Sometime process exists and cannot be killed due to:

• being zombie. I.e. process which parent did not read the exit status. Such process does not consume any resources except PID entry. In top it is signalled Z
• errornous uninterruble sleep. It should not happen but with combination of buggy kernel code and/or buggy hardware it sometime does. The only method is to reboot or wait. In top it is signalled by D.

Sometime process exists and cannot be killed due to:

• being zombie. I.e. process which parent did not read the exit status. Such process does not consume any resources except PID entry. In top it is signaled Z
• erroneous uninterruptible sleep. It should not happen but with a combination of buggy kernel code and/or buggy hardware it sometime does. The only method is to reboot or wait. In top it is signaled by D.