hanno@lava.de
http://www.lava.de/~hanno/
``Ages 6 and up. Batteries included.''
This document does not describe how to install Linux on laptops, but how to optimize a ready-configured Linux for use on laptops. Please read the Installation-HOWTO or your distributor's handbook for help with installing Linux.
This document does not describe how to use an uninterruptable
power supply and the powerd daemon, either (even though
a ups is a big battery). Read the UPS-HOWTO for details
about that subject.
More and more people own portable computers these days and in turn, more and more people install Linux on such machines.
Installing and using Linux on a laptop is usually no problem at all, so go ahead and give it a try. Unlike some other operating systems, Linux still supports and runs well on even very old hardware, so you might give your outdated portable a new purpose in life by installing Linux on it.
If you need help with installing Linux on a laptop or if you
have questions about laptop hardware, you can check the
excellent Linux Laptop webpage at
http://www.cs.utexas.edu/users/kharker/linux-laptop/
where you will find a lot of useful information and detailed
help. The Linux Laptop page describes hardware configuration
for specific laptop models and chipsets.
This HOWTO however will focus on the one problem that is common to all portable systems: Power consumption.
Yet, I have not found a Linux distribution that comes with a configuration optimized for laptops. Since I could not find this kind of information anywhere else, I have started to collect a few simple but effective tricks that will help you save battery power and in turn increase your system's uptime while running on battery.
(Sidenote. I received a complaint by a reader that these tips were not very effective with his laptop. So does all this really work? Yes, but don't expect miracles. I was able to increase my laptop's battery time from 90 minutes to more than 120 minutes.)
If you are a laptop pro, you can probably skip the General Information section. If you are a Linux pro, what you really want to know can be found in the Changing some general system settings section. If you are a Linux distributor, please read A message to Linux distributors.
Your feedback is welcome. Please send comments to
hanno@lava.de. Did
it work on your system? Do you have new tips? Are there any outdated links
or addresses in this text?
I am sorry, but I will not be able to help you
with questions about specific laptop models. I don't claim
to be a laptop guru, I just happen to own one laptop myself
and I simply want to share the information I collected. Please
check the Linux Laptop webpage first, probably someone else has
already written a page dedicated to your model. Ask your
manufacturer's technical support. Or go the the laptop newsgroup
comp.sys.laptops
and ask there.
All methods described here were tested by me and worked fine on my laptop, unless noted otherwise. However, I cannot guarantee that any of this won't crash or seriously damage your system. Life is dangerous, so keep backup copies of your important files before playing with your Linux configuration. If things go wrong, I do not take any responsibility for your data loss. In other words: Don't sue me. Thank you.
This document shall be distributed under the standard
HOWTO-copyright notice, found in the HOWTO folder at
http://sunsite.unc.edu/mdw/linux.html.
This section describes a few technical things about laptop batteries and some general power saving tips. This information is not Linux-specific and if you are experienced with laptops, you might already know all this.
(Please note the credits for this section.)
There are currently three types of batteries commonly used for portable computers.
The memory effect is caused by crystallization of the battery's substances and can permanently reduce your battery's lifetime, even make it useless. To avoid it, you should completely discharge the battery and then fully recharge it again at least once every few weeks.
(A sidenote about the memory effect. James Youngman knows of a rather drastic method to - uhm - ``repair'' batteries: ``If your NiCd battery is suffering from the memory effect, remove it from your computer, hold it about 30cm above a desk or the floor, and drop it (make sure it lands flat).'' He says that this will break the whiskers that have formed in the battery and that are the cause of the memory effect if your battery is already affected by it. ``I don't know if this works for non-NiCd batteries or not.'')
Cadmium is a very hazardous poison, but if returned to your dealer, the material can almost be fully recycled.
Just in case you might be interested, here are some specs for NiCd:
Cell voltage: 1,2 V
Energy / mass: 40 Wh/kg
Energy / volume: 100 Wh/l
max. Energy: 20 Wh
Charge temp.: 10 to 35 C (50 to 95 F)
Discharge temp.: -20 to 50 C (-5 to 120 F)
Storage temp.: 0 to 45 C (30 to 115 F)
However, they have problems at very high or low room temperatures. And even though they use less hazardous and non-poisonous substances, they cannot be fully recycled yet (but this will probably change in the future).
NiMh specs:
Cell voltage: 1,2 V
Energy / mass: 55 Wh/kg
Energy / volume: 160 Wh/l
max. Energy: 35 Wh
Charge temp.: 10 to 35 C (50 to 95 F)
Discharge temp.: 0 to 45 C (30 to 115 F)
Storage temp.: 0 to 30 C (30 to 85 F)
LiIon specs:
Cell voltage: 3,6 V
Energy / mass: 100 Wh/kg
Energy / volume: 230 Wh/l
max. Energy: 60 Wh
Charge temp.: 0 to 45 C (30 to 115 F)
Discharge temp.: -20 to 60 C (-5 to 140 F)
Storage temp.: -20 to 60 C (-5 to 140 F)
Even if the battery case looks the same, you cannot just upgrade to another battery technology. The recharging process is different for the kind of battery you use.
Some manufacturers integrate the recharging circuit inside the laptop's external ac adapter, so you might just get away with buying a new power supply to upgrade. A good indication for an external recharging unit is when your ac adapter uses a proprietary connector with a lot of power lines.
Other manufacturers put the recharging unit inside the laptop case where users cannot simply replace it with a newer technology. If your ac adapter only uses two power lines to connect to the computer (just like mine), the recharging unit is probably inside the laptop.
When in doubt, ask your manufacturer if your laptop supports a more modern battery.
A battery that is not used for a long time will slowly discharge itself. And even with greatest care, a battery needs to be replaced after 500 to 1000 recharges. But still it is not recommended to run a laptop without the battery while on ac power - the battery often serves as a big capacitor to protect against voltage peaks from your ac outlet.
As the manufacturers change the shapes of their batteries every few months, you might have problems to find a new battery for your laptop in a few years from now. Buy a spare battery now - before it's out of stock.
There are some obvious things that you can do to reduce your system's power consumption. Well, maybe not so obvious, since not very many people follow these rules...
(David Bateman tells me that using a crt screen while on battery and turning off the laptop display will extend battery time by about 30%: ``Not that this is a very useful piece of knowledge though, if you've got the crt plugged in then why not the laptop too.'')
(By the way, I recently read that pcmcia cards are the biggest problem for windows ce palmtops - they drain so much power that the tiny machines' little batteries have to be replaced within minutes...)
If you already have 2nd level cache installed, turning it off will probably not help you very much. Give it a try and write me about your experience.
There are also frankenstein laptops available that use cpus not optimized for portable systems. As I wrote this in May 97, the newest generation pentium-200 laptops ran about 20 minutes on battery and became so hot that they burnt your lap. When writing the second revision in Oct 97, pentium-233 laptops run two hours or longer without ac power. Go figure.
Well, you get the idea. Most of these are restrictions that will probably stop you from doing any serious work with your Linux system. (The best way to save power while on battery is... not to do anything at all. That increases my laptop's battery uptime by almost 100 percent.)
So let's go ahead to some other, more useful measures that will save power without disturbing your work.
Portable systems in general, but even many desktop computers come equipped with support for apm, the ``advanced power management'' scheme. This section describes how to activate apm support in your Linux kernel. People who are experienced with Linux may find this section rather boring and want to skip to the next.
I won't describe it in detail here, check the
Linux APM drivers page at
http://www.cs.utexas.edu/users/kharker/linux-laptop/apm.html
for more
information. All that you need to know is that with the
help of apm, the cpu can tell the bios when there's nothing
really exciting going on so that the bios can take care of
some power saving by itself - e. g. reducing the cpu clock, turning
off the harddisk, turning off the display's backlight etc.
Apm is also responsible for the ``system suspend''
(or ``sleep'') mode and for the ``suspend to disk''
(or ``hiberntation'') mode. And yet
another cool, though not very important feature is
that with the help of apm, shutdown -h will not just
halt your system, but also turn it off.
(By the way, most Linux systems put a shutdown -r in
their /etc/inittab and map it to pressing
control-alt-delete. I prefer having shutdown -h
there, so when pressing the famous key combination, my laptop
simply turns itself off.)
Not all manufacturers implement a correct apm bios, so some laptops have trouble with the Linux apm drivers (if your machine has trouble with apm, it will most likely either lock up at Linux' boot up or after returning from suspend). If you are not sure, check the Linux laptop page for your specific model.
It's easy - just recompile the Linux kernel. Check the Kernel-HOWTO if you don't know how to do that.
When the configuration script reaches the ``character devices'' section, the default setting for full apm bios support in kernel version 2.0.30 or higher is:
Advanced Power Management BIOS support: Yes
Ignore USER SUSPEND: No
Enable PM at boot time: Yes
Make CPU Idle calls when idle: Yes
Enable console blanking using APM: Yes
Power off on shutdown: Yes
Please read the configuration script's help texts. They explain in detail what each option does, so I won't repeat them here.
If your system does not fully support the apm bios standard, some of those options might crash your system. Test all apm features with the new kernel to make sure that everything works as it should.
(A
sidenote
about console blanking: David Bateman tells me that
you should not enable it because it can cause problems with the
current version of XFree 3.2: ``The symptoms are that the screen
will be blank when X starts, and it can be fixed usually by just
hitting a key. It's a small but annoying problem. The next relase
of XFree, will have pretty good DPMS support for a lot of laptop
chipset, which should include code to turn off the LCD. Check out
the manpage for xset in XFree 3.2A.'' David also notes that
the lifetime of your display's backlight is determined by the number
of times it's switched on and off: ``So its a compromise, lifetime
of the battery versus lifetime of the backlight.'')
(Update: With XFree 3.3, this problem still remained on my laptop. I am told that this will be fixed in a future kernel version.)
After recompiling the kernel, don't forget to recompile the linux pcmcia drivers as well.
The precompiled pcmcia drivers that come with most linux distribution have apm support disabled, so that the bios can't instruct your card adapters to turn off.
Also, you must recompile the drivers if you upgrade to a new kernel version and your old kernel was compiled with module version information turned on (this option is found in the ``loadable module support'' section of the kernel configuration).
Read the PCMCIA-HOWTO for detailed
instructions on how to compile the drivers or go to the
Linux PCMCIA drivers homepage at
http://hyper.stanford.edu/HyperNews/get/pcmcia/home.html.
Now that you have APM support installed, go and get the apmd package
from the Linux APM drivers page. You don't really need it, but
it is a very useful collection of programs. The apmd daemon logs your
battery's behaviour and it will send out a warning if you are on
low power. The apm command will suspend your system with a
shell command and xapm shows the current state of your battery.
(BTW, if you have problems with pcmcia cards after returning from
suspend, you
can check out an alternative apmd package at
http://www.cut.de/bkr/linux/apmd/apmd.html. It unloads the
pcmcia driver module before going to suspend and reloads the module
on resume.)
Grant Taylor has been playing a little with the apmd
package and came up with helpful tips.
He found that his laptop's harddisk forgets its hdparm -S
standby period when returning from suspend: ``I modified apmd to
reset this setting on each resume. This may be system-specific;
but it's an important thing to do...''
(Note: On my own laptop, the bios takes care of the harddisk standby period and resets the value on resuming. So I could not test if this little problem is system-specific. If it happens to you as well, send me a message.)
Grant also had a nice trick for screen blanking with
the XFree86 package and
the help of the apmd package, you'll find it there.
If your computer's bios does not offer any power saving
settings (even the old ones without apm should at least allow
to set harddisk and display standby), you can
use hdparm -S to define your harddisk's standby period. This
will already help a lot, since harddisk activity
consumes a lot of power. Your system should have hdparm
installed, so read man hdparm for the command syntax.
After I got Linux up and running on my laptop, I found it accessing the harddisk every few seconds, even when there was no user logged in to the system. The harddisk could never enter its power saving mode. Reducing harddisk activity can greatly increase the battery runtime, so this is why I collected the following recipes.
I tested all this with RedHat 4.1, the locations of some configuration settings may be different for your distribution. (If so, please let me know.)
Check your /etc/crontab file if it starts a process
every minute. You will often find atrun there.
With the at command, you can spool commands that must be
invoked some time in the future. Some Linux systems use a
dedicated atd daemon to take care of this, others
(e. g. RedHat) let the crond daemon run atrun once every
minute.
This is not really necessairy on most systems, since at
commands rarely depend upon being invoked on exact time. So
if you find a line like this in your /etc/crontab:
# Run any at jobs every minute
* * * * * root [ -x /usr/sbin/atrun ] && /usr/sbin/atrun
Then you can safely change this to:
# Run any at jobs every hour
00 * * * * root [ -x /usr/sbin/atrun ] && /usr/sbin/atrun
Read man 5 crontab for details. Some folks can even
work fine without the crond daemon, so if you know
what you are doing, you might want
to consider disabling it completely.
Linux deals with a lot of open file buffers at any given moment, so the system must make sure that file changes are saved to the harddisk as soon possible. Otherwise, those changes will be lost after a system crash.
The update / bdflush daemon takes care of this. (These
are two names for the same program, so you can use either
name to start the daemon). The default settings will make
this daemon call flush every 5 seconds and sync every
30 seconds.
With my Fujitsu disk this caused non-stop access. (It seems that this harddisk flushes its ram cache even when nothing has changed. But this depends on your harddisk's firmware: Other people told me that their harddisk does enter its power saving mode even without the following modification.)
Since Linux does not crash very often anymore, I have changed both values to 3600 seconds (= one hour). This caused no problems at all and the constant disk access has stopped. (But if my system crashes now, there will be more broken files, of course.)
RedHat 4.1: In /etc/inittab, change the update call to:
ud::once:/sbin/update -s 3600 -f 3600
Suse 4.4.1: update is called in /sbin/init.d/boot.
Slackware: update is called in /etc/rc.d/rc.S.
See man update for details.
The syslogd daemon is responsible for the various Linux
system log files that are found in the
/var/log/ directory. By default syslogd will
sync the log file each time after logging a system message.
You can turn that off by preceding the filename with a dash
in /etc/syslog.conf. Here's an example as found in
my system's syslog.conf:
# Log anything (except mail) of level info or higher.
# Don't log private authentication messages!
*.info;mail.none;authpriv.none -/var/log/messages
This again means that if the system crashes, the message that reported the problem may not have been stored to disk. Dilemma...
During the bootup, the initial processes and daemons will be
started using the init command. This command (yet again)
calls sync before each process it creates.
You can change this by removing the sync() call in the
source code and recompiling the command.
To avoid problems with lost file buffers, you should add a
call to sync in your system's
/etc/rc.d/init.d/halt script, right before the script
unmounts the file systems.
The Linux swap partition is used to increase the physical ram space
with virtual memory. This again is a possible reason for harddisk
access. If your laptop already has a lot of ram or if
the applications that you use are quite simple
(think of vi), you might want to consider turning it off.
This of course depends on what you plan to do. 4 to 8 megs are not enough, you must use a swap partition then. With 8 to 16 megs, text console applications will work fine and if you can avoid using a lot of multitasking features, you can safely disable swap. The X-Windows enviroment requires a lot of ram and you should not use it without a swap partition unless you really have a lot more than 16 megs.
(Sidenote: My laptop with 16 megs and disabled swap partition can run
an emacs session, four bash shells and compile a
kernel without running out of memory. That's enough for me.)
If you already have installed a swap partition, you can disable
it by preceding the swapon
command that is called in /etc/rc.d/rc.sysinit with
a hash mark. If you don't want to make it a permanent move, let
the system ask during boot if you want to use the swap
partition. In /etc/rc.d/rc.sysinit (RedHat 4.1) or
/sbin/init.d/boot (Suse 4.4.1):
echo "Should the system use swap?"
echo " 0: No."
echo " 1: Yes."
/bin/echo "Your choice: \c"
read SWAPCHOICE
case "$SWAPCHOICE" in
0)
# Do nothing.
echo "(Swap partitions disabled)"
;;
*)
# Start up swapping.
echo "Activating swap partitions"
swapon -a
esac
Then you can use the swap partition while on ac power and drop it while on battery.
I am using my laptop to develop and test cgi scipts for websites, that is why I am running a local webserver on it. The standard configuration is a bit too much if all you want to do is just test a script or check a page from time to time.
In httpd.conf, just change the values of
MinSpareServers and StartServers to 1. This
will be enough for a local test site.
If you wish to turn off the webserver's logging, you must
recompile the httpd daemon. Read the documentation for
details.
Grant Taylor recompiled apache's logging and found
that this ``didn't make it stop churning the disk. So I used
another, IMHO better, solution: I configured apache to run
from inetd instead of standalone.'' Read man inetd for
details.
Configuring XFree86 for laptops is a story of its own. And yet again, I have to refer you to the Linux Laptop page where you will find a lot of help on this.
X's console blanking only turns the screen black, but does
not turn it off. As mentioned in the
sidenote about console blanking,
you can use xset's dpms option to change this.
However, this feature depends on your laptop's
graphics chipset and bios.
Grant Taylor uses the following setup to send his laptop to
sleep with the help of apmd and the screensaver:
# Run xscreensaver with APM program
xscreensaver -timeout 5 \
-xrm xscreensaver.programs:apm_standby \
-xrm xscreensaver.colorPrograms:apm_standby &
Where ``apm_standby is a suid perl script that allows only
certain people to run apm -S.''
Ok, emacs is not an editor, but a way of life. Here's
a tip from Florent Chabaud: ``If you use emacs, perhaps
you have noticed that the editor makes some automatic saves.
This is of course useful and should not be disabled, but
the default parameters can be adjusted to a laptop use.
I have put in the file
/usr/share/emacs/site-lisp/site-start.el
the two following lines:
(setq auto-save-interval 2500)
(setq auto-save-timeout nil)
This disables auto-saving based on time, and makes the auto-saving be done every 2500 keyboard actions. Of course if you are typing a text this last parameter should be reduced, but for programming it is sufficient. Since every action (up, down, left, backspace, paste, etc...) is counted, 2500 actions are reached very rapidly.''
If your Linux system still seems to access the harddisk too
often, you can find out what is going on inside by using
the ps ax command. This will show all running processes
and their full name, sometimes it also reveals the command
line arguments of each process.
Now read the man page of each process to find out what
it does and how to change its behaviour. With this
method, you will most likely find the process that is
responsible. You may also find strace helpful.
Please send me an email if you found something new.
If you happen to be a Linux distributor, thank you for reading all this. Laptops are becoming more and more popular, but still most Linux distributions are not very well prepared for portable computing. Please make this document obsolete and change this for your distribution.
apmd package with your
distribution.
Please mail me if your distribution is optimized for portable computing and what kind of features you added for that. Future versions of this HOWTO will include a section where you can advertise your distribution's laptop features.
http://www.heise.de/.
Frithjof Anders <anders@goethe.ucdavis.edu>
David Bateman <dbateman@ee.uts.edu.au>
Florent Chabaud <chabaud@celar.fr>
Markus Gutschke <gutschk@uni-muenster.de>
Kenneth E. Harker <kharker@cs.utexas.edu>
Bjoern Kriews <bkr@rrz.uni-hamburg.de>
R. Manmatha <manmatha@bendigo.cs.umass.edu>
Juergen Rink <jr@ct.heise.de>
Grant Taylor <gtaylor@picante.com>
James Youngman <JYoungman@vggas.com>
This text mentions batteries 53 times.
The current version of this and many other HOWTOs,
most of them a lot more useful than this one,
can be found at the main Linux documentation site
http://sunsite.unc.edu/mdw/linux.html or at
one of its many mirror sites.
Most of this text was written during my trips between Hamburg and Hannover on German rail. (The new ice-2 coaches have power outlets for laptops, yeah!).
And now hum along with me: ``...on the road again...''