Let the laptop battery appear as the one of an uninterruptible power supply, using NUT

by Stephan K.H. Seidl

Version 1, Mon, 09 Jun 2014 11:57:53 +0200


With the development of heavy middleware systems as the Distributed Computing Environment (DCE) with their appropriate desktops in the early 1990s, the UNIX-type operating systems got as user-friendly and, at the same time, as slow as the Windows-type operating systems are. Before DCE, there were essentially two efficient manners to work with UNIX, either with the Emacs editor alone or with the Vi editor under X11 to have the mouse for Cut/Copy and Paste. Running both Emacs and X11 at the same time did not perform on normal machines in the past, and running the Vi on the command line alone is awful. The latter of the ancient, but still highly efficient working manners, Vi plus X11, is up to now very interesting, especially if X11 goes together with Fvwm as the virtual window manager. The pair X11 plus Fvwm runs well on skimpy hardware as the EeePC 1000H, for example, and logging from such a system into an even slower one, as a router, via ssh, and running a Vi editor there does not really degrade the efficiency anymore.

The problem

Deselecting heavy desktops as KDE and Gnome in our days has, on the other hand, the disadvantage that basic software functionalities do not come automatically. One of those functionalities is proper laptop battery management. Proper battery management is of vital importance on laptops. So it has to be done by hand.

The solution

The systems in question here run Debian 6 and 7 with kernels 2.6.34 through 3.2.0. and nut 2.4.3 through 2.6.4. It is important that the directories /sys/class/power_supply/ACAD or /sys/class/power_supply/?*[0-9] are provided such that the files type and uevent there can be read by /usr/sbin/laptopbat2ups. The daemon /usr/sbin/laptopbat2ups updates /var/tmp/laptop-battery-status once per 17 seconds. The file /var/tmp/laptop-battery-status is the input for the dummy-ups driver of nut. nut is configured in such a manner that the operating system automatically shuts down if the remaining battery capacity is less than 20 % or if the remaining runtime on battery is less than 5 minutes. Here is the list of the files that have to be created or updated, respectively.

-rwxr-xr-x ... root root ... /etc/init.d/laptopbat2ups (click here for download)
-rw-r----- ... root nut  ... /etc/nut/nut.conf         (click here for download)
-rw-r----- ... root nut  ... /etc/nut/ups.conf         (click here for download)
-rw-r----- ... root nut  ... /etc/nut/upsd.conf        (click here for download)
-rw-r----- ... root nut  ... /etc/nut/upsd.users       (click here for download)
-rw-r----- ... root nut  ... /etc/nut/upsmon.conf      (click here for download)
-rw-r----- ... root nut  ... /etc/nut/upssched.conf    (click here for download)
-rwxr-xr-x ... root root ... /sbin/upsschedcmdscript   (click here for download)
-rwxr-xr-x ... root root ... /usr/sbin/laptopbat2ups   (click here for download)
-rwxr-xr-x ... root root ... /usr/sbin/upsstatus       (click here for download)

It should not be forgotten to create the symlinks if there is a file /etc/init.d/.legacy-bootordering or to do whatever is necessary for any other init system.

/usr/sbin/upsstatus is a supporting script that shows the situation when on battery. When on line, the given remaining battery time is not more than a rough guess. An output of /usr/sbin/upsstatus might look as follows.

1000H on battery
Discharging battery
Battery charge 98 %
Battery runtime 295 min
Shutdown command after 235 min due to remaining capacity of 20 %
Load 100 %
Real output power 9.7 W


For me, it works fine. Try it, if you want.

Mon, 09 Jun 2014 11:57:53 +0200
Stephan K.H. Seidl