Psensor is a free and open source system temperature monitor application for Linux. Using Psensor you can monitor motherboard, CPU, NVidia and ATI/AMD GPU and Hard Disk Drives temperatures, fan speed and CPU usage details. It is a simple and easy to use tool. You can open it in anew windows or view all details from system topbar try app indicator. It is based on Psensor lm-sensors, XNVCtrl, ATI ADL SDK, hddtemp, libatasmart and udisks2.