[gentoo-user] Re: Exact setting in grub to default to a kernel by name?

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2021-06-13, Walter Dnes <waltdnes@waltdnes.org> wrote:
> On Sun, Jun 13, 2021 at 05:38:53PM -0000, Grant Edwards wrote
>> On 2021-06-13, Walter Dnes <waltdnes@waltdnes.org> wrote:
>> 
>> >   I'd be tempted to do a manual gub.cfg if I had documentation.
>> 
>> I gave up on the grub2 auto-magical config system many years ago. My
>> grub.cfg is typically 10-20 lines long. The documentation is at
>> 
>>   https://www.gnu.org/software/grub/manual/grub/grub.html
>> 
>> For manual confiuration: see section 6:
>> 
>>   https://www.gnu.org/software/grub/manual/grub/html_node/Configuration.html#Configuration
>
>   When experimenting with this, I'll backup grub.cfg.  If things go
> awry, boot with the USB key I used for the install, and copy back the
> old known working grub.cfg.  I've done a first crack at this.  I assume
> that nothing in /etc/default/grub will have any effect.  Questions...
>
> 1) Is "insmod extfs3" necessary? I've built extfs3 into the kernels.

I've never used it it, and my boot partitions are always ext3/4 

> 2) I assume that the the first "menuentry" will be the default boot?

Unless you set the `default` variable to something other than 0

> 3) Is the default timeout still 5 seconds?

Dunny, I always set 'timeout=10'

> 3) I assume that 640x480 is supported on just about every monitor
>    out there.  I want as large text as possible.  My eyes are
>    getting old... just like me.  Any obvious errors in the following
>    grub.cfg?



>
>=====================================================================
> menuentry 'Linux Experimental' --class gnu-linux {
>         set gfxpayload=640x480
>         insmod ext3fs
>         set root='hd0,gpt1'
>         linux   /vmlinuz-experimental root=/dev/sda2 ro  noexec=on net.ifnames=0 intel_pstate=disable ipv6.disable=1
> }

I don't know if you really need the gfxpayload or the insmod lines, I don't
recall ever needing those to boot kernels from ext3/4 partitions.

All my grub.cfg files looks like this:

========================================================================
timeout=10
root=hd0,1
default=0

menuentry 'vmlinuz-5.10.27-gentoo' {
  linux /boot/vmlinuz-5.10.27-gentoo root=/dev/sda1
  }
 
menuentry 'vmlinuz-5.4.97-gentoo' {
  linux /boot/vmlinuz-5.4.97-gentoo root=/dev/sda1
  }
========================================================================

> Something that occured to me.  Can I move the duplicated lines to the
> top of the file and take them out of the menuentries?  E.g.

Yes.