Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (NetBSD-6.1.5)
Apropos / Subsearch:
optional field

DISKLESS(8)                 System Manager's Manual                DISKLESS(8)

     diskless -- booting a system over the network

     The ability to boot a system over the network is useful for two kinds of

     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
               application 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

     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
     transform 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
     protocols 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
     configured 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.

     When booting a system over the network, there are three phases of
     interaction 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

     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
     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
     architecture 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,
     2.   The kernel gets the NFS file handle for root using the same
          procedure 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.

     Before a client can bootstrap over the network, its server must be
     configured.  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

     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.

     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:


     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

     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
     accessible by a filename composed of the client's IP address in
     hexadecimal, a dot, and the architecture name (all upper case).  For

           # 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.

     If booting an HP 300-series system, 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

     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.

     Add myclient to the bootparams database in /etc/bootparams:

           myclient  root=myserver:/export/myclient/root \
                     swap=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
     distribution.  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
     carefully 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).

     Export the client-populated file systems on the NFS server in

           /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.

     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" > 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).

     /etc/hosts        table of associated IP addresses and IP host names; see
     /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
     /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)

     bootparams(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.


NetBSD 6.1.5                    October 7, 2006                   NetBSD 6.1.5