What are the Zombie
Processes?
Note : Here number of Zombie Process is Zero.
On
Unix and Linux systems, the zombie (or defunct) processes are
dead processes that still apear in the process table, usually because of bugs
and coding errors. A zombie process remains in the operating system and does
nothing until the parent process determines that the exit status is no longer needed.
When does a process turn into a zombie?
Normally, when a process finishes execution, it reports the
execution status to its parent process. Until the parent process decides that
the child processes exit status is not needed anymore, the child process turns
into a defunct or zombie process. It does not use resources and it cannot be
schuduled for execution. Sometimes the parent process keeps the child in the
zombie stateto ensure that the future children processes will not receive the
same PID.
How to find and kill a zombie process:
You can find the zombie processes with ps aux | grep Z. The
processes with Z in the STATE field are zombie processes:
$ ps aux | grep Z
How to kill a zombie process:
To
kill a zombie process, find the zombie’s parent PID (PPID) and send him the
SIGCHLD (17) signal: kill -17 ppid
I use this command to find a PPID: ps -p PID -o ppid
I use this command to find a PPID: ps -p PID -o ppid
$ ps
-p 20736 -o ppidPPID20735$ kill -17 20735
Note: If you kill the
parent of a zombie proceess, also the zombie process dies.
What are the Orphan Processes?
An Orphan Process is a process whose parent is dead
(terminated). A process with dead parents is adopted by the init process.
When does a process become an orphan process?
Sometimes, when a process crashes, it leaves the children processes alive, transforming them into orphan processes. A user can also create a orphan process, by detaching it from the terminal.
When does a process become an orphan process?
Sometimes, when a process crashes, it leaves the children processes alive, transforming them into orphan processes. A user can also create a orphan process, by detaching it from the terminal.
How to find orphaned processes:
This command will not display only the orphaned processes, but all the processes having the PPID 1 (having the init process as it’s parent).
This command will not display only the orphaned processes, but all the processes having the PPID 1 (having the init process as it’s parent).
$ ps -elf |
awk '{if ($5 == 1){print $4" "$5" "$15}}'298 1 upstart-udev-bridge302 1 udevd438 1 /usr/sbin/sshd[...]
Orphan
processes use a lot of resources, so they can be easily found with top or htop.
To kill an orphaned process, use kill -9 PID.
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