Here are some rough notes describing how to update the BIOS on a Lenovo T420s laptop.

Lenovo offers a BIOS update utility that runs under Windows or as a bootable CD. Both of these options did not work for me as I was running Linux and had no blank media for burning a CD.

Instead I plugged in a spare flash drive and did the following:

  • Download the latest ‘BIOS Update Bootable CD’ from Lenovo.

  • You can’t directly copy this ISO to a flash drive since the ISO is formatted as a bootable CD. Instead, extract the boot image using a Perl script called geteltorito.pl.

    wget -O geteltorito.pl http://goo.gl/4OCagK
    

  • Run geteltorito.pl with the ISO image as first parameter and redirect output to a file.

    perl geteltorito.pl xxxxxxxx.iso > bios.img
    

  • Use dd to copy the newly created file to a flash drive (where sdX is actual flash drive letter).

    sudo dd if=bios.img of=/dev/sdX bs=512K
    

  • Reboot. Boot from flash drive and update BIOS.

Make sure you download the correct BIOS version. I initially downloaded the BIOS for the T420 instead of the T420s.