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Another useful view is the 
tree view
, which allows you to see a list of processes 
organized by their parent/child relationship, rather than just a flat list. In practice, 
it's common for a process to be spawned by another process. In fact, all processes 
in Linux are spawned from at least one other process, and this view shows that 
relationship directly. In a situation where you are stopping a process only to have it 
immediately re-spawn, you would need to know what the parent of that process is 
in order to stop it from resurrecting itself. Pressing 
F5
 will switch 
htop
 to tree view 
mode, and pressing it again will disable the tree view.
With the tree view activated, 
htop
 will appear similar to the following:
Figure 8.9: htop with tree view activated
As I've mentioned, 
htop
 updates its stats every 2 seconds by default. Personally, I 
find this to be ideal, but if you want to change how fast it refreshes, you can call 
htop
 
with the 
-d
 option and then apply a different number of seconds (entered in tenths 
of seconds) for it to refresh. For example, to run 
htop
 but have it update every 7 
seconds, start 
htop
 with the following command:
htop -d 70 
To kill a process with 
htop
, use your up and down arrow keys to highlight the 
process you wish to kill and press 
F9
. A new menu will appear, giving you a list 
of signals you are able to send to the process with 
htop
. 
SIGTERM
, as we discussed 
before, will attempt to gracefully terminate the process. 
SIGKILL
 will terminate 
it uncleanly. Once you highlight the signal you wish to send, you can send it by 
pressing 
Enter
 or cancel the process with 
Esc
.

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Monitoring System Resources