19.7 Diskless Operation

19.7.2.1 Configuration Using ISC DHCP

The ISC DHCP server can answer both BOOTP and DHCP requests.

ISC DHCP needs a configuration file to run, (normally named /usr/local/etc/dhcpd.conf). Here follows a commented example, where host margaux uses etherboot and host corbieres uses PXE:

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 "/data/misc/kernel.diskless"; 
    option root-path "192.168.4.4:/data/misc/diskless"; 
  }
  host corbieres {
    hardware ethernet 00:02:b3:27:62:df;
    fixed-address corbieres.example.com;
    next-server 192.168.4.4;
    filename "pxeboot";
    option root-path "192.168.4.4:/data/misc/diskless";
  }
}
          

19.7.2.2 Configuration Using BOOTP

Here follows an equivalent bootpd configuration (reduced to one client). This would be found in /etc/bootptab.

Please note that etherboot must be compiled with the non-default option NO_DHCP_SUPPORT in order to use BOOTP, and that PXE needs DHCP. The only obvious advantage of bootpd is that it exists in the base system.

.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
          

19.7.2.3 Booting with PXE

By default, the pxeboot(8) loader loads the kernel via NFS. It can be compiled to use TFTP instead by specifying the LOADER_TFTP_SUPPORT option in /etc/make.conf. See the comments in /etc/defaults/make.conf (or /usr/share/examples/etc/make.conf for 5.X systems) for instructions.

There are two other undocumented make.conf options which may be useful for setting up a serial console diskless machine: BOOT_PXELDR_PROBE_KEYBOARD, and BOOT_PXELDR_ALWAYS_SERIAL.

To use PXE when the machine starts, you will usually need to select the Boot from network option in your BIOS setup, or type a function key during the PC initialization.

19.7.2.4 Configuring the TFTP and NFS Servers

If you are using PXE or etherboot configured to use TFTP, you need to enable tftpd on the file 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.

In all cases, you also need to enable NFS and export the appropriate filesystem on the NFS server.

19.7.2.5 Building a Diskless Kernel

If using etherboot, you need to 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
	

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

These option names are historical and slightly misleading as they actually enable indifferent use of DHCP and BOOTP inside the kernel (it is also possible to force strict BOOTP or DHCP use).

Build the kernel (see Chapter 9), and copy it to the place specified in dhcpd.conf.

19.7.2.6 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 following sections describe two ways to do it.

#!/bin/sh
export DESTDIR=/data/misc/diskless
mkdir -p ${DESTDIR}
cd /usr/src; make world && make kernel
cd /usr/src/etc; make distribution

19.7.2.7 Configuring Swap

If needed, a swap file located on the server can be accessed via NFS.

19.7.2.8 Miscellaneous Issues