In this section I assume you want to boot a Linux kernel. Booting a FreeBSD kernel will be documented soon. Booting a DOS kernel is similar, the main differences being in the way you set up the tagged image.
Etherboot expects to download a tagged image containing the code to be executed. Briefly explained, a tagged image is a wrapper around the pieces of code or data that need to be put in various places in the computer's memory. It contains a directory telling how large the pieces are and where they go in memory. It also says where to start execution.
A tagged image is created using a utility program. The utility program is specific to the kernel you want to load. The version for Linux is called mknbi-linux and that for DOS is mknbi-dos. These utilities are found in the netboot-<version> directory of the distribution.
You will almost certainly have to compile a custom kernel because the kernel needs to have the "Root file system on NFS" option compiled in. You should also select "BOOTP support". "RARP support" is not needed. In 2.2 kernels you have to enable the "Kernel level autoconfiguration" option under IP networking to access the BOOTP support question. And unless you are using an initrd (initial ramdisk) you will have to compile in the driver for your network card too. For details, see the file /usr/src/linux/Documentation/nfsroot.txt in a Linux kernel source distribution.
After you have compiled the custom kernel, make the tagged image, typically like this:
mknbi -x -k zImage -o /tftpdir/vmlinuz.xterm
Then put the tagged image in where the tftp daemon expects to find it, in this example /tftpdir. Make sure it is world-readable because typically the tftp daemon runs as an unprivileged user. It is recommended that you set a path explicitly to tftpd instead of relying on any defaults. For example:
tftp dgram udp wait root /usr/sbin/tcpd in.tftpd /tftpdir
Now set up a bootp daemon. In RedHat 5.2 this means installing the bootp RPM package, making sure that the bootps service is active in /etc/inetd.conf, and editing /etc/bootptab. The essential pieces of information you need to put in bootptab are:
Here is an example of a /etc/bootptab for the bootpd supplied with RedHat Linux 5.2 and probably many versions of Unix:
.default:\
:ht=ethernet:\
:hd=/tftpdir:bf=null:\
:ds=nameserver:\
:hn:to=36000:
xterm.ken.net.au:tc=.default:ha=08002BB7F380:ip=192.168.26.100:bf=vmlinuz.xterm
The first entry sets up some common defaults which applies to all succeeding entries which can be "included" using the tc=.default attribute. The first field is the domain name of the machine. The ha attribute is the Ethernet address. The ip attribute is self-explanatory. The bf field specifies the tagged image filename. For more details, consult the bootptab man page.
Please note that if you use the ef (extension file) attribute to be able to send more configuration data to the diskless machine, you must run bootpef everytime bootptab is modified.
As an alternative to bootp, you could set up a DHCP server which has the advantage of automating the handing out of IP addresses. In RedHat 6.0, bootpd is not supplied and DHCPD is preferred. However the kernel will still do a bootp request to find the IP address for mounting the NFS filesystem. You may then wish to investigate the option in mknbi-linux which tells the kernel to take the address from the initial DHCP reply.
This is the roughly equivalent dhcpd.conf file to the above bootptab:
option domain-name "ken.net.au";
option domain-name-servers 192.168.26.1;
option broadcast-address 192.168.26.255;
use-host-decl-names on;
subnet 192.168.26.0 netmask 255.255.255.0 {
filename "/tftpdir/vmlinuz.xterm";
host xterm {
hardware ethernet 08:00:2B:B7:F3:80;
fixed-address xterm.ken.net.au;
filename "/tftpdir/vmlinuz.xterm";
}
}
You don't have to use fixed addresses, of course, but if you use dynamic addresses, then you have to deal with the resulting issues of NFS mounting.
More information about DHCP can be found at the DHCP FAQ Web Page.
If you are on a local network that is not directly connected to the Internet, you can use the "private" IP addresses 192.168.x.y (or in the other ranges mentioned in RFC1918). Otherwise please ask either your network administrator or your Internet service provider for your own IP address(es).
Now set up a tftp daemon. This means installing the tftp package and making sure that the tftp service is active in /etc/inetd.conf. You probably want to use the secure (-s) option if it is required so that files can only be fetched from /tftpdir or people may be able to fetch arbitrary files from your server.
If you are booting many clients you should be aware of the limitations of
running tftpd from inetd. Typically inetd has limits on how often a daemon
can be spawned, to detect runaway daemons. If many clients request the
tftp service within a short period, inetd may shutdown that service. If
you have a setup where there are many clients, it may be better use a more
flexible replacement for inetd, such as xinetd. Another solution is to run
a dedicated tftpd that is not spawned from inetd. One such tftpd can be
found here at: ftp://nilo.on.openprojects.net/pub/nilo/snapshots