246 lines
12 KiB
TeX
246 lines
12 KiB
TeX
% ----------------------------------------------------------------------------
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% cconfig
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% ----------------------------------------------------------------------------
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\documentclass[11pt,a4paper]{article}
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\usepackage[latin1]{inputenc} % Ascii-Format dieses Dokuments
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\usepackage{longtable} % lange Tabellen
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\usepackage[dvips]{epsfig}
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\usepackage{fancyhdr}
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\pagestyle{fancy}
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\fancyhead[R]{Nico Schottelius}
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\fancyhead[L]{cconfig}
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\renewcommand{\headrulewidth}{0.4pt}
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% ----------------------------------------------------------------------------
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\newcommand{\cemail}{nico-linux-cconfig ((at)) schottelius.org}
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% ----------------------------------------------------------------------------
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\begin{document}
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\title{cconfig 0.1}
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\date{2005-08-28}
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\author{Nico Schottelius (\cemail)}
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% ----------------------------------------------------------------------------
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% Title
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% ----------------------------------------------------------------------------
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\maketitle
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\newpage
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% ----------------------------------------------------------------------------
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% Inhaltsverzeichnis
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\tableofcontents
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\newpage
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\section{Introduction}
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cconfig is a proposal for configurations on Unix-alike
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systems\footnote{In fact it can be used on any system, which
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fits the requirements. See \ref{requirements}, \pageref{requirements} for more
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information}. This includes, but is not limited to services, packages,
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user settings or the system configuration. cconfig main idea is
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\begin{itemize}
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\item to simplify the layout of configurations
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\item to make it easier to configure
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\item to allow smooth editing from automatically running programs,
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\item thus to avoid parsing where possible,
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\item to use the available resources (libraries, functions, ...)
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\item and to prevent doubled implementations.
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\end{itemize}
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% ----------------------------------------------------------------------------
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\section{Layout}
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Every cconfig starts below a given directory. This directory
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should be named after the process using the configuration
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(auth, cinit, mini-lpd, yourutils) and be put under the
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appropriate configuration directory (/etc, /usr/packages/yourutil/etc, ...).
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A cconfig consists of objects and attributes.
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\subsection{Objects}
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An object is a subdirectory below your configuration directory.
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An object can also be a subobject, means a subdirectory of a
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directory (this may be continued as deep as you
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need\footnote{Have a look at the portability issue, \ref{port-dir},
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page \pageref{port-dir}.}.
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% ----------------------------------------------------------------------------
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\subsection{Attributes}
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Attributes describe a specific configuration option.
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They may exist directly below the configuration directory or below objects.
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% ----------------------------------------------------------------------------
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\subsection{Links}
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With links you can reuse attributes or objects under a different name
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or at a different location\footnote{Have a look at the portability issue,
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\ref{port-links}, page \pageref{port-links}.}.
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% ----------------------------------------------------------------------------
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\section{Portability}
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\label{requirements}
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cconfig should in general be portable between Unix-systems, still
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there \textit{can} be problems exchanging cconfig data. To prevent
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them, take care of the following sections.
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% ----------------------------------------------------------------------------
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\subsection{Exchanging}
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Transferring a cconfig should be done encapsulated in a tar\cite{tar} archive.
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Tar saves the most important information (date, rights, names, ...)
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and is available on every Unix-system\footnote{As of the current date
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tar seems \textbf{not} to be able to save ACLs (access control lists).}.
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If the configuration is very big, consider compressing it with bzip2\cite{bzip2}.
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% ----------------------------------------------------------------------------
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\subsection{File names}
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The file- and directory names and the content of the files should either be
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\begin{itemize}
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\item plain ASCII
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\item or UTF-8\cite{utf8}
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\end{itemize}
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Currently there is no specification, that specifies that a filesystem
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must support UTF-8, but practically most modern systems do have
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UTF-8 support\footnote{Reiserfs, ext2, ext3, xfs should work fine, jfs
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is reported to had problems with some characters.}.
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% ----------------------------------------------------------------------------
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\subsection{File contents}
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The same rules as in "`File names"' apply.
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% ----------------------------------------------------------------------------
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\subsection{Using (symbolic) links (absolute and relative)}
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\label{port-links}
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Hard links are not a problem, because when transferring the data they look
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as different files, tar will not see the difference between a totally
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different file and a hard link.
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When using symbolic links one has to distinguish between absolute
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and relative links. Using a symbolic link can be a problem in general, if
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you link outside of the configuration directory. If you link to other
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files or directories in the configuration directory you should prefer
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relative links. When using absolute links the linked files
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may be non-existent, when using relative links to files outside
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the files may be unreachable, because the cconfig is extracted
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below a different hierarchy position.
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Some operating system implement links differently, you need
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to have a tool, which converts standard links (as used on POSIX
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systems) to those used on other system and the other way
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round\footnote{Those systems are most likely \textbf{not} Unix-alike and
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have a general different design with complex and broken registries.}.
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% ----------------------------------------------------------------------------
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\subsection{Quantity of objects}
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\label{port-dir}
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Some filesystems limit the count of directories (how deep directories
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may be nested). For normal configurations you'll never reach this
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limit\footnote{Please report if you ever reach this limit on a filesystem,
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I would be interested in how deep the limit is. Currently one person
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reported that after 125 subdirectories the limit is reached in the
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operating system with the blue screen.}.
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% ----------------------------------------------------------------------------
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\section{Examples}
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So far said, let us see some examples after the theoretic part.
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% ----------------------------------------------------------------------------
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\subsection{printer daemon (mini-lpd)}
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mini-lpd is a small, non-queueing lpd implementation. It uses
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\verb=/etc/mini-lpd= as its configuration directory. Every directory
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below is the name of a queue:
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\begin{verbatim}
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[15:09] hydrogenium:~# ls -l /etc/mini-lpd
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total 0
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drwx------ 2 root root 6 Aug 28 15:09 lp0
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drwx------ 2 root root 6 Aug 28 15:09 lp1
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\end{verbatim}
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Those "`objects"' (directories) contain an attribute "`device"', which
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is where the mini-lpd writes the incoming data to:
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\begin{verbatim}
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[15:10] hydrogenium:~# ls -l /etc/mini-lpd/lp*
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/etc/mini-lpd/lp0:
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total 0
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lrwxrwxrwx 1 root root 9 Aug 28 15:10 device -> /dev/null
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/etc/mini-lpd/lp1:
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total 0
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lrwxrwxrwx 1 root root 8 Aug 28 15:10 device -> /dev/lp0
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\end{verbatim}
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You could add other attributes like "`filter"' (unsupported currently), which
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could be a link to a program filtering the input before mini-lpd
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would write it to the device.
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% ----------------------------------------------------------------------------
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\subsection{Samba}
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Samba\cite{samba} is the well-known Unix SMB server. It exists and
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does \textbf{not} use cconfig for its configuration, but this describes
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how it could:
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"`/etc/samba"' is currently the configuration directory. Instead of
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the smb.conf you would have the object "`config"'. Bool
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variables\footnote{Those which can either be TRUE or FALSE.} could simply
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be represented by "`file exists"' (true) or "`file does not exist"'.
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Variables with text could be realised with writing the text into the file:
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"`/etc/samba/config/workgroup"' could contain "`cworkgroup"'.
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Shares could be objects below "`/etc/samba/shares"':
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"`/etc/samba/shares/cdrom"' could contain a file name "`path"' which links
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to the real path, a file "`groups"' which would contain a \verb=\n= seperated
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list of groups which may access this share.
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% ----------------------------------------------------------------------------
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\subsection{init system (cinit)}
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Cinit\cite{cinit} is a fast init system, which uses cconfig.
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"`/etc/cinit"' is its basic configuration directory. Below that directory
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exist the basic configuration:
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\begin{verbatim}
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wasserstoff# ls -l /etc/cinit
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total 8
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drwxr-xr-x 10 root root 4096 Aug 20 20:55 getty
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drwxr-xr-x 3 root root 56 Aug 24 22:04 init
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drwxr-xr-x 2 root root 1 Aug 20 20:38 local-services
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drwxr-xr-x 5 root root 32 Aug 24 22:14 local-tuning
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drwxr-xr-x 10 root root 72 Aug 24 06:40 mount
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drwxr-xr-x 7 root root 48 Aug 28 13:57 network
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drwxr-xr-x 4 root root 16 Aug 20 20:51 remote-services
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drwxr-xr-t 2 root root 60 Aug 28 14:00 tmp
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\end{verbatim}
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"`/etc/cinit/init"' is the first service cinit normally boots,
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from there it has dependencies to other services:
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\begin{verbatim}
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wasserstoff# ls -l /etc/cinit/init/*
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lrwxrwxrwx 1 root root 9 Aug 20 20:43 /etc/cinit/init/on -> /bin/echo
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-rw-r--r-- 1 root root 22 Aug 20 20:43 /etc/cinit/init/on.params
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/etc/cinit/init/wants:
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total 0
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lrwxrwxrwx 1 root root 12 Aug 20 20:43 getty -> ../../getty/
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lrwxrwxrwx 1 root root 21 Aug 20 20:51 local-services -> ../../local-services/
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lrwxrwxrwx 1 root root 19 Aug 20 20:42 local-tuning -> ../../local-tuning/
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lrwxrwxrwx 1 root root 12 Aug 20 20:51 mount -> ../../mount/
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lrwxrwxrwx 1 root root 14 Aug 20 20:51 network -> ../../network/
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lrwxrwxrwx 1 root root 22 Aug 20 20:51 remote-services -> ../../remote-services/
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\end{verbatim}
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The "`wants"' describe soft-dependencies, "`on"' specifies what to start
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and "`on.params"' are the parameters to pass.
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% ----------------------------------------------------------------------------
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\section{Problems}
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cconfig is not a standard currently.
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No tools exists to convert to other formats like XML.
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There is no description language (like DTD or XSLT for XML).
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The portability is ensured between most Unices, but Win32 will
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most likely be broken as long as nobody writes a "`cconfigtar2win32fs"'
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convert tool.
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% ----------------------------------------------------------------------------
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\section{Personal statement}
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I wrote this because I think configuring things this way is very logic
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and helps to intuitively use your system. Furthermore it is really
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easy to see what is configured (\verb=find /the/cconfig/dir=). I implemented
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variants of cconfig in cinit\cite{cinit} and mini-lpd\cite{mini-lpd}.
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Many people I know, who use xml\cite{xml} and have problems, because
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the parser is too slow, were very happy when I told them about cconfig.
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I hope you can also benefit from it. I would really like to hear some
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feedback from you at \cemail.
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% ----------------------------------------------------------------------------
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\appendix
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\begin{thebibliography}{666}
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\bibitem{posix} Posix and SUS;\\
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\verb=http://www.opengroup.org/platform/single_unix_specification/=
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\bibitem{cinit} cinit;\\
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\verb=http://linux.schottelius.org/cinit/=
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\bibitem{utf8} UTF-8;\\
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\verb=http://www.utf-8.com/=;\\
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\verb=http://www.cl.cam.ac.uk/~mgk25/unicode.html=
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\bibitem{mini-lpd} mini-lpd;\\
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\verb=http://linux.schottelius.org/mini-lpd/=
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\bibitem{tar} tar;\\
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\verb=http%3A//www.gnu.org/software/tar/tar.html=
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\bibitem{bzip2} bzip2;\\
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\verb=http://www.bzip.org/=
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\bibitem{samba} Samba;\\
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\verb=http://www.samba.org/=
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\bibitem{xml} XML;\\
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\verb=http://www.w3.org/XML/=
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\end{thebibliography}
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\end{document}
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