Diskless netboot

Context and aim

Aim

We aim to use the same distribution everywhere. The client doesn't need any hard drive to run, they will retrieve the file system from the TFTP server and use a NFS share as hard drive. The system will only run in RAM disk.

So:

• All the clients will share the installation, configuration files and so on.

• Each client will run a dedicated instance of the operating system in his own RAM disk

• Logs will be centralized on the common NFS server - so we don't loose data on each reboot.

• The user will be able to choose the O.S to run on boot - thanks to a PXE menu

Requirements:

• DHCP server
• NetBoot server

Optional:

• DNS server

Target folder tree

This is how we'll setup our files and folders:

# TFTP root
/tftpboot/                                 

# Ubuntu installation NetBoot disk
/tftpboot/rescue/                          

###############
# Network bootable image(s) using NFS technology
################       

#### Boot file            
/tftpboot/pxelinux.0                   # Initial boot file - only use to load the PXE NetBoot manager
/tftpboot/{menu.c32 || vesamenu.c32}   # PXE interactive menu managers (text or graphical)
/tftpboot/pxelinux.cfg/                # PXE configuration(s)
/tftpboot/pxelinux.cfg/default         # default PXE configuration

#### Kernel file

/tftpboot/images/      

# Debian 7.x [Wheezy] 
/tftpboot/images/wheezy/   
/tftpboot/images/wheezy/vmlinuz
/tftpboot/images/wheezy/initrd.img

# Ubuntu 14.04 [Trusty] 
/tftpboot/images/trusty/  
/tftpboot/images/trusty/vmlinuz
/tftpboot/images/trusty/initrd.img


#### NFS 
# This is where the runnable will be. Each image will be in a dedicated folder.
/nfs/                    

# Debian 7.x [Wheezy] 
/nfs/wheezy/   

# Ubuntu 14.04 [Trusty] 
/nfs/trusty/

Installation

NFS support

apt-get install nfs-kernel-server nfs-common

Debootstrap (manage netboot image)

apt-get install debootstrap

Initramfs (to manage "virtual disks")

apt-get install initramfs-tools

Preparation

You have to create a dedicated folder on your server where you will host the distributions kernels + Boot settings.

mkdir -p /tftpboot/pxelinux.cfg
chmod -R 755 /tftpboot/pxelinux.cfg

mkdir -p /tftpboot/images
chmod -R 755 /tftpboot/images

The pxelinux.cfg/ folder is mandatory. Inside you can provide:

• configuration for a specific IP @ or hostname
• configuration for a group
• default configuration (required)

Boot menu and Kernel setup

The first thing to do is to setup a booting kernel. To do so we'll use the "syslinux" files.

Root file: pxelinux.0

The pxelinux.0 is the root file. That's the file that allows the netboot.

This is the file that is serve by the TFTP server.

cp /usr/lib/syslinux/pxelinux.0 /tftpboot/

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.

Init Kernel files

Create directories

Create the target kernel folders. You should create 1 folder for each distribution you'd like to provide in NetBoot.

# Debian 7.x
mkdir -p /tftpboot/images/wheezy

# Ubuntu 14.04
mkdir -p /tftpboot/images/trusty

Prepare initramfs to boot over NFS

This step must to be run on the machine that has the kernel you are going to serve to your clients.

>>> In our case it has to be run on the TFTP server

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 

#### Change the following options
BOOT=nfs
MODULE=netboot

Copy and prepare kernel

You have to copy your current kernel files to the boot folder:

# Debian 7.x
cp /boot/vmlinuz-`uname -r` /tftpboot/images/wheezy/vmlinuz
cp /boot/initrd.img-`uname -r` /tftpboot/images/wheezy/initrd.img

# Ubuntu 14.04
cp /boot/vmlinuz-`uname -r` /tftpboot/images/trusty/vmlinuz
cp /boot/initrd.img-`uname -r` /tftpboot/images/trusty/initrd.img

Enable NFS boot on target kernel:

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 have to run mkinitramfs for each kernel you'll provide

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

NFS server setup

Configuration

The NFS configuration is done in the /etc/exports file

vim /etc/exports

Add something like that:

  /nfs     192.168.2.0/24(ro,no_root_squash,no_subtree_check,async,insecure)

Adjust "192.168.2.0/24" to your own network address

• rw : Allow clients to read as well as write access
• ro : Read only access
• insecure : Tells the NFS server to use unpriveledged ports (ports > 1024).
• no_subtree_check : If the entire volume (/users) is exported, disabling this check will speed up transfers.
• async : async will speed up transfers.
• no_root_squash: This phrase allows root to connect to the designated directory.

- NOTE -

• It's always a good idea to use Read-Only if you plan to share this disk. That will avoid user to mess with your image!

• There must not be any space between network IP and "("

Security

Like TFTP, this part is insecure !

You must restrict the access to your NFS server by a firewall script and filtering BEFORE reaching the LAN !

NFS is using dynamic ports numbers because it runs over rpcbind. Making NFS using specifics port is a pain in the ass !! :(

So, instead of that you should allow your LAN communication.

    IPTABLES=`which iptables`
    LAN_ADDRESS="192.168.2.0/24"

    # Allow LAN communication
    $IPTABLES -A INPUT -s $LAN_ADDRESS -d $LAN_ADDRESS -m state ! --state INVALID -j ACCEPT
    $IPTABLES -A OUTPUT -s $LAN_ADDRESS -d $LAN_ADDRESS -m state ! --state INVALID -j ACCEPT

Management

service nfs-kernel-server {status|start|stop|restart}

Test the server

Install the NFS v4 client:

apt-get install nfs-common

To mount the default path:

mount -t nfs nfs-server:/ /mnt

You'll see: "/nfs"

It's better to do:

mount -t nfs nfs-server:/nfs /mnt

NFS client image

There are different way to setup a NFS client image.

The main ones are:

• Manually

• • debootstrap

• • copying the install from your server

• • Manual install on a client, then, when the system is ready, copy everything to the NFS share

• Using script and software like "Puppet" or "Chef"

Setup client distribution

You have to create one target for each distribution you want to serve:

mkdir -p /nfs/trusty
mkdir -p /nfs/wheezy

- NOTES -

• The folder name should match your NetBoot settings. Folder name = a LABEL in the NetBoot config.

• The folder name should match a Linux (Debian like) distribution name

Configure client distribution

• Manual configuration: Diskless image configuration - manual setup

• Automatic [Puppet || Chef] configuration: Diskless image configuration - script setup

Kernel modules and source

If you're using a local kernel as the default NetBoot kernel, then you need to do copy the modules + kernel source to every distribution.

# Copy kernel modules
cp -r /lib/modules/`uname -r` /nfs/trusty/lib/modules

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

Note that you have to adjust the /nfs/XXX

Backup distribution

You can create an archive of your current distribution for later restore / re-use.

Compression

cd /nfs
tar cvpjf trusty.tar.bz2 ./trusty

Restoration

cd /nfs
tar -xvjf trusty.tar.bz2

Custom NetBoot configuration

Basic menu

See the previous § to learn how to setup a super simple boot menu without any interaction.

Text menu

The text menu required a new file: menu.c32

cp /usr/lib/syslinux/menu.c32 /tftpboot/pxelinux.cfg/

Graphic menu

The graphic menu required a new file: vesamenu.c32

cp /usr/lib/syslinux/vesamenu.c32 /tftpboot/pxelinux.cfg/

Then you can add an image file to display as menu background.

Remember:

• You'll have to specify the exact size of the picture later on - so note the picture size !! Recommendation: 640x480
• Remember that the SysLinux cannot display more than depth=16 and 65536 colors

ImageMagic command to convert a picture:

convert -depth 16 -colors 65536 my_custom_image.png splash.png

Then copy the splash:

cp splash.png /tftpboot/pxelinux.cfg/
chown -R root:root /tftpboot/pxelinux.cfg/splash.png

Configure / setup menu content

Edit the PXE NetBoot file:

vim /tftpboot/pxelinux.cfg/default

Put:

#### GENERIC OPTIONS #####
# Enable text menu
#DEFAULT pxelinux.cfg/menu.c32
# Enable graphical menu
DEFAULT pxelinux.cfg/vesamenu.c32
# Prompt for user input? (0 = choose from menu, 1 = you can type anything)
PROMPT 0
# Allow or not the user to left the menu (1 = user is locked to the menu)
NOESCAPE 1
# Time before using default option
TIMEOUT 50


#### Menu settings #####
MENU TITLE my super netboot menu
# Setup background image (the resolution is $WIDTH $HEIGHT and must match the given picture)
MENU RESOLUTION 640 480
MENU BACKGROUND pxelinux.cfg/splash.png
# Setup text properties
MENU WIDTH 80
MENU ROWS 14
MENU MARGIN 10


#### Distributions #####
# Debian wheezy
LABEL wheezy
    MENU LABEL Debian 7.x [wheezy]
    MENU DEFAULT
    # Kernel and boot files
    KERNEL images/wheezy/vmlinuz 
    APPEND boot=nfs root=/nfs/wheezy initrd=images/wheezy/initrd.img nfsroot=192.168.2.2:/nfs/wheezy

# Ubuntu 14.04
LABEL trusty
    MENU LABEL Ubuntu 14.04 [trusty]
    # Kernel and boot files
    KERNEL images/trusty/vmlinuz
    APPEND boot=nfs root=/nfs/trusty initrd=images/trusty/initrd.img nfsroot=192.168.2.2:/nfs/trusty

Note all the "MENU" commands + PROMPT 0

More about the menu configuration: http://www.syslinux.org/doc/menu.txt

Security notes

in order to work you must adjust the rights of your "/var/lib/tftpboot/".

chmod 777 /pxe-boot/*
chmod 777 /pxe-boot/pxelinux.cfg/*

DHCP note

Don't forget to adjust your DHCP configuration if you plan to serve a specific file for a client!

vim /etc/dhcp/dhcp.conf

References

Ubuntu diskless how-to: https://help.ubuntu.com/community/DisklessUbuntuHowto

Super video tutorials:

• https://www.youtube.com/watch?v=js9imsrqAMk
• http://www.stepladder-it.com/bivblog/14/ to /16/
• https://blog.dlasley.net/2013/01/pxe-server-ubuntu/