*Update so this doesn't work it must be something to do with the path of nfs or something else but the installer fails with "Installer crashed" at the end whereas with the CD/USB it works.
This assumes you've already installed and configured a separate PXE/DHCP server somewhere else and your /tftpboot directory is setup.
This is for Linux Mint 18.1 but generally applies to most versions although you may have tro change things like "casper" according to the code name of the current release in the directory specifications below.
This work occurs on the source tftp/pxe/dhcp server of course.
Assumptions/things to change
Check the IP 192.168.1.43 (change to your tftp/nfs server).
Step 1 - Setup Working Paths in /tftpboot
mkdir -p /tftpboot/images/linuxmintmount
mkdir -p /tftpboot/images/linuxmint18
Step 2 - Mount and copy appropriate files from .iso into /tftpboot
mount -o loop -t iso9660 linuxmint-18.1-mate-64bit.iso linuxmintmount/
cp -rp linuxmintmount/* linuxmint18
Step 3 - Setup your boot menu
MENU TITLE PXE Menu
LABEL LinuxMint 18
APPEND root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.1.43:/tftpboot/images/linuxmint18 initrd=images/linuxmint18/casper/initrd.lz nosplash --
Step 4 - Setup NFS
yum -y install nfs-utils
Specify the network range you want to access to the tftpboot over nfs or it will fail.
ln -s /tfpboot /srv/
Setup your exports properly or you'll get this log error:
uxmint18): unmatched host
May 30 19:36:46 localhost rpc.mountd: refused mount request from 192.168.1.51 for /tftpboot/images/linuxmint18 (/tftpboot/images/linuxmint18): unmatched host
Things to double check
Make sure your firewall is off on the pxe server.