On my Fedora Core 9 webserver with kernel 2.6.18.8, init isn't reaping zombie processes. This would be bearable if it wasn't for the process table eventually reaching an upper limit where no new processes can be allocated.
Sample output of ps -el | grep 'Z':
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
5 Z 0 2648 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
1 Z 51 2656 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
1 Z 0 2670 1 0 75 0 - 0 exit ? 00:00:02 crond <defunct>
4 Z 0 2874 1 0 82 0 - 0 exit ? 00:00:00 mysqld_safe <defunct>
5 Z 0 28104 1 0 76 0 - 0 exit ? 00:00:00 httpd <defunct>
5 Z 0 28716 1 0 76 0 - 0 exit ? 00:00:06 lfd <defunct>
5 Z 74 10172 1 0 75 0 - 0 exit ? 00:00:00 sshd <defunct>
5 Z 0 11199 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11202 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11205 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11208 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11211 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11240 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11246 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11249 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
5 Z 0 11252 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
1 Z 0 14106 1 0 80 0 - 0 exit ? 00:00:00 anacron <defunct>
5 Z 0 14631 1 0 75 0 - 0 exit ? 00:00:00 sendmail <defunct>
Is this an OS bug? misconfiguration? I'm looking for inspiration as to the source of this problem.
Thanks
Best Answer
A process will become a zombie if the parent dies. If so, init will become the new parent of the orphan process.
Init will, periodically , execute wait() and will so reap any processes with init as parent. This happens synchronously, meaning, it waits to reap each process individually. This may make the process longer at times, if a processes doesn't reap properly.
It may suggest a bug in the system, it may not. I suggest kernel mailing list or dist specific mailing list that deals with the kernel.