Linksys NSLU2

• Hacking into the Linksys NSLU2
• Debian/NSLU2
• How to build a new Debian/NSLU2 image

See the NSLU2.

Obviously we want Debian GNU/Linux on it!

See Installing Debian on the Linksys NSLU2

Put the NSLU2 in upgrade mode, as described into the HOWTO. Then run the following commands:

apt-get install upslug2 slugimage
wget http://cyrius.com/debian/nslu2/files/sda1-2.6.18.dfsg.1-13etch2
upslug2 -i sda1-2.6.18.dfsg.1-13etch2

The above is an official Debian image, for a system installed onto /dev/sda1. Unfortunately it does not support the integrated Ethernet interface (Intel IXP4xx) because it needs a proprietary microcode to operate.

After flashing the firmware, we can prepare a Debian base system on and USB memory stick. I prepared a 2 Gb USB stick following this Manual install.

There is also an unofficial Debian installer NSLU image that can be found here: www.slug-firmware.net. This image contains a Debian installer that let you to start a standard installation. It contains also the microcode for the Ethernet port.

After flashing the Debian installer image you can login into the NSLU2 via ssh (login/password: installer/install):

ssh installer@192.168.1.77

Note: I tried to install the Debian system on a 2Gb USB stick. I got problems using the debian-5.0beta1 installer: the system crashed several times at different stages of progress, so I was unable to complete it. I experienced some trouble also with the debian-4.0r3 installer: the program insists on crashing during partition format, so I pre-formatted the USB stick. During setup I loaded these modules:

• ext3-modules-2.6.18-6-ixp4xx-di
• partman-ext3
• usb-storage-modules-2.6.18-6-ixp4xx-di

If you boot the NSLU2 with the serial line connected to an host (I use minicom to debug the boot process), then you will find that reboot or halt commands will be ignored.

I did not investigate much, just discovered that /etc/init.d/rc {0|6} works.

By default, RedBoot, APEX and the Linux kernel all use 115200,8,N,1 settings.

Install the slugimage package, download the original image and unpack it:

slugimage --unpack --input sda1-2.6.18.dfsg.1-13etch2

Several files will be extracted:

• apex.bin: second stage boot loader for ARM chip (little-endian image)
• ramdisk.gz: initramfs image (little-endian, gzip, cpio archive)
• RedBoot: RedBoot boot manager
• SysConf: Configuration of the NSLU2
• Trailer: Trailer
• vmlinuz: kernel image (little-endian image)

I changed the kernel image vmlinuz and the init ramdisk ramdisk.gz with customized versions

Note that the extracted files are little-endian, where the images provided by me are big-endian, so I byte-swapped them before packing back. Also note that the initramfs image must be padded to 4 Mb size.

dd if=ramdisk.gz of=ramdisk-pad.gz ibs=4M conv=sync
byteswap.py vmlinuz vmlinuz-swap
byteswap.py ramdisk-pad.gz ramdisk-pad.gz-swap
slugimage --pack --output myfirmware-2.6.18-5-ixp4xx-1.bin -k vmlinuz-swap -r ramdisk-pad.gz-swap -L apex.bin

Do not use the --little option of slugimage to byte-swap kernel and initramfs images, because it swaps also the apex.bin file.

Here it is the byteswap.py Python utility I used to byte-swap the files:

#!/usr/bin/python
# swap every 32bit word in input and write it to output
 
import array, sys
 
if len(sys.argv) != 3:
  sys.stderr.write('Invalid arguments.\n')
  sys.stderr.write('Usage: %s <input> <output>\n' % sys.argv[0])
  sys.exit(1)
 
if sys.argv[1] == '-':
  file = sys.stdin
else:
  file = open(sys.argv[1], 'rb')
 
input = file.read()
a = array.array('I')
# add padding if needed
a.fromstring(input + '\0' * (4-len(input)&3))
a.byteswap()
 
if sys.argv[2] == '-':
  file = sys.stdout
else:
  file = open(sys.argv[2], 'wb')
 
a.tofile(file)

The NSLU2 does not support the Always-On natively, there are several recipes to implement this feature, I choosed a simple one (a simple wire) from this page.