Set the default kernel in GRUB

How can I pick which kernel GRUB 2 should load by default? I recently installed a Linux real-time kernel and now it loads by default. I’d like to load the regular one by default.

So far I only managed to pick the default OS… and for some reason the /boot/grub.cfg already assumes that I want to load the real-time kernel and put it into the generic Linux menu entry (in my case Arch Linux).

Asked By: TomTom

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As mentioned in the comments, you can set the default kernel to boot into using the grub-set-default X command, where X is the number of the kernel you want to boot into. In some distributions you can also set this number by editing the /etc/default/grub file and setting GRUB_DEFAULT=X, and then running update-grub.

The number is the index to an array of kernels/kernel settings shown in the GRUB menu during boot, with 0 being the first (top-most) entry. You can usually find the right number by looking for menuentry lines in /boot/grub/grub.cfg, like so:

grep menuentry /boot/grub/grub.cfg

You’ll see each kernel listed with the name that is shown in the GRUB boot menu. The first one is 0, the second is 1, and so on.

Answered By: jkt123

jkt123’s answer will work for most distributions, I guess. However, for Arch Linux it didn’t work, at least not with the packages I have available.

The indices you can set with grub-set-default only correspond to the main menu entries. The kernel options are however in a submenu. So either you move the kernel entry out of the submenu into the main menu or you put the entry on top of the submenu list and select the submenu.

My GRUB Menu

  • Arch Linux
  • Advanced options for Arch Linux
    • Kernel 1
    • Kernel 2
  • Windows

To be able to boot Kernel 2, you have to either swap it with Kernel 1 or you put it outside the submenu on the same level as Arch Linux or Windows. And then set the default number to one of the main menu indices. For example, in the menu above "0" boots "Arch Linux" and "1" boots Kernel 1.

To change the hierarchy and swap, open /boot/grub/grub.cfg and move the entry you wish to move. An entry could look like this

menuentry 'ENTRY NAME'
   ... some code ...
}

Then you need to apply your changes. In my case with grub-mkconfig. But this might vary from system to system.

Answered By: TomTom

Simply doing grep 'menuentry' /boot/grub/grub.cfg lists additional entries that are not related to the actual kernel or OS versions. For instance, it lists

if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
  menuentry_id_option=""
export menuentry_id_option

I would like to propose a small improvement to the method of searching that file:

$ awk '/menuentry/ && /class/ {count++; print count-1"****"$0 }' /boot/grub/grub.cfg
0****menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-86df21bf-d95f-435c-9292-273bdbcba056' {
1****   menuentry 'Ubuntu, with Linux 3.19.0-26-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.19.0-26-generic-advanced-86df21bf-d95f-435c-9292-273bdbcba056' {
2****   menuentry 'Ubuntu, with Linux 3.19.0-26-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.19.0-26-generic-recovery-86df21bf-d95f-435c-9292-273bdbcba056' {
3****   menuentry 'Ubuntu, with Linux 3.13.0-62-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.13.0-62-generic-advanced-86df21bf-d95f-435c-9292-273bdbcba056' {
4****   menuentry 'Ubuntu, with Linux 3.13.0-62-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.13.0-62-generic-recovery-86df21bf-d95f-435c-9292-273bdbcba056' {

With the command above and its output, you can see the code corresponding to each OS version, which gives you the number to use in the /etc/default/grub file.

Instead of editing the /etc/default/grub file by hand, I suggest using sed. In the following command, replace X with the appropriate number as determined above:

sudo sed -i 's/GRUB_DEFAULT=0/GRUB_DEFAULT=X/g' /etc/default/grub; sudo update-grub

Answered By: Sergiy Kolodyazhnyy

I think most distributions have moved additional kernels into the advanced options sub menu at this point, as TomTom found was the case with his
Arch.

I didn’t want to alter my top level menu structure in order to select a previous kernel as the default. I found the answer here.

To summarize:

  1. Find the $menuentry_id_option for the submenu:

    $ grep submenu /boot/grub/grub.cfg
    submenu 'Advanced options for Debian GNU/Linux' $menuentry_id_option 'gnulinux-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
    
  2. Find the $menuentry_id_option for the menu entry for the kernel you want to use:

    $ grep gnulinux /boot/grub/grub.cfg
    menuentry 'Debian GNU/Linux' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
    submenu 'Advanced options for Debian GNU/Linux' $menuentry_id_option 'gnulinux-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.18.0-0.bpo.1-rt-amd64' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.18.0-0.bpo.1-rt-amd64-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.18.0-0.bpo.1-rt-amd64 (recovery mode)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.18.0-0.bpo.1-rt-amd64-recovery-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.18.0-0.bpo.1-amd64' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.18.0-0.bpo.1-amd64-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.18.0-0.bpo.1-amd64 (recovery mode)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.18.0-0.bpo.1-amd64-recovery-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.17.0-0.bpo.1-amd64' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.17.0-0.bpo.1-amd64-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.17.0-0.bpo.1-amd64 (recovery mode)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.17.0-0.bpo.1-amd64-recovery-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.9.0-8-amd64' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.9.0-8-amd64-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
        menuentry 'Debian GNU/Linux, with Linux 4.9.0-8-amd64 (recovery mode)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.9.0-8-amd64-recovery-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc' {
    
  3. Comment out your current default grub in /etc/default/grub and replace it with the sub-menu’s $menuentry_id_option from step one, and the selected kernel’s $menuentry_id_option from step two separated by >.

    In my case the modified GRUB_DEFAULT is:

    #GRUB_DEFAULT=0
    
    GRUB_DEFAULT="gnulinux-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc>gnulinux-4.18.0-0.bpo.1-amd64-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc"
    
  4. Update grub to make the changes. For Debian this is done like so:

    $ sudo update-grub
    

Done.

Now when you boot, the advanced menu should have an asterisk and you should boot into the selected kernel. You can confirm this with uname.

$ uname -a
Linux NAME 4.18.0-0.bpo.1-amd64 #1 SMP Debian 4.18.0-0 (2018-09-13) x86_64 GNU/Linux

Changing this back to the most recent kernel is as simple as commenting out the new line and uncommenting #GRUB_DEFAULT=0:

GRUB_DEFAULT=0

#GRUB_DEFAULT="gnulinux-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc>gnulinux-4.18.0-0.bpo.1-amd64-advanced-38ea4a12-6cfe-4ed9-a8b5-036295e62ffc"

then rerunning update-grub.

Specifying IDs for all the entries from the top level menu is mandatory. The format for setting the default boot entry can be found in the documentation.

Answered By: William L-K

As recently as CentOS-6.6 grub.conf looked like this can could be manually edited to change the default selection:

default=1
timeout=5
splashimage=(hd0,0)/boot/grub/splash.xpm.gz
Answered By: Mike

After struggling for 2 hours, I have found a much easier way to achieve this. I just RTFM. 😉

Add two lines to /etc/default/grub

GRUB_SAVEDEFAULT=true
GRUB_DEFAULT=saved

Do the sudo update-grub, reboot, get into your grub menu and select whichever menu or submenu item you need. The choice will be saved every time and then your computer will boot into it automatically. When you manually choose a different entry, that becomes the new default.

Answered By: Jimmy Falcon

Debian Stretch:

Rather than messing around with config files, create a folder in /noot (call it what you want), leave the kernel you want, along with the matching config and system files, in /boot and move the rest to this new folder.

Run update-grub.

Double check the /boot folder that your kernel version and matching config and system files are are still there (in case you copied something you shouldn’t have) and reboot.

Answered By: Pinkie Perie

In order to do it with a GUI, I use Grub Customizer (I’m in Mint and have installed it like this.).

The idea is to keep the Advanced options in the grub list in case the default list is changed within Grub Customizer.

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Then, under General settings select the default entry: previous booted entry.

enter image description here

Then, reboot, and during boot select the "Advanced options" entry in the grub list:

enter image description here

and select the desired kernel

enter image description here

On the next reboot, the "Advanced options" item will be the one selected by default in the grub list and the last selected kernel from under there will be booted (without opening the full list of kernels).

In case Windows is used, or other option in the grub list, remember to re-do the previous procedure.

Answered By: cipricus

Solution without worrying about index number or identifiers

This is what worked for me on an archlinux VPS:

In addition to setting the following in /etc/default/grub:

GRUB_SAVEDEFAULT=true
GRUB_DEFAULT=saved

I used the following option to set the mainline Linux kernel as the default:

sudo grub-set-default 'Advanced options for Arch Linux>Arch Linux, with Linux linux'
sudo grub-mkconfig -o /boot/grub/grub.cfg

The above works because the man 8 grub-set-default page says this about MENU_ENTRY option:

MENU_ENTRY is a number, a menu item title or a menu item identifier.

If you make the mistake of just using Arch Linux, with Linux linux for example, it will still work but you will get a warning when you run the grub-mkconfig command.

Answered By: smac89

In short, steps that work for me:

  • Edit /etc/default/grub
GRUB_DEFAULT=0

The indexing of all installed kernel/OSes starts with ‘0’.
Pick yours, if not ‘0’.

  • Regenerate the grub configuration

    sudo grub-mkconfig -o /boot/grub/grub.cfg

    In some cases, it might be grub2. Choose accordingly.

  • Reboot (reboot)

4MoreInfo

Answered By: parasrish
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