GRUB2 Migration/pl
This guide provides instructions for smooth migration from GRUB Legacy to GRUB.
Background
What's GRUB?
GRUB is one of the most commonly found boot loaders in use on non-embedded Linux machines. The role of GRUB is to facilitate the Linux kernel being loaded from the disk into memory and start executing the Linux kernel.
Why migrate?
Firstly, GRUB Legacy is no longer maintained and as such no longer receives updates. GRUB Legacy was created at a time when the developers felt safe in making several assumptions which no longer hold true today. For example, GRUB Legacy is unable to boot from disks larger than 2 TB and assumes that newer filesystems wouldn't come to replace /boot.
GRUB2 aims to be more robust, more portable, more powerful and is maintained with a cleaner code base. GRUB2 supports more hardware configurations, more filesystems and more drive layouts than its predecessor.
Migration to GRUB2
Migration to GRUB2 is fairly straightforward: it will be pulled in as part of the regular upgrade process by the package manager. If it is not pulled in automatically, it can always be merged via the sys-boot/grub:2 package atom:
root #emerge --ask sys-boot/grub:2Boot drive
The first important part is to understand which drive is bootable. For those who followed the Gentoo Handbook it should be /dev/sda. For those who are uncertain, the easiest way to find out is to look at the existing GRUB Legacy configuration. Viewing the /boot/grub/grub.conf file is the main place to check.
Be sure the /boot partition is mounted to be able to view these files. It should be as simple as
root #mount /bootThe grub.conf file will look something like this:
/boot/grub/grub.confdefault 0
timeout 30
splashimage=(hd0,0)/boot/grub/splash.xpm.gz
title Gentoo Linux 3.2.12
root (hd0,0)
kernel /boot/kernel-3.2.12-gentoo root=/dev/sda3 quiet dolvm
initrd /boot/initramfs-genkernel-x86_64-3.2.12-gentoo
Based on the above file it is possible to know that (hd0) is the boot drive but we must map this to a real device. To know this, look at the /boot/grub/device.map file. An example one is provided below.
/boot/grub/device.map(fd0) /dev/fd0
(hd0) /dev/sda
(hd1) /dev/sdb
When suspecting that /boot/grub/device.map is not accurate, run the following command to recreate the file:
root #grub-install --recheck /dev/sdaBased on the above file we know that /dev/sda is the boot drive.
Installing and configuring GRUB2
The next step is to install and configure GRUB2 for the /boot partition without removing GRUB Legacy from the drive's Master Boot Record (MBR). The example below uses /dev/sda — replace it with the correct boot drive path.
First install the necessary GRUB2 files to /boot/grub.
root #grub-install --grub-setup=/bin/true /dev/sdaInstallation finished. No error reported.
The
--grub-setup=/bin/true option tells grub-install to not install GRUB2 in the MBR. If this option is omitted, GRUB Legacy will be overwritten and chainloading GRUB2 from GRUB Legacy later on will not be possible.Now we can scan the available kernels and generate a suitable config file to /boot/grub/grub.cfg. Skip this step when using a Manual Configuration.
root #grub-mkconfig -o /boot/grub/grub.cfgGenerating grub.cfg ... Found linux image: /boot/kernel-3.2.12-gentoo Found initrd image: /boot/initramfs-genkernel-x86_64-3.2.12-gentoo done
GRUB2 uses the configuration file /boot/grub/grub.cfg whereas GRUB Legacy used /boot/grub/grub.conf so please make sure not to use the old file by mistake, e.g. by using tab-completion if the old file is still there.
grub-mkconfig has strict naming requirements for kernels and initramfs images. A kernel must be named
kernel-${version} or vmlinuz-${version} while an initramfs must be named initramfs-${version}.img, initramfs-genkernel-${version}, initramfs-genkernel-${arch}-${version}, initrd-${version}.img, initrd.img-${version}, initrd-${version}.gz, or initrd-${version}. These files must be available in /boot.{{{1}}}
Chainloading GRUB2 from GRUB Legacy to test the setup
Because a broken GRUB configuration could mean an unbootable system, we want to test our GRUB2 configuration before making it permanent. To do this we will chainload GRUB2 from GRUB Legacy. This is done by adding a new section into /boot/grub/grub.conf. An example is shown below.
Be aware that the root partition may be different from
(hd0,0) used in the example, and make sure to reuse the same root value from the /boot/grub/grub.conf configuration file./boot/grub/grub.confdefault 0
timeout 30
splashimage=(hd0,0)/boot/grub/splash.xpm.gz
title GRUB2 Chainload
root (hd0,0)
kernel /boot/grub/i386-pc/core.img
boot
title Gentoo Linux 3.2.12
root (hd0,0)
kernel /boot/kernel-3.2.12-gentoo root=/dev/sda3 quiet dolvm
initrd /boot/initramfs-genkernel-x86_64-3.2.12-gentoo
At this point the machine should be rebooted, and GRUB2 Chainload selected from the GRUB menu when the machine begins to boot. Another GRUB menu will be presented which should advertise itself as GRUB 2.0.0 or higher at the top and show the available kernel(s) to boot. Should this not work, simply reboot the system and pick the normal boot option instead of GRUB2 Chainload.
Replacing and removing GRUB Legacy
Jeżeli wszystko działa poprawnie, podmień GRUB Legacy i usuń go z systemu.
Since the system has been rebooted, it might be necessary to mount /boot again. Make sure to use the right boot drive path instead of /dev/sda as this is merely an example. If /boot is not mounted before running grub-install, the system will become unbootable.
As previously mentioned, if GRUB2 was emerged with the
multislot USE flag then grub2-install must be used instead of grub-install. In this case, after GRUB Legacy is removed from the system in the next step, GRUB2 should be re-emerged without the multislot USE flag so that grub-install and grub-mkconfig can become GRUB2 commands.root #grub-install /dev/sdaInstallation finished. No error reported.
At this point use the package manager to remove sys-boot/grub:0.
root #emerge --ask -vc sys-boot/grub:0The migration is now complete.
Maintaining GRUB2
Whenever a new kernel is installed, perform the next step so that the GRUB2 configuration recognizes the new kernel (except when using a manual configuration).
Make sure the /boot partition is mounted for this step.
root #grub-mkconfig -o /boot/grub/grub.cfgGenerating grub.cfg ... Found linux image: /boot/kernel-3.3.8-gentoo Found initrd image: /boot/initramfs-genkernel-x86_64-3.3.8-gentoo Found linux image: /boot/kernel-3.2.12-gentoo Found initrd image: /boot/initramfs-genkernel-x86_64-3.2.12-gentoo done
This page is based on a document formerly found on our main website gentoo.org.
The following people contributed to the original document: Cardoe
They are listed here because wiki history does not allow for any external attribution. If you edit the wiki article, please do not add yourself here; your contributions are recorded on each article's associated history page.