When I issue
ps aux | grep mtp
ubuntu-+ 15934 0.1 0.0 519848 7068 ? Sl 21:13 0:00 /usr/lib/gvfs/gvfsd-mtp --spawner :1.9 /org/gtk/gvfs/exec_spaw/20
So the PID in this case is 15934. But every new time this is run the PID is different. Is there any other way to kill a process other than by PID?