One of our engineers wanted to get debug information about ISAKMP after a system reboot but found it was difficult to login quickly enough after the reboot. He found a way to get debug running without needing to login to the router and manually enter the debug commands.
For IOS devices which support the “do” command it is possible to put a “do debug …” string b into a text copy of the config file and then TFTP this file to startup.
When the router reboots, the debugs run. It worked well for him, in terms of getting debug output when he wanted it.
(Of course, be careful about running debugs on your running network…)