How to setup grub manually

• What to do when you have a grub error, you can simply reinstall grub.
• In this tutorial I will explain how to achieve this.
• You will learn how to setup a grub disk and install grub

Before we start: How Grub Calls Stuff

This is the only odd thing in grub: It doesn’t call the disks as we are used to. But don’t worry, is not as weird as with devfs (/dev/boo/lun/foo/bar/../../disk/stuff/…/…/and/so/on).
It’s only a bit different:

• Grub uses brackets to declare a device
• The /dev/ part is not used
• device numbers and partitions are defined with numbers starting from 0

This example will show you how it works (It’s easier to understand as it is to explain):

Linux standard GRUB
———————————–
/dev/hda1 (hd0,0)
/dev/hda2 (hd0,1)
/dev/hdd1 (hd3,0)

Even Easier : a=0 b=1 c=2 d=3 and the partition is N-1

NEXT STEP

• Put your USB disk into working linux computer (don’t mount it). On my computer it is typically recognized as /dev/sda. If your USB stick is recognized differently (and/or your hard disk is /dev/sda) then you must replace all the instances below of /dev/sda with whatever your actual USB stick is being recognized. This is, well, kinda important.
• Create a single partition. I typically do this with:

Feel free to create a FAT32 partition if you want to use this stick on different machines with different operating systems (including Windows).

Note – make not of “–root-directory=/mnt” <- (this should match the directory you mounted your usb stick)

Also if you get an error that says you need to use blocklists, you can add –force to the above Install grub line.

That should of create a /mnt/boot/grub directory.

• Now comes the hard part. You need a grub configuration that will make sense for the server you are booting.

If you are using grub1…

Hopefully you have a copy of the menu.lst file from the server. In that case, simply copy it to /mnt/boot/grub/ and you are ready to go. Otherwise, you’ll need to craft one. Below is a sample.

If you are using grub2…

Then edit. You might want something like:

serial –unit=0 –speed=115200 –word=8 –parity=no –stop=1 terminalinput serial terminaloutput serial insmod raid insmod mdraid insmod part_gpt set default=0 set timeout=5

menuentry “Debian GNU/Linux, with Linux 2.6.32-trunk-vserver-amd64” –class debian –class gnu-linux –class gnu –class os { set root='(hd0,1)’ search –no-floppy –fs-uuid –set 7682a24c-b06f-456b-b3d4-bcb7294d81e2 echo Loading Linux 2.6.32-trunk-vserver-amd64 … linux /vmlinuz-2.6.32-trunk-vserver-amd64 root=/dev/mapper/vg_chicken0-root ro quiet echo Loading initial ramdisk … initrd /initrd.img-2.6.32-trunk-vserver-amd64 }

• Put the USB stick into the target computer, configure it to boot from the USB stick via bios, and then you should see the GRUB menu come up.
• It’s possible that your computer will just boot with your menu.lst file. In that case – congrats! See the last step below to figure out how to ensure it can boot without your USB stick. On the other hand, if it fails, you’ll need to experimentally figure out which disk has which partitions and which kernels. Fortunately grub supports tab completion which makes this job easier:
  • When the grub menu comes up, pick from the menu list the most likely candidate and press ‘e’ for edit.
  • You should see the various lines from the stanzas for the list item you picked (i.e. a root, kernel, and initrd stanza). You may use the up/down arrows to select a line. If that doesn’t work, look for hints on the screen for how to get around. Going left and right on a given line may require Ctl-b and Ctl-f for back and forward. You also may need to use the delete key (not backspace) to delete characters
  • Select a line, delete the characters from the end of the line, and then try tab completion with various options. For example, on the root line try typing simply:

root (

• And then tab. You should be presented with the available disks (numbered 0 and up). Try typing one of the disks and hitting tab and you should be presented with the available partitions. Continue this process until you find the one that seems right.
• When you are done and you have successfully booted, you can ensure that boots will work without the usb key by installing grub on all available disks:

grub-install /dev/sdb

If you have questions email nick@nicktailor.com