Scheduled Activity: cron and at
The user's interface to the crontab and at commands is very similar across different versions of Unix, but implementations of underlying directory structures, daemons, and access controls may differ. Be sure to review your system documentation to take advantage of all aspects of these powerful commands.
There's practically no limit to the use of crontab and at, but let me offer a few words of warning. First, consider security issues when enabling user crontab and at permissions. Obviously, a disgruntled co-worker could leave a “time-bomb” of some sort, limited only by his other permission restrictions. Many versions of crontab and at allow you to specify “allow” and “deny” files to control which users have access to the utilities. You could also use root's crontab to check for and remove user crontabs (or any other files) if you want to.
Also, debug your crontab file entries thoroughly. Check that they are working. These entries are usually scheduled to execute at times of low-usage, so it is unlikely you'll be around to observe them at the time.
John Raithel is a consulting technical writer specializing in documenting the system and network administration of the Unix operating system, and is currently working on World Wide Web and firewall documentation for Silicon Graphics, Inc. He lives in a small town on the central California coast where he plays with his Linux and SunOS “mini-network”. He can be reached via e-mail at email@example.com.
Getting Started with DevOps - Including New Data on IT Performance from Puppet Labs 2015 State of DevOps Report
August 27, 2015
12:00 PM CDT
DevOps represents a profound change from the way most IT departments have traditionally worked: from siloed teams and high-anxiety releases to everyone collaborating on uneventful and more frequent releases of higher-quality code. It doesn't matter how large or small an organization is, or even whether it's historically slow moving or risk averse — there are ways to adopt DevOps sanely, and get measurable results in just weeks.
Free to Linux Journal readers.Register Now!
- August 2015 Issue of Linux Journal: Programming
- Django Models and Migrations
- Hacking a Safe with Bash
- Secure Server Deployments in Hostile Territory, Part II
- The Controversy Behind Canonical's Intellectual Property Policy
- Huge Package Overhaul for Debian and Ubuntu
- Shashlik - a Tasty New Android Simulator
- Embed Linux in Monitoring and Control Systems
- KDE Reveals Plasma Mobile
- diff -u: What's New in Kernel Development