Cisco kron - the Cisco job scheduler

Cisco provides a job scheduler called "kron" which is similar to the unix crontab service. It allows us to schedule and run certain exec mode commands once or recurringly. The feature was first introduced in IOS version 12.3(1). The prerequisite for using kron is that Cisco clock time must be set - either locally or using an NTP source.

Check your IOS version first:

R1_Balancer#show version | include ^Cisco IOS(.+)Version
Cisco IOS Software, 3700 Software (C3725-ADVENTERPRISEK9-M), Version 12.4(18), RELEASE SOFTWARE (fc1)

The "kron" configuration has two parts, configuring "Scheduler Policy List" and then setting "Scheduler Occurrences". A scheduler policy list is similar to a shell script in unix. Every policy list will have a name and will contain one or more exec cli commands added sequentially. A scheduler occurrence is the setting that tells you when a policy list should be executed. You can associate one or more policy lists to a policy schedule.

Now let us create a kron policy with policy name my_policy_1. The commands that can be added in a policy should not generate any prompt or have the ability to be terminated using keystrokes. The simplest command that I can remember is write, which will save the running config to startup config( you can't use "copy running-config startup-config" since it will ask you to confirm the destination file name )

R1_Balancer(config)#kron policy-list my_policy_1
R1_Balancer(config-kron-policy)#cli write
R1_Balancer(config-kron-policy)#exit

You can view the policy from running configuration.

R1_Balancer#sh run | section include kron
kron policy-list my_policy_1
cli write

Let us create a schedule called schedule_1 now. This is set to run once at next Sunday night 11.45

R1_Balancer(config)#kron occurrence schedule_1 at 23:45 sun oneshot
Clock currently not set it reads 02:58:44 UTC Fri Mar 1 2002

If the clock is not set properly you will get a message as above. So set the time.

R1_Balancer#clock set 22:14:20 may 10 2009
R1_Balancer#show clock
22:17:29.487 UTC Sun May 10 2009

R1_Balancer(config)#kron occurrence schedule_1 at 23:45 sun oneshot
R1_Balancer(config-kron-occurrence)#policy-list my_policy_1
R1_Balancer(config-kron-occurrence)#exit

In the schedule you can optionally specify a user under which the kron should run. Now let us see the full kron configurations.

R1_Balancer#show run | section include kron
kron occurrence schedule_1 at 23:45 Sun oneshot
policy-list my_policy_1
kron policy-list my_policy_1
cli write

To view the schedule you can run this command:

R1_Balancer#show kron schedule
Kron Occurrence Schedule
schedule_1 inactive, will run once in 0 days 01:24:51 at 23:45 on Sun

For detailed information on kron, visit this Cisco link.