[gentoo-user] Root device as UUID not properly detected

[João Miguel]

Hello all,

I have decided to make a pen drive with Gentoo Linux installed, to have
a permanent pocket installation I can use in any computer as if it were
my own. The Gentoo Wiki guided me very well through it.

The problem I'm having only appears when I try to boot the pen drive
physically. That is, if I use a VM as such:

$ qemu-system-i386 -hda /dev/sdb -enable-kvm -m 2G

I have no error messages displayed. However, if I try to boot it from a
real PC, I get an error message alike "Could not find the root block
device in UUID=...". Now what is weird is this: in some PCs, if I click
Enter to try and use the same device, the system boots normally, or if I
drop to the shell, I can do blkid and see the root partition (usually
sdb4 or sdc4). But in at least one PC, the root device is not detected.
The same message appears even if I try for minutes. If I manually enter
the UUID or partition, it doesn't work either. It shows "Could not find
the root block device in ." (like in this question
https://forums.gentoo.org/viewtopic-t-971416.html)

The command I used to make the kernel and initram was
# genkernel --install --disklabel all
as I need basic support for any hardware.

I also found https://forums.gentoo.org/viewtopic-t-701116-start-0.html,
I expect the --disklabel option to help but the results are the same.

I use both UUIDs in /etc/fstab and /boot/syslinux/syslinux.cfg (tried
setting real_root and rootfstype besides root, no difference).

What sense does this problem make?! The BIOS sees the pen, syslinux
boots it using the UUID, why does the system suddenly forget where the
pen is?  Why does it have different behaviours in different computers,
and no problem as a VM? Is this a problem with the initrd, or with mdev?
I had a pen like this with Arch Linux and it ran just fine, maybe it was
because it used udev instead?

I hope you can help me, it's the 1st time I try Gentoo and it was going
so well! Thank you in advance,

João Miguel