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The Debian System -- Concepts and Techniques The Debian System -- Concepts and Techniques
Martin F. Krafft Open Source Press / No Starch Press ISBN 3-937514-07-4 / 1-593270-69-0
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Mappings are applied iteratively (page 332)

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Reported on: 2005-07-26

In chapter 6. Debian system administration on page 332:

When the second paragraph in the subsection "Interface mappings" in section 6.7.1 states that only the first matching mapping is applied, it is only partially correct. Mappings are applied iteratively until no further mappings match.


It is true that a configuration identifier is mapped by the first matching mapping stanza; mapping stanzas further down in the file are not applied.

However, the result of a mapping is another configuration identifier. After applying a mapping, ifupdown repeats the process and tries to find the first mapping whose glob matches the new configuration identifier. This process continues until no more matching mapping stanzas are available, at which point the iface stanzas are considered.

This allows for interface configuration hierarchies and conditional mappings. For instance, in combination with guessnet (see p. 335ff), you can run certain location checks only if others were successful; you may only want to check for the presence of a certain router if a specific wireless access point is available.


Noel Davis, Can you imagine a book about Debian GNU/Linux stretching to 600 pages? No, not covering any of the applications that ship with Debian, nor delving into general configuration of, say, X or Samba. Just pure Debian; that is to say, the book covers Debian-specific utilities only, in densely printed pages with hardly any screenshots. Yup, a book like that has just been published under the name of The Debian System - Concept and Techniques. Written by Martin Krafft, this is one of the most comprehensive and detailed accounts of the largest Linux distribution in existence.


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