http://sikotec.wordpress.com/2009/12/02/linuxkill-process-kill-%E4%B8%8D%E6%8E%89%E5%95%8F%E9%A1%8C/
以下有二個 httpd (20098 17027) 使用 kill -9 或 killall 或 ./apachectl stop 就是殺不掉問題，
到最後使用 kill -18 才殺掉
[root@server bin]# ps aux | grep httpd
root 2383 0.0 0.0 51076 584 pts/2 S+ 11:50 0:00 grep httpd
500 17027 0.0 1.6 430628 67628 ? Tl Nov27 0:02 /usr/local/server/bin/httpd -k start -DSSL
500 20098 0.0 0.6 380948 26900 ? Tl Oct07 0:01 /usr/local/server/bin/httpd -k start -DSSL
[root@server bin]# pidof httpd
20098 17027
[root@server bin]# kill -18 20098 17027
[root@server bin]# pidof httpd
[root@server bin]#
