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Linksys NSLU2 default 2009-08-10 01:41:46 +0200 2009-12-06 14:01:10 +0100 true
know-how
hacking
hardware
linksys
nas
storage

NSLU2 means Network Storage Link for USB 2.0 Disk Drives. Also see here.

![NSLU2]({{ site.url }}/assets/nslu2.jpg)

Custom firmwares

The NSLU2 supports different firmwares. The original one is rather outdated. The most used firmwares are:

  • Unslung --- an add-on to the original firmware, keeping the web-interface and all standard features
  • SlugOS/BE --- a firmware optimized for small devices; using opkg and ipkg you can install various applications/services
  • Debian/NSLU2 --- a stripped down Debian linux with all things you know from Debian, but packages are not optimized for small memory devices

SlugOS/BE

Bad network performance

My network consists of a WLAN repeater which bridges the network of my neighbor with mine. Access to the Internet is provided by a gateway in my neighbor's network. The NSLU2 device has severe problems downloading files from the Internet. All downloads stall after a few bytes. Some tests showed that my side of the network works fine but everything behind the WLAN bridge is almost unreachable from the NSLU2. All other devices in my network can use the Internet fine.

My current solution is using tcpwatch-httpproxy on my Desktop-PC and a file ~/.wgetrc on my NSLU2 with the contents:

timeout = 10
http_proxy = <my IP>:8080

Debian/NSLU2

Power button for shutdown instead of reboot

To make pushing the power button shut down the Slug instead of rebooting it, edit the file /etc/inittab and replace the line

ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

by

ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -h now

Afterwards do a

telinit q

Free memory

Since ARM packages from Debian are not optimized for small memory footprint, you might want to free up some memory by deactivating several services which are not needed.

bash

To save even more memory, you could replace bash by dash in your /etc/passwd file.

exim4

Exim4 is a complete mail exchanger. Most people will only need a simple MTA to send some logs to the admin. So remove exim4 and use ssmtp instead.

getty

If you don't have/use the serial console on the NSLU2, you should disable getty. Edit the file /etc/inittab and comment out the following line:

#T0:23:respawn:/sbin/getty -L ttyS0 115200 linux

Afterwards do a

telinit q

ipv6

If you don't use IPv6, you should blacklist the kernel module to save some more RAM. Add the following line to /etc/modprobe.d/blacklist:

blacklist ipv6

sshd

If you don't use sshfs or some other special features of OpenSSH, you could replace it by dropbear.

Emergency firmware

If your DebianSlug doesn't boot and the root disk is perfectly clean, you might have a firmware problem. To create a working firmware, you'll need the files vmlinuz-2.6.30-2-ixp4xx, initrd.img-2.6.30-2-ixp4xx1 and the di-nslu2.bin (the DebianSlug installer image).

  1. make sure you have installed the packages slugimage and devio

  2. copy the di-nslu2.bin to an empty directory and run this:

     slugimage -u -i di-nslu2.bin

  3. now copy the two other files also in that directory

  4. prepare the kernel image: (This will pad the file to 1441760 Bytes and then switch the Endianess of the file.)

     dd if=vmlinuz-2.6.30-2-ixp4xx of=vmlinuz-2.6.30-2-ixp4xx.padded ibs=1441760 conv=sync
 devio "<<"vmlinuz-2.6.30-2-ixp4xx.padded > vmlinuz-2.6.30-2-ixp4xx.swapped "xp $,4"

  5. prepare the initrd image:

     dd if=initrd.img-2.6.30-2-ixp4xx of=initrd.img-2.6.30-2-ixp4xx.padded ibs=6291440 conv=sync
 devio "<<"initrd.img-2.6.30-2-ixp4xx.padded > initrd.img-2.6.30-2-ixp4xx.swapped "xp $,4"

  6. now compile the new firmware image:

     slugimage -p -b RedBoot -s SysConf -L apex.bin -k vmlinuz-2.6.30-2-ixp4xx.swapped -r initrd.img-2.6.30-2-ixp4xx.swapped -t Trailer -o debianslug.bin

Finally you only have to burn the new image to the NSLU2 using upslug2:

upslug2 -i debianslug.bin

If you want to make changes to the initrd, take a look at cyrius.com.

UPDATE: Here is a little script which does the above in a more comfortable way. Just throw it into the directory together with the di-nslu2.bin, the initrd.img-2.xxx and vmlinuz-2.xxx. Download: [emergencyfw.sh]({{ site.url }}/assets/emergencyfw.sh)

Tools

iStat Server

iStat is an app for the iPhone to show performance statistics of different machines. I compiled their iStat Server on my Slug and made a little DEB package.

![iStat]({{ site.url }}/assets/istat.png)

Download: [istatd_0.5.4_armel.deb]({{ site.url }}/assets/istatd_0.5.4_armel.deb)

  1. both found in /boot on the root partition of the NSLU2-disk ↩︎