when does kill -9 pid not work?

[Thomas_McFadden.Henr801M at xerox.com]

Marty,

Using kill -9 does not work when a process is waiting on i/o to complete or
when the priority of the process is set by the kernel to be less than PZERO
found in <sys/param.h>. Your process may have caused this if it was doing
alot of i/o and the kill program never got a chance to post the signal to
the run away process. Otherwise, the kernel may have increased the priority
of your process and gone to sleep waiting for some event (i.e. i/o) to
complete. The kernel does this so that another process doesn't come along,
use the same process memory space or other shared resource, and get
trashed.

Tom