DISKLESS(8) OpenBSD System Manager's Manual DISKLESS(8)
diskless - booting a system over the network
The ability to boot a machine over the network is useful for diskless or
dataless machines, or as a temporary measure while repairing or re-in-
stalling filesystems on a local disk. This file provides a general de-
scription of the interactions between a client and its server when a
client is booting over the network. The general description is followed
by specific instructions for configuring a server for diskless Sun
When booting a system over the network, there are three phases of inter-
action between client and server:
1. The PROM (or stage-1 bootstrap) loads a boot program.
2. The boot program loads a kernel.
3. The kernel does NFS mounts for root and swap.
Each of these phases are described in further detail below.
In phase 1, the PROM loads a boot program. PROM designs vary widely, so
this phase is inherently machine-specific. Sun and Motorola machines use
RARP to determine the client's IP address and then use TFTP to download a
boot program from whoever sent the RARP reply. HP 300-series machines
use the HP Remote Maintenance Protocol to download a boot program. Other
machines may load a network boot program either from diskette or using a
special PROM on the network card.
In phase 2, the boot program loads a kernel. Operation in this phase de-
pends on the design of the boot program. The boot program:
2.1 gets the client IP address using RARP.
2.2 gets the client name and server IP address by broadcasting an RPC /
BOOTPARAMS / WHOAMI request with the client IP address.
2.3 gets the server path for this client's root using an RPC /
BOOTPARAMS / GETFILE request with the client name.
2.4 gets the root file handle by calling mountd(8) with the server path
for the client root.
2.5 gets the kernel file handle by calling NFS lookup on the root file
2.6 loads the kernel using NFS read calls on the kernel file handle.
2.7 transfers control to the kernel entry point.
In phase 3, the kernel does NFS mounts for root and swap. The kernel re-
peats much of the work done by the boot program because there is no stan-
dard way for the boot program to pass the information it gathered on to
the kernel. The procedure used by the kernel is as follows:
3.1 The kernel finds a boot server using the same procedure as described
in steps 2.1 and 2.2 above.
3.2 The kernel gets the NFS file handle for root using the same proce-
dure as described in steps 2.3 through 2.5 above.
3.3 The kernel calls the NFS getattr function to get the last-modified
time of the root directory, and uses it to check the system clock.
3.4 If the kernel is configured for swap on NFS, it uses the same mecha-
nism as for root, but uses the NFS getattr function to determine the
size of the swap area.
Before a client can boot over the network, its server must be configured
correctly. This example will demonstrate how a Sun client might be con-
figured -- other clients should be similar.
Assuming the client's hostname is to be "myclient",
1. Add an entry to /etc/ethers corresponding to the client's ethernet
This will be used by rarpd(8).
2. Assign an IP address for myclient in your /etc/hosts or DNS
3. If booting a Sun or Motorola client, ensure that /etc/inetd.conf is
configured to run tftpd(8) in the directory /tftpboot.
If booting an HP 300-series machine, ensure that /etc/rbootd.conf is
configured properly to transfer the boot program to the client. An
entry might look like this:
08:00:09:01:23:E6 SYS_UBOOT # myclient
See the rbootd(8) manual page for more information.
4. If booting a Sun or Motorola client, install a copy of the appropri-
ate diskless boot loader (such as boot.net from the root directory
of the OpenBSD sparc tree) in the /tftpboot directory. Make a link
such that the boot program is accessible by a file name composed of
the client's IP address in HEX, a dot, and the architecture name
(all upper case). For example:
# cd /tftpboot
# ln -s boot.net C0C5600C.SUN4
Some architectures, such as the Sun3 and Ultrasparc machines, do not
append the architecture name. It this case, the name would be just
C0C5600C. The name used is architecture dependent, it simply has to
match what the booting client's PROM wishes to it to be. If the
client's PROM fails to fetch the expected file, tcpdump(8) can be
used to discover which filename the client is trying to read.
If booting an HP 300-series machine, ensure that the general purpose
boot program SYS_UBOOT (which may be called netboot.lif before in-
stallation) is installed in the directory /usr/mdec/rbootd.
5. Add myclient to the bootparams database /etc/bootparams:
myclient root=server:/export/myclient/root \
Note that some bootparam servers are somewhat sensitive. Some re-
quire fully qualified hostnames or partially qualified hostnames
(which can be solved by having both fully and partially qualified
entries). Other servers are case sensitive.
6. Build the swap file for myclient:
# mkdir /export/myclient
# cd /export/myclient
# dd if=/dev/zero of=swap bs=1m count=120
This creates a 120 Megabyte swap file.
7. Populate myclient's / filesystem on the server. How this is done
depends on the client architecture and the version of the OpenBSD
distribution. It can be as simple as copying and modifying the
server's root filesystem, or perhaps you need to get those files out
of the standard binary distribution.
8. Export the required filesystems in /etc/exports:
/usr -ro myclient
# for SunOS:
# /export/myclient -rw=myclient,root=myclient
# for OpenBSD:
/export/myclient -maproot=root -alldirs myclient
If the server and client are of the same architecture, then the
client can share the server's /usr filesystem (as is done above).
If not, you must build a properly fleshed out /usr partition for the
client in some other place.
If your server was a sparc, and your client a sun3, you might create
and fill /export/usr.sun3 and then use the following /etc/exports
/export/usr.sun3 -ro myclient
9. Copy and customize at least the following files in
# cd /export/myclient/root/etc
# cp fstab.nfs fstab
# cp /etc/hosts hosts
# echo myclient > myname
# echo inet 126.96.36.199 > hostname.le0
Note that "le0" above should be replaced with the name of the net-
work interface that the client will use for booting.
10. Correct the critical mount points in the client's /etc/fstab (which
will be /export/myclient/root/etc/fstab) i.e.,
myserver:/export/myclient/root / nfs rw 0 0
myserver:/usr /usr nfs rw 0 0
/etc/ethers Ethernet addresses of known clients
/etc/bootparams client root and swap pathnames
/etc/exports exported NFS mount points
/etc/rbootd.conf configuration file for HP Remote Boot Daemon
/tftpboot location of boot programs loaded by the Sun PROM
/usr/mdec/rbootd location of boot programs loaded by the HP Boot ROM
bootparams(5), ethers(5), exports(5), mountd(8), nfsd(8), rarpd(8),
rbootd(8), reboot(8), rpc.bootparamd(8), tftpd(8)
OpenBSD 3.6 October 2, 1994 3