Grub – Emergency Boot

If Grub fails to boot your operating system, you can take steps to find and boot your system then reinstall grub to fix the problem. The following example shows you how to use commands in the emergency grub command line to find your operating system and boot it. Lines that start with the comment character ‘//’ is a description of what the command is doing.

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Problems booting Linux on HP G7 laptops

Update: this may no longer be necessary with newer kernels.

There is a major problem running Linux on HP laptops; during the boot process, the screen will go black and never display anything. This issue is due to the LCD backlighting.

You can fix the issue by appending the text

acpi_osi=Linux acpi_backlight=vendor

to the linux boot line. You can do this manually in the Grub menu by editing the commands before booting; you highlight the boot entry and press either the “e” key or the “tab” key, depending on the version of Grub you are running.

Reinstalling Grub

When Microsoft Windows is reinstalled on a multiboot computer, it will overwrite the MBR wiping out the existing Grub install. To reinstall Grub do the following:

1. Boot to the most recent ArchLinux install CD and select the correct architecture (on dual ISOs).
2. Mount your existing ArchLinux install on /mnt: mount /dev/sda# /mnt
3. If necessary, mount your boot partition: mount /dev/sda# /mnt/boot
4. Reinstall grub: grub-install –root-directory=/mnt /dev/sda

Older instructions

To install the grub bootloader from a LiveCD:

• Mount the root filesystem
  • mkdir /mnt/root
  • mount -t ext2 /dev/?da? /mnt/root
• Populate the dev and proc filesystems
  • mount -o bind /dev /mnt/root/dev
  • mount -t proc none /mnt/root/proc
• Change to the mounted root filesystem
  • chroot /mnt/root
• Install grub in MBR
  • grub
  • find /boot/grub/stage1
  • root (hd0,0) # Use the info from the above find command
  • setup (hd0) # Use the info from the above find command
  • quit
• Reboot!