ISC DHCP server (the isc-dhcp-server Ubuntu package). 

if substring (option vendor-class-identifier, 0, 3) = "d-i" { filename "http://host/preseed.cfg"; } 

Note: The above example limits this filename to DHCP clients that identify themselves as "d-i", so it will not affect regular DHCP clients, but only the installer. You can also put the text in a stanza for only one particular host to avoid preseeding all installs on your network. 

A good way to use the DHCP preseeding is to only preseed values specific to your network, such as the Ubuntu mirror to use. This way installs on your network will automatically get a good mirror selected, but the rest of the installation can be performed interactively. Using DHCP preseeding to fully automate Ubuntu installs should only be done with care. 

## B.3. Creating a preconfiguration file 

The preconfiguration file is in the format used by the debconf-set-selections command. The general format of a line in a preconfiguration file is: 

<owner> <question name> <question type> <value> 

There are a few rules to keep in mind when writing a preconfiguration file. 

• Put only a single space or tab between type and value: any additional whitespace will be interpreted as belonging to the value. 

• A line can be split into multiple lines by appending a backslash (“ \ ”) as the line continuation character. A good place to split a line is after the question name; a bad place is between type and value. Split lines will be joined into a single line with all leading/trailing whitespace condensed to a single space. 

• For debconf variables (templates) used only in the installer itself, the owner should be set to “d-i”; to preseed variables used in the installed system, the name of the package that contains the corre- sponding debconf template should be used. Only variables that have their owner set to something other than “d-i” will be propagated to the debconf database for the installed system. 

• Most questions need to be preseeded using the values valid in English and not the translated values. However, there are some questions (for example in partman ) where the translated values need to be used. 

• Some questions take a code as value instead of the English text that is shown during installation. 

The easiest way to create a preconfiguration file is to use the example file linked in Section B.4 as basis and work from there. 

An alternative method is to do a manual installation and then, after rebooting, use the debconf-get- selections from the debconf-utils package to dump both the debconf database and the installer’s cdebconf database to a single file: 

