Grub 2 Basics

[drs305]

I do not want this to touch the sda MBR. (As per above, all other OS's are booting perfectly via chainloading.) I only want to get Mythbuntu to boot now (which I believe requires putting grub into sda9).

Any time you run "grub-install" it is going to run several scripts, among which is "grub-setup". This writes to the MBR. I believe the way to make sure it gets written to the partition and not the MBR is to run "grub-setup" directly and using the "--force" option. This is not the devs recommended way of handling things, and if you try putting it on a partition via the "grub-install" command it will complain about it.

The command would be:

grub-setup --force /dev/sda9

Herman's site has a lot more technical information than does this post, and I would advise you to refer to his site for confirmation and a better understanding of how to put GRUB 2 on the partition without also writing to the MBR.

Herman's Illustrated Dual Boot Site:
http://members.iinet.net/~herman546/...to_a_Partition

You can always use the dd command to copy the MBR before you attempt this so you can put it back the way it was if the results aren't what you expected.

[mithrandir77]

Hi all,

I am reading all the guides about grub2 but I cannot understand if it provide a way to run os_prober just manually (through update-grub) and avoid to run it at every boot of the system: I have a lot of partitions and kernels and these make grub2 to take quite 20 seconds to show the boot menu.

Thanks a lot in advance

[drs305]

Hi all,

I am reading all the guides about grub2 but I cannot understand if it provide a way to run os_prober just manually (through update-grub) and avoid to run it at every boot of the system: I have a lot of partitions and kernels and these make grub2 to take quite 20 seconds to show the boot menu.

Thanks a lot in advance

Several users filed bug reports on the delay between seeing "loading grub" and seeing the menu. In some cases, the reason was because the computer's BIOS was first looking at a device other than the one GRUB was on. Making sure GRUB 2 was installed on the same device as the BIOS was first looking solved the delay problems.

I don't believe the 30_os-prober script is responsible for the delay during boot. You can check by disabling it and seeing if the delay remains:

sudo chmod -x /etc/grub.d/30_os-prober

If you remove the executable bit "update-grub" will not search for your OSs/kernels on other than your system partition. Thus it will not see your other OSs or put them in the menu.

If they do not change often, you could move them to a custom menu, such as 40_custom. This would allow you to leave 30_os-prober off but still have the items on the menu. It would speed up "update-grub" at the cost of not updating the information on other installed OSs.

[mithrandir77]

If they do not change often, you could move them to a custom menu, such as 40_custom. This would allow you to leave 30_os-prober off but still have the items on the menu. It would speed up "update-grub" at the cost of not updating the information on other installed OSs.

Hi,

thank you a lot for your support.
As I can understand from your message, I can disable 30_os-prober and the configure static entries in a 40_custom file or similar.

In order to add static entries to 40_custom, can I use "as are" the menu entries found in /boot/grub/grub.cfg?

For example

menuentry "Ubuntu 9.04, kernel 2.6.28-16-generic (on /dev/sda9)" {
saved_entry=${chosen}
save_env saved_entry
insmod ext2
set root=(hd0,9)
search --no-floppy --fs-uuid --set c9318744-47e2-4083-8085-8d574bcf8373
linux /boot/vmlinuz-2.6.28-16-generic root=UUID=c9318744-47e2-4083-8085-8d574bcf8373 ro quiet splash vga=791
initrd /boot/initrd.img-2.6.28-16-generic
}

Thanks again

[drs305]

As I can understand from your message, I can disable 30_os-prober and the configure static entries in a 40_custom file or similar.

In order to add static entries to 40_custom, can I use "as are" the menu entries found in /boot/grub/grub.cfg?)

Yes. In fact, that is the safest way to do it. I would recommend creating your 40_custom menu and run "sudo update-grub" before you disable 30_os-prober.

Check all the items at the bottom of your menu (the 40_custom entries) and once you are sure they are working you can then disable 30_os-prober and run "sudo update-grub" again.

If you would like your custom entries to appear at the top of the menu, you can save the file as "06_custom". Make it executable before you run "update-grub" so it will be entered into your grub.cfg file.

[robinparriath]

Thanks. This is a great tutorial!

I had been editing the grub.cfg file to customize my menus. (I know... wrong method) and had to redo it each time I did an update-grub (or simply started Start-up manager).

But since I came across your tutorial, I haven't had to... Thanks again!

Is there any way to get a screenshot of the Grub2 bootmenu? (instead of taking a picture of course!)

[drs305]

Is there any way to get a screenshot of the Grub2 bootmenu? (instead of taking a picture of course!)

There is a graphic of a sample boot menu on the GRUB2 Ubuntu help site:
https://help.ubuntu.com/community/Gr...0to%20GRUB%202
Step 5 under "Upgrading to GRUB 2".

If you mean you want to take a pic of yours, someone else will have to reply. I made the images in the above doc by using a virtual machine and taking a screenshot of the VM window.

[robinparriath]

If you mean you want to take a pic of yours

Yup... that's what I meant. It's not that critical though...

[mithrandir77]

Yes. In fact, that is the safest way to do it. I would recommend creating your 40_custom menu and run "sudo update-grub" before you disable 30_os-prober.

Check all the items at the bottom of your menu (the 40_custom entries) and once you are sure they are working you can then disable 30_os-prober and run "sudo update-grub" again.

If you would like your custom entries to appear at the top of the menu, you can save the file as "06_custom". Make it executable before you run "update-grub" so it will be entered into your grub.cfg file.

I disabled 30_os-prober, created my own 40_custom with my static entries, added GRUB_DISABLE_LINUX_RECOVERY=true
to /etc/default/grub, updated grub.cfg by update-grub, but at the next boot grub2 still took about 15 seconds to show its menu: it seemed to be looking for all the Os present on my system, like before disabling os-prober...



Is there a way to make it to boot quickly? When you need to reboot the system for whatever reason, it is frustrating to wait a lot of seconds for grub's menu...

[drs305]

at the next boot grub2 still took about 15 seconds to show its menu: it seemed to be looking for all the Os present on my system, like before disabling os-prober...



Is there a way to make it to boot quickly? When you need to reboot the system for whatever reason, it is frustrating to wait a lot of seconds for grub's menu...

mithrandir77,

This sounds exactly like what happens when your BIOS boots to one device and the /boot partition is on another drive. GRUB 2 will search all of the first drive looking for the files before finding them on the second. That accounts for the delay.

The 'conventional' solution is to change the BIOS to boot from the same partition as the one with the /boot folder (or you could move the /boot folder to the first device I suppose).

There may be ways to change some of the GRUB 2 settings internally but I've not investigated this.