Cisco: How to use kron to automate tasks

Now and then everybody in IT network industry has to stay awake over the night to accomplish some tasks that cannot be performed during the work hours because will disturb regular activity. Some of this task usually need your presence in field (virtually or in place), to assure that everything is working fine and you don’t have any unwanted surprise the next day.Skipping this tasks, there are other ones with less impact in case of a failure, which I believe you rather prefer to do it automatically and to check the results when you can. I’m talking here usually about configuration save or archive, IP addresses being renew by DHCP  or data backup

All this stuff can be achieved by using the Cisco “kron” present in the IOS. I think that everybody who’s ready this post heard about cron jobs, so I will issue just a small explanation. Cron jobs are tasks definite to run at one certain moment or to be recursive over a period of time. In human terms, cron jobs can help us sleep well why they are doing the job over the night.

Speaking now about Cisco “kron” command, you should know that it appear starting with IOS version 12.3(1), so don’t try to find it if you have a previous version installed. Also, The EXEC CLI specified in a Command Scheduler policy list must not generate a prompt or have the ability to be terminated using keystrokes. Command Scheduler is designed as a fully automated facility and no manual intervention is permitted. Command Scheduler allows you to schedule fully-qualified EXEC mode CLI commands to run once, at specified intervals, or at specified calendar dates and times.
Command Scheduler has two basic processes. A policy list is configured containing lines of fully-qualified EXEC CLI to be run at the same time or interval. One or more policy lists are then scheduled to run after a specified interval of time or at a specified calendar date and time. Each scheduled occurrence can be set to run once only or on a recurring basis. Policy lists can be configured after the policy list has been scheduled, but each policy list must be configured before it is scheduled to run.  Policy lists consist of one or more lines of fully-qualified EXEC CLI commands. All commands in a policy list are executed when the policy list is run by Command Scheduler using the kron occurrence command. Use separate policy lists for CLI commands to be run at different times.

One mandatory tasks is that before you try to run “kron”, your Cisco device has to know the time. Either manully set or through NTP server. If the device does not know the time, than a warning message will appear when you’ll try to configure kron tasks.

Please see below some brief examples about how you can configure kron tasks.

Cisco: kron