| Figure 1: kutti in action. The flat object on the left its disk. The pen leaning against kutti is to gauge her size. |
Debian on a Slug |
One of the things that caught my eye at SCalE5x was the booth of the “Sluggers”. One consequence of this is that I am typing this article while listening to music emerging from a slug which also acts as my file backup service. I'm getting ahead of the story. So let me start in a more practical way …at the beginning.
It is now possible (and has been since about 2003) to set up Debian GNU/Linux on a small network attached storage (NAS) device which can act as:
…and possibly do all of these at once. One such NAS is called the NSLU2 and is made by Linksys (now a division of Cisco). There are other such NASes available—see http://www.nslu2-linux.org/ for details.
Figure 1: kutti in action. The flat object on the left its disk. The pen leaning against kutti is to gauge her size.
Once an NAS device is “converted” to the “Church of Free Software” it is known as a “Slug” to its friends like “GNU” and “Tux”.
Placing an order for an NAS device is easy but one needs to make sure that one also has a USB disk storage device with at least 2GB of spare storage—I happened to have an 80GB disk which I use to carry around1 my music collection.
A “flash” type disk will also work but for the typical installation you need at least 1GB and preferably two. Since the NSLU2 has only 32MB of RAM you must create a swap partition. Also note that:
So some more impatience waiting for an external disk. It all turned out well in the end since the new RC2 Debian installer became available on the same day that the disk arrived.
The NAS has an ethernet port and you can use that to connect to it with a PC for the installation phase. At the same time the NAS will be using that same port to download software so your PC needs to have some way to get onto the network. I used my laptop which has two interfaces—ethernet and wi-fi. I connected the NAS to the laptop via ethernet and used the wi-fi to connect the laptop to the net. An alternative is to plug the NAS directly into a LAN which is connected to your PC. It is enough if your PC can use this same connection to access the internet; you don't want to put your slug onto the internet until it has “grown up”!
Like any conversion process, the initial steps are the hardest.
Have we burnt all our bridges?
I recalled the time when I first installed GNU/Linux on a PC, as the same fears were present then. This was more critical when the cost was a large proportion of ones monthly earnings—like > 100%! At least this is no longer true.
It is clear now that those fears were unfounded and I think the words “Don't Panic” should be printed in large letters on all these gadgets2. At the same time it must be said that it is possible to “brick” your device. However, if you follow the instructions then it is unlikely3.
In the case of PCs, we have learnt that all is well as long as one does not damage the BIOS4. For the slug the equivalent is “RedBoot”—you do not erase/replace the RedBoot on a slug unless you are very confident with a soldering iron or are a slug-killer. Anyway, all the interesting stuff happens after the RedBoot has done its stuff so why bother to change the RedBoot?
In spite all the helpful hints all over the Web the actual decision to go ahead with the installation was the hardest step. After some vacillation the following thought occurred to me: “If I don't install Debian on this it will feel like a brick to me anyway!”
The NSLU2 already runs Linksys' own version of GNU/Linux. They have posted the sources on their web page as well. So you needn't feel guilty about connecting to the NSLU2 and playing with the web interface—even if you are a true believer.
The default boot-up address of the NSLU2 is 192.168.1.77 and so you
need to have an address in that network to connect to it. The
simplest way to do this is:
ifconfig eth:0 192.168.1.1 netmask 255.255.0.0
An advantage of using the 192.168.1.1 address is that the
NSLU2 uses that as its DNS server and gateway. After you have this
set up you can point your browser window (even w3m works!) at
http://192.168.1.77/ to play with the Linksys web interface.
The manual explains that you can login as admin with password
admin in order to perform administrative tasks.
The NSLU2 can also be reached during the RedBoot phase. Immediately
after pressing the power-on switch (<2 seconds
after boot up) you can do telnet 192.168.0.77. Note the
`0' instead of the `1'. This is the reason for the
netmask chosen above. I didn't do anything much with this interface
except to get familiar with it “just in case”!
Meanwhile, you may wish to have the following preparatory tasks done on the laptop. (I am never that efficient but at least others can be!)
slug-firmware.net web site. The patch is required since the
NSLU2 ethernet card requires firmware which can be downloaded from the
Intel web-site after accepting an end-user license; The patch adds
this to the RC2 image.
mke2fs on the partition chosen for root.
7z x debian-etch-rc2-2007-03-08.zipshould do. This will result in a file called
di-nslu2.bin.
The first step of the conversion (appropriately) is to “flash” the NSLU2. You unplug all hard disks from the NSLU2 (and perhaps reboot it just to be on the safe side).
There are two ways to do the firmware upgrade—the way I describe
below and the recommended way. Martin Michlmayr was kind enough to
point out that the recommended way is to use upslug2. To do
this install the upslug2 package on your laptop/PC (it is
running Debian isn't it?!). The man page that comes with the program
is excellent.
I felt that “hard reset” was an unkind step to perform on my soon-to-be slug. So I followed the steps outlined below.
Under the Linksys configuration interface you go to the “Advanced”
configuration menu and within that you choose “Upgrade”. This will
give you the option of upgrading the firmware by uploading a file. Put
the full path of your Debian Installer image di-nslu2.bin in
the slot for the file name—don't press the submit button just yet!
Open another window or tab in your browser (w3m now has tabs!).
Go through the same steps as above in this other window. Now press
the submit button (actually it is labelled “Start Upgrade”) in one
of the two windows. The NSLU2 will sometimes close this connection to
the browser (due to some bug in the Linksys software). You then need to
resubmit this “Start Upgrade” request after about 30-60 seconds–aren't
you glad that you still have another window/tab open at the same place?
The NSLU2 will indicate by means of a flashing amber light that it is
uploading the firmware and installing it. This takes about 2-3
minutes and at the end of it the NSLU2 will reboot. Didn't work?
Well, you know that adage “If at first you don't succeed, try, try
again!” It is sometimes tricky getting the timing right. Also, the
“hard reset” approach using upslug2 is less tricky.
When the NSLU2 next reboots it has become an “infant slug”. It takes a while for it to boot into the installer (about 7 minutes) and then it emits three beeps. If you listen carefully, it is saying “Give me more!” Now that it has a taste of Debian (via the Debian Installer) it really needs the whole thing. At this point, you can in principle shut the slug down using the power-off button (or be even more unkind and detach the power cord!). I needed to do this as I had to move my setup to a place that had good enough network connectivity to download all the base Debian packages.
Next I set things up to use a proxy service on my laptop to serve
the Debian packages to the slug. I could have used apt-proxy
but since I already have polipo setup on my laptop, I used
that. This service listens at port 8123 on the localhost interface.
Next step. Connect up the slug to the laptop as before. This time also connect the USB disk to the slug and boot it up. Wait for the three beeps and then log in with ssh:
ssh -R 8123:localhost:8123 installer@192.168.1.77
The -R 8123:localhost:8123 is a forethought which I wish I
had had! This log in takes you into the Debian installer from where
one can continue as usual for a Debian installation except for the
following:
http://localhost:8123/“Eh?!”, you say. “Where is the proxy server on the slug?” Now you understand the point of the
-R switch.
The real proxy server is on your laptop and ssh is
just forwarding the connection.
…and two (or more!) hours later your slug is all grown up and read to roll.
The last stage of the Debian installer is when it writes the kernel
to the firmware of the slug and reboots. It is no longer beeping
since it now has a base Debian install and can easily feed itself!
You can ssh to it as before. At this point you may want to
make it a full-fledged member of the network and give its own static
IP address — or you may configure it to use DHCP.
One nice thing to note is that only the kernel and the initial
ramdisk (initrd) are on the firmware. If your slug is switched
off you can just connect the USB disk to your laptop in order to edit
the file system. This is useful. For example, if you managed to
completely screw up your network configuration so that you can't
even ssh into the slug. I used this method to create the LVM
partition on the USB disk and copy my music collection to it.
One worthwhile way to spend those two hours is to go and shop for a USB audio device. Or you may been clever and bought it at the same time as you bought the NSLU2!
It is relatively easy to setup your slug to use this device. Just
plug the USB audio device into the “other” USB slot on your system
and you should see the audio device being nicely auto-detected by
udev. Use alsamixer to set up your volume and try
aplay /usr/share/sounds/alsa/Noise.wav
What? No sound! Did you remember to plug in the speakers into the USB audio device—or a headset. I didn't!
You can now play all your .wav files through the system.
However, don't start installing your favourite music playing software
from the Debian archive just yet. The problem is that the ARM
processor has no floating point unit and so the players that use
floating point computations to perform music decompression will not
be able to do those computations fast enough to produce anything
resembling music!
Luckily, there is already mpg321 which uses an integer
arithmetic based decompression routine for .mp3 files. There
is also a version of the Xiph(TM) library for .ogg files
called “Tremor” which does integer arithmetic base decompression
for those files. I found nicely detailed instructions to setup the
mpd music playing daemon using these libraries at the
nslu2-linux.org site. Voila! Or if you prefer—Violin!
Your slug is complete Debian system which is much faster than
that old 386 box with 20MB hard disk and 4MB of RAM which you use as
a mail and DNS server. So go ahead and create an account for yourself
where you can backup your files using rsync (with the promise
to yourself that next time you will definitely learn enough to set it
up as a subversion, git or mercurial repository).
You can also setup a web server like mathopd (or even apache).
This is Debian with 16,000 (…and counting!) packages. The
possibilities are limitless. Remember that it is a slug but it
“ain't no” slouch.
You aren't quite done yet. Don't forget to file your Debian
installation report using reportbug. It is also good manners
to donate something to the guys who setup up the nslu2-firmware
binaries which helped you to get your slug rolling and will help in
the creation of more slugs in future. If you have some money left
then investigate all the USB devices that there are out
there—infra-red, bluetooth, Wi-Fi, VGA adaptor …. Of course,
you need to first buy a USB multi-port hub since the
NSLU2 has unfortunately only two USB ports!
The following sites provided extremely useful information:
First of all, I would like to thank CalTech for inviting me for a long period. This gave me enough resources (time and money) to go to SCalE5x and see the NSLU2-Linux booth there. More importantly, I thank the guys at nslu2-linux who have worked hard all these years to make the slug the great friend of the gnu and the penguin that it has become. I also thank Martin MichlMayr and the other Debian developers who have made installation of Debian on the NSLU2 a breeze; in particular, Martin also answered a number of questions that I posted in my installation report. I also toast all the contributors to the Wiki at the nslu2-linux.org web site; there are so many ideas there it would take a lifetime to try them all!
Coming back to the money angle a bit. If I look at the amount of
money (less than USD 100) that I have spent on getting my slug
(baptized kutti) up and running, it is certainly money well
spent. Not
just because it is my slug, but because it is a genuinely useful
computer in my menagerie. However, when I translate this amount into
Indian Rupees, I realise that it is not an amount that could be
“thrown away” on an experimental project funded from one's own
earnings. Which is why
I wrote this article—to try to convince others that this is not
“experimental” anymore. Go forth and multiply those slugs!
This document was translated from LATEX by HEVEA.