cronjob

Preventing duplicate cron job executions

I feel like sometimes cron jobs create more problems than they solve. It's not the fault of cron, but rather the jobs being executed. This is especially true when the jobs result in duplicate running instances like the following example. $ ps -elf | grep forever 4 S vagrant 4095 4094 0 80 0 - 1111 wait 21:59 ? 00:00:00 /bin/sh -c /var/tmp/forever.sh 0 S vagrant 4096 4095 0 80 0 - 2779 wait 21:59 ?

Cheat Sheet: Crontab by Example

Today's article may be pretty basic for regular readers but hopefully some may find it useful. This article will cover creating a crontab entry and show some examples of common crontabs. The Cron daemon is a service that runs on all main distributions of Unix and Linux and specifically designed to execute commands at a given time. These jobs commonly refereed to as cronjobs are one of the essential tools in a Systems Administrators tool box.

Sar & Sysstat: Linux Performance Statistics with Ease

Whenever I perform any type of activity that requires me to look at historical system statistics such as load average, CPU utilization, I/O wait state, or even memory usage; I usually skip the System Monitoring Applications like Nagios or Zenoss and start running the sar command. While I'm not saying that sar completely replaces those tools, I am saying that sar is quick and dirty and if all you want is some raw numbers from a certain time frame; sar is a great tool.

How to check if a cron job ran

Cron is a time based scheduled task daemon that runs on most common Unix/Linux distributions. Because cronjobs are time based sometimes it is necessary to validate that the job ran at the scheduled time. Sometimes people will configure a cron to send the output of the script to a user via system mail or redirect the output to a file; however not all crons are setup the same and many times they may be configured to send output to /dev/null hindering any ability to validate the job ran.