How is it possible that kill -9 for a process on L

Question

I'm writing a plugin to highlight text strings automatically as you visit a web site. It's like the highlight search results but automatic and for many words; it could be used for people with allergies to make words really stand out, for example, when they browse a food site.

But I have problem. When I try to close an empty, fresh FF window, it somehow blocks the whole process. When I kill the process, all the windows vanish, but the Firefox process stays alive (parent PID is 1, doesn't listen to any signals, has lots of resources open, still eats CPU, but won't budge).

So two questions:

1. How is it even possible for a process not to listen to kill -9 (neither as user nor as root)?

2. Is there anything I can do but a reboot?

[EDIT] This is the offending process:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
digulla  16688  4.3  4.2 784476 345464 pts/14  D    Mar28  75:02 /opt/firefox-3.0/firefox-bin

Same with ps -ef | grep firefox

UID        PID  PPID  C STIME TTY          TIME CMD
digulla  16688     1  4 Mar28 pts/14   01:15:02 /opt/firefox-3.0/firefox-bin

It's the only process left. As you can see, it's not a zombie, it's running! It doesn't listen to kill -9, no matter if I kill by PID or name! If I try to connect with strace, then the strace also hangs and can't be killed. There is no output, either. My guess is that FF hangs in some kernel routine but which?

[EDIT2] Based on feedback by sigjuice:

ps axopid,comm,wchan

can show you in which kernel routine a process hangs. In my case, the offending plugin was the Beagle Indexer (openSUSE 11.1). After disabling the plugin, FF was a quick and happy fox again.

Answer 1

You can also do a pstree and kill the parent. This makes sure that you get the entire offending process tree and not just the leaf.

Answer 2

sudo killall -9 firefox

Should work

EDIT: [PID] changed to firefox

Answer 3

I lately get trapped into a pitfall of Double Fork and had landed to this page before finally finding my answer. The symptoms are identical even if the problem is not the same:

• WYKINWYT :What You Kill Is Not What You Thought

The minimal test code is shown below based on an example for an SNMP Daemon

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>

int main(int argc, char* argv[])
{
    //We omit the -f option (do not Fork) to reproduce the problem
    char * options[]={"/usr/local/sbin/snmpd",/*"-f","*/-d","--master=agentx", "-Dagentx","--agentXSocket=tcp:localhost:1706",  "udp:10161", (char*) NULL};

    pid_t pid = fork();
    if ( 0 > pid ) return -1;

    switch(pid)
    {
        case 0: 
        {   //Child launches SNMP daemon
            execv(options[0],options);
            exit(-2);
            break;
        }
        default: 
        {
            sleep(10); //Simulate "long" activity

            kill(pid,SIGTERM);//kill what should be child, 
                              //i.e the SNMP daemon I assume
            printf("Signal sent to %d\n",pid);

            sleep(10); //Simulate "long" operation before closing
            waitpid(pid);
            printf("SNMP should be now down\n");

            getchar();//Blocking (for observation only)
            break;
        }
    }
    printf("Bye!\n");
}

During the first phase the main process (7699) launches the SNMP daemon (7700) but we can see that this one is now Defunct/Zombie. Beside we can see another process (7702) with the options we specified

[nils@localhost ~]$ ps -ef | tail
root       7439      2  0 23:00 ?        00:00:00 [kworker/1:0]
root       7494      2  0 23:03 ?        00:00:00 [kworker/0:1]
root       7544      2  0 23:08 ?        00:00:00 [kworker/0:2]
root       7605      2  0 23:10 ?        00:00:00 [kworker/1:2]
root       7698    729  0 23:11 ?        00:00:00 sleep 60
nils       7699   2832  0 23:11 pts/0    00:00:00 ./main
nils       7700   7699  0 23:11 pts/0    00:00:00 [snmpd] <defunct>
nils       7702      1  0 23:11 ?        00:00:00 /usr/local/sbin/snmpd -Lo -d --master=agentx -Dagentx --agentXSocket=tcp:localhost:1706 udp:10161
nils       7727   3706  0 23:11 pts/1    00:00:00 ps -ef
nils       7728   3706  0 23:11 pts/1    00:00:00 tail

After the 10 sec simulated we will try to kill the only process we know (7700). What we succeed at last with waitpid(). But Process 7702 is still here

[nils@localhost ~]$ ps -ef | tail
root       7431      2  0 23:00 ?        00:00:00 [kworker/u256:1]
root       7439      2  0 23:00 ?        00:00:00 [kworker/1:0]
root       7494      2  0 23:03 ?        00:00:00 [kworker/0:1]
root       7544      2  0 23:08 ?        00:00:00 [kworker/0:2]
root       7605      2  0 23:10 ?        00:00:00 [kworker/1:2]
root       7698    729  0 23:11 ?        00:00:00 sleep 60
nils       7699   2832  0 23:11 pts/0    00:00:00 ./main
nils       7702      1  0 23:11 ?        00:00:00 /usr/local/sbin/snmpd -Lo -d --master=agentx -Dagentx --agentXSocket=tcp:localhost:1706 udp:10161
nils       7751   3706  0 23:12 pts/1    00:00:00 ps -ef
nils       7752   3706  0 23:12 pts/1    00:00:00 tail

After giving a character to the getchar() function our main process terminates but the SNMP daemon with the pid 7002 is still here

[nils@localhost ~]$ ps -ef | tail
postfix    7399   1511  0 22:58 ?        00:00:00 pickup -l -t unix -u
root       7431      2  0 23:00 ?        00:00:00 [kworker/u256:1]
root       7439      2  0 23:00 ?        00:00:00 [kworker/1:0]
root       7494      2  0 23:03 ?        00:00:00 [kworker/0:1]
root       7544      2  0 23:08 ?        00:00:00 [kworker/0:2]
root       7605      2  0 23:10 ?        00:00:00 [kworker/1:2]
root       7698    729  0 23:11 ?        00:00:00 sleep 60
nils       7702      1  0 23:11 ?        00:00:00 /usr/local/sbin/snmpd -Lo -d --master=agentx -Dagentx --agentXSocket=tcp:localhost:1706 udp:10161
nils       7765   3706  0 23:12 pts/1    00:00:00 ps -ef
nils       7766   3706  0 23:12 pts/1    00:00:00 tail

Conclusion

The fact that we ignored the double fork mechanism made us think that the kill action did not succeed. But in fact we simply killed the wrong process !!

By adding the -f option ( Do Not (Double) Fork ) all go as expected

Answer 4

ps -ef | grep firefox; and you can see 3 process, kill them all.

Answer 5

Double-check that the parent-id is really 1. If not, and this is firefox, first try sudo killall -9 firefox-bin. After that, try killing the specific process IDs individually with sudo killall -9 [process-id].

How is it even possible for a process not to listen to kill -9 (neiter as user nor as root)?

If a process has gone <defunct> and then becomes a zombie with a parent of 1, you can't kill it manually; only init can. Zombie processes are already dead and gone - they've lost the ability to be killed as they are no longer processes, only a process table entry and its associated exit code, waiting to be collected. You need to kill the parent, and you can't kill init for obvious reasons.

But see here for more general information. A reboot will kill everything, naturally.

Answer 6

Is it possible, that this process is restarted (for example by init) just at the time you kill it?

You can check this easily. If the PID is the same after kill -9 PID then the process wasn't killed, but if it has changed the process has been restarted.