computer temperature

If you are using Ubuntu (and not Kubuntu, Edubuntu, etc.), you can install (using the Synaptic Package Manager in the system menu named "System" -> "Administration") the package named computertemp (full name is Computer Temperature Monitor), you can install also the suggested package named hddtemp for the hard disk temperature (during the installation process check the box so that hddtemp is launch upon boot and just select "Forward" for the other screens).

Then right click on the top panel for example (where you have the system menus, time and date, etc.) and select "Add to panel" in the popup menu that appears. Choose the applet named Computer Temperature Monitor, you can add one per CPU, one per hard disk, per GPU, etc. It all depends what Linux will have detected for sensors. You can change which temperature is monitored in the applet preferences.