Ubuntu: Install Kernel and Set GRUB Default Kernel

ubuntu_update_booting_kernel.md

Ubuntu: Install Kernel and Set GRUB Default Kernel

Install Kernel

Install the default kernel:

sudo apt install linux-generic

Set GRUB Default Kernel

1. Find entrance from /boot/grub/grub.cfg
   • Get the $menuentry_id_option:

     grep submenu /boot/grub/grub.cfg

     Example output:

     submenu 'Advanced options for Ubuntu' $menuentry_id_option 'gnulinux-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf' {

     'gnulinux-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf' is what we need.
   • Get the specific kernel option:

     grep gnulinux-4.15.0 /boot/grub/grub.cfg

     Example output:

     menuentry 'Ubuntu, with Linux 4.15.0-126-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.15.0-126-generic-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf' {

     'gnulinux-4.15.0-126-generic-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf' is what we need.
2. Set GRUB_DEFAULT in /etc/default/grub
   • Join two entry strings obtained above by '>', set to GRUB_DEFAULT.

     GRUB_DEFAULT='gnulinux-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf>gnulinux-4.15.0-126-generic-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf'

3. Update grub

   sudo update-grub

4. Reboot the machine

I have tried following this steps but update-grub isn't updating the grub file.
what am I missing?

Nice instructions. Thanks

Thanks.

Let scripts do the work:

KERNELVER=5.15.0-58-generic
MID=$(awk '/Advanced options for Ubuntu/{print $(NF-1)}' /boot/grub/grub.cfg | cut -d\' -f2)
KID=$(awk "/with Linux $KERNELVER/"'{print $(NF-1)}' /boot/grub/grub.cfg | cut -d\' -f2 | head -n1)

# echo "GRUB_DEFAULT='${MID}>${KID}'" >> /etc/default/grub

# or prefer put it in a seprate file
cat > /etc/default/grub.d/95-savedef.cfg <<EOF
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true
EOF
grub-editenv /boot/grub/grubenv set saved_entry="${MID}>${KID}"
update-grub

And here's to UNDO the changes

# UNDO  changes ?
grub-editenv /boot/grub/grubenv unset saved_entry
rm -f /etc/default/grub.d/95-savedef.cfg
update-grub

After that I can remove the old kernel files?

After that I can remove the old kernel files?

Sure, after successfully booted into particular version and supposing everything went well, you may delete the old kernels, headers and other related packages.

Works as advertised, just make sure to put quotes:

   GRUB_DEFAULT='gnulinux-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf>gnulinux-4.15.0-126-generic-advanced-4591a659-55e2-4bec-8dbe-d98bd9e489cf'

Doesn't seem to work here, doesn't matter how I try it ... My ids look like:

gnulinux-6.2.0-20-generic-advanced-7ceb1b1a-7139-409e-aff6-4e6ea53ce07b

and

gnulinux-5.17.5-051705-generic-recovery-7ceb1b1a-7139-409e-aff6-4e6ea53ce07b

The automatic option it creates is always for the first one, while I want the deafult to be 5.17.5...

Worked for me thanks 👍

thanks for the script @boypt

Came here looking for the exact same thing, kernel 6.5 seems to be having problems with nvida gpu (390).
I made a function (put it in your .bash_aliases file or create a .bash_functions that you source at login)

kernel-default () {
 local _action=$1
 local _kernelver=$2
 if [[ ! "${_action}" =~ ^(set)$ || ! "${_kernelver}" ]] && [[ ! "${_action}" =~ ^(unset)$ ]]; then
    echo -e "\n\e[90m kernel-default <set|unset> (default list)\e[m"
     echo -e "\e[91m\n  No \e[4maction\e[;91m or \e[4;91mkernel\e[;91m ver defined, issue \e[mkernel-default set \$(uname -r)\e[91m as example,"
     echo -e "  or use any of the following existing:\e[m $(kernel-mgmt | awk -F "[-]" '/image/ {print $3 "-" $4}' | sed '$!N;s/\n/, /g')"
     echo -e "\n\e[94m    Example:\e[m kernel-default set $(uname -r | cut -d '-' -f1-2)\e[m\n"

     local _savedcustom=$(grub-editenv list | cut -d '>' -f2)
     if [ "${_savedcustom}" ]; then
         echo -e "\e[90m Default kernel override active: \e[m${_savedcustom}\n"
     else
         echo -e "\e[90m Default kernel override active: \e[mnone\n"
     fi
 elif [ "${_action}" == "set" ]; then
    local _mid=$(awk '/Advanced options for Ubuntu/{print $(NF-1)}' /boot/grub/grub.cfg | cut -d\' -f2)
    local _kid=$(awk "/with Linux $_kernelver/"'{print $(NF-1)}' /boot/grub/grub.cfg | cut -d\' -f2 | head -n1)
    echo -e "GRUB_DEFAULT=saved\nGRUB_SAVEDEFAULT=true" | sudo tee /etc/grub.d/95-savedef.cfg
    sudo chmod +x /etc/grub.d/95-savedef.cfg
    sudo grub-editenv /boot/grub/grubenv set saved_entry="${_mid}>${_kid}"
    sudo update-grub
 elif [ "${_action}" == "unset" ]; then
    sudo grub-editenv /boot/grub/grubenv unset saved_entry
    sudo rm -f /etc/grub.d/95-savedef.cfg
    sudo update-grub
 fi
}

you can use this to get the specific kernel you need, assuming is currently in use:

grep gnulinux-$(uname -r) /boot/grub/grub.cfg