19.6 Diskless Operation

19.6.1.1 Configuring DHCP/BOOTP

There are two protocols that are commonly used to boot a workstation that retrieves its configuration over the network: BOOTP and DHCP. They are used at several points in the workstation bootstrap:

• etherboot uses DHCP (by default) or BOOTP (needs a configuration option) to find the kernel. (PXE uses DHCP).

• The kernel uses BOOTP to locate the NFS root.

It is possible to configure a system to use only BOOTP. The bootpd(8) server program is included in the base FreeBSD system.

However, DHCP has a number of advantages over BOOTP (nicer configuration files, possibility of using PXE, plus many others not directly related to diskless operation), and we shall describe both a pure BOOTP, and a BOOTP+DHCP configuration, with an emphasis on the latter, which will use the ISC DHCP software package.

              default-lease-time 600;
              max-lease-time 7200;
              authoritative;
    
              option domain-name "example.com";
              option domain-name-servers 192.168.4.1;
              option routers 192.168.4.1;
    
              subnet 192.168.4.0 netmask 255.255.255.0 {
                use-host-decl-names on; 
                option subnet-mask 255.255.255.0;
                option broadcast-address 192.168.4.255;
    
                host margaux {
                  hardware ethernet 01:23:45:67:89:ab;
                  fixed-address margaux.example.com;
                  next-server 192.168.4.4;
                  filename "/tftpboot/kernel.diskless";
                  option root-path "192.168.4.4:/data/misc/diskless";
                }
              }
             

              .def100:\
                :hn:ht=1:sa=192.168.4.4:vm=rfc1048:\
                :sm=255.255.255.0:\
                :ds=192.168.4.1:\
                :gw=192.168.4.1:\
                :hd="/tftpboot":\
                :bf="/kernel.diskless":\
                :rp="192.168.4.4:/data/misc/diskless":
    
              margaux:ha=0123456789ab:tc=.def100
             

19.6.1.2 Preparing a Boot Program with Etherboot

Etherboot's Web site contains extensive documentation mainly intended for Linux systems, but nonetheless containing useful information. The following will just outline how you would use etherboot on a FreeBSD system.

You must first install the net/etherboot package or port. The etherboot port can normally be found in /usr/ports/net/etherboot. If the ports tree is installed on your system, just typing make in this directory should take care of everything. Else refer to Chapter 4 for information about ports and packages.

For our setup, we shall use a boot floppy. For other methods (PROM, or dos program), please refer to the etherboot documentation.

To make a boot floppy, insert a floppy in the drive on the machine where you installed etherboot, then change your current directory to the src directory in the etherboot tree and type:

         # gmake bin32/devicetype.fd0
       

devicetype depends on the type of the Ethernet card in the diskless workstation. Refer to the NIC file in the same directory to determine the right devicetype.

19.6.1.3 Configuring the TFTP and NFS Servers

You need to enable tftpd on the TFTP server:

You can place the tftpboot directory anywhere on the server. Make sure that the location is set in both inetd.conf and dhcpd.conf.

You also need to enable NFS and export the appropriate filesystem on the NFS server.

19.6.1.4 Building a Diskless Kernel

Create a kernel configuration file for the diskless client with the following options (in addition to the usual ones):

              options     BOOTP          # Use BOOTP to obtain IP address/hostname
              options     BOOTP_NFSROOT  # NFS mount root filesystem using BOOTP info
              options     BOOTP_COMPAT   # Workaround for broken bootp daemons.
       

You may also want to use BOOTP_NFSV3 and BOOTP_WIRED_TO (refer to LINT).

Build the kernel (See Chapter 9), and copy it to the tftp directory, under the name listed in dhcpd.conf.

19.6.1.5 Preparing the root Filesystem

You need to create a root filesystem for the diskless workstations, in the location listed as root-path in dhcpd.conf.

The easiest way to do this is to use the /usr/share/examples/diskless/clone_root shell script. This script needs customization, at least to adjust the place where the filesystem will be created (the DEST variable).

Refer to the comments at the top of the script for instructions. They explain how the base filesystem is built, and how files may be selectively overridden by versions specific to diskless operation, to a subnetwork, or to an individual workstation. They also give examples for the diskless /etc/fstab and /etc/rc.conf files.

The README files in /usr/share/examples/diskless contain a lot of interesting background information, but, together with the other examples in the diskless directory, they actually document a configuration method which is distinct from the one used by clone_root and /etc/rc.diskless[12], which is a little confusing. Use them for reference only, except if you prefer the method that they describe, in which case you will need customized rc scripts.

19.6.1.6 Configuring Swap

If needed, a swap file located on the server can be accessed via NFS. The exact bootptab or dhcpd.conf options are not clearly documented at this time. The following configuration suggestions have been reported to work in some installations using isc-dhcp 3.0rc11.

19.6.1.7 Miscellaneous Issues