Booting Slax Linux from OpenWrt PXE server

First of all, if you don't know what is Slax, it's a highly usable and compact slackware based GNU/Linux live CD distro just around 230 MB.

It's one of the most complete and flexible live CD around I've tried so far. With a stripped down KDE 4 desktop and precisely chosen applications. Here's the official site , you can download and try yourself.

Slax, despite it's small size, has many features like copy to RAM, load user made changes, act as a PXE boot server to boot other systems over network and many more.

Installing and managing software packages is also easy, squashfs based software packages are highly modular.

You can boot Slax from a CD or USB drive very easily. But, to boot it from network with the standard initramfs image(initrfs.img in this case), you've to pull some tricks.

Slax's default initramfs is very small(~ 750 KB) compared to other Linux distros. And it's without networking support, though enough for booting from CD/DVD or USB drive.

So you'll need a different initramfs image with networking support and different init script. How to generate this special initramfs image ?

This is another extension of main article about OpenWrt PXE server. So have a look there before going further.

1. Generate PXE boot capable initramfs

The Slax initramfs is called initrfs.img , there is a nice shell script named pxe under the /sbin directory in Slax live to generate it automatically. To generate this, you have to boot Slax live CD and run

/sbin/pxe

Now copy the PXE boot capable initrfs.img file from the /var/state/dnsmasq/root folder to the OpenWrt PXE boot server. I did it by running Slax Live in Virtualbox and copied it to a USB drive.

cp /var/state/dnsmasq/root/initrfs.img /media/sdb2/initrfs_pxe.img 
cp /var/state/dnsmasq/root/PXEFILELIST /media/sdb2/

Note: Both of these commands are meant to be run on the Slax live environment and make sure that you changed the commands according to your system.

2. Copy the Slax data

This step depends on your Slax download, if you downloaded the zip archive simply unzip it to the right partition of the USB drive. Or if you downloaded the ISO file, loop mount it some where and copy the data. You can perform this on a PC running any Linux distro.

sudo mount slax_7.0.8.iso /mnt/

cp -r /mnt/slax/ /media/user_name/drive_name/  # example

cd /media/user_name/drive_name/

mv initrfs_pxe.img slax/

sync

Note: Don't forget to modify the commands which matches to your system. Now un-mount the USB drive from the PC and connect it to the OpenWrt router.

3. Create the pxelinux configuration

Now login to your OpenWrt router using SSH, you need to run some commands below there.

First write the pxelinux configuration for the OpenWrt PXE boot server to boot Slax, assuming you have read the the previous guide of setting up OpenWrt PXE boot server.

You need to do one more step before editing the configuration, check the PXEFILELIST file to know about the absolute minimum number of files required for a successfull pxe boot.

cd /mnt/sda2

mv initrfs_pxe.img slax/

mv PXEFILELIST slax/

ln -s /mnt/sda2/slax/ /mnt/sda2/PXEboot/

Edit the /mnt/sda2/PXEboot/pxelinux.cfg/default file and add the configuration bellow

LABEL Slax PXE
KERNEL /slax/boot/vmlinuz
IPAPPEND 1
APPEND initrd=/slax/initrfs_pxe.img load_ramdisk=1 prompt_ramdisk=0 rw printk.time=0 slax.flags=xmode

As a note, on OpenWrt, the PXE server is also managed by dnsmasq alsong wth dns, dhcp and tftp.

4. Setup a HTTP server at port 7529 in OpenWrt

The Slax LiveKit init script will download the Slax data files from a HTTP server running at port 7529. Creating a lightweight HTTP server with OpenWrt is very easy with the uhttpd . There is a good probability that your system has uhttpd installed, if not install it.

opkg install uhttpd

Now start the server at port 7529 binding all available interfaces

uhttpd -p 0.0.0.0:7529 -h /mnt/sda2/slax/

Check if the HTTP server is working or not

wget -q 192.168.1.1:7529/PXEFILELIST -O -

To start the http server automatically at boot up, add this line bellow

uhttpd -p 0.0.0.0:7529 -h /mnt/sda2/slax/

at the /etc/rc.local file before the exit 0 line.

Now boot up a PC or virtual machine from the OpenWrt PXE server and select the Slax PXE to test this setup.

5. TO DO and conclusion

However, any user made changes are not saved form the changes.dat file. You can create a custom shell script and run rsync on a interfal to fix this issue.

It seems that currently the Slax copy to ram feature doesn't work while booting from PXE server. But the system will be as responsive as it's running from ram. Because the boot process downloads all the squashfs modules (sb files) to RAM. Use the losetup command to check all the mounted slax bundles while running.

losetup -a

This little guide will help you to boot Slax from a PXE server, please leave your suggestion or question through the comments. If you find this tutorial useful, please share it with your friends.