DISKLESS(8) BSD System Manager's Manual DISKLESS(8)NAMEdiskless — booting a system over the network
DESCRIPTION
The ability to boot a system over the network is useful for two kinds of
systems:
diskless a system with no attached mass storage media to boot or run
from (e.g. a network computer).
dataless a system with a hard drive that only contains system and appli‐
cation software, and user data is mounted over the network from
a central server.
It can also be done as a temporary measure while repairing or re-
installing file systems on a local disk. This capability is necessarily
platform dependent because of its dependence on system firmware support;
not all platforms supported by NetBSD are capable of being network
booted.
The protocols used to obtain a network address (e.g. an IP host address),
include, but are not limited to:
RARP Reverse Address Resolution Protocol (ARP)
DHCP Dynamic Host Configuration Protocol
BOOTP Bootstrap Protocol
This information can also be derived from non-volatile RAM or by a trans‐
form of a network interface (e.g. Ethernet) MAC address.
The protocols used to load a NetBSD kernel over a network include, but
are not limited to:
TFTP Trivial File Transfer Protocol
NFS Sun Network File System
RMP HP Remote Maintenance Protocol
MOP DEC Maintenance Operations Protocol
Derivation of the filename of the secondary bootstrap program can be done
by a transform of a network interface MAC address (or other protocol
address), or provided by a server as with BOOTP, and DHCP. How this is
done is platform dependent; see boot(8).
The NetBSD kernel doesn't care how it gets loaded and started. The pro‐
tocols used to boot NetBSD can be completely different than the ones that
NetBSD uses operationally, i.e. you can netboot the system using HP RMP
and the NetBSD kernel can use IP to communicate after bootstrap.
There is no standard way to pass all the required information from a boot
loader to an operating system kernel, so the NetBSD kernel usually has to
recapitulate the same (or similar) protocol exchanges over the network to
obtain a network address, determine which servers to use, and so on.
NetBSD supports obtaining this information from RARP, BOOTP, DHCP, and
Sun RPC "bootparams". See options(4) for a list of methods that can be
compiled into a NetBSD kernel.
NetBSD only supports the Sun Network File System (NFS) for mounting its
root file system over a network. NetBSD can use any local mass storage
device for which it has a driver, after bootstrap, even if that device is
not supported by the system's firmware for booting.
N.B. DHCP is essentially a series of extensions to BOOTP; the NetBSD
dhcpd(8) is capable of responding to both kinds of protocol requests.
In the majority of configurations, network boot servers and clients are
attached to the same LAN so that broadcast queries from the clients can
be heard by the servers. Unless specially configured, routers block
broadcasts from propagating from LAN to LAN; some routers can be config‐
ured to "forward" broadcast BOOTP packets to another LAN attached to that
router, which permits a server on that remote LAN to respond to the
client's broadcast query.
OPERATION
When booting a system over the network, there are three phases of inter‐
action between client and server:
1. The system firmware (or stage-1 bootstrap) loads a boot program.
2. The boot program loads a NetBSD kernel.
3. The NetBSD kernel performs an NFS mount of the root file system.
Each of these phases are described in further detail below.
1. loading a boot program
In phase 1, the system firmware loads a boot program. Firmware designs
vary widely, so this phase is inherently machine-specific. Some exam‐
ples:
DEC Alpha systems use BOOTP to determine the client's IP address and then
use TFTP load a secondary bootstrap program from the server and filename
specified in the BOOTP reply. DEC Alpha systems can also use MOP to load
a program to run the system.
Sun systems use RARP to determine the client's IP address, transform that
address to a hexadecimal string to form the filename of the secondary
boot program, and then use TFTP to download the boot program from the
server that sent the RARP reply.
HP 300-series systems use the HP RMP to download a boot program.
Typical personal computers may load a network boot program either from
diskette or from a PROM on a Network Interface Card (NIC). Some BIOSes
support booting from a network interface.
2. loading a kernel
In phase 2, the secondary boot program loads a kernel. Operation in this
phase depends on the design of the boot program (the design described
here is the one used by Sun and NetBSD/hp300). The boot program:
1. gets the client IP address using RARP.
2. gets the client name and server IP address by broadcasting an RPC /
BOOTPARAMS / WHOAMI request with the client IP address.
3. gets the server path for this client's root using an RPC /
BOOTPARAMS / GETFILE request with the client name.
4. gets the root file handle by calling mountd(8) with the server path
for the client root file system.
5. gets the kernel file handle by calling NFS lookup() on the root file
handle.
6. loads the kernel using NFS read calls on the kernel file handle.
7. transfers control to the kernel entry point.
A BOOTP and/or DHCP secondary bootstrap program will do the following:
1. query for the client's bootstrap parameters. The response must
include the client's IP address, and a TFTP server to load the
NetBSD kernel from.
2. loads the NetBSD kernel from the TFTP server.
3. transfers control to the kernel entry point.
3. NFS mounting the root file system
In phase 3, the kernel performs an NFS mount of the root file system.
The kernel repeats much of the work done by the boot program because
there is no standard way for the boot program to pass the information it
gathered on to the kernel.
In general, the GENERIC kernel config(1) file for any particular archi‐
tecture will specify compile-time options to use the same protocol used
by the secondary boot program for that architecture. A NetBSD kernel can
be compiled to use any of BOOTP, DHCP, or Sun RPC BOOTPARAMS; see
options(4).
The procedure typically used by the kernel is as follows:
1. The kernel finds a boot server using the same procedures as
described above to determine the client's IP address, an NFS server,
etc.
2. The kernel gets the NFS file handle for root using the same proce‐
dure as described above.
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.
SERVER CONFIGURATION
Before a client can bootstrap over the network, its server must be con‐
figured. Each daemon that implements these protocols must be set up so
that it can answer queries from the clients. Some of these daemons are
invoked as packets come in, by inetd(8), and some must run independently,
started from /etc/rc; see rc.conf(5).
Protocol Program Startup
RARP rarpd rc.conf(5)
DHCP dhcpd rc.conf(5)
BOOTP bootpd inetd.conf(5)
TFTP tfptd inetd.conf(5)
Sun RPC rpcbind rc.conf(5)
Sun RPC rpc.bootparamd rc.conf(5)
Sun NFS mountd rc.conf(5)
Sun NFS nfsiod rc.conf(5)
HP RMP rbootd rc.conf(5)
N.B. DHCP is essentially a series of extensions to BOOTP; the NetBSD
dhcpd(8) is capable of responding to both kinds of protocol requests.
Since they both bind to the same UDP port, only one may be run on a given
server.
In the following examples, the client's hostname is myclient; the server
is myserver, and the addresses are all fictional. In these examples the
hostnames may be Fully Qualified Domain Names (FQDN, e.g.
"myclient.mydomain.com") provided that they are used consistently.
RARP
For clients that use RARP to obtain their IP address, an entry must be
added for each client to /etc/ethers with the client's Ethernet MAC
address and Internet hostname:
8:0:20:7:c5:c7 myclient
This will be used by rarpd(8) to reply to queries from the clients.
There must be one entry per client system.
A client system's Ethernet MAC address is often printed on the system
case, or on a chip on its motherboard, or on the NIC. If not, "sniffing"
the network with tcpdump(8) when the client is powered-on should reveal
its Ethernet MAC address.
Each client system that uses RARP must have its own, unique IP address
assigned to it. Assign an IP address for myclient in your /etc/hosts
file, or in the master file for your DNS zone. For /etc/hosts the entry
should look like:
192.197.96.12 myclient
DHCP/BOOTP
The NetBSD DHCP server dhcpd(8) was developed by the Internet Software
Consortium (ISC); http://www.isc.org/
DHCP can provide a wide range of information to a requesting client; the
key data for bootstrapping a diskless client are:
1. an IP address
2. a subnet mask
3. a TFTP server address for loading the secondary bootstrap and the
NetBSD kernel
4. a filename of the secondary bootstrap
5. an NFS server address for the client's file system
6. the client's root file system path, to be NFS mounted.
An example for /etc/dhcpd.conf
host myclient {
hardware ethernet 8:0:20:7:c5:c7;
fixed-address myclient; # client's assigned IP address
filename "myclient.netboot"; # secondary bootstrap
next-server myserver; # TFTP server for secondary bootstrap
option swap-server myserver; # NFS server for root filesystem
option root-path "/export/myclient/root";
}
That host declaration goes inside a subnet declaration, which gives
parameters for all hosts on the subnet that will be using DHCP, such as
the "routers" (the default route), "subnet-mask", "broadcast-address",
"domain-name-servers", etc. See dhcpd.conf(5) for details. In that
example, myclient has an assigned IP address.
The DHCP parameters required for network bootstrapping a system will vary
from platform to platform, as dictated by each system's firmware. In
particular, because the DHCP is extensible, some hardware vendors have
specified DHCP options to return information to requesting clients that
are specific to that platform. Please see your platform's boot(8) for
details.
TFTP
If booting a Sun system, or other system that expects to use TFTP, ensure
that inetd(8) is configured to run tftpd(8). The tftpd(8) server should
be set up to serve the directory /tftpboot.
If booting a SPARC system, install a copy of the appropriate diskless
secondary boot loader (such as /usr/mdec/boot or ofwboot.net) in the
/tftpboot directory. Make a link such that the boot program is accessi‐
ble by a filename composed of the client's IP address in hexadecimal, a
dot, and the architecture name (all upper case). For example:
# cd /tftpboot
# ln -s boot C0C5600C.SUN4
For a Sun-3 or UltraSPARC system, the filename would be just C0C5600C
(these systems' firmware does not append the architecture name). The
name used is architecture dependent, it simply has to match what the
booting client's system firmware wishes to it to be.
If the client's system firmware fails to fetch the expected file,
tcpdump(8) can be used to discover which filename the client is being
requested. Also, examination of tftpd(8) log entries (typically in
/var/log/messages) should show whether the server is hearing the client
system, and what filename the client is asking for.
HP RMP
If booting an HP 300-series system, ensure that /etc/rbootd.conf is con‐
figured properly to transfer the boot program to the client. An entry
might look like this:
08:00:09:01:23:E6 SYS_UBOOT # myclient
The secondary bootstrap program for an HP 300-series system SYS_UBOOT
(which may be called uboot.lif before installation) must be installed in
the directory /usr/mdec/rbootd.
See the rbootd(8) manual page for more information.
Sun RPC BOOTPARAMS
Add myclient to the bootparams database in /etc/bootparams:
myclient root=myserver:/export/myclient/root \
swap=myserver:/export/myclient/root/swap \
dump=myserver:/export/myclient/root/swap
and ensure that rpc.bootparamd(8) and rpcbind(8) are running. Both
myclient and myserver must have IP addresses in the DNS or /etc/hosts.
Diskless Client File Systems
Build the swap file for myclient on the NFS server:
# cd /export/myclient/root
# dd if=/dev/zero of=swap bs=16k count=1024
This creates a 16 megabyte swap file.
Populate myclient's root file system on the NFS server. How this is done
depends on the client architecture and the version of the NetBSD distri‐
bution. It can be as simple as copying and modifying the server's root
file system, or unpack a complete NetBSD binary distribution for the
appropriate platform.
If the NFS server is going to support multiple different architectures
(e.g. Alpha, PowerPC, SPARC, MIPS), then it is important to think care‐
fully about how to lay out the NFS server's exported file systems, to
share what can be shared (e.g. text files, configuration files, user home
directories), and separate that which is distinct to each architecture
(e.g. binary executables, libraries).
NFS
Export the client-populated file systems on the NFS server in
/etc/exports:
/usr -ro myclient
# for SunOS:
# /export/myclient -rw=myclient,root=myclient
# for NetBSD:
/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 file system (as is done above). If not, you
must build a properly fleshed out /usr partition for the client in some
other part of the server's file system, to serve to the client.
If your server is a SPARC, and your client a Sun-3, you might create and
fill /export/usr.sun3 and then use the following /etc/exports lines:
/export/usr.sun3 -ro myclient
/export/myclient -rw=myclient,root=myclient
Of course, in either case you will have to have an NFS server running on
the server side.
CLIENT CONFIGURATION
Copy and customize at least the following files in /export/myclient/root:
# cd /export/myclient/root/etc
# vi fstab
# cp /etc/hosts hosts
# echo 'hostname="myclient"' >> rc.conf
# echo "inet 192.197.96.12" > ifconfig.le0
Note that "le0" above should be replaced with the name of the network
interface that the client will use for booting; the network interface
name is device dependent in NetBSD.
Correct the critical mount points and the swap file 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
/swap none swap sw 0 0
Note, you must specify the swap file in /etc/fstab or it will not be
used! See swapctl(8).
FILES
/etc/hosts table of associated IP addresses and IP host names; see
hosts(5)
/etc/ethers table of associated Ethernet MAC addresses and IP host
names used by rarpd(8); see ethers(5)
/etc/bootparams client root pathname and swap pathname; see
bootparams(5)
/etc/exports exported NFS mount points; see exports(5)
/etc/rbootd.conf configuration file for HP RMP; see rbootd(8)
/usr/mdec/rbootd location of boot programs offered by rbootd(8)
/tftpboot location of boot programs offered by tftpd(8)SEE ALSObootparams(5), dhcpd.conf(5), ethers(5), exports(5), fstab(5), hosts(5),
networks(5), boot(8), dhcpd(8), mopd(8), mountd(8), nfsd(8), rarpd(8),
rbootd(8), reboot(8), rpc.bootparamd(8), tftpd(8)
Reverse Address Resolution Protocol, RFC, 903, June 1984.
Bootstrap Loading using TFTP, RFC, 906, June 1984.
Bootstrap Protocol, RFC, 951, September 1985.
The TFTP Protocol (Revision 2), RFC, 1350, July 1992.
Dynamic Host Configuration Protocol, RFC, 2131, March 1997.
DHCP Options and BOOTP Vendor Extensions, RFC, 2132, March 1997.
http://www.rfc-editor.org/
BSD October 7, 2006 BSD
