[TriLUG] Live Linux on USB Flash Drive

[Alan Porter]

I found this script for converting a Ubuntu 7.10 CD to
a bootable USB.  I have not dissected it to see how it
works... something I plan to do, since I wrote a similar
utility for Tekelec.

Most of these scripts seem to use SYSLINUX (or ISOLINUX),
a tool that boots off of a CDROM and then loads the kernel
and initramfs into memory and then boots the kernel.

Alan

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#!/bin/bash
# Convert an Ubuntu live CD iso so that it's bootable off of a USB stick
# Copyright 2007  Red Hat, Inc.
# Jeremy Katz <katzj at redhat.com>
# Jani Monoses <jani at ubuntu.com> (slightly adapted to Ubuntu LiveCD)
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Library General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.


export PATH=/sbin:/usr/sbin:$PATH

usage() {
     echo "$0 [--reset-mbr] [--noverify] <isopath> <usbstick device>"
     exit 1
}

cleanup() {
     [ -d "$CDMNT" ] && umount $CDMNT && rmdir $CDMNT
     [ -d "$USBMNT" ] && umount $USBMNT && rmdir $USBMNT
}

exitclean() {
     echo "Cleaning up to exit..."
     cleanup
     exit 1
}

getdisk() {
     DEV=$1

     p=$(udevinfo -q path -n $DEV)
     if [ -e /sys/$p/device ]; then
	device=$(basename /sys/$p)
     else
	device=$(basename $(readlink -f /sys/$p/../))
     fi
     if [ ! -e /sys/block/$device -o ! -e /dev/$device ]; then
	echo "Error finding block device of $DEV.  Aborting!"
	exitclean
     fi

     device="/dev/$device"
}

resetMBR() {
     getdisk $1
     cat /usr/lib/syslinux/mbr.bin > $device
}

checkMBR() {
     getdisk $1

     bs=$(mktemp /tmp/bs.XXXXXX)
     dd if=$device of=$bs bs=512 count=1 2>/dev/null || exit 2

     mbrword=$(hexdump -n 2 $bs |head -n 1|awk {'print $2;'})
     rm -f $bs
     if [ "$mbrword" = "0000" ]; then
	echo "MBR appears to be blank."
	echo "Do you want to replace the MBR on this device?"
	echo "Press Enter to continue or ctrl-c to abort"
	read
	resetMBR $1
     fi

     return 0
}

checkPartActive() {
     dev=$1
     getdisk $dev

     # if we're installing to whole-disk and not a partition, then we
     # don't need to worry about being active
     if [ "$dev" = "$device" ]; then
	return
     fi

     if [ "$(/sbin/fdisk -l $device 2>/dev/null |grep $dev |awk {'print $2;'})" != "*" ]; then
	echo "Partition isn't marked bootable!"
	echo "You can mark the partition as bootable with "
         echo "    # /sbin/parted $device"
	echo "    (parted) toggle N boot"
	echo "    (parted) quit"
	exitclean
     fi
}

checkFilesystem() {
     dev=$1

     USBFS=$(/lib/udev/vol_id -t $dev)
     if [ "$USBFS" != "vfat" -a "$USBFS" != "msdos" -a "$USBFS" != "ext2" -a "$USBFS" != "ext3" ]; then
	echo "USB filesystem must be vfat or ext[23]"
	exitclean
     fi

     USBLABEL=$(/lib/udev/vol_id -u $dev)
     if [ -n "$USBLABEL" ]; then
	USBLABEL="UUID=$USBLABEL" ;
     else
	USBLABEL=$(/lib/udev/vol_id -l $dev)
	if [ -n "$USBLABEL" ]; then
	    USBLABEL="LABEL=$USBLABEL"
	else
	    echo "Need to have a filesystem label or UUID for your USB device"
	    if [ "$USBFS" = "vfat" -o "$USBFS" = "msdos" ]; then
		echo "Label can be set with /sbin/dosfslabel"
	    elif [ "$USBFS" = "ext2" -o "$USBFS" = "ext3" ]; then
		echo "Label can be set with /sbin/e2label"
	    fi
	    exitclean
	fi
     fi
}

checkSyslinuxVersion() {
     if [ ! -x /usr/bin/syslinux ]; then
	echo "You need to have syslinux installed to run this script"
	exit 1
     fi
     if ! syslinux 2>&1 | grep -qe -d; then
	SYSLINUXPATH=""
     else
	SYSLINUXPATH="syslinux"
	#menu texts are trimmed when syslinux is not in / no idea why
	SYSLINUXPATH=""
     fi
}

if [ $(id -u) != 0 ]; then
     echo "You need to be root to run this script"
     exit 1
fi

while [ $# -gt 2 ]; do
     case $1 in
	--noverify)
	    noverify=1
	    ;;
	--reset-mbr|--resetmbr)
	    resetmbr=1
	    ;;
	*)
	    usage
	    ;;
     esac
     shift
done

ISO=$1
USBDEV=$2

if [ -z "$ISO" -o ! -e "$ISO" ]; then
     usage
fi

if [ -z "$USBDEV" -o ! -b "$USBDEV" ]; then
     usage
fi

if [ -z "$noverify" ]; then
     # verify the image
     echo "Not verifying image...(no checkisomd5 in Ubuntu so skipping)!"
     #checkisomd5 --verbose $ISO
     if [ $? -ne 0 ]; then
	echo "Are you SURE you want to continue?"
	echo "Press Enter to continue or ctrl-c to abort"
	read
     fi
fi

# do some basic sanity checks.
checkSyslinuxVersion
checkFilesystem $USBDEV
checkPartActive $USBDEV
checkMBR $USBDEV
[ -n $resetmbr ] && resetMBR $USBDEV

# FIXME: would be better if we had better mountpoints
CDMNT=$(mktemp -d /media/cdtmp.XXXXXX)
mount -o loop $ISO $CDMNT || exitclean
USBMNT=$(mktemp -d /media/usbdev.XXXXXX)
mount $USBDEV $USBMNT || exitclean

trap exitclean SIGINT SIGTERM

if [ -d $USBMNT/casper ]; then
     echo "Already set up as live image.  Deleting old in fifteen seconds..."
     sleep 15

     rm -rf $USBMNT/casper
fi

echo "Copying live image to USB stick"
if [ ! -d $USBMNT/$SYSLINUXPATH ]; then mkdir $USBMNT/$SYSLINUXPATH ; fi

for file in \
	 README.diskdefines md5sum.txt \
	.disk casper pool dists preseed install;do
	cp -a $CDMNT/$file $USBMNT/
done

cp $CDMNT/isolinux/* $USBMNT/$SYSLINUXPATH

echo "Installing boot loader"
if [ "$USBFS" = "vfat" -o "$USBFS" = "msdos" ]; then
     # syslinux expects the config to be named syslinux.cfg
     # and has to run with the file system unmounted
     mv $USBMNT/$SYSLINUXPATH/isolinux.cfg $USBMNT/$SYSLINUXPATH/syslinux.cfg
     cleanup
     if [ -n "$SYSLINUXPATH" ]; then
	syslinux -d $SYSLINUXPATH $USBDEV
     else
	syslinux $USBDEV
     fi
elif [ "$USBFS" = "ext2" -o "$USBFS" = "ext3" ]; then
     # extlinux expects the config to be named extlinux.conf
     # and has to be run with the file system mounted
     mv $USBMNT/$SYSLINUXPATH/isolinux.cfg $USBMNT/$SYSLINUXPATH/extlinux.conf
     extlinux -i $USBMNT/syslinux
     cleanup
fi

echo "USB stick set up as live image!"

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