TFTP server manage netboot kernels

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/

Update kernel into TFTP

If you haven't configure TFTP boot yet, check-out TFTP_server_PXE_configuration

To use your new kernel you just need to update TFTP configuration file.

vim /tftpboot/pxelinux.cfg/default

Put the following instead of the previous kernel:

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

Debug kernel

During NetBoot client startup you might encounter some modprobe errors.

That means the thin client failed to access your kernel's libraries and / or modules.

NFS image update

Access your NFS image by CHROOT /nfs/... + login

1. Be sure to install the kernel's header on the NFS image:

apt-get install linux-headers-3.13.0-32
apt-get install linux-headers-3.13.0-32-generic

Replace "3.13.0-32" by your version

2. Check the symlinks

Sometimes when there is just 1 kernel the OS will check for libraries in /lib/modules instead of /lib/modules/kernel-version

You can try to copy all the modules files to /lib/modules and adjust the symlink.

cd /lib/modules
mv 3.13.0-32-generic/* . 
rm -rf 3.13.0-32-generic 
ln -s /lib/modules/ /lib/modules/3.13.0-32-generic

Replace "3.13.0-27" by your version

That should do !