db2 instance is going into inactive state

Hi,

I'm pretty new to db2. I have a shell script where we'll do first catalog database then restart db. While performing catalog it was successful, but when db2 restart was initiated it threw the error
SQL1032N No start database manager command was issued. SQLSTATE=57019
which means db2instance is not started. If instance is not started how come catalog got succeeded. Is there any timeout as such that db2instance will go into inactive state.

Note: This is on AIX.

Any help is appreciated.

thanks,
chinni