DISKLESS(8)

NAME
diskless - booting a system over the network

DESCRIPTION
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-installing filesystems on a local disk. This file provides a general description 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 clients.

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

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 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. Typical personal computers 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 depends on the design of the boot program. (The design described here is the one used by Sun and NetBSD/hp300.) 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 handle.
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. 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. 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 procedure 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.

CONFIGURATION
Before a client can boot over the network, its server must be configured correctly. This example will demonstrate how a Sun client might be configured -- 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 address:
        8:0:20:7:c5:c7          myclient

    This will be used by rarpd(8).

2.  Assign an IP address for myclient in your /etc/hosts or DNS database:
        192.197.96.12           myclient

3.  If booting a Sun machine, 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 SPARC machine, install a copy of the appropriate diskless boot loader (such as /usr/mdec/boot) 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 C0C5600C.SUN4

    For a Sun3 machine, the name would be just C0C5600C (the sun3 PROM does not append the architecture name). 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 network boot program SYS_UBOOT (which may be called uboot.lif before installation) is installed in the directory /usr/mdec/rbootd.
5.  Add myclient to the bootparams database /etc/bootparams:
        myclient  root=server:/export/myclient/root

6.  Build the swap file for myclient:
        # mkdir /export/myclient
        # cd /export/myclient
        # dd if=/dev/zero of=swap bs=16k count=1024

    This creates a 16 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 NetBSD 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.

    Note that, unlike SunOS, you need to create a mount point for the client's swap:
        # mkdir /export/myclient/root/swap

8.  Export the required filesystems 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 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 lines:
        /export/usr.sun3 -ro myclient
        /export/myclient -rw=myclient,root=myclient

9.  Copy and customize at least the following files in /export/myclient/root:
        # cd /export/myclient/root/etc
        # cp fstab.nfs fstab
        # cp /etc/hosts hosts
        # echo myclient > myname
        # echo 192.197.96.12 > hostname.le0

    Note that "le0" above should be replaced with the name of the network interface that the client will use for booting.

10. Correct the critical mount points and the swap file in the client's /etc/fstab (which will be /export/myclient/root/etc/fstab) ie.
        myserver:/export/myclient/root / nfs rw 0 0
        myserver:/usr /usr nfs rw 0 0
        myserver:/export/myclient/swap none swap sw,nfsmntpt=/swap

    Note, you must specify the swap file in /etc/fstab or it will not be used!

FILES
/etc/ethers
    Ethernet addresses of known clients
/etc/bootparams
    client root pathname
/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

SEE ALSO
bootparams(5), ethers(5), exports(5), bootparamd(8), mountd(8), nfsd(8), rarpd(8), rbootd(8), reboot(8), tftpd(8)