Booting FreeBSD via PXE (Preboot Execution Environment)
Version: v1.2
Publish Date: Dec 5, 2000.
Updated: Oct 18, 2003.
Audience: Unix System Administrators
Objective: Document the steps necessary to boot and/or install a
FreeBSD 5.x system using a DHCP, NFS, & TFTP server.
Background: FreeBSD can boot and install off a variety of mediums. The
common and most useful are floppies, cd-roms, and the network (ppp,
NFS, & ftp). All the methods work essentially the same, you bootstrap
the helpless machine off floppies (yes, even the CD boot uses floppy
emulation) and the mini-FreeBSD system then has enough smarts to
initialize CD-ROM drives, Ethernet, and PPP interfaces. This all works
fairly good for installing FreeBSD on one machine but what happens
when you want to install it on 20, or 50, or 1,000 machines? Right now
the process is pretty much a manual one on every machine. This is
expensive, error prone, and slow.
Excuse: I had quite a few reasons to embark upon this project.
1. It's a Royal PITA [TM] to build a custom FreeBSD install CD. I
literally spent days fuddying with cramming all the stuff I wanted
onto a 2.88M disk image and burning a lot of coasters getting it
perfected. The process of building bootable media isn't documented
well and worse yet, the only real documentation is found by
searching mailing lists. This is less than convenient as I found
myself compiling lots of post-it notes.
2. Even when I successfully built a bootable CD I was severely
limited because I was stuck in the confines of 2.88M. You must
wrestle with picobsd and the unless you're a good programmer (I'm
not) you're pretty much stuck living with the choices that were
made by others for their (apparently) obtuse reasons. No matter how
hard I tried, I just couldn't have as much fun as I'd like to when
booting off a CD.
3. Building a restore CD (to boot a failed server) that boots,
rebuilds, and restores an entire system is not easy. I needed a
simpler method of getting a machine bootstrapped than spending
hours building a custom boot CD that would let a clue deficient NOC
operator restore my servers.
4. The only time the CDROM drive gets used is when I'm installing
the OS. It's quite a waste to buy servers with Cd-Roms when you're
only going to use them once. You can do more with 1U and 2U
hardware when you've got another drive bay to play with.
5. In my spare time I'm building a cluster of FreeBSD machines.
It's primary purpose thus far is the conversion of electricity to
heat in my garage. I figure at some point I'll find a use for it
but until then, just building it has provided me with ample
motivation to learn a lot of cool new stuff about FreeBSD.
At BSDCon 2000 I sat in on a panel taught by Doug White on automated
system installations. It gave me the impetus to charge forth and
conquer the beast known as PXE. I'm too lazy to look up some of the
facts (again) so anywhere I use <>, please feel free to send me the
relevant information and URL's where I can verify and I'll update my
documentation.
Some time ago <date please> Intel developed a technology known as PXE
and began blessing their wonderful EtherExpress Pro Server Adapters
with this spiffy new feature. <Some 3Com NIC cards> also include PXE
technology. PXE is designed to allow a NIC card to fetch a
configuration from a DHCP server and boot up a computer via it's
network interface. John Baldwin and Paul Saab at FreeBSD saw the
usefulness of this feature and wrote a little boot loader
appropriately named pxeboot. Pxeboot is included in FreeBSD 4.1 and
higher.
So, how does it work you ask? Very well, I must say. Once you satisfy
it's many dependencies, things work great. Getting everything
satisfied wasn't as simple as I'd hoped. Anyway, follow the steps
below to reach enlightenment.
Requirement 1: FreeBSD distribution. It would be nice for FreeBSD to
just magically appear on your hard drive but alas, we've got to get it
from somewhere. I suppose you could fetch it from the FTP server but I
simply copied the CD contents to a NFS exported file system on my
server.
Requirement 2: Ethernet adapter with PXE boot roms. The Intel
Management adapters all include PXE but even our newest batches
required flash updating to get FreeBSD booted properly. This is what
my oldest Intel's looked like at first:
This version of PXE bios does not work. It will load the pxeboot
loader but fails soon thereafter. A visit to Intel's web site had me
downloading a file named 8255x.zip. Within that archive was three very
useful things. The first was a directory name 8255x containing the
boot ROM's for the Intel 8255x adapters. Logical huh? :-) The other
useful tool was the fboot.exe program. I created a DOS boot floppy and
copied these programs onto the boot floppy. I then installed five
Intel adapters into the PCI slots of my server and proceeded to update
them all.
After installing the new firmware the PXE bios looks like this:
Intel (R) Boot Agent Version 4.0.12
PXE 2.0 Build 082 (Wfm 2.0), RPC v2.7.3
Press Ctrl+S to enter the Setup Menu
Requirement 3: DHCP Server. I already had ISC-DHCP 3.0b installed so I
merely had to add a couple lines to my DHCP configuration. Here's what
a working configuration looks like:
Requirement 4: DNS server. I'm not sure it's its necessary but I'm
sure it's at least a good idea. Create an entry in your DNS records
for dhcpserver.yourdomain.com and records for all the addresses in
your DHCP pool. It's saves us a lot of time waiting for DNS timeouts
when we've got DNS set up correctly.
Requirement 5: TFTP server. The DHCP configuration tells the booting
client that it's supposed to grab the filename "pxeboot" from the TFTP
server (next-server) at 192.168.254.3. Here's how mine is set up:
This is pretty easy to configure. On most systems, simply comment out
the tftp line in your /etc/inetd.conf and restart inetd (killall -HUP
inetd).
NOTE: TFTP has virtually no built in security. You should only enable
a TFTP server on an internal (trusted) network or use a firewall to
restrict access to it. At a minimum, use TCP wrappers.
Requirement 6: PXEBOOT. Copy the pxeboot file from your /usr/src/sys
tree to the /tftpboot directory and you're all set:
# cp /sys/boot/i386/pxeldr/pxeboot /tftpboot
Once your machine has loaded the NIC cards PXE bios, it will (assuming
it's the chosen boot device) make the tftp request for the file
"pxeboot" from the tftp server. The tftp server, being properly
configured will hand it the file "pxeboot" which is comparable to the
FreeBSD loader program.
NOTE: The pxeboot program can be compiled to fetch the loader via TFTP
or NFS. NFS is the default but you can add this
"LOADER_TFTP_SUPPORT=YES" to your /etc/make.conf and recompile pxeboot
(#cd /usr/src/sys/boot; make clean; make depend; make; cp
i386/pxeldr/pxeboot /tftpboot).
Requirement 7: Boot loader. Once PXE boot is loaded it will fetch the
files it needs from the /boot directory that's defined within the
root-path directive your DHCP server handed it. Since we've defined a
root path of /usr/local/export/pxe, it'll be looking within the /boot
directory there for the second and third stage boot loaders. Here's
what we've got set up there:
You can get these files in a couple ways. You can either snag them off
the mfsroot.flp (follow the instructions on Alfred Perlstein's
page http://people.freebsd.org/~alfred/pxe/ ) or just copy them from
your source tree (like I did):
You'll need to create the contents of the loader.rc file to look
something like this:
# more /usr/local/export/pxe/boot/loader.rc
echo Loading Kernel...
load /boot/kernel/kernel
load linux.ko
set choice=freebsd-ide
echo
echo You have 5 seconds to select one of the following:
echo
echo mylex
echo scsi
echo ide
echo mailserver
echo
read -t 5 -p "Type in your selection EXACTLY: " choice
echo
include /boot/loader.rc-$choice
echo booting...
echo 07 07
echo initializing h0h0magic...
set vfs.root.mountfrom=ufs:/dev/md0c"
#set console="comconsole" #(very useful if you don't have a kvm on
the box)
boot
I also wanted to have the ability to select which mfsroot I wanted to
boot off so I figured out how to script the loader process a little
bit. You'll notice that the loader.rc calls another file (ex.
/boot/loader.rc-freebsd-ide). Here's all that file looks like:
# more loader.rc-ide
echo Loading FreeBSD installer mfsroot for IDE/UDMA drives...
load -t mfs_root /mfsroot-ide
Requirement 8: NFS Server. Since we're going to use pxeboot's default
retrieval method of NFS, we'd better export the /usr/local/export/pxe
directory. Once most systems it's as easy as putting a line in
/etc/exports that looks like this: "/usr -alldirs -maproot=root -ro".
That exports the entire /usr file system with read only permissions.
Once you've added that line to the exports file, you need to restart
(or start) mountd. To set everything up on a FreeBSD system, just do
this:
# echo "/usr -alldirs -maproot=root -ro" >> /etc/exports
# if mountd is running "killlall -HUP mountd`"
# if mountd is not running "nfsd -t -u; mountd"
If you want this machine to be a NFS server every time you reboot, add
this to your /etc/rc.conf: "nfs_server_enable="YES".
NOTE: NFS security is adequate at best. Use IPFIREWALL or IPFILTER (I
use IPFIREWALL) to restrict access to it.
Requirement 9: Bootable Kernel. At this point your new machine has
just run the loader program which, as instructed by the loader.rc
file, is going to try loading the file named "kernel" from our root
path. Lucky for us, we've got a perfectly good kernel floating around
in our / directory so we just copy it from there over to our exported
directory.
There are some requirements for this kernel, most specifically the MFS
support but if you just use a GENERIC kernel, things will work out
just fine for you. The reason you don't want to use the kernel off the
boot.flp or kern.flp images is that they pause at the kernel
configuration screen. Using a custom kernel also gives you the
flexibility to load klm's (kernel loadable modules) for your custom
install packages if you need to (I did).
Once the kernel loads we'll proceed to the next line of the loader.rc
file and that's fetching the mfsroot file. The mfsroot is just that, a
memory based file system that's stored in a file.
Requirement 10: MFSROOT. You have a couple options here. The first is
to simply use the mfsroot disk image that comes with the version of
FreeBSD you are installing. There are instructions for doing so on
Alfred Perlstein's page (http://people.freebsd.org/~alfred/pxe/).
If your needs are modest and can be met with the tools provided on
the mfsroot floppy then have at it. However, that defeats half the
purpose of doing this exercise in the first place.
I create a directory with the entire FreeBSD CD on my drive. I do it
like this:
The real power behind this is that you can create your own mfsroot
with no size restrictions. Weehee, let's make a really big 25 megabyte
mfsroot:
cd /usr/local/export/pxe
dd if=/dev/zero of=mfsroot bs=1k count=25000
mdconfig -a -t vnode -f mfsroot -u0
disklabel -r -w md0 auto
newfs /dev/md0c
mkdir -p /mnt/mfs
mount /dev/md0 /mnt/mfs
There, now we've got 25 megs of space mounted on /mnt to play with.
The basic rule of thumb here to keep in mind is that you are building
a root file system for FreeBSD. Everything the kernel, sysinstall, and
your install programs needs from the root file system is what you need
to have in your /mnt directory. To get started we'll copy the contents
of the distribution mfsroot.flp to our new mfsroot:
Voila, now we've got a bootable mfsroot partition and tons of space to
play with. One thing to keep in mind, when you place any of your
spiffy utilities on there, make sure you compile them statically. This
is usually as easy as changing into the appropriate source directory,
editing the Makefile and adding "-static" to the CFLAGS. You've got
plenty of room to hack up your own sysinstall or anything else that
you want/need on your root partition.
At this point, you can simply umount the mfsroot (umount /mnt/mfs;
mdconfig -d -u 0) or build it up the way you want/need. We have some
pretty ugly kludges we've made which including hacking sysinstall and
a few other goodies that use about 20 megs. I'm sure you'll find some
creative ways to use all that space. Just drop in your statically
compiled binary and run with it. My system looks like this at boot
time:
Intel (R) Boot Agent Version 4.0.12
PXE 2.0 Build 082 (Wfm 2.0), RPC v2.7.3
Press Ctrl+S to enter the Setup Menu
Building the boot loader arguments
Relocating the loader and the BTX
Starting the BTX loader
BTX loader 1.00 BTX Version 1.01
Console: internal video/keyboard
BIOS drive A: is disk0
PXE Version 2.1, real mode entry point @9db3:0106
BIOS 639kB/392180kB available memory
FreeBSD/i386 bootstrap loader, Revision 0.8
(root@matt.simerson.net), Thu Nov 30 11:45:41 PST 2000)
pxe_open: server addr: 192.168.254.3
pxe_open: server path: /usr/local/export/pxe
pxe_open: gateway ip: 192.168.254.1
Hit [Enter] to boot immediately, or any other key for command
prompt.
Booting [kernel]
Requirement 11: Install.cfg. If you're installing FreeBSD via the
Ethernet adapter, (as opposed to just using PXE to netboot) then
you'll want to script sysinstall. Why go though all this bother if you
have to sit in front of the box and answer questions? Anyway, now our
loader.rc has requested the mfsroot file and pulled our 25 meg image
across it's 100Megabit interface. The loader.rc also tells the kernel
to get it's root file system from memory disk 0 (md0c) that we loaded.
The kernel then had it's root partition set up based on the contents
of our mfsroot partition. Once it checks out our hardware it looks for
/sbin/init which doesn't exist and then falls back to running
sysinstall.
Sysinstall checks to see if the file /install.cfg exists and if so,
uses it to control it's behavior. The script syntax is documented in
"man sysinstall" which you might need to install (cd
/usr/src/release/sysinstall; make install). There's a sample
install.cfg installed at: /usr/src/usr.sbin/sysinstall/install.cfg and
here's what my install.cfg looks like:
# Turn on extra debugging.
#debug=yes
#noWarn=YES
tryDHCP=YES
################################
# My host specific data
hostname=new.simerson.net
domainname=simerson.net
nameserver=192.168.254.3
defaultrouter=192.168.254.3
#ipaddr=204.216.27.230
#netmask=255.255.255.240
################################
################################
_ftpPath=ftp://ftp.cdrom.com/pub
nfs=192.168.254.3:/usr/local/export/freebsd
netDev=fxp0
mediaSetNFS
#mediaSetFTP
#mediaSetCDROM
#mediaSetHTTP
#mediaSetUFS
#mediaGetType
#netInteractive
################################
################################
# Select which distributions we want.
dists=bin doc manpages catpages proflibs dict info crypto compat22
compat3x compat4x ssecure sbase ssys setc ports
distSetCustom
################################
################################
# Now set the parameters for the partition editor on da0. Set to
use the
# disk exclusively (could also be "all" to use the whole disk but
# respecting the MBR or "free" to use only unallocated space for
FreeBSD).
diskInteractive=0
disk=da0
#disk=ad0
partition=all
#partition=exclusive
#partition=free
bootManager=booteasy
#bootManager=standard
diskPartitionEditor
################################
################################
# All sizes are expressed in 512 byte blocks!
# A 500MB root partition
da0s1-1=ufs 1024000 /
# And a 2GB swap partition
da0s1-2=swap 4096000 none
# And a 3GB var partition
da0s1-3=var 6144000 none
# Followed by a /usr partition using all remaining space (size 0 =
free space)
# and with softupdates enabled (non-zero arg following mountpoint).
da0s1-4=ufs 0 /usr 1
# Let's do it!
diskLabelEditor
################################
################################
# Now partition the 2nd disk.
#disk=ad1
#partition=exclusive
#diskPartitionEditor
#ad1s1-1=ufs 40960 /var
#ad1s1-2=ufs 0 /usr/src
#diskLabelEditor
################################
# OK, everything is set. Do it!
installCommit
# Install some packages at the end.
package=bash-2.05b.007
packageAdd
package=ncftp1-1.9.5
packageAdd
package=rsync-2.5.6_1
packageAdd
package=sudo-1.6.7.4
packageAdd
package=gmake-3.80
packageAdd
package=libtool-1.3.4_4
packageAdd
package=gdm2-2.4.1.4_1
packageAdd
package=cvsup-16.1h
packageAdd
#package=simerson-net
#packageAdd
#
#system /stand/my.custom.installer
shutdown
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