How is grub updated after kernel installation

BW-userx · 05-11-2019, 07:35 AM

here is a grub on my one laptop.

Code:

$ cat /etc/default/grub
#
# Configuration file for GRUB.
#
GRUB_DEFAULT=saved
#save last distro booted
GRUB_SAVEDEFAULT=true
#GRUB_DEFAULT=0
#GRUB_HIDDEN_TIMEOUT=0
#GRUB_HIDDEN_TIMEOUT_QUIET=false
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="Void"
GRUB_CMDLINE_LINUX_DEFAULT="loglevel=4 slub_debug=P page_poison=1"
# Uncomment to use basic console
#GRUB_TERMINAL_INPUT="console"
# Uncomment to disable graphical terminal
#GRUB_TERMINAL_OUTPUT=console
#GRUB_BACKGROUND=/usr/share/void-artwork/splash.png
GRUB_BACKGROUND=/boot/grub/images/tuxkiller3.png
GRUB_GFXMODE=1920x1080x32,1600x900x32,1600x900x24,1600x900x16,auto
GRUB_GFXPAYLOAD="keep"
#GRUB_DISABLE_LINUX_UUID=true
#GRUB_DISABLE_RECOVERY=true
# Uncomment and set to the desired menu colors.  Used by normal and wallpaper
# modes only.  Entries specified as foreground/background.
GRUB_COLOR_NORMAL="light-blue/black"
GRUB_COLOR_HIGHLIGHT="light-cyan/blue"

what you are looking for is the advance options in the menu when you boot up, saving last boot might help, I'll have to reboot to check that, also you might be able to use 40_custom and write a menu in there that will always point to your specific kernel that you want to boot.

open up your /boot/grub/grub,cfg and use that as a template for the kernel you want. Where you can actually find it in the cfg file then copy that over into your 40_custom file in /etc/grub.d, save, update-grub, reboot, cross fingers.

Code:

    menuentry 'Slackware 14.2 x86_64 (post 14.2 -current) (on /dev/sdb2)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-/boot/vmlinuz-generic-4.19.41--d830e5b3-b05a-479f-9431-8cbd4dc0ccd6' {
                savedefault
                insmod part_msdos
                insmod ext2
                set root='hd1,msdos2'
                if [ x$feature_platform_search_hint = xy ]; then
                  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  d830e5b3-b05a-479f-9431-8cbd4dc0ccd6
                else
                  search --no-floppy --fs-uuid --set=root d830e5b3-b05a-479f-9431-8cbd4dc0ccd6
                fi
                linux /boot/vmlinuz-generic-4.19.41 root=/dev/sdb2
        }

the bold is where you'll find the kernel you are looking for to use.

with your last selection saved in your default grub if it does work then it will always default to that kernel unless you pick something different, because it works off of last menu option selected.

if all you want is the latest kernel installed on a particular OS, then just add this, and as stated, it will always be set to whichever menu option you used last, because it will always be selected on next boot. Just by adding this to your grub file.

Code:

GRUB_DEFAULT=saved
#save last distro booted
GRUB_SAVEDEFAULT=true

It is under advance options where that gets tricky because there usually is more than one kernel and mode to pick from and all that is being selected on the boot menu is the option to go into advance options where you then have to move to the kernel and mode yo want, then just go back to the beginning of this post and give that idea a try.

colorpurple21859 · 05-11-2019, 10:39 AM

At the grub menu when you first boot select the kernel you want to use. The next boot the same kernel you selected at the first boot should be saved kernel for the default.

mra90 · 05-12-2019, 04:21 AM

@BW-userx, @colorpurple21859, but I am afraid the next time I will build and install new kernel it will all be overwritten again right?

BW-userx · 05-12-2019, 02:09 PM

this is why we have version numbering system, and should have means for a custom naming scheme. So you can have a back up kernel if you want one. therefore, if you use the same version of kernel then apply the naming scheme to identify it for what it is.

You'll have to read up on that, or wait and hope someone else clues you in on the details more on that. Because I do not roll my own kernels.

colorpurple21859 · 05-12-2019, 08:57 PM

another option is to use grub-customizer to set default http://tipsonubuntu.com/2018/03/11/i...ntu-18-04-lts/

SaintDanBert · 09-27-2020, 02:38 PM

Quote:

Originally Posted by BW-userx

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colorpurple21859 · 10-01-2020, 03:44 PM

Quote:

@BW-userx, @colorpurple21859, but I am afraid the next time I will build and install new kernel it will all be overwritten again right?

Yes the default will change, However, as long as grub picks up the new kernel when update-grub is run, it will become the default when selected from the grub menu. The saved default lines in /etc/default/grub are for this when update-grub is run

zeebra · 10-04-2020, 06:10 AM

Quote:

Originally Posted by mra90

Thanks for the answer,

There are no words to express how GRUB annoys me

I try to setup default grub, I even found similar problem here

So what I do is I set GRUB_DEFAULT in /etc/default/grub to kernel name - FAIL, still boots the exact same kernel #0 from list. Then I didn't give up and try setting GRUB_DEFAULT to number/index regarding to menuentry in /boot/grub/grub.cfg - no luck again.

Here is content of my /etc/default/grub

Does anybody know why this crap doesn't boot the kernal I specify by GRUB_DEFAULT?

PS: of cource I do sudo grub-update after I change that /etc/default/grub file

Grub2 works on the principles of magic, prayer and hope. You can do and hope or you can try and pray, but generally things are just magically happening the way grump2 says it is to happen with no apparent logic or consistency..

autogen.magix