Hi,
I am very new to Linux. I started reading a tutorial.
I came across a process called Zombie.

I understand this is a process entry in the process table for a process which is already died.

This happens when the parent is not cleaning the process id from the process table. This is done by wait system call.

sometimes if the parent exits then init process do the cleaning work

Now my doubt is--->
suppose I have so many zombies in my process table.
Then what is the problem they may create? Why I need to kill them

You can't kill a zombie because it is already dead.

It isn't unusual to see a few zombie processes in your process table over time.

However, if you see multiple zombies all from the same parent it typically means there is an issue with the application or some resource it is trying to obtain. You should therefore focus your efforts on trying to find out what the issue is with the application and not waste time on the zombies themselves as they are a symptom of a larger issue.

By the way - sometimes if you can find the parent of a zombie and kill that process then sometimes it will clean up the zombies when it dies. Note you should always do progressive kill i.e. kill -1 <pid>, kill -15 <pid> and only as last resort kill -9 <pid>. Kill -9 tells a process to die without doing any cleanup so can cause tie up of resources or leave bits of itself in tables.

well,
if you have hundreds of zombies they will fill up your process table
and you won't be able to do anything.
your shell will say "too many processes" typically.

great fun.
we've all done it.

zombies get cleaned up eventually by init(8)

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Which is why you should focus on what is causing them. If you get too many processes chances are you're going to have to reboot to clear everything anyway.

Thank you for your answers.