How to efficiently back up and restore crontab

When a database environment is being patched, entries from crontab are commented and then removed when patching is completed. The process works well when there are only a few entries from crontab, but it does not scale when crontab has dozens of entries and when some entries are commented and some are not. I believe a more efficient method is to backup and restore the existing crontab.

The Problem with Manual Crontab Management

Managing crontab entries by commenting them out during maintenance is error-prone. It's difficult to track which jobs were originally active and which were intentionally disabled prior to the maintenance window.

Current Crontab State

Here is our starting point for the demo:

[oracle@racnode-dc1-1 ~]$ crontab -l  */05 * * * * /bin/date > /tmp/date.out 2>&1  */15 * * * * /bin/date > /tmp/date.out 2>&1  #*/25 * * * * /bin/date > /tmp/date.out 2>&1  */35 * * * * /bin/date > /tmp/date.out 2>&1  */45 * * * * /bin/date > /tmp/date.out 2>&1  */55 * * * * /bin/date > /tmp/date.out 2>&1 

A Better Way: Backup, Remove, and Restore

Instead of manual editing, we can export the entire table to a file and clear the crontab for the duration of the patching.

1. Backing Up the Crontab

Backup crontab and display contents. Extra precaution in case crontab.save.dinh is removed.

[oracle@racnode-dc1-1 ~]$ crontab -l > crontab.save.dinh; cat crontab.save.dinh  */05 * * * * /bin/date > /tmp/date.out 2>&1  */15 * * * * /bin/date > /tmp/date.out 2>&1  #*/25 * * * * /bin/date > /tmp/date.out 2>&1  */35 * * * * /bin/date > /tmp/date.out 2>&1  */45 * * * * /bin/date > /tmp/date.out 2>&1  */55 * * * * /bin/date > /tmp/date.out 2>&1 

2. Clearing the Active Schedule

Remove crontab to ensure no jobs run during the patching window.

[oracle@racnode-dc1-1 ~]$ crontab -r; crontab -l  no crontab for oracle 

3. Restoring the Original Schedule

Once maintenance is complete, restoring is a single-step process.

[oracle@racnode-dc1-1 ~]$ crontab crontab.save.dinh; crontab -l  */05 * * * * /bin/date > /tmp/date.out 2>&1  */15 * * * * /bin/date > /tmp/date.out 2>&1  #*/25 * * * * /bin/date > /tmp/date.out 2>&1  */35 * * * * /bin/date > /tmp/date.out 2>&1  */45 * * * * /bin/date > /tmp/date.out 2>&1  */55 * * * * /bin/date > /tmp/date.out 2>&1 

Efficiency for the "Lazy" Admin

If you are lazy like me, then backup can be done in one command.

[oracle@racnode-dc1-1 ~]$ crontab -l > crontab.save.dinh; cat crontab.save.dinh; crontab -r; crontab -l  */05 * * * * /bin/date > /tmp/date.out 2>&1  */15 * * * * /bin/date > /tmp/date.out 2>&1  #*/25 * * * * /bin/date > /tmp/date.out 2>&1  */35 * * * * /bin/date > /tmp/date.out 2>&1  */45 * * * * /bin/date > /tmp/date.out 2>&1  */55 * * * * /bin/date > /tmp/date.out 2>&1  no crontab for oracle  [oracle@racnode-dc1-1 ~]$ 

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