Resource Monitoring Tools
There are programs available to watch various aspects of your system.
See active internet connections. e.g.
# iftop -i eth1
See RAM usage. Can be watched, to monitor swapping. e.g.
$ vmstat 3
Leave it running. It will update every 3 seconds.
See HDD accesses. e.g.
# iotop --only
only flag will show active processes only