At Command in Linux

At Command in Linux

At Command in Linux

We hope this post helped you to find out  At Command in Linux

at is a command-line utility that permits you to schedule instructions to be executed at a selected time. Jobs created with at are executed solely as soon as.

On this article, we’ll clarify find out how to use at and its companion utilities batchatqatrm to view, delete, and create jobs to be executed at a later time.

installing in at #

Relying on the distribution, at might or might not be current in your Linux system.

If at will not be put in, you may simply set up it utilizing the bundle supervisor of your distribution.

Install at on Ubuntu and Debian

sudo apt update 
sudo apt install at

Install at on CentOS and Fedora

sudo yum install at

As soon as this system is put in ensure that atd, the scheduling daemon is working and set to start out on boot:

sudo systemctl enable --now atd

How you can Use the at Command 

The simplified syntax for the at command is as follows:

The at command takes the date and time (runtime) if you need to execute the job as a command-line parameter, and the command to be executed from the usual enter.

Let’s create a job that might be executed at 9:00 am:

at 09:00

When you hit Enter, you’ll be offered with the at command immediate that almost all typically begins with at>. You additionally see a warning that tells you the shell wherein the command will run:

warning: commands will be executed using /bin/sh
at>

Enter one or more command you want to execute:

tar -xf /home/linuxize/file.tar.gz

When you’re done entering the commands, press Ctrl-D to exit the prompt and save the job:

at> <EOT>
job 4 at Tue May  5 09:00:00 2020

The command will show the job quantity and the execution time and date.

There are additionally different methods to go the command you need to run, in addition to coming into the command within the at immediate. A method is to make use of echo and pipe the command to at:

echo "command_to_be_run" | at 09:00

Another option is to use Here document:

at 09:00 <<ENDcommand_to_be_runEND

To read the commands from a file instead of the standard input, invoke the command with -f option following by the path to the file. For example, to create a job that will run the script /home/linuxize/script.sh:

at 09:00 -f /home/linuxize/script.sh

By default if the command produces output, at will send an email including the output to the user once the job is completed. Invoke at with the -M option to suppress the email notification:

at 09:00 -M

Use the -m to send an email even if there is no output:

at 09:00 -m

batch Command #

batch or its alias at -b schedules jobs and executes them in a batch queue when the system load degree allow. By default, the roles are executed when the system load common is under 1.5. The worth of the load might be specified when invoking the atd daemon. If the system load common is larger the desired one, the roles will wait within the queue.

To create a job with batch, go the instructions you need to execute:

echo "command_to_be_run" | batch

Specifying the Execution Time #

The at utility accepts a variety of time specs. You possibly can specify time, date, and increment from the present time:

  • Time – To specify a time, use the HH:MM or HHMM type. To point a 12-hour time format, use am or pm after the time. You can even use strings like nowmidnightmidday, or teatime (16:00). If the desired time is handed, the job might be executed the following day.
  • Date – The command permits you to schedule job execution on a given date. The date might be specified utilizing the month title adopted by the day and an non-compulsory yr. You need to use strings, akin to right this momenttomorrow, or weekday. The date might be additionally indicated utilizing the MMDD[CC]YYMM/DD/[CC]YYDD.MM.[CC]YY or [CC]YY-MM-DD codecs.
  • Increment – at additionally accepts increments within the now + depend time-unit format, the place depend is a quantity and time-unit might be one of many following strings: minuteshoursdays, or weeks.

Time, date and increment might be mixed, listed here are few examples:

  • Schedule a job for the approaching Sunday at a time ten minutes later than the present time: at sunday +10 minutes
  • Schedule a job to run at 1pm two days from now: at 1pm + 2 days
  • Schedule a job to run at 12:30 Oct 21 2020: at 12:30 102120
  • Schedule a job to run one hour from now: at now +1 hours

You can even specify a time and date within the [[CC]YY]MMDDhhmm[.ss] utilizing the -t possibility. Right here is an instance:

at -t 202005111321.32

Specifying Queue #

By default, the roles created with at are scheduled within the queue named a and jobs created with batch are scheduled within the b queue.

Queries can have a reputation from a to z and A to Z. Queues with decrease letters run with decrease niceness, which suggests they’ve precedence over these with larger letters.

You possibly can specify the queue with the -q possibility. For instance, to set a job within the L queue, you’ll run:

at monday +2 hours -q L

Listing Pending Jobs #

To list the user’s pending jobs run the atq or at -l command:

atq

The output will list all jobs, one per line. Each line includes the job number, date, time, queue letter, and username.

9	  Tue May  5 12:22:00 2020 a linuxize
12	Wed Oct 21 12:30:00 2020 a linuxize
15	Tue May  5 09:00:00 2020 a linuxize
6	  Tue May  5 09:00:00 2020 a linuxize
13	Mon May  4 23:08:00 2020 a linuxize
11	Wed Jul  1 10:00:00 2020 a linuxize
4	  Tue May  5 09:00:00 2020 a linuxize

When atq is invoked as an administrative user, it will list the pending jobs of all users.

Removing Pending Jobs #

To remove a pending job invoke the atrm or at -r command followed by the job number. For example, to remove the job with number nine, you would run:

atrm 9

Restricting Users #

The /etc/at.deny and /etc/at.allow files allow you to control which users can create jobs with at or batch command. The files consist of a list of usernames, one user name per line.

By default, only the /etc/at.deny file exists and is empty, which means that all users can use the at command. If you want to deny permission to a specific user, add the username to this file.

If the /etc/at.allow file exists only the users who are listed in this file can use the at command.

If neither of the files exists, only the users with administrative privileges can use the at command.

Conclusion #

The at utility reads instructions from normal enter and executes them at a later time. Not like crontab, jobs created with at are executed solely as soon as.

For extra details about all accessible choices of the at command sort man at in your terminal.

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We hope this post helped you to find out  At Command in Linux  . You may also want to see – Kill Command in Linux

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