How to kill zombie process

Question

I launched my program in the foreground (a daemon program), and then I killed it with kill -9, but I get a zombie remaining and I m not able to kill it with kill -9. How to kill a zombie process?

If the zombie is a dead process (already killed), how I remove it from the output of ps aux?

root@OpenWrt:~# anyprogramd &
root@OpenWrt:~# ps aux | grep anyprogram
 1163 root      2552 S    anyprogramd
 1167 root      2552 S    anyprogramd
 1169 root      2552 S    anyprogramd
 1170 root      2552 S    anyprogramd
10101 root       944 S    grep anyprogram
root@OpenWrt:~# pidof anyprogramd
1170 1169 1167 1163
root@OpenWrt:~# kill -9 1170 1169 1167 1163
root@OpenWrt:~# ps aux |grep anyprogram
 1163 root         0 Z    [anyprogramd]
root@OpenWrt:~# kill -9 1163
root@OpenWrt:~# ps aux |grep anyprogram
 1163 root         0 Z    [anyprogramd]

Answer 1

A zombie is already dead, so you cannot kill it. To clean up a zombie, it must be waited on by its parent, so killing the parent should work to eliminate the zombie. (After the parent dies, the zombie will be inherited by pid 1, which will wait on it and clear its entry in the process table.) If your daemon is spawning children that become zombies, you have a bug. Your daemon should notice when its children die and wait on them to determine their exit status.

An example of how you might send a signal to every process that is the parent of a zombie (note that this is extremely crude and might kill processes that you do not intend. I do not recommend using this sort of sledge hammer):

# Don't do this.  Incredibly risky sledge hammer!
kill $(ps -A -ostat,ppid | awk '/[zZ]/ && !a[$2]++ {print $2}')

Answer 2

You can clean up a zombie process by killing its parent process with the following command:

kill -HUP $(ps -A -ostat,ppid | awk '{/[zZ]/{ print $2 }')

Answer 3

I tried:

ps aux | grep -w Z   # returns the zombies pid
ps o ppid {returned pid from previous command}   # returns the parent
kill -1 {the parent id from previous command}

this will work :)

Answer 4

Found it at http://www.linuxquestions.org/questions/suse-novell-60/howto-kill-defunct-processes-574612/

2) Here a great tip from another user (Thxs Bill Dandreta): Sometimes

kill -9 <pid>

will not kill a process. Run

ps -xal

the 4th field is the parent process, kill all of a zombie's parents and the zombie dies!

Example

4 0 18581 31706 17 0 2664 1236 wait S ? 0:00 sh -c /usr/bin/gcc -fomit-frame-pointer -O -mfpmat
4 0 18582 18581 17 0 2064 828 wait S ? 0:00 /usr/i686-pc-linux-gnu/gcc-bin/3.3.6/gcc -fomit-fr
4 0 18583 18582 21 0 6684 3100 - R ? 0:00 /usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.6/cc1 -quie

18581, 18582, 18583 are zombies -

kill -9 18581 18582 18583

has no effect.

kill -9 31706

removes the zombies.

Answer 5

I tried

kill -9 $(ps -A -ostat,ppid | grep -e '[zZ]'| awk '{ print $2 }')

and it works for me.

Answer 6

Sometimes the parent ppid cannot be killed, hence kill the zombie pid

kill -9 $(ps -A -ostat,pid | awk '/[zZ]/{ print $2 }')

Answer 7

Combining a few answers here into an elegant approach where you confirm which process is gone zombie before killing it. Add the script to .bashrc/.zshrc and run the killZombie command.

killZombie() {
    pid=$(ps -A -ostat,ppid | awk '/[zZ]/ && !a[$2]++ {print $2}');
    if [ "$pid" = "" ]; then
        echo "No zombie processes found.";
    else
        cmd=$(ps -p $pid -o cmd | sed '1d');
        echo "Found zombie process PID: $pid";
        echo "$cmd";
        echo "Kill it? Return to continue… (ctrl+c to cancel)";
        read -r;
        sudo kill -9 $pid;
    fi
}

Answer 8

On mac non of the above commands/instructions worked. To remove zombie processes you can right click on docker-icon->troubleshot->clean/purge Data.

Answer 9

I do not dare to try above methods.

My solution is htop then detect which process have multiprocessing.spawn and kill -9 it.