Re: [gentoo-user] Can't boot btrfs

[Rich Freeman]

On Fri, Jul 31, 2015 at 5:35 AM, Peter Humphrey <peter@××××××××××××.uk> wrote:
> menuentry 'Gentoo Linux 4.0.5, no network' {
>         linux /boot/kernel-x86_64-4.0.5-gentoo root=/dev/sda3 softlevel=nonet
> net.ifnames=0 irqpoll
> }

As Neil already pointed out, if you're not using an initramfs you need
to put all your devices on this line if they're part of an array.  The
kernel will not scan to find the others.

If you do use an initramfs you really should use a UUID or label
instead of a device name, but a device name will work as long as it
happens to not get reordered on you.

>
> The other thing I've tried is to build an initramfs with dracut. I tried to
> include its btrfs module but it refused because it couldn't find a command
> btrfs. So I recompiled the kernel with btrfs as a module and added
> 'filesystems+="btrfs" ' into dracut.conf. Still no success.
>

Do you have btrfs-utils installed?  Dracut should work fine with btrfs
built into the kernel natively or as a module, though if you want to
boot directly it will have to be native (which is one of the reasons
most distros always use an initramfs - they want a modular kernel but
can't predict what your root is running on).

I believe that as long as dracut can find the btrfs utility it will
put it in the initramfs.

Otherwise there isn't much more to this - I think these two issues are
the only real problems you're having, depending on which route you
decide to take with the initramfs (which I still recommend, but you
could of course have separate grub lines to boot with and without it
if you want to experiment).

-- 
Rich