Grub: Difference between revisions
(Booting Windows partition) |
|||
| Line 36: | Line 36: | ||
== Restore / Troubleshoot == |
== Restore / Troubleshoot == |
||
=== Grub === |
|||
To repair a broken / lost GRUB, do from any grub prompt (live CD...) [http://forums.fedoraforum.org/showthread.php?p=1255524]: |
To repair a broken / lost GRUB, do from any grub prompt (live CD...) [http://forums.fedoraforum.org/showthread.php?p=1255524]: |
||
grub> '''find /boot/grub/stage1''' |
grub> '''find /boot/grub/stage1''' |
||
| Line 55: | Line 56: | ||
* In my example I set root to (hd0,4) make sure you set it to whatever the find command returns |
* In my example I set root to (hd0,4) make sure you set it to whatever the find command returns |
||
* Always run 'setup (hd0)' to install grub on the MBR of the first drive. For second drive use (hd1) etc |
* Always run 'setup (hd0)' to install grub on the MBR of the first drive. For second drive use (hd1) etc |
||
=== Grub 2 === |
|||
Here the procedure in the case of '''grub 2'''. Let's assume the boot partition is on '''dev/sda6''' (use <tt>sfdisk</tt> to know) (see [http://www.ohbuntu.blogspot.com/2009/11/repair-grub2-after-install-windows-7.html]). |
|||
<source lang="bash"> |
|||
sudo mount /dev/sd6 /mnt/myroot |
|||
sudo grub-install --root-directory=/media/myroot /dev/sda |
|||
#reboot |
|||
sudo update-grub2 # Optional - in case entry are missing from the grub2 menu |
|||
</source> |
|||
Another solution involve '''chroot'''ing to the mounted media ([http://tolearnfree.blogspot.com/2009/12/how-to-fix-grub2-on-ubuntu-910.html]). <font color="red">But this method does not work if the current linux architecture (32-bit/64-bit) does not match the architecture of the target (because chroot will re-run the current shell from target and the architecture must match)</font>: |
|||
<source lang="bash"> |
|||
sudo mount /dev/sd6 /mnt/myroot |
|||
sudo mount --bind /dev/ /media/myroot/dev |
|||
sudo chroot /media/myroot |
|||
sudo grub-install /dev/sda |
|||
sudo grub-install --recheck /dev/sda |
|||
sudo exit |
|||
</source> |
|||
Revision as of 19:03, 26 March 2010
Documentation
- Official manual here.
Boot from CDROM / Windows
When booting on HDD, it is possible to tell Grub to boot from CDROM instead. The same command-set can be used to boot the Windows partition (in case it has been removed from Grub menu)
- Press esc to quit Grub GUI menu.
- Press c to go to command-line mode.
- Enter the following commands (assuming CDROM is on hd2 / Windows is on hd0). Note that Grub uses hd0,hd1... not /dev/sda...):
grub>rootnoverify (hd2) #or (hd0,0) for Windows partition grub>chainloader +1 grub>boot
Note that this might be actually a hack that only works on my machine. More information:
- GRUB Manual - Boot
- http://www.mail-archive.com/bug-grub@gnu.org/msg10280.html
- http://gentoo-wiki.com/TIP_Chainloading_a_bootable_CD-ROM_from_GRUB
Grubonce
grubonce is an handy tool to force the system to immediately boot a given grub entry at the next reboot.
By default, grubonce can only be run by root, but we can use sudo to allow any user to use grubonce. Make the following change to the /etc/sudoers file (use command visudo to edit this file):
Defaults env_keep = "DISPLAY ..." # add DISPLAY env var to the list of kept var ALL ALL = (ALL) NOPASSWD: /usr/sbin/grubonce
Now, you can reboot immediately a grub entry with:
$ sudo grubonce
# 0: openSUSE 11.0 - 2.6.25.20-0.1
# 1: Failsafe -- openSUSE 11.0 - 2.6.25.20-0.1
# 2: windows
# 3: Floppy
$ sudo grubonce 2
Restore / Troubleshoot
Grub
To repair a broken / lost GRUB, do from any grub prompt (live CD...) [1]:
grub> find /boot/grub/stage1 find /boot/grub/stage1 (hd0,4) grub> root (hd0,4) root (hd0,4) Filesystem type is ext2fs, partition type 0x83 grub> setup (hd0) setup (hd0) Checking if "/boot/grub/stage1" exists... yes Checking if "/boot/grub/stage2" exists... yes Checking if "/boot/grub/e2fs_stage1_5" exists... yes Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 23 sectors are embedded. succeeded Running "install /boot/grub/stage1 (hd0) (hd0)1+23 p (hd0,4)/boot/grub/stage2 /boot/grub/grub.conf"... succeeded
- try find /grub/stage1 if the first find command doesn't work
- In my example I set root to (hd0,4) make sure you set it to whatever the find command returns
- Always run 'setup (hd0)' to install grub on the MBR of the first drive. For second drive use (hd1) etc
Grub 2
Here the procedure in the case of grub 2. Let's assume the boot partition is on dev/sda6 (use sfdisk to know) (see [2]).
sudo mount /dev/sd6 /mnt/myroot
sudo grub-install --root-directory=/media/myroot /dev/sda
#reboot
sudo update-grub2 # Optional - in case entry are missing from the grub2 menu
Another solution involve chrooting to the mounted media ([3]). But this method does not work if the current linux architecture (32-bit/64-bit) does not match the architecture of the target (because chroot will re-run the current shell from target and the architecture must match):
sudo mount /dev/sd6 /mnt/myroot
sudo mount --bind /dev/ /media/myroot/dev
sudo chroot /media/myroot
sudo grub-install /dev/sda
sudo grub-install --recheck /dev/sda
sudo exit