4.5. Preparing Files for TFTP Net Booting
| Chapter 4. Obtaining System Installation Media |

## 4.5. Preparing Files for TFTP Net Booting

If your machine is connected to a local area network, you may be able to boot it over the network from another machine, using TFTP. If you intend to boot the installation system from another machine, the boot files will need to be placed in specific locations on that machine, and the machine configured to support booting of your specific machine.

You need to set up a TFTP server, and for many machines a DHCP server, or BOOTP server.

BOOTP is an IP protocol that informs a computer of its IP address and where on the network to obtain a boot image. The DHCP (Dynamic Host Configuration Protocol) is a more flexible, backwards-compatible extension of BOOTP. Some systems can only be configured via DHCP.

The Trivial File Transfer Protocol (TFTP) is used to serve the boot image to the client. Theoretically, any server, on any platform, which implements these protocols, may be used. In the examples in this section, we shall provide commands for SunOS 4.x, SunOS 5.x (a.k.a. Solaris), and GNU/Linux.

| Note
For an Ubuntu or Debian server we recommend `tftpd-hpa`. It's written by the same author as the `syslinux` bootloader and is therefore least likely to cause issues. A good alternative is `atftpd`.

### 4.5.1. Setting up a DHCP server

One free software DHCP server is ISC dhcpd. For Ubuntu, the `isc-dhcp-server` package is recommended. Here is a sample configuration file for it (see `/etc/dhcp/dhcpd.conf`):

    option domain-name "example.com";
    option domain-name-servers ns1.example.com;
    option subnet-mask 255.255.255.0;
    default-lease-time 600;
    max-lease-time 7200;
    server-name "servername";

    subnet 192.168.1.0 netmask 255.255.255.0 {
      range 192.168.1.200 192.168.1.253;
      option routers 192.168.1.1;
    }

    host clientname {
      filename "/tftpboot.img";
      server-name "servername";
      next-server servername;
      hardware ethernet 01:23:45:67:89:AB;
      fixed-address 192.168.1.90;
    }

In this example, there is one server `servername` which performs all of the work of DHCP server, TFTP server, and network gateway. You will almost certainly need to change the domain-name options, as well as the server name and client hardware address. The `filename` option should be the name of the file which will be retrieved via TFTP.

After you have edited the dhcpd configuration file, restart it with `/etc/init.d/isc-dhcp-server restart`.

#### 4.5.1.1. Enabling PXE Booting in the DHCP configuration

Here is another example for a `dhcp.conf` using the Pre-boot Execution Environment (PXE) method of TFTP.

    option domain-name "example.com";

    default-lease-time 600;
    max-lease-time 7200;

    allow booting;
    allow bootp;

    # The next paragraph needs to be modified to fit your case
    subnet 192.168.1.0 netmask 255.255.255.0 {
      range 192.168.1.200 192.168.1.253;
      option broadcast-address 192.168.1.255;
    # the gateway address which can be different
    # (access to the internet for instance)
      option routers 192.168.1.1;
    # indicate the dns you want to use
      option domain-name-servers 192.168.1.3;
    }

    group {
      next-server 192.168.1.3;
      host tftpclient {
    # tftp client hardware address
      hardware ethernet  00:10:DC:27:6C:15;
      filename "pxelinux.0";
     }
    }

Note that for PXE booting, the client filename `pxelinux.0` is a boot loader, not a kernel image (see Section 4.5.4, “Move TFTP Images Into Place” below).

### 4.5.2. Setting up a BOOTP server

There are two BOOTP servers available for GNU/Linux. The first is CMU bootpd. The other is actually a DHCP server: ISC dhcpd. In Ubuntu these are contained in the `bootp` and `isc-dhcp-server` packages respectively.

To use CMU bootpd, you must first uncomment (or add) the relevant line in `/etc/inetd.conf`. On Debian or Ubuntu, you can run `update-inetd --enable bootps`, then `/etc/init.d/inetd reload` to do so. Just in case your BOOTP server does not run Debian or Ubuntu, the line in question should look like:

    bootps  dgram  udp  wait  root  /usr/sbin/bootpd  bootpd -i -t 120

Now, you must create an `/etc/bootptab` file. This has the same sort of familiar and cryptic format as the good old BSD `printcap`, `termcap`, and `disktab` files. See the `bootptab` manual page for more information. For CMU bootpd, you will need to know the hardware (MAC) address of the client. Here is an example `/etc/bootptab`:

    client:\
      hd=/tftpboot:\
      bf=tftpboot.img:\
      ip=192.168.1.90:\
      sm=255.255.255.0:\
      sa=192.168.1.1:\
      ha=0123456789AB:

You will need to change at least the “ha” option, which specifies the hardware address of the client. The “bf” option specifies the file a client should retrieve via TFTP; see Section 4.5.4, “Move TFTP Images Into Place” for more details.

By contrast, setting up BOOTP with ISC dhcpd is really easy, because it treats BOOTP clients as a moderately special case of DHCP clients. Some architectures require a complex configuration for booting clients via BOOTP. If yours is one of those, read the section Section 4.5.1, “Setting up a DHCP server”. Otherwise you will probably be able to get away with simply adding the `allow bootp` directive to the configuration block for the subnet containing the client in `/etc/dhcp/dhcpd.conf`, and restart dhcpd with `/etc/init.d/isc-dhcp-server restart`.

### 4.5.3. Enabling the TFTP Server

To get the TFTP server ready to go, you should first make sure that tftpd is enabled.

In the case of `tftpd-hpa` there are two ways the service can be run. It can be started on demand by the system's `inetd` daemon, or it can be set up to run as an independent daemon. Which of these methods is used is selected when the package is installed and can be changed by reconfiguring the package.

| Note
Historically, TFTP servers used `/tftpboot` as directory to serve images from. However, Ubuntu packages may use other directories to comply with the Filesystem Hierarchy Standard. For example, `tftpd-hpa` by default uses `/srv/tftp`. You may have to adjust the configuration examples in this section accordingly.

All in.tftpd alternatives available in Ubuntu should log TFTP requests to the system logs by default. Some of them support a `-v` argument to increase verbosity. It is recommended to check these log messages in case of boot problems as they are a good starting point for diagnosing the cause of errors.

### 4.5.4. Move TFTP Images Into Place

Next, place the TFTP boot image you need, as found in Section 4.2.1, “Where to Find Installation Images”, in the tftpd boot image directory. You may have to make a link from that file to the file which tftpd will use for booting a particular client. Unfortunately, the file name is determined by the TFTP client, and there are no strong standards.

For PXE booting, everything you should need is set up in the `netboot/netboot.tar.gz` tarball. Simply extract this tarball into the tftpd boot image directory. Make sure your dhcp server is configured to pass `pxelinux.0` to tftpd as the filename to boot.

4.4. Preparing Files for Hard Disk Booting |  | 4.6. Automatic Installation