How to use lmsensors to show CPU temperature and voltages

Install the user space packages:

aptitude install lm-sensors hddtemp

Configure sensors:

sensors-detect

Then reboot, or load kernel modules manually this time:

modprobe modulename

To show CPU and motherboard temperature sensor output:

sensors

To show hard disk temperatures:

hddtemp /dev/sda

If your interested in monitoring the health of your disks you might also like to look at smartd.