Starting, Stopping, and Replacing Users' Cron Jobs
John Spurgeon and Ed Schaefer
When performing system maintenance, we often disable certain users' cron jobs temporarily. When the maintenance activities are complete, the original crontab files are restored. To facilitate these tasks, we developed two Bourne shell scripts, stop_cron (
Listing 1
) and start_cron (
Listing 2
). A related script, replace_cron (
Listing 3
), was developed to remove a user's current crontab file and replace it with the standard file for that user.
The syntax is similar for each script. The names of users whose crontab files will be affected may be supplied as operands. If no user names are specified on the command line, the list of users is read from standard input. To manipulate another user's crontab file, the scripts must execute with root permissions.
Each script depends on the SortingHat utility, which we discussed in our previous Sys Admin article (April, 2007). SortingHat provides the ability to back up the current version of a file and restore the backup copy -- exactly the type of thing we need to do with users' crontab files. If you don't want to install SortingHat, it should be easy to develop alternative implementations for stop_cron and start_cron. However, changing replace_cron might be more complicated, since the program relies on SortingHat to locate a standard crontab file.
Stop cron
For each user specified, stop_cron first verifies that the user is listed in /etc/cron.d/cron.allow and then checks to see whether the user's crontab file exists in /var/spool/cron/crontabs/.
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