Thoughts on running Linux from a Flash card.
When I was away on vacation last month, I realized that it would be *really* great if I could have carried my computer with me on my travels, but who wants to lug a whole computer through the Swiss Alps?!
I had previously heard about Puppy Linux and qemu-puppy which are tailor-made linux distributions that come directly as a bootable ISO image and can be put on a flash disk. This seemed like a great compromise: Bring your whole ‘computer’ sans hardware, wherever you go. qemu-puppy was of particular interest to me, because it could either be booted directly from a USB disk, or it could be run in the qemu emulator.
There are a lot of situations where re-booting just isn’t possible. Think about visiting an internet cafe: You don’t want to be seen rebooting their computer, changing the BIOS to be able to boot from USB, and then rebooting into your own system. Never mind hotel lobbies, or your friends desktop at home. Making these kinds of changes are just not cool.
Evaluating emulation
So, If rebooting isn’t an option, then that leaves emulation. There are several emulated or virtual environments available, so I took a look at the 3 main options available. Here’s my summary:
- VMWare (Linux, Windows, Mac)
- Con: Requires administrator install. (This will be impossible in internet cafes, and rude on friends/family computers)
- Con: Uses proprietary image creation tools (Although some workarounds exist)
- Pro: Fast & fairly standard. May be pre installed in some locations?
- Con: No ‘unaccellerated’ (i.e. fully emulated) mode available.
- Qemu (Linux, Windows, Mac)
- Con: Requires administrator install for accelleration
- Pro: Can run unaccellerated without administrator install, which is slow, but works.
- Pro: Player can be used without running an installer.
- Pro: Open source tools for image creation.
- Con: Because of limitations in qemu disk format and fat32, 4GB is the largest single disk that can be made.
- Pro: Supports both encrypted and sparse image formats.
- Pro: Available on Mac, Linux, Windows for free.
- kvm (Linux-only)
- Pro: Just like qemu, except fully accellerated when available on Linux systems.
- Con: Would require an administrator install if not already present.
So, I began to focus in on building a system inside a qemu image, that would run either accellerated when available (i.e. at home and work) and that still had reasonable performance when running un-accellerated. So, I began to download and install a variety of pre-packaged distributions, and that also made me come up with my personal requirements, which I’ll include here first:
System requirements
- Must run in qemu, both accellerated (kqemu, kvm, etc.) and unaccellerated. Worst case boot time must still be ‘reasonable’.
- Must include some way to run X11 applications, including a fully fledged browser and windowing tools (Firefox 3.x, window manager, toolbar, terminal emulator, etc.)
- Ideally would be based on a standard distribution, and easily upgradeable as new software arises
- Must also include a reasonable set of commandline tools for doing terminal-only work when running unaccellerated (i.e. emacs, screen, and all the other ‘regular’ unix tools)
- Must not boot directly into X11, and must not use an X11 login (gdm, etc.) screen. These are too heavyweight when booting unaccellerated
- Must fit in a 4G image.
- Must have a clean, uncluttered X11 interface
The distributions
- Puppy Linux & qemu-puppy
- Too ugly
- Has a graphical login screen
- Uses a non-standard web browser
- Uses a non-standard distribution, so hard to upgrade
- DSL (Damn Small Linux)
- Boots *really* fast!
- Ugly
- Uses a non-standard web browser
- Uses a non-standard distribution, so hard to upgrade
- Lots of missing tools, and no ‘apt-get’ to install things (i.e. emacs)
- ubuntulite
- Con: Has a weird install process with alternate repos
- Con: Still uses graphical login
- Pro: Mostly standard ubuntu
- Con: Not any better than a trimmed down ubuntu-jeos
- xubuntu
- Con: Way too many services running for a small VM
- Con: Uses too much CPU when sitting “idle”
- ubuntu-jeos
- Pro: Kernel built specifically for VMs
- Pro: Standard ubuntu otherwise (trimmed down base install)
- Con: No X11 or graphical UI at all (but easy to install!)
- Pro: Easy to install new packages, easy to upgrade.
- Pro: Installs as a ‘real’ fully fledged distro, not as a live CD or specially tailored distro.
- Con: Only Xorg server is available (no Xvesa, as far as I can tell).
So, I decided to start with ubuntu-jeos as my base, and to customize from there. My biggest insight wast that I realized that I don’t really need to run a “physical” X11 server, I could just run a VNC server, and export a graphical display that way. The VNC server is much lighter weight than Xorg, its easy to start and stop on the commandline (no complicated configs) and it makes the VNC viewer take the brunt of the CPU needed to power the display. Some quick experiments showed that this was all true!
My best case image is now:
- Base ubuntu-jeos install
- VNC server
- emacs-nox
- sshd
Which gives me all kinds of interesting options. The system boots up in text mode, and from there, I can either:
- Work strictly in the text UI, if I’m just doing something simple.
- Start a VNC server and run programs inside that, if local X11 isn’t available.
- If local X11 is available, then I can use ssh with X11 forwarding to run programs in the VM and have them displayed locally.
This is a really flexible setup! A 4GB flash drive is large enough to hold the entire VM image, as well as some local tools, like Windows & Mac SSH clients, VNC viewers, qemu emulator binaries, etc. So, on one flash drive, I have a complete computer (sans hardware) and enough support binaries in the emulators to run it pretty much any way I like, with no install on the host computer necessary! Sweet!
I am thinking about putting a system like this together myself, any hints? I have been using qemu puppy for a couple of weeks now, and it is great, the one advantage of it over your system is that (at least I think) it can be booted natively as well, and when it is it runs very fast, which is at least nice to get it up and running as a system. I would love to hear how this worked out for you though…
This looks really good and I would love to have the same setup on a USB but from the article I’m not sure how to go about it. Please could you make it a little more step-by-step or link to another resource
Thank you.
I tried the steps above to discover that Ubuntu under qemu runs extremely slowly on a 3.2 GHz dual core. This is because the accelerated mode is only runnable if the administrator privileges are accessible. Since they aren’t on this computer, that means that it takes about 10 miinutes to start up the Ubuntu Live CD, two minutes to open the networking dialogue, five seconds (or more) to see the results of any click on a menu item.
Any hints to speed it up?
Hi Tom,
I haven’t tried this method with newer (9.04) ubuntu installations, but I know that the Live CD is a graphical installer, and that will be outrageously slow, as you mention. The JEOS respin was canned for 9.04, so I would suggest starting with the “alternate” install disk, which will have a text based installer. You can download that from here: http://www.ubuntu.com/getubuntu/downloadmirrors#alternate
The biggest thing to remember is that you don’t want to boot directly into a graphical system when you’re running off flash under emulation. That will be horribly slow. The right way to think about it is to boot into text mode, and use either VNC or a remote display to do any graphical work that you need to do.
Granted, without accelleration, it will still be slow, but I found VNC under emulation to actually be a fairly workable solution.