017 = root

Note: In Above Example, it was a (The 'a' queue is the default for at) and when job is running, its symbol becomes =

Example-4

batch execute commands when system load levels permit; in other words, when the load average drops below 1.5 (this can vary), or the value specified in the invocation of atrun. The syntax for the batch command is identical, except you do not set an execution time. The b is default queue for batch.

root:/ghostcache/Automation/PyUnit# batch
warning: commands will be executed using /bin/sh
at> echo "Hello World"
at> sleep 300
at> 
job 3 at Wed Jun  7 09:49:00 2017
root:/ghostcache/Automation/PyUnit# uptime
 09:53:08 up 78 days, 58 min,  1 user,  load average: 0.10, 0.13, 0.15
root:/ghostcache/Automation/PyUnit# atq
3    Wed Jun  7 09:49:00 2017 = root