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====== Switching from Lilo to Grub2 (legacy/mode bios mbr) ======
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===== Introduction =====

If you use UEFI and/or GPT, then don't use this. If you still want to use it, you can probably set your UEFI to BIOS legacy mode and deactivate GPT. This is meant to be simple. But the process should be somewhat similar with UEFI/GPT.

**Summary:**
<code>
cd /etc/grub.d/
chmod -x 20_linux_xen 30_os_prober 30_uefi_firmware 41_custom
nano /etc/grub.d/40_custom
grub-mkconfig -o /boot/grub/grub.cfg
nano /boot/grub/grub.cfg
grub-install /dev/sda
</code>
===== Preparations =====

<code>cd /etc/grub.d</code>

Deactivate autoconfig files according to your need, **example**:
<code>chmod -x 20_linux_xen 30_os_prober 30_uefi_firmware 41_custom</code>
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===== Generating a useful template (optional) =====

Grub2 is not very intuitive to write config entries for, so you can modify a good example to your need instead.
Pipe some examples to a file: 
<code>grub-mkconfig > examples.file</code>

Edit the file to only include one example config entry (Including curly brackets and if you want submenu) \\

Then append the example in the file to the custom grub entry file: (You need to append the info into the file, as you need to preserve the uncommented info already there, lest it should not work.)
<code>cat examples.file >> 40_custom</code>
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===== Edit custom config =====

Edit the custom entry to fit whatever you want to do..
<code>nano /etc/grub.d/40_custom</code>
Some useful tools you can use for info here: blkid, fstab

<note warning>
If you run into an unbootable system, boot from Slackware USB/DVD and follow
the instructions there to boot with the USB/DVD Kernel into your root file
system. Like: <code>huge.s root=/dev/sdaX initrd= ro</code> You can chroot into your root partition like described at the end of this article and rebuild Grub there. Ps. By root is meant the location of your Slackware root and could be for example /dev/sda5</note>
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===== Config =====

Once you are ready or think so, you can **prepare** grub: (this generates the config file from any executable files in /etc/grub.d/ and replaces editing menu.lst from grub1)
<code>grub-mkconfig -o /boot/grub/grub.cfg</code>
The above generates the necessary files in /boot/grub including the config file. Every time you CHANGE anything in the config folder /etc/grub.d/, you need to run the above command again for it to take effect. You can now inspect the /boot/grub/grub.cfg file to evaluate if it looks right.
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===== Install =====

Then INSTALL grub: (this example installs to master boot record on the first disk, you could install it to a boot disk or elsewhere instead..)
<code>grub-install /dev/sda</code>
You should be given feedback about it being successfull or not. Then cross your fingers and reboot.
<note tip>You don't need to repeat this last step if you reconfigure grub. The step before it just replaces menu.lst, so once grub is installed, it reads the generated config file "dynamically"</note>
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===== Doing these steps during your Slackware installation =====

You can do these steps when you install and set up Slackware with a CD or USB, by dropping into a shell after the installation. Simply "finish" the installation and don't reboot or exit, but select the shell option.
The Slackware installation has already mounted your root filesystem and any other partitions you used during the installation into /mnt. You can also do that manually if you reboot and boot into the cd/usb again, or if something is not right.
<code>mount /dev/sdaX /mnt
mount -o bind /dev/ /mnt/dev/
mount -o bind /proc/ /mnt/proc/
mount -o bind /sys/ /mnt/sys/</code>

If all went well, you can change root into your Slackware root filesystem currently on /mnt (or any other location you may have used instead)..
<code>chroot /mnt</code>

Once this is done, you can proceed to do configuration and installation of Grub2 as described above.
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===== Configuring other Grub2 default options =====

Grub2 contains some other options you can easily change or add too. These are kind of default and global options for Grub2, and in some few cases you have to not only use grub-mkconfig, but also grub-install for them to be effective. These options can be found in /etc/default/grub.
<code>nano /etc/default/grub</code>

Some options are already included in this file, commented or uncommented and can be activated and deactivated. But many more options exists that you can add or change in this file.
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===== Further info =====

If you think there is too much info here, you could use the minimalist guide to Grub2 instead: \\
[[howtos:slackware_admin:grub_on_first_install | Mini Grub2 guide]] \\
Those using UEFI might want to use this howto as well: \\
[[howtos:slackware_admin:set_up_grub_as_boot_loader_on_uefi_based_hardware | Grub2 UEFI info]] \\
Another one, dealing with GPT partitions in particular: \\
[[howtos:slackware_admin:installing_with_gpt_without_uefi | Grub2 GPT info]] \\

====== Sources ======

 * Originally written by [[wiki:user:zeebra | zeebra]]


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{{tag>howtos misc grub2 author_zeebra}}