E.7. Power Saving Techniques

• If you don't need infrared support, disable it in the BIOS or shutdown the IrDA ® device driver. There are also some IrDA ® features of the kernel which are useful for saving power.
  
• PCMCIA services consume much power, so shut them down if you don't need them.
  
• I'm not sure to which extend the backlight consumes power.
  
         
  
  As far as I know this device can only bear a limited number of uptime circles. So avoid using screensavers, which turn off the backlight.
  
  If you want do it anyhow, you may use xset +dpms and xset dpms 0 0 300 This turns the screen off after 5 minutes of inactivity. Works only if the display is DPMS capable.
  

• For some examples to build batteries with increased uptime up to 8 hours look at Repair4Laptop: Battery .
  
• For information about APM look at the chapter APM above.
  
• The "noatime" option when mouting filesystems tells the kernel to not update the access time information of the file. This information, although sometimes useful, is not used by most people. Therefore, you can safely disable it, then preventing disk access each time you cat a file. Here is an example of a /etc/fstab with this power-saving option: /dev/hda7 /var ext2 defaults,noatime 0 2
  
• hdparm hdparm is a Linux IDE disk utility that lets you set spin-down timeouts and other disk parameters. It works also for some SCSI features.
  
• Mobile Update Daemon This is a drop-in replacement for the standard update daemon, mobile-update minimizes disk spin ups and reduces disk uptime. It flushes buffers only when other disk activity is present. To ensure a consistent file system call sync manually. Otherwise files may be lost on power failure. mobile-update does not use APM. So it works also on older systems.
  

• noflushd : noflushd monitors disk activity and spins down disks that have been idle for more than <timeout> seconds. It requires a kernel >=2.2.11 . Useful in combination with hdparm and mount with noatime option to bring down disk activity.
  
  Here are some comments and thoughts by Nat Makarevitch about a possible approach which may reduce the disk activity under Linux (sparing energy, especially with noflushd) the file Documentation/filesystems/proc.txt of the Linux sourcetree documents some useful features, esp. in the /proc/sys/vm section. Under Linux 2.2 I used:
  
     
  

  echo "100 5000 8 256 500 60000 60000 1884 2" > /proc/sys/vm/bdflush
  

  
  especially under Linux 2.4 which uses its spare time to 'pre-save' the less-used memory pages into the swap, increasing the disk activity I tried to figure the more adequate parameters (Linux 2.4.9, 192 MB RAM, Toshiba 3480 laptop) beware: some of those parameters may be dangerous or useless (I have not gathered serious data about the practical efficiency). moreover do not forget that delaying disk writes of data is intrinsically dangerous
  
     
  

  echo 99 512 32 512 0 300000 60 0 0 > /proc/sys/vm/bdflush
  # is '60' the max value for age_super?
  echo 1 1 96 >