Network Boot

PXE booting with SYSTEM and /storage mounted via NFS is supported on Generic x86_64 and current Raspberry Pi devices (Pi 4 and newer). Older Raspberry Pi devices can also be booted over the network, but they require a different procedure. In the following writeup the server is Ubuntu 18.04 LTS.

Server (Ubuntu)

In Ubuntu we need to install and configure DHCP, TFTP, and NFS services:

sudo apt install isc-dhcp-server tftpd-hpa nfs-kernel-server

DHCP

Edit /etc/dhcp/dhcpd.conf and change the DHCP range if needed. Create entries in the host section for your client(s):

authoritative;
allow booting;
allow bootp;

ddns-update-style none;

default-lease-time 86400;
max-lease-time 86400;

subnet 192.168.0.0 netmask 255.255.255.0
{
  option subnet-mask 255.255.255.0;
  option broadcast-address 192.168.0.255;
  option domain-name-servers 192.168.0.2, 192.168.0.1;
  option routers 192.168.0.1;

  range 192.168.0.10 192.168.0.200;
  next-server 192.168.0.2;
  filename "/pxelinux.0";

  host <name>
  {
    hardware ethernet 00:0a:0b:0c:0d:0e;
    fixed-address 192.168.0.5;
  }
}

Edit /etc/default/isc-dhcp-server to set the interface name handling DHCP requests:

INTERFACES="eth0"

NFS

Create the directories that will contain your /storage userdata and TFTP boot files, e.g.

sudo mkdir /mnt/media/storage
sudo mkdir -m777 /mnt/tftpboot

Download the LibreELEC image for your device. On x86 systems, copy the KERNEL and SYSTEM files into the /mnt/tftpboot directory:

sudo cp KERNEL /mnt/tftpboot
sudo cp SYSTEM /mnt/tftpboot

On a Raspberry Pi, just copy all files into the /mnt/tftpboot directory:

sudo cp * /mnt/tftpboot

If you want to place the files in a subdirectory it is required to adjust the include directive in config.txt.

Then add the following lines to the /etc/exports file:

/mnt/media/storage      192.168.0.2/255.255.255.0(no_root_squash,rw,async,no_subtree_check)
/mnt/tftpboot           192.168.0.2/255.255.255.0(no_root_squash,rw,async,no_subtree_check)

TFTP

Create directories for the TFTP bootfiles. In this example they are served from a different disk:

sudo mkdir /mnt/tftpboot/pxelinux.cfg
sudo cp -p /usr/lib/syslinux/pxelinux.0 /mnt/tftpboot

You may also want to copy the KERNEL and SYSTEM files to /mnt/tftpboot

Add the following lines to /etc/default/tftpd-hpa and save the file:

RUN_DAEMON="yes"
TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/mnt/tftpboot"
TFTP_ADDRESS="0.0.0.0:69"
TFTP_OPTIONS="--secure"

Create /mnt/tftpboot/pxelinux.cfg/default (or instead of default use the MAC-Address of your device in the format 90-91-92-93-94-95) and insert the following:

DEFAULT LibreELEC
PROMPT 0

LABEL LibreELEC
kernel /KERNEL
append ip=dhcp boot=NFS=192.168.0.2:/mnt/tftpboot disk=NFS=192.168.0.2:/mnt/media/storage

Replace 192.168.0.1 with the NFS server IP address. The overlay parameter is not required if you only intend to boot one system. LibreELEC is now configured to boot using TFTP and NFS!

NFSv4

Today many server use NFSv4 while the kernel still default to NFSv3. In such a case set the correct NFS dialect via the vers= option:

  APPEND ip=dhcp boot=NFS=192.168.0.1:/mnt/store/libreelec,vers=4.2 disk=NFS=192.168.0.1:/mnt/store/libreelec/storage,vers=4.2 overlay

Valid nfs versions are 2 3 4 4.0 4.1 4.2.

Firewall

If using the default Ubuntu firewall (UFW) add the following rules to allow ports for TFTP (69) and ONRPC (111):

sudo ufw allow proto udp from 192.168.0.0/24 to any port 69
sudo ufw allow proto tcp from 192.168.0.0/24 to any port 111

Clients normally connect to the NFS server on random ports, so it the firewall is active "mountd" needs to be told to use a fixed port allowed through the firewall, or boot will hang.

Edit /etc/default/nfs-kernel-server and replace the current RPCMOUNTDOPTS line. In the example below 8765 is a randomly chosen port:

RPCMOUNTDOPTS="-p 8765"

Create a matching firewall rule to allow the port:

sudo ufw allow proto tcp from 192.168.0.0/24 to any port 8765

Services

And finally, start services:

sudo service isc-dhcp-server start
sudo service nfs-kernel-server start
sudo service tftpd-hpa start