1. Is there any side effect if we change maximum number of jobs that can be run simultaneously for cron from default value of 100 to 400 or 500 in file "queuedefs" ?

2. What can be the effective way to check whether the cron job is already running or not, so that the next job should not start
e.g. 4,9,14,19,24,29,34,39,44,49,54,59 * * * ksh /usr/home/tmp/t.sh 10 0 11

Thank you in Advance.

Please don't post questions in the faq queue. You need to pick an appropiate forum.

1. Yes. Server load for one thing.

2. Put a check in the script. Either get it to create some sort of lock file (and remove it when it's finished - remember to set up traps), and then when it's executed see if the lock file exists, if it does, exit. You could also grep through ps output, etc... more than one way to skin this cat.

Cheers
ZB