How do I restore Grub2 after Windows reinstall?

[kahlil88]

My friend recently re-installed WinXP on his laptop, but I'm having trouble getting Grub2 working. I followed a guide online, but when I booted it back up again, I got a Grub prompt instead of a boot menu.

[garvinrick4]

My friend recently re-installed WinXP on his laptop, but I'm having trouble getting Grub2 working. I followed a guide online, but when I booted it back up again, I got a Grub prompt instead of a boot menu.

Grub/XP/Vista Bootloader - Ubuntu Forums (http://ubuntuforums.org/showthread.php?t=1014708)

[kahlil88]

Yeah, that's what I tried, but I still get a prompt every time. :(

[garvinrick4]

Yeah, that's what I tried, but I still get a prompt every time. :(


http://www.dedoimedo.com/computers/grub-2.html#mozTocId905459

Do not give up on it.

[garvinrick4]

Using CLI to Boot

If the user has problems booting but the menu is available, the easiest method to boot the system is to edit the existing menu. Refer to Editing Menus During Boot (https://help.ubuntu.com/community/Grub2#Editing%20Menus%20During%20Boot). If GRUB 2 fails to find a usable grub.cfg file it should revert to the grub-rescue mode. The command line prompt will display grub-rescue> and no menu will be displayed. From this command line the user can attempt to manually enter the instructions to boot to a usable system.
If the command line prompt is not already active press "c" to enter the Command Line mode. You will see the GRUB 2 prompt: grub> or grub rescue>
https://help.ubuntu.com/community/Grub2?action=AttachFile&do=get&target=info.png If you wish to cancel and start over at any time, ESC will remove changes and return the user to the previous menu.
Use the following two commands to determine the device (drive) and partition of the system you wish to boot.


set

When set is typed without additional entries the command displays the current GRUB 2 settings.
ls

Run ls to see the devices recognized by GRUB 2. Example: (hd0) (hd0,1) (hd1,5) In this example sda, sda1, sdb5 are recognized.


Express Boot to the Most Recent Kernel



Command Summary *:
set root=(hdX,Y)


linux /boot/vmlinuz root=/dev/sdXY ro


initrd /boot/initrd


boot

Expanded Instructions *:

Press ENTER after completing each line. Some entries will not provide feedback. This is normal.
If a "file not found" or similar error message is displayed while running these commands, ensure you are using the correct X,Y values. The ls command can help determine the correct values. Once the X,Y values are confirmed run the following command:

set prefix=(hdX,Y)/boot/grub



1*. set root=(hdX,Y)
Type with correct X,Y results from the ls command and press ENTER. Remember GRUB 2 counts the first drive as 0, the first partition as 1. Example: If the Ubuntu system is on sda5, enter: set root=(hd0,5)
2*. linux /vmlinuz root=/dev/sdXY ro
Example: linux /vmlinuz root=/dev/sda3 ro


* Wubi users see note.
3. initrd /initrd.img
Selects the latest initrd image.
4. boot
Boot to the latest kernel on the selected partition.
* Wubi users only - substitute these commands in Steps 1 & 2:



set root=(loop0)
linux /vmlinuz root=/dev/sdXY loop=/ubuntu/disks/root.disk ro

These changes are not permanent. After successfully booting into the system the user should run sudo update-grub and inspect the GRUB 2 configuration file (/boot//grub/grub.cfg). For problems with booting the main linux kernel, ensure the search, linux, and initrd lines in the [### BEGIN /etc/grub.d/10_linux ###] section of the file now correctly point to the correct locations. The user may need to reinstall GRUB 2 (sudo grub-install /dev/sdX).




Boot a Specific Kernel Manually

If a GRUB 2 menu is not available for editing during the boot process the command line may still allow booting a specific kernel. If GRUB 2 is looking in the correct location a user may be able to enter all the necessary information on the command line in a single entry. This section will provide a step-by-step guide on how to enter this information. The line will look similar to the following when completed:


Command Summary *:
set


linux /boot/vmlinuz-<your version> root=/dev/sdXY ro


initrd /boot/initrd-<your version>


boot

Expanded Instructions *:

Press ENTER only after completing each step ("1", "2", "3" and "4").

Step 1*. Set the Root Partition

set root=(hdX,Y)
Use the correct X,Y results from the ls command and ENTER. Remember GRUB 2 counts the first drive as 0, the first partition as 1. For example, if the Ubuntu system is on sda5, enter: set root=(hd0,5)
* For a Wubi install inside Windows, substitute the following command:

set root=(loop0)



Step 2*. Enter the "linux" line information



linux /boot/vmlinuz-<your version> root=/dev/sdXY ro
* For a Wubi install inside Windows, substitute the following command:

root=/dev/sdXY loop=/ubuntu/disks/root.disk

Afer typing linux /boot/, the user can TAB to display the available kernels. There is no space character after "/". If no kernels are visible, the address in the "Set Root" section may be incorrect. Enter the correct kernel by typing or using tab completion.
For the root=/dev/ section use the correct device such as "/dev/sda1", "/dev/sdb5", etc
Add any options, such as ro (read-only), at the end of the line (normally not required).
Once all the information on the line is correct it should look similar to the sample below.
linux /boot/vmlinuz-2.6.31-16-generic root=/dev/sda1 ro

When correctly typed and ENTER, if the linux kernel is found, a line similar to the "Linux-bzImage" confirmation line highlighted below will appear.

https://help.ubuntu.com/community/Grub2?action=AttachFile&do=get&target=grub2.cli.boot.png
If a "file not found" or similar error message occurs, either the device/partition/file does not exist or GRUB 2 is not looking at the correct drive, partition and/or folder. Determine the correct location using the ls command and then run the following command. Repeat Step 2.
set prefix=(hdX,Y)/boot/grub


Step 3. Enter the "initrd" line information



initrd /boot/initrd.img-<your version>

Afer typing initrd /boot/, the user can TAB to display the available initrd images. Do not leave a space after the "/". If no images are visible, the address in the "Set Root" section may be incorrect. Enter the correct image by typing or using tab completion.
Once all the information on the line is correct it should look similar to the sample below. Press ENTER. Look for confirmation.
initrd /initrd-2.6.31-16-generic root=/dev/sda1 ro

When correctly typed and entered, if the initrd image is found, a line similar to the "Initrd"" confirmation line highlighted in the graphic above should appear.

Step 4. Boot
boot
Type the command and press ENTER.




Rescue Mode

The rescue mode is a major GRUB 2 enhancement. If GRUB 2 fails to find a useable grub.cfg and is unable to transfer control to a kernel it will drop to a grub-rescue> prompt. From this prompt the user can investigate problems, make changes, and retry the boot.
The rescue mode provides fewer commands than the normal GRUB prompt line, but also provides these additional commands:
Command


Result
dump

Clears memory
exit


Exit GRUB 2
normal


Return to the standard "grub>" mode if possible.

The following commands can be used in the grub rescue mode:





boot
cat
chainloader
dump
exit
freebsd
freebsd_loadenv
freebsd_module
help
initrd
insmod
linux
lsmod
multiboot
normal
rmmod
set
unset

While not all the following commands are necessary to boot to a linux kernel, running all the commands will provide a better chance of success by allowing the user to identify problems before the boot command is executed.

https://help.ubuntu.com/community/Grub2?action=AttachFile&do=get&target=info.png If additional commands are needed, the user might try loading the normal GRUB 2 module with insmod normal. If successful, help and additional commands will be available.
Command Summary *:

1. ls
2. set prefix=(hdX,Y)/boot/grub
3*. set root=(hdX,Y)
4. set
5. ls /boot
6. insmod /boot/grub/linux.mod
7*. linux /vmlinuz root=/dev/sdXY ro
8. initrd /initrd.img
9. boot

* For Wubi installs (within Windows) only substitute these commands in Steps 3 & 7:



set root=(loop0)
linux /vmlinuz root=/dev/sdXY loop=/ubuntu/disks/root.disk ro

Expanded Instructions:

1. ls This will display the known devices and partitions. From this information, the user must determine the device and partition on which the system is installed.
2. set prefix=(hdX,Y)/boot/grub If incorrect, "no such disk" or "not found" errors will occur later.
3. set root=(hdX,Y) In this command, X is the device/drive, starting with 0. Y is the partition, starting with 1. Example: (hd0,1) is sda1. (hd2,5) is sdc5.
4. set Inspect the "prefix=" listing. It should match the root designation in Step 3, in the following format: prefix=(hdX,Y)/boot/grub.
5. ls /boot/ Inspect the contents. The user should see varioius kernels, initrd images and the grub folder. If not, use the ls command to inspect the device and attempt to find these files and folders. If necessary, set another device as root.
6. insmod /boot/grub/linux.mod Load (insert module) the linux module. Without this module loaded, the user will receive an "Unknown command linux" message when trying to load the kernel.
7. linux /vmlinuz root=/dev/sdXY ro Load the linux kernel, substituting the correct designations for "X" and "Y" (example: sda1). The user will see a message showing the kernel has been loaded. (See graphic in the previous section above)
* Wubi users must use the alternate command presented earlier.
8. initrd /initrd.img Load the initrd image. When pressing ENTER the user may or may not see a message in the terminal. (See highlighted graphic above)
9. boot Attempt to boot using the information entered.

These changes are not permanent. After successfully booting into the system the user should run sudo update-grub and inspect the GRUB 2 configuration file (/boot//grub/grub.cfg). For problems with booting the main linux kernel, ensure the search, linux, and initrd lines in the [### BEGIN /etc/grub.d/10_linux ###] section of the file now point to the correct locations. The user may need to reinstall GRUB 2 using sudo grub-install /dev/sdX.