"kill -9" fails... why?

Kill -9 >> Process still alive !!!!


A signal is a message sent to a process to interrupt it and cause a response. If the process has been designed to respond to signals of the type sent it does so; otherwise, it terminates. There are 42 signals, as defined in the signal(5) man page. 


Why sometime process cannot be killed with kill -9?

If the process is hung waiting for I/O (or some other kernel resource) it will behave that way. The problem is the process is hung waiting for an I/O to return and is unable to service the signal. So it never gets killed. Usually reboot is the only solution for this condition.

Sometimes a process will be waiting for kernel to do some I/O and the kernel is waiting for a timeout because of a hardware error, etc. This can happen if you try to do a file copy for instance and a harddrive fails. The 'cp' command may not be killable until the kernel timeout has occurred (this may hang indefinately).

stale NFS mounts will cause the issue if hard mount is used. One way to avoid hung processes is to "soft" mount the NFS mounts. 


https://forums.oracle.com/thread/2398407

http://docs.oracle.com/cd/E19455-01/806-1360/processmanagerusing-62/index.html