Building your own USB pendrive Linux image
I don’t know about you, but whenever I leave the house I have the same six items in my pockets (in order of certainty with which I believe I’m going to need them) - keys, wallet, phone, handkerchief, penknife and, as of the end of December, a 1GB USB stick with a basic Debian Live system on it.
Before December, had I been asked at a party “Exactly how geeky are you?”, I’d have meekly to have replied “Fairly.”. Henceforth, though, I shall be able to reach in to my pocket and say “Well, if you have a computer that can boot from USB mass storage and that’s configured to do so in the BIOS, I can show you…”. Of course, having such a device won’t just make you popular with the ladies - there’s a chance it’ll also have practical applications. Without further ado then…
First thing you’ll need is (at time of writing) a Debian Lenny (or more recent) install. Real men run unstable, but if you’re sitting there with Etch (running Firefox 0.0.1a on your Linux 2.0.34 machine) you can easily enough conjure up a suitable chroot with the standard:
debootstrap lenny chroot chroot chroot
(There is, I should warn, some scope for confusion when you attempt the following inside a chroot, because the scripts create their own chroot)
Next thing to do is to install the helper packages:
apt-get install live-helper
We’re going to build the image in a fresh folder somewhere. You’ll want to pick a filesystem with plenty of disk space (~5GB) just to be on the safe side. In the fresh folder, typing lh_config will create the config directory for the image building scripts:
mkdir live cd live lh_config
We want to tweak some of the config files - it’d be pretty dull to go to this effort just to build a vanilla image. Below I’ve listed the changes I made to build my ‘dream’ install. The variables listed already exist in the files - you just need to change them to match what’s below:
# In 'config/binary' LH_BINARY_IMAGES="usb-hdd" LH_BOOTAPPEND_LIVE="locale=en_GB.UTF-8 keyb=uk" # In 'config/bootstrap' LH_SECTIONS="main contrib non-free" # In 'config/chroot' (you won't want the linebreaks) LH_PACKAGES="dns2tcp doc-base dsniff ettercap ettercap-common less vim wireless-tools iceweasel icedove gaim curl openssh-client openssh-server irssi centerim hexdump iproute iptables nemesis nmap ntop privoxy socat tcpdump tor wireshark wireshark-common firmware-ipw3945 ipw3945d ipw3945-modules-2.6-486 ncftp telnet netcat fluxbox eterm xserver-xorg xfonts-base"
The idea with those package selections is a) to make you dangerous and b) to enable you to punch a hole through to the internet wherever possible. Once online, you can obviously install whatever else you need.
You’ll also want to:
mkdir -p config/chroot_local-includes/etc/skel/ echo fluxbox > config/chroot_local-includes/etc/skel/.xinit
This image boots to console, but typing startx will give you an X session (assuming it can detect and load the correct graphics driver).
To build the image, simply type
lh_build
Your completed image will appear as binary.img in that folder (weighing in at around 235Mb). In the event that something screws up, it’s important to understand that the state for the build process is tied up in the .stage folder. Until you notice that hiding there, the whole system can seem a bit mysterious.
All that remains is to transfer the image to your pendrive.
CAUTION: This next instruction is a dd onto a block device. My pendrive is /dev/sdb, but for all I know on your system that’s the SATA hard disk containing the only copy of your doctoral thesis.
dd if=binary.img of=/dev/sdb
You’re done. You should be able to reboot into that (assuming your BIOS supports it and is correctly configured). Couple of extra things to point out. The dd copies across a boot sector and the first partition. You can use fdisk to create further partitions on the device if you want a little read-write space. Specifically, if you type live persistent at the SysLinux prompt:
live-initramfs will look for persistent and snapshot partitions or files labeled “live-rw”, “home-rw”, and files called “live-sn*”, “home-sn*” and will try to, in order: mount as /cow the first, mount the second in /home, and just copy the contents of the latter in appropriate locations (snapshots). Snapshots will be tried to be updated on reboot/shutdown. Look at live-snapshot(1) for more informations.
More details in the manpage. To label a partition, you’re looking for:
mke2fs -L your_label /dev/sdbX
after you’ve created it in fdisk
The astute among you may spot the live-magic package. This is a GUI front-end to the process I’ve just described, but not something I’ve actually tried to use.