[1SaltwaterC]

IIRC is the only case where you can not kill a process under unices. It goes into the D state (uninterruptible sleep). Usually waiting for I/O is the reason for a process going into a D state. From my own experience, had this issue with faulty hardware and network filesystems. Here's something easy for reproducing a process going into uninterruptible sleep: GlusterFS 3.0.4 (Ubuntu 10.04 packages that version, a single machine setup is sufficient). A bug in Gluster turns into a deadlock and the process that triggers that bug does into the D state. Cause: using file locks without explicit unlock when releasing the file descriptor. The process can't be killed as it waits for the FS while the FS waits for the process to release the lock (which never happens). Had fun debugging that on a live deployment where each process got stuck one by one till the process pool was exhausted, while monit could not restart the daemon that managed the process pool.