TFTP server manage netboot kernels

TFTP configuration

TFTP can manage different configurations, up to 1 per host!

This is how a ThinClient (= netBoot client) will retrieve its configuration:

As you can see you have 3 possibilities:

1. MAC @ filter. Configuration file name must be:

• Start with ARP type '01-'
• all in lower case hexadecimal
• dash '-' separators instead of ';'

for example a MAC @ 88:99:AA:BB:CC:DD would search for the filename 01-88-99-aa-bb-cc-dd.

2. IP @ filter. Configuration file name must be:

• host IP / network address in hexadecimal
• all in upper case

e.g. 192.0.2.91 -> C000025B

3. Default configuration

To learn more about all the available option, check out http://www.syslinux.org/wiki/index.php/PXELINUX.

---

Prepare NetBoot kernel

All these steps must be done on the server who has the kernel you want to extract.

Best practice: you should perform the kernel extraction on the TFTP server!

IMPORTANT NOTES

You're about to extract a server kernel and make it available for NetBooting. Make sure that:

• The kernel has all the drivers installed and configured
• The kernel doesn't need a reboot

If your client(s) will use some specifics drivers then you MUST install these drivers before going through the following steps. 

You need to be very careful, especially if you plan to use some smart-card reader!

Create TFTP Kernel directory

Create the TFTP kernel's folder. You should create 1 folder for each kernel you'd like to provide in NetBoot.

# Ubuntu 14.04 - Kernel version 3.13.0.32 (August 2014)
mkdir -p /tftpboot/images/trusty

Enable NFS support

Copy initramfs settings for PXE boot

cp -r /etc/initramfs-tools /etc/initramfs-pxe

Adjust PXE boot configuration

cd /etc/initramfs-pxe/
vim /etc/initramfs-pxe/initramfs.conf

Add / adjust the following options:

BOOT=nfs
MODULE=netboot

Copy and prepare kernel

Copy kernel's files

cp /boot/vmlinuz-`uname -r` /tftpboot/images/trusty/vmlinuz
cp /boot/initrd.img-`uname -r` /tftpboot/images/trusty/initrd.img

Enable NFS boot option

mkinitramfs -d /etc/initramfs-pxe -o /tftpboot/images/trusty/initrd.img

Adjust rights

chmod -R 755 /tftpboot/images/

Notes:

• Do NOT use some symlink for "vmlinuz" and "initrd.img" !! It won't work.

• If you don't want to use `uname -r` [current kernel version and architecture] then adjust the values to target kernel number + architecture. You can use the `uname -r`command's result.

• You have to run mkinitramfs for each kernel you'll provide

• Don't forget to adjust the rights to 755 for every distribution

Kernel modules and source

Your NFS image must have the kernel's libraries and modules, and that must match the kernel's version of the TFTP server!!

Since Linux kernel is evolving every month or so, you need to backup your kernel's libraries and modules for future use.

Create kernel source directory

# Ubuntu 14.04 - Kernel version 3.13.0.32 (August 2014)
mkdir -p /tftpboot/sources-images/trusty/lib/modules
mkdir -p /tftpboot/sources-images/trusty/usr/src

Copy libraries and modules

# Copy kernel modules
cp -r /lib/modules/`uname -r` /tftpboot/sources-images/trusty/lib/modules

# Copy kernel sources
cp -r /usr/src/linux-headers-`uname -r` /tftpboot/sources-images/trusty/usr/src/

Create NetBoot menu | defaults

Now, we have to specify which kernel to use and which distributions are available for NetBoot.

Create the default configuration file:

vim /tftpboot/pxelinux.cfg/default

Put the following:

# Debian 7.x
LABEL wheezy
    kernel images/wheezy/vmlinuz
    initrd images/wheezy/initrd.img

# Ubuntu 14.04
LABEL trusty
    kernel images/trusty/vmlinuz
    initrd images/trusty/initrd.img


# Prompt user for selection
PROMPT 1
# No timeout
TIMEOUT 0

• Each LABEL is a specific configuration that will displayed on the NetBoot menu.
• PROMPT 0 = enable user prompt so you can choose the configuration
• TIMEOUT 0 = timeout (in seconds) before the default option is chosen. 0 == no timeout

Note that I used a reference to "trusty/", that's a folder I need to create later on.