Linux killing zombie process

Killing zombie processes on Linux using kill command

Z ombie process is an inactive computer process. On Unix, including Linux operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table, allowing the process that started it to read its exit status. In the term’s colorful metaphor, the child process has died but has not yet been reaped. Let us see how to list and kill zombie processes on Linux command line options.

How do I find out zombie processes on Linux?

Use the top command or ps command along with grep command/egrep command:
# top
Try the following commands to find zombie processes as root user:
# ps aux | awk ‘< print $8 " " $2 >‘ | grep -w Z
Here is what we see

To get more human readable outputs try:
# ps aux | egrep «Z|defunct» | grep -v ‘grep’

How to find zombie process on Linux

How do I kill zombie process or processes on Linux?

You cannot kill zombies, as they are already dead. But if you have too many zombies then kill parent process or restart service. For example, you can kill zombie process using PID obtained from any one of the above commands. First, get parent PID for child PID called 1313
# ps -o ppid=1313
Next, kill zombie process having parent PID 4104:
# kill -s SIGCHLD 4104

Killing zombie processes for good

If above command failed, try the following command to kill its parent process:
# kill -9 4104
Please note that kill -9 does not guarantee to kill a zombie process. In extreme, condition you may have to reboot your Linux box by typing the shutdow command/reboot command:
$ sudo reboot
## OR ##
$ sudo shutdown -r now

How do I automate zombie process killing?

Write a shell script and schedule as a cron job to kill zombie process.

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Conclusion

You learned how to list and kill zombie processes on Linux operating systems. See kill command man page online or by typing the following command:
$ man kill
$ man ps

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Comments on this entry are closed.

My friend is using something as follow (he calls it as linux zombies kill script.. LOL)

for each in `ps jauxww | grep Z | grep -v PID | awk ‘’`; do for every in `ps auxw | grep $each | grep cron | awk ‘’`; do kill -9 $every; done; done

Hope it will be useful to someone.

awk: cmd. line:1: . awk: cmd. line:1: ^ syntax error
awk: cmd. line:2: (END OF FILE)
awk: cmd. line:2: syntax error
ERROR: Conflicting format options.

Just copy and paste the code. I have fixed the css code problem.

grepping for the “word” Z won’t show Zombies that are also session leaders (such as Xorg) which show up as Zs

recommend ending with “| grep Z”

You should read the Wikipedia article more closely. There is no point sending a SIGKILL to a zombie process.

$ cat makezombie.c
#include
#include
#include
#include

int main(int argc, char *argv[])
<
pid_t child;

for (;;)
<
child = fork();
if (0 == child)
<
/* Whaddya know, I am the walrus^Wchild. Announce myself and
* exit immediately, making myself a zombie.
*/
fprintf(stdout, “Child PID is %ldn”, (signed long int)getpid());
exit(0);
>
else if (child > 0)
<
/* I’m the parent. Loop without
* reaping the child.
*/
for (;;)
<
sleep(1);
>
>
else
<
/* fork() failed. Wait and try again. */
perror(“fork”);
sleep(1);
>
>
>
$ cc makezombie.c -o makezombie
$ ls -l makezombie
-rwxr-x— 1 youngman eng 9871 Mar 27 16:52 makezombie
$ ps
PID TTY TIME CMD
1769 pts/2 00:00:00 bash
2348 pts/2 00:00:00 ps
$ ./makezombie &
[1] 2351
$ Child PID is 2352
ps
PID TTY TIME CMD
1769 pts/2 00:00:00 bash
2351 pts/2 00:00:00 makezombie
2352 pts/2 00:00:00 makezombie
2353 pts/2 00:00:00 ps
$ kill -9 2352; echo $?
0
$ ps
PID TTY TIME CMD
1769 pts/2 00:00:00 bash
2351 pts/2 00:00:00 makezombie
2352 pts/2 00:00:00 makezombie
2356 pts/2 00:00:00 ps
$ kill 2351
$ ps
PID TTY TIME CMD
1769 pts/2 00:00:00 bash
2364 pts/2 00:00:00 ps
[1]+ Terminated ./makezombie
$

Plz tell me !
The difference between a thread and a process.
Plz give a detailed explanation.
I hope you will not let me down.
Thank you.

The first script has major issues with it. This is the one that I use

for each in `ps -ef | grep ” | grep -v PID | awk ‘< print $3 >’`; do for every in `ps -ef | grep $each | grep -v cron | awk ‘< print $2 >’`; do kill -9 $every; done; done

thanks.
I Got my ans of zombie Process.

The thread is some thing like background job for the process smiler to project count from 1 till 100 and the main purpose of the project is get each number value.
eg in our daily life is some programs can’t do any thing until it’s main job done like some sort of Anti Virus’s when you tried to do another job the program dosen’t respond to any command in the main time i’s in the same process but it take her own mem space 😀
i hope i was any useful for you 😀

Updated and tested with HP-UX 11i, Solaris 10, Debian, RHEL4 and SUSE 10

Quick ‘n dirty hack:

ps ax | awk ‘< if ($NF == “”) print $1 >’ | xargs kill -9

I guess the html is stripped, hope at least one works, I mean $NF == defunct between “less than” and “greater than”:

ps ax | awk ‘< if ($NF == “”) print $1 >’ | xargs kill -9

You need to send the parent process a SIGCHLD or kill it

ps -eo pid,ppid,user,args,stat –sort stat | grep Z | awk ‘< print $2 >’ | sort -u

gives you the parent process id(s)

kill -s SIGCHLD
or
kill
…

First things first, I am amazed at the amount of time so many people have put into dealing with such a non-issue. Zombie processes are dead, they consume nearly zero system resources. The only time you should be concerned is if you have a large number of them and said number is continuing to grow, in which case getting rid of the zombies is not your problem. You need to find out why you have them in the first place. Removing them is like taking a cold tablet, you are deling with the symptom, not the real problem.

That said, you should never, ever be using ‘kill -9’, that is an absolute last-ditch resort for dealing with a system that is almost non-functional or in some other critical state. Having a few zombie processes tying up nearly no resources at all is not a critical state, and using kill -9 is like chasing a mouse with a heavy hammer; you’re not likely to get the mouse, but you may do extensive damage to everything around you in the process.

So, what to do? find out what is spawning these processes, and why it is not shutting them down when they exit. See if there is a patch that fixes the issue. Make a report to the maintainers of the package. Restart the parent process. Or to reiterate, find out the cause of the problem and fix that.

you’re not likely to get the mouse, but you may do extensive damage to everything around you in the process.

if I use kill -9 to erase zombies from servers what kind of problems might I cause ?
can you give me a hint
thanks

ps -ef | grep defunct | awk ‘< print $3 >’ | xargs kill -9

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Выполняю установку, настройку, сопровождение серверов. Для уточнения деталей используйте форму обратной связи

Что же это такое?
Это дочерний процесс в Unix-системе, завершивший своё выполнение, но ещё присутствующий в списке процессов операционной системы, чтобы дать родительскому процессу считать код завершения. Процесс при завершении освобождает все свои ресурсы (за исключением PID — идентификатора процесса) и становится «зомби» — пустой записью в таблице процессов, хранящей код завершения для родительского процесса.
Система уведомляет родительский процесс о завершении дочернего с помощью сигнала SIGCHLD. Предполагается, что после получения SIGCHLD он считает код возврата с помощью системного вызова wait(), после чего запись зомби будет удалена из списка процессов. Если родительский процесс игнорирует SIGCHLD (а он игнорируется по умолчанию), то зомби остаются до его завершения.

А теперь возникают вопросы: как же всё-таки их найти и убить? Найти их очень просто. Вот несколько вариантов:

1)
top | grep zombie
225 processes: 1 running, 222 sleeping, 2 zombie

2)
ps aux | grep -w Z
root 3994 0,0 0,0 0 0 ?? Z 13июн11 16:23,02
root 3995 0,0 0,0 0 0 ?? Z 13июн11 13:43,28

3)
ps -alx | awk ‘$10

Что касается «убийства», то их нельзя просто так убить. Самый правильный вариант — найти родительский процесс и перезапустить его. Некоторые могут посоветовать и перегрузиться, но это не выход.

Находим родительский процесс:

ps ajx | grep -w Z
root 3994 3992 3992 3992 0 Z ?? 16:23,02
root 3995 3992 3992 3992 0 Z ?? 13:43,28

3-я колонка как раз и показывает pid родительского процесса. Смотрим, что это за процесс:

ps auxww | grep 3992
root 3992 0,0 0,2 30664 9872 ?? Ss 13июн11 0:08,21 [exilog_agent] (perl5.12.3)

Собственно мы нашли виновника. Это exilog_agent. А дальше — либо просто прибиваем родительский процесс либо перезапускаем его:

#kill -9 3992
#top | grep zombie
#

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Killing zombie processes in Linux

I have a problem with zombie-processes. When I close the connection from the client side, zombie childs don’t die. If I close the connection from the server side, everything is OK. There is no zombie child. I’m using the code below

2 Answers 2

A zombie process consumes only the entry in the process table. The kernel maintains it to allow for the parent process’ wait(2) system call (and family) to be aware that there’s actually a process to be waited for and don’t fail about calling wait() without having subprocesses walking around. Those walking dead processes are there to ensure kernel data consistency and, as such, you cannot kill them (even as root user) The only way to ensure that a living parent doesn’t have this bunch of zombies around is to do one wait(2) call for each fork() it has done before (which you don’t do at all). As in your code the thread is going to die just after closing the file descriptor, you have a chance to do a waitpid(pid_of_child, . ); there, so you’ll wait for the proper child. See waitpid(2) for more info about this system call. This approach will have a non-visible drawback (your thread will last until the child dies). The reason this works normally with processes (the non-need to do wait() in the parent process) is that you are not dying the parent (the parent lives after the thread dies) and so, the fork()/wait() relationship maintains. When a parent dies, the kernel makes init (process with id == 1 ) the parent of your process, and init(8) is always making wait(2) s for the orphaned children in the system.

By just adding the following code after

or, as you are not going to check how did the child terminate

This has another drawback, is that you are going to wait for the child to terminate and will not get into the accept(2) system call before your child terminates, which can be not what you want. If you want to avoid creating child zombie processes, there’s another alternative (but it has some other drawbacks) is to ignore the SIGCHLD signal in the whole process, which makes the kernel not create those zombies (legacy way to do, there are other ways to avoid zombie children) or you can have a new thread just making the needed wait() s and dispatch the returned values from the children to the proper place, once they die.

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