Can a "normal" user see all processes with htop?

Solution 1:

Yes, you can see all processes with htop as the default user.

Note that if you for example use virtualization to run multiple systems on one, htop will only show you the virtualization program as a process - not the processes running within that virtual machine.

Whether or not it makes sense to use sudo htop depends on the context. If you run htop as an ordinary user, you do not get the full information on all processes - i.e. processes started by other user's will be listed, but with incomplete numbers. If you need the full set of data about processes started by other users, sudo htop definitely makes sense.

On the other hand, as soon as you start htop with sudo you need to aware that you have full privileges - for example it is possible to kill system processes and programs started by other users. If this not your intention, starting htop without sudo removes the risk of doing that by mistake.