Boot an Ubuntu ISO through network (with EFI)

install-ubuntu-by-netboot.md

Netboot Ubuntu with EFI

This method is not netinst. The ISO is downloaded from a URL into RAM, and mounted. After that, installation proceeds exactly as if it was a pen drive / CDROM, and the network cable can be disconnected if you want.

You do not need internet in either computer, just the ISO file.

We don't touch any system files, just delete $TFTPROOT and dnsmasq.conf when you're done.

Before you begin

Make sure 7z and dnsmasq are installed. Download your Ubuntu ISO somewhere.

You'll also need syslinux and its modules:

apt install syslinux-common
# or
pacman -S syslinux

Steps

1. Set variables for the following commands (examples shown here):

   INTERFACE=eth0
   ISOPATH=/tmp/ubuntu-20.04.2-desktop-amd64.iso
   TFTPROOT=/tmp/tftp
   cd /tmp

2. Prepare TFTP root: syslinux + ldlinux module, and the kernel + initrd from the ISO

   mkdir -p $TFTPROOT
   cp /usr/lib/syslinux/efi64/{syslinux.efi,ldlinux.e64} $TFTPROOT
   7z x $ISOPATH casper/{vmlinuz,initrd} -o$TFTPROOT

3. Create configuration file for syslinux:

   • boot kernel + initrd with the same command line (look at boot/grub/grub.cfg in the ISO file)
   • add ip=dhcp url=<URL> to tell it to download the ISO through HTTP

   mkdir -p $TFTPROOT/pxelinux.cfg
   echo "
   DEFAULT install
   LABEL install
     KERNEL casper/vmlinuz
     INITRD casper/initrd
     APPEND ip=dhcp url=http://192.168.4.1:8111/ubuntu.iso root=/dev/ram0 ramdisk_size=1500000 file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash
   " > $TFTPROOT/pxelinux.cfg/default

4. Start HTTP server to provide the ISO file:

   ln -s $ISOPATH $TFTPROOT/ubuntu.iso
   python3 -m http.server 8111 -d $TFTPROOT &

5. Start DHCP+TFTP server that boots syslinux.efi:

   echo "
      bind-interfaces
      listen-address=192.168.4.1
      dhcp-range=192.168.4.100,192.168.4.200
      dhcp-boot=syslinux.efi
      enable-tftp
      tftp-root=$TFTPROOT
   " > dnsmasq.conf
   
   nmcli dev set $INTERFACE managed no  # <-- if you're using NetworkManager, make sure it won't mess with the interface
   sudo ip address add dev $INTERFACE 192.168.4.1/24
   sudo ip link set dev $INTERFACE up
   sudo dnsmasq -C dnsmasq.conf -l dhcp.leases -d &

Boot the other computer by network (remember to disable Secure Boot first).

Variations

• I've only tested the Desktop version, but works with server (in fact this is adapted from a Ubuntu Server guide).

• If you want to use legacy BIOS instead of UEFI, you only need to change the following (more info):

  • /usr/lib/syslinux/bios/{pxelinux.0,ldlinux.c32} instead of /usr/lib/syslinux/efi64/{syslinux.efi,ldlinux.e64}
  • dhcp-boot=pxelinux.0 instead of dhcp-boot=syslinux.efi

• Ubuntu installers (their initrd) support this mode of installation through the url argument, but I don't know what other distributions support it.