What are the Linux commands to monitor what processes are running?
You can use:
ps - report a snapshot of the current processes.
pstree - display a tree of processes
top - display updated view of busiest processes
htop - interactive process viewer (uses ncurses)
gtop - Gnome top
See man pages for more info.
The /proc directiory has a subdirectory for each running process.
So search for numbered directories shows whats running:
ls /proc | egrep '[0-9]'
My favorite way of invoking ps:
ps -eo user,pid,%cpu,start,args --forest