Here are some important Linux diagnostic tool:
1) Memtest86
http://www.memtest86.com/
2) S.M.A.R.T. Monitoring Tools
http://smartmontools.sourceforge.net/
3) Temperature Sensor:
http://lm-sensors.org/
[from http://www.html.it/articoli/linux-i-migliori-tool-per-la-diagnostica-3/]