init never reaping zombie/defunct processes

Question

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

Answer 1

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.

Answer 2

Zombies cannot be reaped by init. This is responsibility of the parent process to reap them by calling wait*(). These processes are left so that parent can take the return values.

Answer 3

2.6.18.8 is way to out-dated, for e. g., RedHat uses at least 2.6.18-194, so you'd better update your system.