at, cron, and anacron
Scheduling Commands and Scripts

© Lead Image © rawpixel, 123RF.com
The at command and the related cron and anacron can help you efficiently schedule tasks, whether one-time events or jobs to be done repeatedly.
Scheduling tasks is as old as Unix. Usually, it is a concern for root users, handy for making sure that jobs like backups are done regularly. However, scheduling can also be useful for regular users, if only to broadcast a message to themselves to take a break. Either way, you have three scheduling systems for your needs: at
[1] and its related commands, cron
[2], and anacron
[3]. The three overlap, but each has its own peculiarities for configuration and scheduling.
The at Family of Commands
At
and its associated commands are for scheduling of a one-time event. By default, the commands can only be run by root. However, other users can also be permitted to run at
if you create a file called /etc/at.allow
, adding names one per line. You can also add users to /etc/at.deny
if there are users whom you specifically do not want to use the commands, including users that exist for administrative purposes or users that might be created by intruders, such as guest
(Figure 1).
To schedule a command to run once, enter the command followed by a time. The time must be precise down to minutes and can be precise down to seconds using the MMDDhhmm[.ss]
format. You can also specify the fixed times midnight
, noon
, or teatime
(4pm) or a specific date followed by the time. Similarly, you can specify now
, today
, or tomorrow
, optionally adding a time after now
or today
. For instance, 5pm + 1 week
or noon August 2
would both be valid time entries. Should you enter a time that has already passed, such as 11am today
when it is 4pm, the command will be run in about five minutes.
[...]
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.

News
-
Linux Kernel 6.17 is Available
Linus Torvalds has announced that the latest kernel has been released with plenty of core improvements and even more hardware support.
-
Kali Linux 2025.3 Released with New Hacking Tools
If you're a Kali Linux fan, you'll be glad to know that the third release of this famous pen-testing distribution is now available with updates for key components.
-
Zorin OS 18 Beta Available for Testing
The latest release from the team behind Zorin OS is ready for public testing, and it includes plenty of improvements to make it more powerful, user-friendly, and productive.
-
Fedora Linux 43 Beta Now Available for Testing
Fedora Linux 43 Beta ships with Gnome 49 and KDE Plasma 6.4 (and other goodies).
-
USB4 Maintainer Leaves Intel
Michael Jamet, one of the primary maintainers of USB4 and Thunderbolt drivers, has left Intel, leaving a gaping hole for the Linux community to deal with.
-
Budgie 10.9.3 Now Available
The latest version of this elegant and configurable Linux desktop aligns with changes in Gnome 49.
-
KDE Linux Alpha Available for Daring Users
It's official, KDE Linux has arrived, but it's not quite ready for prime time.
-
AMD Initiates Graphics Driver Updates for Linux Kernel 6.18
This new AMD update focuses on power management, display handling, and hardware support for Radeon GPUs.
-
AerynOS Alpha Release Available
With a choice of several desktop environments, AerynOS 2025.08 is almost ready to be your next operating system.
-
AUR Repository Still Under DDoS Attack
Arch User Repository continues to be under a DDoS attack that has been going on for more than two weeks.