If you have a server which is not working very well, it is posible that the process that you want to use is in a zombie state. You can see that there is a zombie process with top for example. But with top you can't not alway see which process it is.
If we use the following command we can see which process are zombies.
ps -el | grep 'Z'
With a normal ps -el or ps-aux command you see an output with in the second colum the state of the process. Here are some states:
S : sleeping
R : running
D : waiting (over het algemeen voor IO)
T : gestopt (suspended) of getrasseerd
Z : zombie (defunct)
The output under this text is an example. We can see that dovecot-auth is the zombie.
[root@s324 /]# ps -el | grep 'Z'
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
1 Z 0 1213 589 0 75 0 - 0 funct> ? 00:00:00 dovecot-auth