Booting from USB Drives?

GilesP asks: "With so many USB flash drives around (like the pendrive, Targus Go-Anywhere, and others), and with the demise of the floppy disk, I began to wonder if it would be possible to boot from a USB drive? So your BIOS is going to need to support booting from a USB device, but what else would be involved? I'm primarily thinking about Linux here, but other OSes would be interesting too. These devices come in a range of sizes from 8Mb up to 1Gb, so there is plenty of room to hold a Linux installation. Has anybody done anything like this?"

Comments

Re:booting from pendrive

[disappear]

So, you need an initrd. No problem provided you can get lilo or grub or whateverelse to find and load it. All your initrd needs to do is to load up your USB modules, mount your root fs off of usb mass storage (/dev/sda1 or whatever weird devfs name you use) and then pivot_root over to it. This is mostly equivalent to an initrd setup for something like a network booting system that uses NFS root or fibre channel or something like that. Any initrd HOWTO will cover setting up an initrd that loads modules and performs configuration to mount the root device that the kernel cannot do on its own.

You missed a step:
The initrd has to have about a one-second delay before you attempt to mount the drive from USB. This is because it takes a little while to detect it.

If you make this one change (a little static binary that does 'sleep 1', essentially) to a standard Red Hat 'mkinitrd' ramdisk, you can indeed do USB if your BIOS supports it.

I've done it. It was a @!#$% to debug the first time around: every time I dropped into sash everything worked, but if I didn't drop into sash it didn't. :-)