On 09/05/16 13:32, Trent W. Buck via luv-main wrote:
Allan Duncan via luv-main <luv-main@luv.asn.au> writes:
I have a number of bootable USB sticks, all 32 bit. These work fine on all my boxes, and work quite well with the one box that will actually _boot_ USB3.
I would like to do a 64 bit variant of this and just tweaked an existing system to fit onto a 16 G USB stick. This starts off booting and then times out because it can't find the root device. Delving around in the minimalist emergency environment shows that the USB device is indeed not present - blkid shows all the other devices. The normal boot uses UUID identifiers and non-EFI.
The kernel in the initramfs has all the USB drivers builtin. Btw - is there an easy way to unpick initramfs - I found I needed to lop off the uncompressed leading cpio to get at the gzipped cpio filesystem that followed?
First of all we need to know what distro this is.
Debian (initramfs-tools) & Fedora (dracut) ramdisks work very differently. I've never seen the "lop off" part you describe on Debian. (I negligible experience with other ramdisks.)
Fedora. The first 12K or so is a two byte file "early_cpio" ("1\n") and a file structure "kernel/x86/microcode/AuthenticAMD.bin" The were wrapped with the usual cpio Header and Trailer. Immediately after the Trailer is the gzip "1f8b" magic number, and gunzip gave a file that I could use cpio to extract a fully populated filesystem with which to boot. The whole point of this exercise was to confirm the USB modules were in fact built in. In the distant past when I pulled apart the old format initrd there was no prolog, just straight into the gzip. I just went off chasing something about cpio in the kernel docos and found Documentation/x86/early-microcode.txt which talks about the above structure in reference to initrd, so it isn't very shiny new nor Fedora specific. Still doesn't explain why my 32 bit sticks boot. It doesn't help that I can't remember how I created the first of them.