More #FreeBSD Power Saving Notes

Its been a while since I needed to be mobile with FreeBSD again. I remembered that there’s several out of the box tuning things that you should do in /etc/rc.conf and a few modules you should load for your mobile workstation.


These will slow your laptop down when running of battery and should give you the needed juice to take notes and update your remote projects. I wouldn’t recommend them for a machine you need to do buildworlds upon. 🙂


This one is a module that I forgot about for some time. If you load it, you’ll get a couple of new tunables that can be used to turn down the backlight, which is useful even if all you want is to not disturb your better-half when you are reading at night.

sysctl 50 80

You can throw these into your /etc/sysctl.conf at whatever value you like. See the man page, man 4 acpi_video for more information.

% acpiconf -i0|less
Design capacity:        3900 mAh
Last full capacity:     3827 mAh
Technology:             secondary (rechargeable)
Design voltage:         11100 mV
Capacity (warn):        390 mAh
Capacity (low):         118 mAh
Low/warn granularity:   39 mAh
Warn/full granularity:  39 mAh
Model number:           DELL 9C26T33
Serial number:          48476
Type:                   LION
OEM info:               SMP
State:                  discharging
Remaining capacity:     52%
Remaining time:         3:07
Present rate:           640 mA (6935 mW)
Present voltage:        10837 mV

Not too shabby for power savings. Not sure if .6 Amp is really enough to make this solid. I think this gives me a solid 4 hours of note taking and walking around.