10 Using GRUB with vendor power-on keys

Some laptop vendors provide an additional power-on button which boots another OS. GRUB supports such buttons with the ‘GRUB_TIMEOUT_BUTTON’, ‘GRUB_TIMEOUT_STYLE_BUTTON’, ‘GRUB_DEFAULT_BUTTON’, and ‘GRUB_BUTTON_CMOS_ADDRESS’ variables in default/grub (see Simple configuration). ‘GRUB_TIMEOUT_BUTTON’, ‘GRUB_TIMEOUT_STYLE_BUTTON’, and ‘GRUB_DEFAULT_BUTTON’ are used instead of the corresponding variables without the ‘_BUTTON’ suffix when powered on using the special button. ‘GRUB_BUTTON_CMOS_ADDRESS’ is vendor-specific and partially model-specific. Values known to the GRUB team are:

Dell XPS M1330M

121:3

Dell XPS M1530

85:3

Dell Latitude E4300

85:3

Asus EeePC 1005PE

84:1 (unconfirmed)

LENOVO ThinkPad T410s (2912W1C)

101:3

To take full advantage of this function, install GRUB into the MBR (see Installing GRUB using grub-install).

If you have a laptop which has a similar feature and not in the above list could you figure your address and contribute? To discover the address do the following:

• boot normally

• sudo modprobe nvram
  sudo cat /dev/nvram | xxd > normal_button.txt
  

• boot using vendor button

• sudo modprobe nvram
  sudo cat /dev/nvram | xxd > normal_vendor.txt
  

Then compare these text files and find where a bit was toggled. E.g. in case of Dell XPS it was:

byte 0x47: 20 --> 28

It’s a bit number 3 as seen from following table:

0x47 is decimal 71. Linux nvram implementation cuts first 14 bytes of CMOS. So the real byte address in CMOS is 71+14=85 So complete address is 85:3