====== Pure TFTP booting ======
===== Build Stage =====
First, a staging dir is needed to place all the tftp files in, for example: ''%%/usr/local/tftp/%%''.

Then bzip2 support is needed in the pxeboot binary, so add these to {make,src}.conf and rebuild pxeboot:

<code>
LOADER_NO_GELI_SUPPORT=y
LOADER_BZIP2_SUPPORT=y
</code>

A custom KERNEL can be a good idea to cut down on the size and make it faster to load and less prone to errors.  I use this config file:

<code>
include MINIMAL
ident NETBOOT

nomakeoptions	DEBUG		# Build kernel with gdb(1) debug symbols
nomakeoptions	WITH_CTF		# Run ctfconvert(1) for DTrace support

nooptions         COMPAT_FREEBSD32
nooptions         COMPAT_FREEBSD4
nooptions         COMPAT_FREEBSD5
nooptions         COMPAT_FREEBSD6
nooptions         COMPAT_FREEBSD7
nooptions         COMPAT_FREEBSD9
nooptions         COMPAT_FREEBSD10
nooptions         COMPAT_FREEBSD11
nooptions         KTRACE
nooptions         AUDIT
nooptions         CAPABILITY_MODE
nooptions         CAPABILITIES
nooptions         MAC
nooptions         KDTRACE_FRAME
nooptions         KDTRACE_HOOKS
nooptions         DDB_CTF

nooptions 	DEADLKRES
nooptions 	INVARIANTS
nooptions 	INVARIANT_SUPPORT
nooptions 	WITNESS	
nooptions 	WITNESS_SKIPSPIN

# USB support
options 	USB_DEBUG		# enable debug msgs
device		uhci			# UHCI PCI->USB interface
device		ohci			# OHCI PCI->USB interface
device		ehci			# EHCI PCI->USB interface (USB 2.0)
device		xhci			# XHCI PCI->USB interface (USB 3.0)
device		usb			# USB Bus (required)
device		ukbd			# Keyboard

nooptions 	XENHVM			# Xen HVM kernel infrastructure
nodevice	xenpci			# Xen HVM Hypervisor services driver

options		GEOM_PART_GPT
options		GEOM_RAID
options		GEOM_LABEL
options		GEOM_UZIP

options		IFLIB
device		em			# Intel PRO/1000 Gigabit Ethernet Family

device		md
device		tmpfs

options         NKPT=128
</code>

Note: Only one Ethernet driver is included, others can be loaded as modules or the config modified to include the appropriate module.

Then a small netboot img is needed to load via TFTP. To cut down the size we can use a custom {src,make}.conf like so:

<code>
WITHOUT_ACPI="YES"
WITHOUT_APM="YES"
WITHOUT_ACCT="YES"
WITHOUT_AMD="YES"
WITHOUT_ASSERT_DEBUG="YES"
WITHOUT_AT="YES"
WITHOUT_ATM="YES"
WITHOUT_AUDIT="YES"
WITHOUT_AUTHPF="YES"
WITHOUT_AUTOFS="YES"
WITHOUT_BHYVE="YES"
WITHOUT_BLACKLIST=YES"
WITHOUT_BLUETOOTH="YES"
WITHOUT_BSDINSTALL="YES"
WITHOUT_BOOTPARAMD="YES"
WITHOUT_BSNMP="YES"
WITHOUT_CALENDAR="YES"
WITHOUT_CAPSICUM="YES"
WITHOUT_CCD="YES"
WITHOUT_CDDL="YES"
WITHOUT_COMPAT32="YES"
WITHOUT_CTM="YES"
WITHOUT_CUSE="YES"
WITHOUT_CXX="YES"
WITHOUT_DIALOG="YES"
WITHOUT_DICT="YES"
WITHOUT_DEBUG_FILES="YES"
WITHOUT_EE="YES"
WITHOUT_EXAMPLES="YES
WITHOUT_FDT="YES"
WITHOUT_FINGER="YES"
WITHOUT_FLOPPY="YES"
WITHOUT_FMTREE="YES"
WITHOUT_FTP="YES"
WITHOUT_FREEBSD_UPDATE="YES"
WITHOUT_GAMES="YES"
WITHOUT_HTML="YES"
WITHOUT_ICONV="YES"
WITHOUT_IPFILTER="YES"
WITHOUT_IPFW="YES"
WITHOUT_ISCSI="YES"
WITHOUT_JAIL="YES"
WITHOUT_KDUMP="YES"
WITHOUT_LEGACY_CONSOLE="YES"
WITHOUT_LIB32="YES"
WITHOUT_LOCALES="YES"
WITHOUT_LPR="YES"
WITHOUT_LZMA_SUPPORT="YES"
WITHOUT_MAKE="YES"
WITHOUT_MAN="YES"
WITHOUT_NDIS="YES"
WITHOUT_NETGRAPH="YES"
WITHOUT_NIS="YES"
WITHOUT_NLS="YES"
WITHOUT_NLS_CATALOGS="YES"
WITHOUT_NS_CACHING="YES"
WITHOUT_PC_SYSINSTALL="YES"
WITHOUT_PF="YES"
WITHOUT_PORTSNAP="YES"
WITHOUT_PPP="YES"
WITHOUT_PROFILE="YES"
WITHOUT_QUOTAS="YES"
WITHOUT_RADIUS_SUPPORT="YES"
WITHOUT_RBOOTD="YES"
WITHOUT_RCMDS="YES"
WITHOUT_RESCUE="YES"
WITHOUT_ROUTED="YES"
WITHOUT_SENDMAIL="YES"
WITHOUT_SERVICESDB="YES"
WITHOUT_SHAREDOCS="YES"
WITHOUT_SSP="YES"
WITHOUT_SYSCONS="YES"
WITHOUT_SVNLITE="YES"
WITHOUT_TALK="YES"
WITHOUT_TELNET="YES"
WITHOUT_TESTS="YES"
WITHOUT_TEXTPROC="YES"
WITHOUT_TFTP="YES"
WITHOUT_TIMED="YES"
WITHOUT_TOOLCHAIN="YES"
WITHOUT_USB="YES"
WITHOUT_WIRELESS="YES"
WITHOUT_VT="YES"
WITHOUT_ZONEINFO="YES"
</code>

Modify as appropriate for your needs.

And a script to build the OS and create the small image:

<code>
#!/bin/sh
DEST='/tmp/netboot'
TFTPROOT='/usr/local/tftp'
JOBS=`sysctl -n hw.ncpu`
for target in buildworld buildkernel installworld distribution; do
	make -j${JOBS} $target \
	SRCCONF=/home/user/netboot/src.conf.netboot \
	__MAKE_CONF=/home/user/netboot/make.conf.netboot \
	DESTDIR=${DEST} \
	KERNCONF=NETBOOT \
	|| exit 1
done

for target in delete-old delete-old-libs; do
	make $target \
	BATCH_DELETE_OLD_FILES=yes \
	SRCCONF=/home/user/netboot/src.conf.netboot \
	__MAKE_CONF=/home/user/netboot/make.conf.netboot \
	DESTDIR=${DEST} \
	|| exit 1
done

rm -rf ${DEST}/var/db/pkg
rm -rf ${DEST}/var/cache/pkg
rm -rf ${DEST}/var/db/services.db
rm -rf ${DEST}/netboot/boot/*

for file in magic magic.mgc mdoc.template operator organization.dot \
            pci_vendors scsi_modes ascii birthtoken bsd-family-tree \
            definitions.units eqnchar flowers iso3166 iso639 latin1 \
            committers-src.dot committers-doc.dot committers-ports.dot; do
	rm -rf /tftpboot/netboot/usr/share/misc/${file}
done

rm -rf ${DEST}/usr/share/misc/committers

mkdir -p /usr/local/tftp/
makefs -M 96m ${TFTPROOT}/netboot.img ${DEST}
cp ${DEST}/sys/NETBOOT/kernel ${TFTPROOT}
cp ${DEST}/sys/boot/i386/pxeldr/pxeboot ${TFTPROOT}
cp ${DEST}/sys/boot/efi/loader/loader.efi ${TFTPROOT}

bzip2 -f ${TFTPROOT}/netboot.img
bzip2 -f ${TFTPROOT}/kernel
</code>

===== Configure Stage =====
DNSMASQ will be used for this step as it supports TFTP and DHCP all at once.