<\/b>HOW TO KILL DEFUNCT OR ZOMBIE PROCESS<\/b><\/p>\n
A “defunct”<\/b> processes
\nis also known as a “zombie” <\/b>processes. A Zombie
\nprocess is referred as dead process <\/b>which is receding on your
\nsystem though it\u2019s completed executing. In one shot we can say it\u2019s a dead
\nprocesses which is still in RAM. This process will be in your process table and
\nconsuming your memory. Having more defunct process will consume your memory
\nwhich intern slows your system. We have to kill the defunct process in order to
\nfree RAM and make system stable.<\/p>\n
What is a zombie process?<\/b><\/p>\n
When a process finishes execution, it will
\nhave an exit status to report to its parent process. Because of this last
\nlittle bit of information, the process will remain in the operating system\u2019s
\nprocess table as a zombie process, indicating that it is not to be scheduled
\nfor further execution, but that it cannot be completely removed (and its
\nprocess ID cannot be reused) until it has been determined that the exit status
\nis no longer needed.<\/p>\n
When a child exits, the parent process will
\nreceive a SIGCHLD signal to indicate that one of its children has finished
\nexecuting; the parent process will typically call the wait() system call at
\nthis point. That call will provide the parent with the child\u2019s exit status, and
\nwill cause the child to be reaped, or removed from the process table.<\/p>\n
Why
\ndefunct process are created?<\/b><\/p>\n
Ans
\n:<\/b> When ever a process ends
\nall the memory used by that process are cleared and assigned<\/b> to
\nnew process <\/b>but due to programming errors\/bugs<\/b> some
\nprocesses are still left in process table. These are created when there is no
\nproper communication between parent process and child proces<\/p>\n
How do I remove zombie
\nprocesses from a system?<\/b><\/p>\n
Well, first you can wait.
\nIt\u2019s possible that the parent process is intentionally leaving the process in a
\nzombie state to ensure that future children that it may create will not receive
\nthe same pid. Or perhaps the parent is occupied, and will reap the child
\nprocess momentarily.<\/p>\n
Secondly, you can send a
\nSIGCHLD signal to the parent (\u201ckill -s SIGCHLD <ppid>\u201c). This will cause
\nwell-behaving parents to reap their zombie children.<\/p>\n
Finally, you can kill the
\nparent process of the zombie. At that point, all of the parent\u2019s children will
\nbe adopted by the init process (pid 1), which periodically runs wait() to reap
\nany zombie children. Then system need reboot to kill zombie process.<\/p>\n
Interview
\nquestions & answers<\/b><\/p>\n
1. How to find a defunct
\nprocess?<\/b><\/p>\n
Run \u201cps aux\u201d and look for a
\nZ in the STAT column.<\/p>\n
ps aux | awk
\n‘”[Zz]” ~ $8 { printf(“%s, PID = %dn”, $8, $2); }’<\/p>\n
2. How can I kill a
\ndefunct process?<\/b><\/p>\n
Ans :<\/b> Just use kill command<\/p>\n
3. Still not able to
\nkill?<\/b><\/p>\n
Ans :<\/b> Then use kill -9 to force
\nkill that process<\/p>\n
4. Still have an issue in
\nkilling it?<\/b><\/p>\n
Ans :<\/b> Then try to kill it\u2019s
\nparent id and then defunct.<\/p>\n
#kill
\nparent-id-of-defunct-pid<\/p>\n
#kill -9
\nparent-id-of-defunct-pid<\/p>\n
Ans<\/b> : If you still find defunct
\nprocess eating up RAM then last and final solution is to reboot your
\nmachine(This is not preferred on production boxes).<\/p>\n
6.What is orphan process?<\/b><\/p>\n
Ans :<\/b> An orphan process is said
\nto be a process which runs through parent process is terminated, these process
\ndo not know what to do and when to terminate.<\/p>\n
7. What is difference
\nbetween orphan and defunct processes?<\/b><\/p>\n
Ans :<\/b> A defunct process is a dead
\nprocess where there is no execution happening whereas orphan process is a live
\nprocess which is still in execution state but don’t have parent process<\/p>\n