Quoting Karanbir Singh mail-lists@karan.org:

nethub@gmail.com wrote:

...

With the decreasing price of USB Flash Memory Drives, I was wondering how I would go about creating a USB Flash Drive that could be used the same as CD 1 to install CentOS on my servers.

While you can boot from the USB Key, install from the usb key is not supported directly under anacoda. What you might need to do is ( if you have a 2.5 gig USB Key ), copy the install media onto the usb key, and then manually mount that under /mnt/sources at the right time.

I guess doing "linux askmethod" and then selecting hard drive (where hard drive is USB key) might work too. Never attempted that though. For minimal install, copying first CD might work. Also making "custom" insatallation tree containing only RPM packages he needs might work too (see http://www.linuxjournal.com/article/6473 for details, it's for RH8, see comments section for changes needed for more recent distros).

you need to get the diskboot.img file from the /images directory on CD1 ( or on mirror.centos.org/centos/4/os/<arch>/images/ ) and copy that onto the key ( eg. dd if=diskboot.img of=/dev/sdc ). reboot the machine, select boot from usb in the BIOS. And you are done.

Not so fast. There's no "standard" organization of data on USB key that every BIOS will recognize and boot. The most common are:

- emulate big floppy - emulate USB HD - emulate USB ZIP

Most will boot from "big floppy" type of USB key. Majority support USB ZIP (kinda complicated to make, see below). USB HD is a bit more rare to find (well, at least in my rather limited experience). I guess most BIOS manufacturers simply don't really care about booting from USB key (or USB devices in general)

I'll use /dev/sdc in examples, change this to whatever device your USB key is!!!

The "Big floppy" USB key is what Karanbir described. No partitions on USB key, you just dd the image to the master device (for example /dev/sdc). This is the least usefull configuration of the USB key, since you will be dedicating it for doing your installs (no point in storing your data on something you are going to flush from time to time).

For BIOSes that support booting from USB HD. You would use fdisk to create partition(s) on USB key (fdisk /dev/sdc), make one of them bootable, flush the image onto it (for example /dev/sdc1). In some cases you would need to use syslinux to install MBR onto /dev/sdc. When making partitions, and if you plan to use your USB key on Windows too, note that Windows will detect all partitions on USB key, but it will refuse to access file systems on anything but partition 1!?. It's just one of the Windows stupidities, you learn to live with it.

For BIOSes that support booting from USB ZIP. This is the most complicated to prepare (at least for general case and/or if you have picky BIOS). Much like USB HD, but you must have very special USB key organization.

First zero out any garbage you might have in first few blocks of you USB key (and you really want to do this, or your USB key might fail to boot after you go thruogh all the trouble preparing it). dd if=/dev/zero of=/dev/sdc count=10 will do the job. You need to use expert mode of fdisk to change number of "heads" to 64 and number of "sectors/track" to 32. These numbers are from real ZIP diskettes, and this is what your BIOS will expect to find.

Calculate how many cylinders you'll need (you must change this if you change number of heads or sectors/track). See output of dmesg or check messages file to see how many blocks your device has and then make calculus based on that. For example, my Kingston reports "SCSI device sdc: 1006592 512-byte hdwr sectors (515 MB)". That gives 1006592/64/32 = 491.5, round down to 491 cylinders (do not round up, you'll exceed the device size).

Back to normal mode, and create partition 4. The partition 4 must be at the beggining of the disk (cylinder 0). Again, this is how real ZIP diskette looks like, and your BIOS expects to find. Some BIOSes don't care if this partition is not entire USB key (so you can create partitions 1, 2, and/or 3 after it for some other purposes). Do not make this partition bootable (some BIOSes don't recognize it as USB ZIP if you do, some will even choke if there's syslinux in MBR, some simply don't care). Finally, dd the image to this partiton (example /dev/sdc4) and hope it will boot.

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