[SOLVED] Grub2 with generic kernel

M0M0 · 02-18-2021, 06:46 AM

The documentation about using the generic Kernel assumes that one uses lilo, but I'm using Grub2. I created inird.gz and when I select the generic Kernel in the Grub menu it works fine. But by default it still boots the huge kernel. So what should I do to boot the generic Kernel by default?

teoberi · 02-18-2021, 06:55 AM

/etc/default/grub
Options:

Code:

GRUB_DEFAULT

Code:

GRUB_DISABLE_RECOVERY="true"

and

Code:

GRUB_DISABLE_SUBMENU=y

/etc/grub.d/10_linux
the line:

Quote:

for i in /boot/vmlinuz-* /vmlinuz-* /boot/kernel-* ; do

allows you to configure menu lines for the desired kernels.
In order not to load initrd to the huge kernel for the time being, the solution found is to comment the line in the /boot/grub/grub.cfg file.

drgibbon · 02-18-2021, 06:57 AM

For that I stole the generic kernel entry from /boot/grub/grub.cfg and put it in /etc/grub.d/06_custom

I'm sure yours will be different, but just for illustration, my 06_custom file:

Code:

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry 'Slackware-14.2+ GNU/Linux (generic)' {
    load_video
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='hd1,msdos1'
    if [ x$feature_platform_search_hint = xy ]; then
        search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1  <drive-uuid>
    else
        search --no-floppy --fs-uuid --set=root <drive-uuid>
    fi
    echo    'Loading Linux ...'
    linux   /vmlinuz-generic root=/dev/mapper/cryptvg-root ro
    echo    'Loading initial ramdisk ...'
    initrd  /initrd.gz
}

After that, a `grub-mkconfig -o /boot/grub/grub.cfg` should generate the right file.

M0M0 · 02-18-2021, 08:07 AM

Quote:

Originally Posted by teoberi

/etc/default/grub
Options:

Code:

GRUB_DEFAULT

Code:

GRUB_DISABLE_RECOVERY="true"

and

Code:

GRUB_DISABLE_SUBMENU=y

/etc/grub.d/10_linux
the line:

allows you to configure menu lines for the desired kernels.
In order not to load initrd to the huge kernel for the time being, the solution found is to comment the line in the /boot/grub/grub.cfg file.

Thanks for your reply! But I do not understand what I should do. If never done any configuration on grub, so how should I configure this line?
Also you suggested to configure /boot/grub/grub.cfg but this files says that it shouldn't be modified so I'm not sure if this is the correct approach.

M0M0 · 02-18-2021, 08:09 AM

Quote:

Originally Posted by drgibbon

For that I stole the generic kernel entry from /boot/grub/grub.cfg and put it in /etc/grub.d/06_custom

I'm sure yours will be different, but just for illustration, my 06_custom file:

Code:

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry 'Slackware-14.2+ GNU/Linux (generic)' {
    load_video
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='hd1,msdos1'
    if [ x$feature_platform_search_hint = xy ]; then
        search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1  <drive-uuid>
    else
        search --no-floppy --fs-uuid --set=root <drive-uuid>
    fi
    echo    'Loading Linux ...'
    linux   /vmlinuz-generic root=/dev/mapper/cryptvg-root ro
    echo    'Loading initial ramdisk ...'
    initrd  /initrd.gz
}

After that, a `grub-mkconfig -o /boot/grub/grub.cfg` should generate the right file.

There is no 06_custom file. I have a 40_custom and a 41_custom. So which one should I modify?

drgibbon · 02-18-2021, 08:34 AM

Quote:

Originally Posted by M0M0

There is no 06_custom file. I have a 40_custom and a 41_custom. So which one should I modify?

Neither, you create a new custom file, but make it a number lower than the 10_linux (which detects Linux kernels). That way when you run `grub-mkconfig -o /boot/grub/grub.cfg` the 06_custom stuff ("06" is not forced, just <10) will come before the auto-detected 10_linux stuff. You set your custom file to pick up your generic kernel only, and then grub will always boot that one first.

No doubt there's other ways to do it, but that's how I've got my system set up. The benefit is that after kernel upgrades it's enough to:

# generate new initrd if necessary (I use `mkinitrd -F`)
# grub-mkconfig -o /boot/grub/grub.cfg

and you're done (no need to edit grub.cfg or anything like that).

colorpurple21859 · 02-18-2021, 10:30 AM

Another option If your not multi-booting with other linux distros is to edit the first menu entry in /boot/grub/grub.cfg and don’t never run grub-mkconfig again.

teoberi · 02-18-2021, 11:28 AM

Quote:

Originally Posted by M0M0

Thanks for your reply! But I do not understand what I should do. If never done any configuration on grub, so how should I configure this line?
Also you suggested to configure /boot/grub/grub.cfg but this files says that it shouldn't be modified so I'm not sure if this is the correct approach.

Code:

        for i in /boot/vmlinuz /boot/vmlinuz-generic ; do

This way you will only have the menu lines for vmlinuz and vmlinuz-generic.
GRUB_DISABLE_SUBMENU and GRUB_DISABLE_RECOVERY from /etc/default/grub (the GRUB configuration file) are easy to understand.

GRUB_DEFAULT=0 defaults to first menu option (vmlinuz)
GRUB_DEFAULT=1 defaults to the second menu option (vmlinuz-generic)
In this way it is not necessary to run the command:

Code:

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

when updating the kernel but it is still necessary to create initrd.
If you can, try in a virtual machine eg. VirtualBox.

upnort · 02-18-2021, 11:47 AM

Quote:

So what should I do to boot the generic Kernel by default?

That is because by default /boot/vmlinuz is sym linked to the huge kernel.

The problem can be avoided by not using the sym link vmlinuz in grub.cfg and instead use the full file name /boot/vmlinuz-generic-4.4.240.

Hangaber · 02-18-2021, 11:52 AM

Possibly just a typo, but if your initrd file is called "inird", change it to initrd.gz or something that the "11_linux_slackcustom" looks for (lines 194 to 204).

The exact filename of the generic kernel is important too. When I run grub-mkconfig, the generic kernel is added first (with the initrd) and so that boots by default.

You can test what order the line teoberi posted is finding files by running something like this one-liner;

Code:

for i in /boot/vmlinuz-* /vmlinuz-* /boot/kernel-*; do echo $i; done

aikempshall · 02-19-2021, 01:33 AM

Quote:

Originally Posted by M0M0

The documentation about using the generic Kernel assumes that one uses lilo, but I'm using Grub2. I created inird.gz and when I select the generic Kernel in the Grub menu it works fine. But by default it still boots the huge kernel. So what should I do to boot the generic Kernel by default?

Once I've convinced myself that the generic kernel gives me all I need, I do this. Delete kernel-huge via slackpkg, then recreate initrd and grub.cfg.

teoberi · 02-19-2021, 02:25 AM

Kernel-huge without loading microcode for the processor and without initrd can be considered as a backup solution in case of problems related to loading microcode or initrd.
I leave it as the first option in the GRUB menu without any changes.
There is also the alternative with Slackware DVD + chroot but it is a bit more work!

M0M0 · 02-19-2021, 02:30 AM

Quote:

Originally Posted by upnort

That is because by default /boot/vmlinuz is sym linked to the huge kernel.

So could I just symlink vmlinuz to the generic kernel? That sounds easiest and least scary to me

teoberi · 02-19-2021, 02:32 AM

Quote:

Originally Posted by M0M0

So could I just symlink vmlinuz to the generic kernel? That sounds easiest and least scary to me

Not!
If you want GRUB, document yourself first, eventually test it in a virtual machine (VirtualBox) and it won't scare you so much!

M0M0 · 02-19-2021, 02:32 AM

Quote:

Originally Posted by aikempshall

Once I've convinced myself that the generic kernel gives me all I need, I do this. Delete kernel-huge via slackpkg, then recreate initrd and grub.cfg.

Thanks, but I would like to keep the huge kernel for a reason: If I move the boot drive to another machine with different hardware I need the huge kernel, right? This is something I need to do some times.