[X-Unix] Zombies

[James Bucanek]

Alex wrote on Sunday, June 13, 2004:

>Could anyone point me to a reference on zombie processes in Mac OS X?

Well, I don't have a reference handy, but I can tell you what it is.  A zombie process is a process that has terminated, but the parent process (for whatever reason) hasn't polled the status of the child process to find out what its termination status was.  Thus, an entry in the process table is maintained to contain said status so (eventually) the parent process can find out what it was.

>My understanding is that zombies shouldn't really cause problems, but I 
>suspect a zombie having something to do with crashing the modemd 
>process.

Well, you might have a problem that's causing a process to terminate, which in turn could be messing up modemd.  But a zombie process can't possibly "do anything" because a zombie process is, by definition, not a process at all.  It's just the whole left by a process that once was.

But here's a hint: Zombie process entries are usually hanging around because the parent process is severely hung up.  It's deadlocked, or permanently suspended on some wait condition or I/O.  Find out what the parent of the zombie is, then find out why it's stuck, and you might be closer to solving your problem.

______________________________________________________
James Bucanek       <mailto:privatereply at gloaming.com>