[gentoo-user] booting - I don't anystand how the (Linux) world works anymore

[Helmut Jarausch]

Hi,

I'm a dino since I still use grub-1 but I prefer recent kernels  
(currently 4.70-rc4)

I don't understand  the   'root=' option on the boot line like
kernel /boot/vmlinuz-4.7.0-rc4 root=/dev/sda1

Here my bad experience:

Having booted by SystemRescueCD from the cdrom device, my root device  
is labelled  /dev/sda1
  BUT trying to use that on the kernel boot line fails (the kernel  
cannot find the root file system)

By trial and error I've found that I have to use   root=/dev/sdb1

but if I plug in an external drive (via USB) this doesn't work any more.

So, I came up with    root=UUID=uuid_number of the root file system.

But to my surprise I now got  a kernel panic
syncing: VFS: unable to mount root fs on unknown block(0,0)

So, please tell me what I'm missing?

Many thanks!!!
Helmut