UNIX for Dummies Questions & Answers

hi .. if one deletes a crontab entry in a live system.. how to relaod it back.. please help

You are doomed if you dont know what it was... unless you had a copy of the cronfile somewhere...
It is a good practice to save a cronfile before modification...
I even more methodically edit a cronfile always placed in /sm/cron (yes custom...) which has on the first line in comment Where it is to be found...
and use it for loading: crontab cronfile ...
Because editing a cronfile with crontab -e can lead to errors ( you deleted the wrong line or someone edited and put garbage in or...) and worse: if I am to resolve an issue on a box with booting or init issues..., I clear the cron(/var/spool/cron/crontabs), you havent a copy? sorry about that but you were warned...

sorry to be askinga gain and again but i am pretty new to unix... i have back up of the crontab so can u explain to me step by step...

Depending on your flavour and version of OS you can do several things. If you are using Linux the easiest (and assuming that the backup is recent and the only change is the line you deleted) you can

Code:

crontab <filename of backup>

which will replace the current with the backup.
On other flavours of Unix it may be as simple as dropping the backup file into the cron drirectory (possibly: /var/spool/cron/user/)

Code:

man crontab

will point you in the right direction

Dont forget after:
crontab -l (|more) # to see the actual cronfile run by cron