Re: [gentoo-user] Booting Gentoo from USB stick

[Jake Moe]

On 16/09/10 21:30, J. Roeleveld wrote:
> On Thursday 16 September 2010 12:01:43 Jake Moe wrote:
>>  On 09/16/10 16:22, J. Roeleveld wrote:
>>> On Thursday 16 September 2010 00:34:39 Jake Moe wrote:
>>>>  On 16/09/10 08:26, Dale wrote:
>>>>> Jake Moe wrote:
>>>>>> Thanks for that, I'll rebuild the genkernel with blkid support.
>>>>>>
>>>>>> As to the second suggestion, there is *no* /dev/sda1 (the partition in
>>>>>> question).  It just doesn't exist for some reason.  However, fstab
>>>>>> shows that it's mounted, and /sys/block has entries for the disk, so
>>>>>> I'm not sure why it's dropped out.  I'm guessing it has something to
>>>>>> do with udevd, or uevents?  Because shortly before that, I tell it to
>>>>>> find the root partition at /dev/sda1, and it starts to boot, but then
>>>>>> it loses it.
>>>>>>
>>>>>> Jake Moe
>>>>> The file fstab doesn't show what is mounted.  Either use the command
>>>>> "mount" with no options or cat /etc/mtab to see what is actually
>>>>> mounted.
>>>>>
>>>>> Dale
>>>>>
>>>>> :-)  :-)
>>>> Gah, it's too early.  That's what I meant to say (and previously said in
>>>> my original post): when I run "mount", it shows /dev/sda1 is mounted on
>>>> /.
>>>>
>>>> Jake Moe
>>> I wonder if it looses the "/dev" tree when it mounts the root-partition
>>> read only prior to running the fsck.
>>> That could explain why it's not there.
>>>
>>> Try building a dummy /dev-tree on your root partition with the correct
>>> device- nodes hardcoded for /dev/sdxxxxxx and see how far you get then?
>>>
>>> --
>>> Joost
>> Erm, you've gone a bit beyond my knowledge there.  Are you saying I
>> should go into the maintenance console, create a dummy /devdir, and try
>> to mknod the hard drive?  I assume I'd use something like 'mknod
>> /dev/sda c 8 0'?  If not, what do you mean, cause you've lost me.
>>
>> Jake Moe
> Ok, what I mean is that I think the following might happen:
>
> 1) root-dir from ramdisk is mounted under /
> 2) dev-tree is mounted under /dev
> 3) /dev/sda1 is mounted under /
> 4) at this point, /dev might no longer be accessible.
>
> Now, if you make sure that on the USB-root (/dev/sda1) the folder /dev is
> actually populated, then it might continue through the boot-process.
>
> Or, as you mentioned, issue "mknod ......."  commands while in that
> maintenance console, then it might be able to find the /dev/sda, /dev/sda1,...
> devices and continue.
>
> Please bear in mind, I have not actually used nor needed a ramdisk to boot
> from ever since I started using Gentoo.
> Not even when I played with booting from USB-sticks myself.
> I simply build the kernel with all the necessary drivers compiled-in and used
> that to boot from.
>
> This might also be an idea for you?
>
> --
> Joost
>
> Eg. if you do the mknod-commands to build the /dev/sda, /dev/sda1,.... device
> nodes, then it should be able to continue.
>
Well, I've finally gotten this to work with a manually config'ed
kernel.  Before, I was only getting kernel panics.  Now, after your
comment "all compiled-in", I took the old config I tried, did a sed to
change all "=m" to "=y", and recompiled, and it worked.  So obviously,
there was some option that I wasn't building into the kernel (only as a
module) that was needed to start from USB.

I had previously started from a working config I had previously used for
the same model PC that I was doing my testing on, and just changed the
USB drivers from modules to built-in, but apparently that's not enough. 
Any ideas what else is needed for a USB-stick boot that's not needed in
a SATA boot?  I'd like to a) find out what I missed, and b) be able to
cull the kernel back down again, so I can build up lots of SATA,
graphics and audio modules to make this able to boot (and work properly)
on other systems.

Jake Moe