cron: Job Scheduler
The Debian and Red Hat distributions come with several pre-configured cron jobs to help control disk usage. Other distributions may provide similar help. The Debian dh_installcron command will install these jobs. Normally, you should not need to run this command—installing the cron package will take care of it for you.
These jobs, located in the file /etc/crontab, use the run-parts command to call all the scripts in directories /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly. For the most part, these scripts control disk usage, compressing and pruning log files in /var/log and cleaning up after indices from the man(1) command. The package maintainers who created these jobs configured them to run during the night, normally a slow time for other system activity. Some of the scripts generate a lot of disk activity, which can slow other I/O-intensive jobs. If you want them to run at other times, edit /etc/crontab or move the scripts among the directories that contain them.
See the list of references in the sidebar for additional reading on cron. Additionally, the man page for the at facility may prove useful. at provides a one-time job-scheduling facility. If you do not keep your Linux system running 24 hours per day, you may want to review Anacron, which does not depend on specific time events to get its work done.
I have provided a brief introduction to the cron facility, a typical part of Linux and other UNIX operating systems. It will provide a starting point for time-related work you want your Linux system to perform. In brief, if you want to schedule repetitive tasks so as not to type the same commands again and again, use cron.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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