Installing Debian in a pendrive formatted with VFAT in a loopback device

Making your own 'Debian live' system on a pendrive formatted with VFAT with debootstrap

Earlier I had some instructions on how to install Debian Squeeze in a pendrive by first formatting it into ext2. This turns not to be a good solution since there are issues with NAND sectors alingnment and such that do not make it a good idea to use ext2 directly in the pendrive.

Debootstrap and a regular linux installation relies on writing a lot of small files. For this, better performance is achieved by using a loopback device formatted with ext2 on top of the vfat partition.

This means switching from grub to SYSLINUX for boot :)

1. Creating the loopback fs
2. Debootstrap over the device
3. Setting up root password and create initrd for loop device
4. Installing syslinux
5. Testing with kvm
6. Reboot, select your pendrive to boot and enjoy :>

1. Creating the loopback fs

To create a 4 GB image, the maximum filesize that can be stored in a FAT32 system:

 .
 cd /mnt/mount_point_for_the_vfat_pendrive
 dd if=/dev/zero of=wheezy.img bs=1M count=4M
 mkfs.ext2 -m 0 wheezy.img
 mount -o loop wheezy.img /mnt/pendrive

2. Debootstrap over the device

I use apt-cacher-ng, change the url of the debian mirror as needed

 debootstrap wheezy /mnt/pendrive/ http://127.0.0.1:3142/ftp.rediris.es/debian/

3. Setting up root password and create initrd for loop device

 mount -o bind /dev/ /mnt/pendrive/dev/
 mount -t proc proc /mnt/pendrive/proc
 mount -t sysfs sys /mnt/pendrive/sys/
 chroot /mnt/pendrive /bin/bash
 passwd root
 apt-get update
 apt-get install locales
 dpkg-reconfigure locales
 # Select a locale of your convenience
 apt-get install linux-image-amd64
 # Get loop script from http://pigeond.net/blog/2006/06/11/pikkoro-episode-2-loopback-rootfs-with-debian/
 cd /usr/share/initramfs-tools/scripts
 wget http://pigeond.net/misc/loop
 cd /etc/initramfs-tools
 # --- cut into vi modules ---
 usbcore
 ehci-hcd
 ohci-hcd
 uhci-hcd
 usb-storage
 sd_mod
 loop
 ext2
 ext3
 vfat
 jbd
 nls_iso8859_1
 nls_cp437
 nls_utf8
 # ---------------------------
 # if you regenerated the vfat in the drive with mkfs.vfat, probably
 # you need nls_utf8 (it was not in the above tutorial). It does no harm
 # tough
 dpkg-reconfigure initramfs-tools
 # A new initramfs is in /boot/initrd.img-3.2.0-4-amd64
 # /preroot is used by the loop script to mount the vfat partition,
 # create it
 mkdir /preroot
 # exit from the chroot
 exit
 # Out of the chroot now
 umount /mnt/pendrive/sys; umount /mnt/pendrive/proc; umount /mnt/pendrive/dev
 cp /mnt/pendrive/boot/vmlinuz-3.2.0-4-amd64 ./vmlinuz
 cp /mnt/pendrive/boot/initrd.img-3.2.0-4-amd64 ./initrd.img
 # Renaming to comply with 8.3 old MSDOS fs limitations
 umount /mnt/pendrive
 cd ..
 umount /mnt/<mount_point_for_the_vfat_pendrive>

4. Installing syslinux

 apt-get install syslinux
 dd conv=notrunc bs=440 count=1 if=/usr/lib/syslinux/mbr.bin of=/dev/sdb
 parted /dev/sdb set 1 boot on
 syslinux --install /dev/sdb1
 
 mount /mnt/<mount_point_for_the_vfat_pendrive>
 cd /mnt/<mount_point_for_the_vfat_pendrive>
 --- copy contents of syslinux.cfg ---
 DEFAULT  Wheezy
 PROMPT   1
                  
 LABEL    wheezy
 KERNEL   vmlinuz
 APPEND   initrd=initrd.img root=/dev/sdb1 boot=loop rootfstype=vfat loopfile=/wheezy.img loopfstype=ext2
 TIMEOUT  100
 -------------------------------------

5. Testing with kvm

We have the root filesystem in /dev/sdb1, and there is no easy way to tell qemu-kvm that we want to boot from hdb (second hard drive, so we trick it a bit (as root):