87

I want to reinstall GRUB 2 and I found these instructions: How to Repair, Restore, or Reinstall Grub 2 with a Ubuntu Live CD or USB. In my case, the boot loader is installed in the EFI partition. If I use the commands provided in this guide, will GRUB be reinstalled to the EFI partition automatically, or will it be installed into the root partition where Ubuntu is installed ? Obviously, I do not want this to happen.

11
  • 6
    The instructions in the provided link are valid for reinstalling GRUB in legacy BIOS mode only, this will not work in your case. To reinstall GRUB to an Ubuntu installation in EFI BIOS mode, please read my answer. :)
    – cl-netbox
    Sep 29, 2016 at 16:36
  • Thank you very much! :) I have some questions: when I installed Ubuntu in my UEFI system, I found two entries in the bios. Is there a way to have a unic ubuntu entry? In case of MBR partition table (so no EFI or any other boot partition), can I use the same commands except for: sudo mount /dev/sd** /mnt/boot/efi ?
    – Generoso
    Sep 30, 2016 at 10:11
  • You can try to remove the second Ubuntu entry with : sudo efibootmgr (lists all entries) | sudo efi bootmgr -b <entry-number> -B .... and to reinstall GRUB in legacy BIOS mode execute these commands : sudo mount /dev/sd** /mnt | sudo grub-install --boot-directory=/mnt/boot /dev/sd* (* = disk | ** = system partition) ! :)
    – cl-netbox
    Sep 30, 2016 at 10:54
  • Perfect :) Anyway, having a UEFI system and so a EFI partition, is there a way to avoid getting grub overriden when I perform a new Windows installation?
    – Generoso
    Sep 30, 2016 at 12:18
  • Well, Microsoft doesn't take care for anything else but their own products, so you can install Linux systems without doing any harm to Windows - unfortunately this isn't the case the other way around - so when you install Windows after you have installed Ubuntu, you have to restore the GRUB boot loader afterwards. :)
    – cl-netbox
    Sep 30, 2016 at 13:23

12 Answers 12

143

Reinstall the GRUB boot loader to your Ubuntu installation in EFI mode this way ...

Boot from the Ubuntu installation medium and select 'Try Ubuntu without installing'.
(Boot your install medium in EFI mode, select the Ubuntu entry with UEFI in front.)

Once you are on the Live desktop, open a terminal and execute these commands :

sudo mount /dev/sdXY /mnt
sudo mount /dev/sdXX /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sdX
update-grub  

Note : sdX = disk | sdXX = efi partition | sdXY = system partition

To identify the partitions use GParted, the tool is included in the installation medium.
After having run the commands GRUB will be installed in the separate EFI partition.

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  • 2
    +1 but why don't you install from Ubuntu itself?
    – user595510
    Nov 8, 2016 at 13:55
  • 3
    @MarkYisri : Thank you very much ! :) Because it is the safest way to reinstall the GRUB boot loader without corrupting things and in case the system does not boot properly ... the only way to do it ! :)
    – cl-netbox
    Nov 8, 2016 at 13:58
  • 5
    In this solution, how does 'grub-install' know it is supposed to install in EFI mode?
    – user334639
    Oct 12, 2017 at 0:38
  • 13
    The important point is to boot the installation media in the correct boot-mode, if we want to reinstall grub-efi we have to boot in UEFI-mode, if we wanty to reinstall grub-pc we have to boot in legacy-mode.
    – mook765
    Mar 6, 2018 at 12:20
  • 4
    This worked for me except with one alteration: I did grub-install /dev/sdXX, i.e. not the disk but the EFI partition was used for installing grub and it worked. Mar 12, 2019 at 21:56
16

this is the only way that worked for me: (System: sdb8, boot: sdb6, efi: sdb2)

sudo mount /dev/sdb8 /mnt 
sudo mount /dev/sdb6 /mnt/boot 
sudo mount /dev/sdb2 /mnt/boot/efi

sudo mount --bind /dev /mnt/dev &&
sudo mount --bind /dev/pts /mnt/dev/pts &&
sudo mount --bind /proc /mnt/proc &&
sudo mount --bind /sys /mnt/sys

sudo chroot /mnt

grub-install --target=x86_64-efi /dev/sdb

grub-install --recheck /dev/sdb

exit &&
sudo umount /mnt/sys &&
sudo umount /mnt/proc &&
sudo umount /mnt/dev/pts &&
sudo umount /mnt/dev &&
sudo umount /mnt
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  • 1
    What does --recheck do? The manual says delete device map if it already exists?
    – MrCalvin
    Mar 27, 2019 at 22:45
  • If I call the boot-entry anything different the the default, e.g. --bootloader-id=Ubuntu_02 the boot fails. It just boot in the grub console...any solution?
    – MrCalvin
    Mar 27, 2019 at 22:47
  • yes. it seems grub-install --recheck is needed. It fixed my non-working USB HDD EFI.
    – solsTiCe
    Aug 19, 2019 at 12:45
  • Worth noting that for --target=x86_64-efi option to work you need a package grub-efi-amd64-bin
    – Hi-Angel
    Jan 20 at 17:28
10

This is how I did it on a standard x86_amd64 EFI desktop, without chrooting, assuming you have a partition containing Ubuntu on your hard drive and possibly an EFI partition where GRUB should be installed.

# boot on a live Ubuntu, I used 18.04 but more recent should work

# if you have currently no EFI partition (maybe it was deleted,
# or you are migrating to a new drive):
# sudo gparted
# - create a FAT 32 partition of around 100 MB on the disk of your choice
# (in general the one that host the Ubuntu partition). If you plan to
# move or resize some paritions, anticipate that (for instance by
# creating the EFI partition at the end of the free space).
# - set the flag esp on this partition (the flag boot will also be selected)

# now assuming that the Ubuntu partition is `/dev/sda2` and the (possibly new) EFI partition is `/dev/sda1`
sudo apt install grub-efi
sudo mkdir /media/root && sudo mount /dev/sda2 /media/root
sudo mkdir /media/efi && sudo mount /dev/sda1 /media/efi
sudo grub-install --target=x86_64-efi /dev/sda --efi-directory=/media/efi --boot-directory=/media/root/boot

This should give:

Installing for x86_64-efi platform.

Installation finished. No error reported.

Then reboot and you should be done. You may have to tell your BIOS which drive to use, or which EFI partition to use, or which EFI binary to use.

If you created a new EFI partition, you may have to add it to /etc/fstab to have update-grub working correctly.

For more information : https://wiki.archlinux.org/index.php/Multiboot_USB_drive#Hybrid_UEFI_GPT_+_BIOS_GPT/MBR_boot

5
  • Thanks for the tips. I used modification of this. Since I was converting VM from BIOS to EFI I just formatted the existing /boot that was ext to fat using command mkfs -t vfat /dev/sda2 (in MY case!) then mounted it with mount /dev/sda2 /mnt/boot/ and also mounted my root (LVM). I've pointed both directory options to same place grub-install --force --target=x86_64-efi --boot-directory=/mnt/boot --efi-directory=/mnt/boot /dev/sda. Then I've edited fstab that was mounted in /mnt/root/etc/fstab and replaced UUIDs with /dev/sda2 + vfat and /dev/mapper/.. for LVM. <continues>
    – LuxZg
    Dec 24, 2020 at 23:23
  • (sorry, comment limit) Anyway, after (successful!!!) reboot, I still repeated it inside the OS (VM) itself, by running grub-install /dev/sda --efi-directory=/boot + update-grub + another reboot. I tested this by installing another kernel, and forcing update-grub, and everything was fine, grub files were updated correctly, and new entries for this kernel were created. So thanks a lot once again, cheers!
    – LuxZg
    Dec 24, 2020 at 23:27
  • My particular case with Ubuntu VM as answer on serverfault: serverfault.com/a/1047507/574185
    – LuxZg
    Dec 24, 2020 at 23:56
  • Helped a lot. The disk in my system was still OK, but reaching it's capacity. So I transferred all the data to the new one (btrfs send/receive), created the new EFI partition, copied contents from the old EFI and followed your instructions. Then after rebooting with the new disk I found that the grub.cfg created by grub-install references the grub.cfg in /boot/grub (that lives on the btrfs partition). This one did still have the previous disk's UUIDs in the menu, so it wouldn't boot. Fixed the ID there (use ls -l /dev/disk/by-uuid to find the new ID), works like a charm now. Thanks! Jul 2, 2021 at 9:06
  • I upvoted this but found that the update-grub step is missing from the instruction, which IMHO is the biggest flaw of this solution as update-grub is most often a critical step that most people cannot miss (and I guess that it has to be done within chroot).
    – xpt
    Sep 5, 2021 at 13:50
6

Thanks to @cl-netbox for the instructions!

After I upgraded (Linux Mint 18.2 Sonya to 18.3 Sylvia) my system wouldn't boot so I followed the instructions above but still no success. I noticed however that my machine has /boot in a separate partition (possibly because I am using LVM) so my slightly modified process was:

sudo mount /dev/sdXXX /mnt
sudo mount /dev/sdXY /mnt/boot
sudo mount /dev/sdXX /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sdX
update-grub 

Note : sdX = disk | sdXX = efi partition | sdXY = boot partition | sdXXX = system partition

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  • 1
    I had a running Ubuntu Bionic system on which I accidentally did rm -Rf /boot/efi ! My system was still running, so I tried using the last two commands (grub-install /dev/mapper/ubuntu--vg-root AND update-grub). Rebooted, and everything work perfectly. Phewy and thanks :) Jul 29, 2018 at 22:04
  • With LVM, the beginning should look like this: sudo vgchange -ay name_of_:the_lvg and then sudo mount /dev/sname_of_:the_lvg/root /mnt Mar 31, 2021 at 22:05
5

Also, if booting from live cd to recover it might happen that you are missing grub-efi-amd64-bin package and then line

"grub-install --target=x86_64-efi /dev/sdb" 

fails with error message: "grub-install: error: /usr/lib/grub/x86_64-efi/modinfo.sh doesn't exist. Please specify --target or --directory."

In this case run this outside of chroot

sudo apt get grub-efi-amd64-bin

and then add /usr/lib/grub/x86_64-efi to chroot mounts.

BTW "/dev/sdb" param is obsolete and is being ignored.

1
  • I wonder what sudo apt get grub-efi-amd64-bin will do.
    – mook765
    Dec 20, 2020 at 4:22
5

During the last months there have been some updates to the libraries involved.

The steps below were useful for me. They took ideas from old answers as well as from other forums.

Make sure that you booted using EFI

efibootmgr -v

Run grub-install

sudo mount /dev/nvme0n1p5 /mnt 
sudo mount /dev/nvme0n1p1 /mnt/boot/efi

for i in /dev /dev/pts /proc /sys /sys/firmware/efi/efivars /run; do sudo mount -B $i /mnt$i; done

sudo chroot /mnt

grub-install --target=x86_64-efi /dev/nvme0n1
grub-install --recheck /dev/nvme0n1

# as a second attempt, you could also try (assuming _debian_ is your distro)
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=debian
# grub-mkconfig -o /boot/grub/grub.cfg

update-grub2

exit &&
sudo umount /mnt/sys &&
sudo umount /mnt/proc &&
sudo umount /mnt/dev/pts &&
sudo umount /mnt/dev &&
sudo umount /mnt

Make sure that efibootmgr lists your Linux as an entry

efibootmgr -v
3

If you happen to lose your EFI partition, it's easy to get it back. You can use a partitioning tool such as fdisk or parted to create a new partition sdXY (e.g. sda1) with type "EFI partition (1)" and format it with:

sudo mkfs.msdos /dev/sdXY

then mount it with:

sudo mount /dev/sdXY /boot/efi

and you can reinstall GRUB by running:

sudo grub-install --efi-directory=/boot/efi

as mentioned in other solutions.

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  • 1
    Surely you format a partition on the disk i.e. /dev/sdX1, and not the whole block device? Mar 27, 2020 at 21:18
3

I can't comment (not enough reputation), but @Chilu Pereira's answer is the way to go in an EFi or multiboot situation. It is similar to the approach in the gentoo-guide. They use a slightly different approach : Instead of a mount --bind they use mount --rbind followed by mount --make-rslave for sys and dev and proc gets simply mounted again. In gentoo I used to create mounts from a live-system like this:

mount -t proc /proc /mnt/proc
mount --rbind /sys /mnt/sys
mount --make-rslave /mnt/sys
mount --rbind /dev /mnt/dev
mount --make-rslave /mnt/dev 
chmod 1777 /mnt/dev/shm

(Anybody knows what is exactly the difference between --bind and --rbind / --make-rslave btw ?)

But today I got two errors in chroot from grub2, I never experienced before :

 connect: No such file or directory
   Please make sure that the zfs-fuse daemon is running

and

grub-install: warning: Cannot read EFI Boot* variables.
grub-install: warning: read_file: could not read from file: Input/output error.

The zfs-fuse error seems not to matter but for Efivars I had to add one more mount :

mount --bind /sys/firmware/efi/efivars /mnt/sys/firmware/efi/efivars

I guess /sys/firmware/efi/efivars does not exist in chroot or maybe it's read only - but anyway it worked

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  • Agreed, that answer was the one that fixed up my grub install without borking the existing Apple partition (I don't think bind-mounting /dev/pts is needed though)
    – Z4-tier
    Jan 23, 2021 at 16:23
  • the /dev/pts thing can be found in many tutorials and manuals . As /dev/pts are pseudo-terminals and a bind mount, it may not be needed. Jan 24, 2021 at 18:51
  • 1
    I just found the explanation why you should prefer --rbind over --bind as --rbind gives access to other bind-mounts underneath the bind-mount you are creating. A better explanation is here : [askubuntu.com/a/1188621/260981] Jan 24, 2021 at 19:14
  • I'm guessing the r is for recursive. I've not heard of that option. I'm not sure offhand if there are any other mount points under '/sys', but if there are then i hope 'rbind' has loop detection!
    – Z4-tier
    Jan 24, 2021 at 19:20
2

in addition to ci-netbox answer.
If your pendrive OS version does not match the one that is installed on the disk, grub-install may have difficulties to identify the right grub installation:

$ sudo chroot /mnt
# grub-install /dev/sdX
grub-install: error: /usr/lib/grub/i386-pc/modinfo.sh doesn't exist. 
Please specify --target or --directory.

Try to identify manually the installation to use

# ls /usr/lib/grub/
grub-mkconfig_lib  x86_64-efi  x86_64-efi-signed

Then restart grub-install :

# grub-install --target=x86_64-efi /dev/sdX 
Installing for x86_64-efi platform.
Installation finished. No error reported.
0

Just used this tool https://help.ubuntu.com/community/Boot-Repair on Ubuntu. That was the easiest way and all was automatic.

0

The simplest for me was to use this small tool (20 Mb) that will let you boot the broken grub system (I used Ventoy to boot the tool):

https://www.supergrubdisk.org/category/download/supergrub2diskdownload/

And once the tool has made its magic and booted your linux systen, do:

sudo grub-install /dev/nvme0n1
sudo update-grub
0

I used Grub-Customizer. I know some of you don't like this program, but in some cases it comes in very handy ( renaming Ubuntu in Kubuntu ( don't have to do that in 'etc/grub.d/10_Linux_Proxy' ), add a theme, or in this case.

File --> Install in MBR.

And all was done.

I don't use Linux based OS's that long ( 7 or 8 months now ), and if I have to write everything down to use in the command-line, it not only takes a long time ( mostly the writing down ), but I can make errors that way.

I had my Windows Bootloader in partition 1 and grub2 in another EFI partition ( 8 )( didn't want to mess up Windows Bootloader ), so every time I wanted to use my Kubuntu ( daily ) or Mint OS I had to press F11, wait, select USB ( don't ask me why ), select Ubuntu, then wait again for Grub and then select my Linux based OS. Now I get Grub2 almost instantly.

Update 211111/1135 Like Organic Marble commented 'MBR doesn't sound right for a UEFI system', he is right. It worked, but only once. What I did is install Grub2Win in my Win10 installation. From Kubuntu I could export my 'grub.conf´ to the 'My Documents'-partition ( NTFS, so Win10 can read that ) and imported it in Grub2Win. Now it is working like it is suposed to.

PS. I saved this page, so I know how to do it when I get rid of Windows.

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  • Installing to MBR doesn't sound right for a UEFI system. Nov 10, 2021 at 12:39
  • 1
    @ Organic Marble. No, you are right. Doesn't sound good. It worked though. Only 1 time. So clearly this is not the right way.
    – Joepie Es
    Nov 11, 2021 at 9:19

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