How to find processor c states without installing additional tools

Processors draw power, but are also “smart” enough to “save” when this power is not required.
To see the supported power states without installing additional tools you can type:

grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name

Here is sample output of an old CPU:

#grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name
/sys/devices/system/cpu/cpu0/cpuidle/state0/name:POLL
/sys/devices/system/cpu/cpu0/cpuidle/state1/name:C1
/sys/devices/system/cpu/cpu0/cpuidle/state2/name:C2