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<title>Debian Policy Manual - Configuration file handling (from old Packaging Manual)</title>

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<link href="ch-scope.html" rel="chapter" title="1 About this manual">
<link href="ch-archive.html" rel="chapter" title="2 The Debian Archive">
<link href="ch-binary.html" rel="chapter" title="3 Binary packages">
<link href="ch-source.html" rel="chapter" title="4 Source packages">
<link href="ch-controlfields.html" rel="chapter" title="5 Control files and their fields">
<link href="ch-maintainerscripts.html" rel="chapter" title="6 Package maintainer scripts and installation procedure">
<link href="ch-relationships.html" rel="chapter" title="7 Declaring relationships between packages">
<link href="ch-sharedlibs.html" rel="chapter" title="8 Shared libraries">
<link href="ch-opersys.html" rel="chapter" title="9 The Operating System">
<link href="ch-files.html" rel="chapter" title="10 Files">
<link href="ch-customized-programs.html" rel="chapter" title="11 Customized programs">
<link href="ch-docs.html" rel="chapter" title="12 Documentation">
<link href="ap-pkg-scope.html" rel="appendix" title="A Introduction and scope of these appendices">
<link href="ap-pkg-binarypkg.html" rel="appendix" title="B Binary packages (from old Packaging Manual)">
<link href="ap-pkg-sourcepkg.html" rel="appendix" title="C Source packages (from old Packaging Manual)">
<link href="ap-pkg-controlfields.html" rel="appendix" title="D Control files and their fields (from old Packaging Manual)">
<link href="ap-pkg-conffiles.html" rel="appendix" title="E Configuration file handling (from old Packaging Manual)">
<link href="ap-pkg-alternatives.html" rel="appendix" title="F Alternative versions of an interface - update-alternatives (from old Packaging Manual)">
<link href="ap-pkg-diversions.html" rel="appendix" title="G Diversions - overriding a package's version of a file (from old Packaging Manual)">
<link href="ch-scope.html#s1.1" rel="section" title="1.1 Scope">
<link href="ch-scope.html#s1.2" rel="section" title="1.2 New versions of this document">
<link href="ch-scope.html#s-authors" rel="section" title="1.3 Authors and Maintainers">
<link href="ch-scope.html#s-related" rel="section" title="1.4 Related documents">
<link href="ch-scope.html#s-definitions" rel="section" title="1.5 Definitions">
<link href="ch-archive.html#s-dfsg" rel="section" title="2.1 The Debian Free Software Guidelines">
<link href="ch-archive.html#s-sections" rel="section" title="2.2 Archive areas">
<link href="ch-archive.html#s-pkgcopyright" rel="section" title="2.3 Copyright considerations">
<link href="ch-archive.html#s-subsections" rel="section" title="2.4 Sections">
<link href="ch-archive.html#s-priorities" rel="section" title="2.5 Priorities">
<link href="ch-binary.html#s3.1" rel="section" title="3.1 The package name">
<link href="ch-binary.html#s-versions" rel="section" title="3.2 The version of a package">
<link href="ch-binary.html#s-maintainer" rel="section" title="3.3 The maintainer of a package">
<link href="ch-binary.html#s-descriptions" rel="section" title="3.4 The description of a package">
<link href="ch-binary.html#s-dependencies" rel="section" title="3.5 Dependencies">
<link href="ch-binary.html#s-virtual_pkg" rel="section" title="3.6 Virtual packages">
<link href="ch-binary.html#s3.7" rel="section" title="3.7 Base system">
<link href="ch-binary.html#s3.8" rel="section" title="3.8 Essential packages">
<link href="ch-binary.html#s-maintscripts" rel="section" title="3.9 Maintainer Scripts">
<link href="ch-source.html#s-standardsversion" rel="section" title="4.1 Standards conformance">
<link href="ch-source.html#s-pkg-relations" rel="section" title="4.2 Package relationships">
<link href="ch-source.html#s4.3" rel="section" title="4.3 Changes to the upstream sources">
<link href="ch-source.html#s-dpkgchangelog" rel="section" title="4.4 Debian changelog: debian/changelog">
<link href="ch-source.html#s-dpkgcopyright" rel="section" title="4.5 Copyright: debian/copyright">
<link href="ch-source.html#s4.6" rel="section" title="4.6 Error trapping in makefiles">
<link href="ch-source.html#s-timestamps" rel="section" title="4.7 Time Stamps">
<link href="ch-source.html#s-restrictions" rel="section" title="4.8 Restrictions on objects in source packages">
<link href="ch-source.html#s-debianrules" rel="section" title="4.9 Main building script: debian/rules">
<link href="ch-source.html#s-substvars" rel="section" title="4.10 Variable substitutions: debian/substvars">
<link href="ch-source.html#s-debianwatch" rel="section" title="4.11 Optional upstream source location: debian/watch">
<link href="ch-source.html#s-debianfiles" rel="section" title="4.12 Generated files list: debian/files">
<link href="ch-source.html#s-embeddedfiles" rel="section" title="4.13 Convenience copies of code">
<link href="ch-source.html#s-readmesource" rel="section" title="4.14 Source package handling: debian/README.source">
<link href="ch-controlfields.html#s-controlsyntax" rel="section" title="5.1 Syntax of control files">
<link href="ch-controlfields.html#s-sourcecontrolfiles" rel="section" title="5.2 Source package control files -- debian/control">
<link href="ch-controlfields.html#s-binarycontrolfiles" rel="section" title="5.3 Binary package control files -- DEBIAN/control">
<link href="ch-controlfields.html#s-debiansourcecontrolfiles" rel="section" title="5.4 Debian source control files -- .dsc">
<link href="ch-controlfields.html#s-debianchangesfiles" rel="section" title="5.5 Debian changes files -- .changes">
<link href="ch-controlfields.html#s-controlfieldslist" rel="section" title="5.6 List of fields">
<link href="ch-controlfields.html#s5.7" rel="section" title="5.7 User-defined fields">
<link href="ch-maintainerscripts.html#s6.1" rel="section" title="6.1 Introduction to package maintainer scripts">
<link href="ch-maintainerscripts.html#s-idempotency" rel="section" title="6.2 Maintainer scripts idempotency">
<link href="ch-maintainerscripts.html#s-controllingterminal" rel="section" title="6.3 Controlling terminal for maintainer scripts">
<link href="ch-maintainerscripts.html#s-exitstatus" rel="section" title="6.4 Exit status">
<link href="ch-maintainerscripts.html#s-mscriptsinstact" rel="section" title="6.5 Summary of ways maintainer scripts are called">
<link href="ch-maintainerscripts.html#s-unpackphase" rel="section" title="6.6 Details of unpack phase of installation or upgrade">
<link href="ch-maintainerscripts.html#s-configdetails" rel="section" title="6.7 Details of configuration">
<link href="ch-maintainerscripts.html#s-removedetails" rel="section" title="6.8 Details of removal and/or configuration purging">
<link href="ch-relationships.html#s-depsyntax" rel="section" title="7.1 Syntax of relationship fields">
<link href="ch-relationships.html#s-binarydeps" rel="section" title="7.2 Binary Dependencies - Depends, Recommends, Suggests, Enhances, Pre-Depends">
<link href="ch-relationships.html#s-breaks" rel="section" title="7.3 Packages which break other packages - Breaks">
<link href="ch-relationships.html#s-conflicts" rel="section" title="7.4 Conflicting binary packages - Conflicts">
<link href="ch-relationships.html#s-virtual" rel="section" title="7.5 Virtual packages - Provides">
<link href="ch-relationships.html#s-replaces" rel="section" title="7.6 Overwriting files and replacing packages - Replaces">
<link href="ch-relationships.html#s-sourcebinarydeps" rel="section" title="7.7 Relationships between source and binary packages - Build-Depends, Build-Depends-Indep, Build-Conflicts, Build-Conflicts-Indep">
<link href="ch-sharedlibs.html#s-sharedlibs-runtime" rel="section" title="8.1 Run-time shared libraries">
<link href="ch-sharedlibs.html#s-sharedlibs-support-files" rel="section" title="8.2 Shared library support files">
<link href="ch-sharedlibs.html#s-sharedlibs-static" rel="section" title="8.3 Static libraries">
<link href="ch-sharedlibs.html#s-sharedlibs-dev" rel="section" title="8.4 Development files">
<link href="ch-sharedlibs.html#s-sharedlibs-intradeps" rel="section" title="8.5 Dependencies between the packages of the same library">
<link href="ch-sharedlibs.html#s-sharedlibs-shlibdeps" rel="section" title="8.6 Dependencies between the library and other packages - the shlibs system">
<link href="ch-opersys.html#s9.1" rel="section" title="9.1 File system hierarchy">
<link href="ch-opersys.html#s9.2" rel="section" title="9.2 Users and groups">
<link href="ch-opersys.html#s-sysvinit" rel="section" title="9.3 System run levels and init.d scripts">
<link href="ch-opersys.html#s9.4" rel="section" title="9.4 Console messages from init.d scripts">
<link href="ch-opersys.html#s-cron-jobs" rel="section" title="9.5 Cron jobs">
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<link href="ch-opersys.html#s-mime" rel="section" title="9.7 Multimedia handlers">
<link href="ch-opersys.html#s9.8" rel="section" title="9.8 Keyboard configuration">
<link href="ch-opersys.html#s9.9" rel="section" title="9.9 Environment variables">
<link href="ch-opersys.html#s-doc-base" rel="section" title="9.10 Registering Documents using doc-base">
<link href="ch-files.html#s-binaries" rel="section" title="10.1 Binaries">
<link href="ch-files.html#s-libraries" rel="section" title="10.2 Libraries">
<link href="ch-files.html#s10.3" rel="section" title="10.3 Shared libraries">
<link href="ch-files.html#s-scripts" rel="section" title="10.4 Scripts">
<link href="ch-files.html#s10.5" rel="section" title="10.5 Symbolic links">
<link href="ch-files.html#s10.6" rel="section" title="10.6 Device files">
<link href="ch-files.html#s-config-files" rel="section" title="10.7 Configuration files">
<link href="ch-files.html#s10.8" rel="section" title="10.8 Log files">
<link href="ch-files.html#s-permissions-owners" rel="section" title="10.9 Permissions and owners">
<link href="ch-customized-programs.html#s-arch-spec" rel="section" title="11.1 Architecture specification strings">
<link href="ch-customized-programs.html#s11.2" rel="section" title="11.2 Daemons">
<link href="ch-customized-programs.html#s11.3" rel="section" title="11.3 Using pseudo-ttys and modifying wtmp, utmp and lastlog">
<link href="ch-customized-programs.html#s11.4" rel="section" title="11.4 Editors and pagers">
<link href="ch-customized-programs.html#s-web-appl" rel="section" title="11.5 Web servers and applications">
<link href="ch-customized-programs.html#s-mail-transport-agents" rel="section" title="11.6 Mail transport, delivery and user agents">
<link href="ch-customized-programs.html#s11.7" rel="section" title="11.7 News system configuration">
<link href="ch-customized-programs.html#s11.8" rel="section" title="11.8 Programs for the X Window System">
<link href="ch-customized-programs.html#s-perl" rel="section" title="11.9 Perl programs and modules">
<link href="ch-customized-programs.html#s-emacs" rel="section" title="11.10 Emacs lisp programs">
<link href="ch-customized-programs.html#s11.11" rel="section" title="11.11 Games">
<link href="ch-docs.html#s12.1" rel="section" title="12.1 Manual pages">
<link href="ch-docs.html#s12.2" rel="section" title="12.2 Info documents">
<link href="ch-docs.html#s12.3" rel="section" title="12.3 Additional documentation">
<link href="ch-docs.html#s12.4" rel="section" title="12.4 Preferred documentation formats">
<link href="ch-docs.html#s-copyrightfile" rel="section" title="12.5 Copyright information">
<link href="ch-docs.html#s12.6" rel="section" title="12.6 Examples">
<link href="ch-docs.html#s-changelogs" rel="section" title="12.7 Changelog files">
<link href="ap-pkg-binarypkg.html#s-pkg-bincreating" rel="section" title="B.1 Creating package files - dpkg-deb">
<link href="ap-pkg-binarypkg.html#s-pkg-controlarea" rel="section" title="B.2 Package control information files">
<link href="ap-pkg-binarypkg.html#s-pkg-controlfile" rel="section" title="B.3 The main control information file: control">
<link href="ap-pkg-binarypkg.html#sB.4" rel="section" title="B.4 Time Stamps">
<link href="ap-pkg-sourcepkg.html#s-pkg-sourcetools" rel="section" title="C.1 Tools for processing source packages">
<link href="ap-pkg-sourcepkg.html#s-pkg-sourcetree" rel="section" title="C.2 The Debian package source tree">
<link href="ap-pkg-sourcepkg.html#s-pkg-sourcearchives" rel="section" title="C.3 Source packages as archives">
<link href="ap-pkg-sourcepkg.html#sC.4" rel="section" title="C.4 Unpacking a Debian source package without dpkg-source">
<link href="ap-pkg-controlfields.html#sD.1" rel="section" title="D.1 Syntax of control files">
<link href="ap-pkg-controlfields.html#sD.2" rel="section" title="D.2 List of fields">
<link href="ap-pkg-conffiles.html#sE.1" rel="section" title="E.1 Automatic handling of configuration files by dpkg">
<link href="ap-pkg-conffiles.html#sE.2" rel="section" title="E.2 Fully-featured maintainer script configuration handling">
<link href="ch-archive.html#s-main" rel="subsection" title="2.2.1 The main archive area">
<link href="ch-archive.html#s-contrib" rel="subsection" title="2.2.2 The contrib archive area">
<link href="ch-archive.html#s-non-free" rel="subsection" title="2.2.3 The non-free archive area">
<link href="ch-binary.html#s3.2.1" rel="subsection" title="3.2.1 Version numbers based on dates">
<link href="ch-binary.html#s-synopsis" rel="subsection" title="3.4.1 The single line synopsis">
<link href="ch-binary.html#s-extendeddesc" rel="subsection" title="3.4.2 The extended description">
<link href="ch-binary.html#s-maintscriptprompt" rel="subsection" title="3.9.1 Prompting in maintainer scripts">
<link href="ch-source.html#s-debianrules-options" rel="subsection" title="4.9.1 debian/rules and DEB_BUILD_OPTIONS">
<link href="ch-controlfields.html#s-f-Source" rel="subsection" title="5.6.1 Source">
<link href="ch-controlfields.html#s-f-Maintainer" rel="subsection" title="5.6.2 Maintainer">
<link href="ch-controlfields.html#s-f-Uploaders" rel="subsection" title="5.6.3 Uploaders">
<link href="ch-controlfields.html#s-f-Changed-By" rel="subsection" title="5.6.4 Changed-By">
<link href="ch-controlfields.html#s-f-Section" rel="subsection" title="5.6.5 Section">
<link href="ch-controlfields.html#s-f-Priority" rel="subsection" title="5.6.6 Priority">
<link href="ch-controlfields.html#s-f-Package" rel="subsection" title="5.6.7 Package">
<link href="ch-controlfields.html#s-f-Architecture" rel="subsection" title="5.6.8 Architecture">
<link href="ch-controlfields.html#s-f-Essential" rel="subsection" title="5.6.9 Essential">
<link href="ch-controlfields.html#s5.6.10" rel="subsection" title="5.6.10 Package interrelationship fields: Depends, Pre-Depends, Recommends, Suggests, Breaks, Conflicts, Provides, Replaces, Enhances">
<link href="ch-controlfields.html#s-f-Standards-Version" rel="subsection" title="5.6.11 Standards-Version">
<link href="ch-controlfields.html#s-f-Version" rel="subsection" title="5.6.12 Version">
<link href="ch-controlfields.html#s-f-Description" rel="subsection" title="5.6.13 Description">
<link href="ch-controlfields.html#s-f-Distribution" rel="subsection" title="5.6.14 Distribution">
<link href="ch-controlfields.html#s-f-Date" rel="subsection" title="5.6.15 Date">
<link href="ch-controlfields.html#s-f-Format" rel="subsection" title="5.6.16 Format">
<link href="ch-controlfields.html#s-f-Urgency" rel="subsection" title="5.6.17 Urgency">
<link href="ch-controlfields.html#s-f-Changes" rel="subsection" title="5.6.18 Changes">
<link href="ch-controlfields.html#s-f-Binary" rel="subsection" title="5.6.19 Binary">
<link href="ch-controlfields.html#s-f-Installed-Size" rel="subsection" title="5.6.20 Installed-Size">
<link href="ch-controlfields.html#s-f-Files" rel="subsection" title="5.6.21 Files">
<link href="ch-controlfields.html#s-f-Closes" rel="subsection" title="5.6.22 Closes">
<link href="ch-controlfields.html#s-f-Homepage" rel="subsection" title="5.6.23 Homepage">
<link href="ch-controlfields.html#s-f-Checksums" rel="subsection" title="5.6.24 Checksums-Sha1 and Checksums-Sha256">
<link href="ch-controlfields.html#s-f-DM-Upload-Allowed" rel="subsection" title="5.6.25 DM-Upload-Allowed">
<link href="ch-relationships.html#s7.6.1" rel="subsection" title="7.6.1 Overwriting files in other packages">
<link href="ch-relationships.html#s7.6.2" rel="subsection" title="7.6.2 Replacing whole packages, forcing their removal">
<link href="ch-sharedlibs.html#s-ldconfig" rel="subsection" title="8.1.1 ldconfig">
<link href="ch-sharedlibs.html#s8.6.1" rel="subsection" title="8.6.1 The shlibs files present on the system">
<link href="ch-sharedlibs.html#s8.6.2" rel="subsection" title="8.6.2 How to use dpkg-shlibdeps and the shlibs files">
<link href="ch-sharedlibs.html#s-shlibs" rel="subsection" title="8.6.3 The shlibs File Format">
<link href="ch-sharedlibs.html#s8.6.4" rel="subsection" title="8.6.4 Providing a shlibs file">
<link href="ch-opersys.html#s-fhs" rel="subsection" title="9.1.1 File System Structure">
<link href="ch-opersys.html#s9.1.2" rel="subsection" title="9.1.2 Site-specific programs">
<link href="ch-opersys.html#s9.1.3" rel="subsection" title="9.1.3 The system-wide mail directory">
<link href="ch-opersys.html#s-fhs-run" rel="subsection" title="9.1.4 /run and /run/lock">
<link href="ch-opersys.html#s9.2.1" rel="subsection" title="9.2.1 Introduction">
<link href="ch-opersys.html#s9.2.2" rel="subsection" title="9.2.2 UID and GID classes">
<link href="ch-opersys.html#s-/etc/init.d" rel="subsection" title="9.3.1 Introduction">
<link href="ch-opersys.html#s-writing-init" rel="subsection" title="9.3.2 Writing the scripts">
<link href="ch-opersys.html#s9.3.3" rel="subsection" title="9.3.3 Interfacing with the initscript system">
<link href="ch-opersys.html#s9.3.3.1" rel="subsection" title="9.3.3.1 Managing the links">
<link href="ch-opersys.html#s9.3.3.2" rel="subsection" title="9.3.3.2 Running initscripts">
<link href="ch-opersys.html#s9.3.4" rel="subsection" title="9.3.4 Boot-time initialization">
<link href="ch-opersys.html#s9.3.5" rel="subsection" title="9.3.5 Example">
<link href="ch-opersys.html#s-cron-files" rel="subsection" title="9.5.1 Cron job file names">
<link href="ch-files.html#s10.7.1" rel="subsection" title="10.7.1 Definitions">
<link href="ch-files.html#s10.7.2" rel="subsection" title="10.7.2 Location">
<link href="ch-files.html#s10.7.3" rel="subsection" title="10.7.3 Behavior">
<link href="ch-files.html#s10.7.4" rel="subsection" title="10.7.4 Sharing configuration files">
<link href="ch-files.html#s10.7.5" rel="subsection" title="10.7.5 User configuration files (&quot;dotfiles&quot;)">
<link href="ch-files.html#s10.9.1" rel="subsection" title="10.9.1 The use of dpkg-statoverride">
<link href="ch-customized-programs.html#s-arch-wildcard-spec" rel="subsection" title="11.1.1 Architecture wildcards">
<link href="ch-customized-programs.html#s11.8.1" rel="subsection" title="11.8.1 Providing X support and package priorities">
<link href="ch-customized-programs.html#s11.8.2" rel="subsection" title="11.8.2 Packages providing an X server">
<link href="ch-customized-programs.html#s11.8.3" rel="subsection" title="11.8.3 Packages providing a terminal emulator">
<link href="ch-customized-programs.html#s11.8.4" rel="subsection" title="11.8.4 Packages providing a window manager">
<link href="ch-customized-programs.html#s11.8.5" rel="subsection" title="11.8.5 Packages providing fonts">
<link href="ch-customized-programs.html#s-appdefaults" rel="subsection" title="11.8.6 Application defaults files">
<link href="ch-customized-programs.html#s11.8.7" rel="subsection" title="11.8.7 Installation directory issues">
<link href="ch-docs.html#s-copyrightformat" rel="subsection" title="12.5.1 Machine-readable copyright information">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-source" rel="subsection" title="C.1.1 dpkg-source - packs and unpacks Debian source packages">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-buildpackage" rel="subsection" title="C.1.2 dpkg-buildpackage - overall package-building control script">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-gencontrol" rel="subsection" title="C.1.3 dpkg-gencontrol - generates binary package control files">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-shlibdeps" rel="subsection" title="C.1.4 dpkg-shlibdeps - calculates shared library dependencies">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-distaddfile" rel="subsection" title="C.1.5 dpkg-distaddfile - adds a file to debian/files">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-genchanges" rel="subsection" title="C.1.6 dpkg-genchanges - generates a .changes upload control file">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-parsechangelog" rel="subsection" title="C.1.7 dpkg-parsechangelog - produces parsed representation of a changelog">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-architecture" rel="subsection" title="C.1.8 dpkg-architecture - information about the build and host system">
<link href="ap-pkg-sourcepkg.html#s-pkg-debianrules" rel="subsection" title="C.2.1 debian/rules - the main building script">
<link href="ap-pkg-sourcepkg.html#s-pkg-srcsubstvars" rel="subsection" title="C.2.2 debian/substvars and variable substitutions">
<link href="ap-pkg-sourcepkg.html#sC.2.3" rel="subsection" title="C.2.3 debian/files">
<link href="ap-pkg-sourcepkg.html#sC.2.4" rel="subsection" title="C.2.4 debian/tmp">
<link href="ap-pkg-sourcepkg.html#sC.4.1" rel="subsection" title="C.4.1 Restrictions on objects in source packages">
<link href="ap-pkg-controlfields.html#s-pkg-f-Filename" rel="subsection" title="D.2.1 Filename and MSDOS-Filename">
<link href="ap-pkg-controlfields.html#s-pkg-f-Size" rel="subsection" title="D.2.2 Size and MD5sum">
<link href="ap-pkg-controlfields.html#s-pkg-f-Status" rel="subsection" title="D.2.3 Status">
<link href="ap-pkg-controlfields.html#s-pkg-f-Config-Version" rel="subsection" title="D.2.4 Config-Version">
<link href="ap-pkg-controlfields.html#s-pkg-f-Conffiles" rel="subsection" title="D.2.5 Conffiles">
<link href="ap-pkg-controlfields.html#sD.2.6" rel="subsection" title="D.2.6 Obsolete fields">

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</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix E - Configuration file handling (from old Packaging Manual)</h1>

<hr>

<p>
<code>dpkg</code> can do a certain amount of automatic handling of package
configuration files.
</p>

<p>
Whether this mechanism is appropriate depends on a number of factors, but
basically there are two approaches to any particular configuration file.
</p>

<p>
The easy method is to ship a best-effort configuration in the package, and use
<code>dpkg</code>'s conffile mechanism to handle updates.  If the user is
unlikely to want to edit the file, but you need them to be able to without
losing their changes, and a new package with a changed version of the file is
only released infrequently, this is a good approach.
</p>

<p>
The hard method is to build the configuration file from scratch in the
<code>postinst</code> script, and to take the responsibility for fixing any
mistakes made in earlier versions of the package automatically.  This will be
appropriate if the file is likely to need to be different on each system.
</p>

<hr>

<h2><a name="sE.1"></a>E.1 Automatic handling of configuration files by <code>dpkg</code></h2>

<p>
A package may contain a control information file called <samp>conffiles</samp>.
This file should be a list of filenames of configuration files needing
automatic handling, separated by newlines.  The filenames should be absolute
pathnames, and the files referred to should actually exist in the package.
</p>

<p>
When a package is upgraded <code>dpkg</code> will process the configuration
files during the configuration stage, shortly before it runs the package's
<code>postinst</code> script,
</p>

<p>
For each file it checks to see whether the version of the file included in the
package is the same as the one that was included in the last version of the
package (the one that is being upgraded from); it also compares the version
currently installed on the system with the one shipped with the last version.
</p>

<p>
If neither the user nor the package maintainer has changed the file, it is left
alone.  If one or the other has changed their version, then the changed version
is preferred - i.e., if the user edits their file, but the package maintainer
doesn't ship a different version, the user's changes will stay, silently, but
if the maintainer ships a new version and the user hasn't edited it the new
version will be installed (with an informative message).  If both have changed
their version the user is prompted about the problem and must resolve the
differences themselves.
</p>

<p>
The comparisons are done by calculating the MD5 message digests of the files,
and storing the MD5 of the file as it was included in the most recent version
of the package.
</p>

<p>
When a package is installed for the first time <code>dpkg</code> will install
the file that comes with it, unless that would mean overwriting a file already
on the file system.
</p>

<p>
However, note that <code>dpkg</code> will <em>not</em> replace a conffile that
was removed by the user (or by a script).  This is necessary because with some
programs a missing file produces an effect hard or impossible to achieve in
another way, so that a missing file needs to be kept that way if the user did
it.
</p>

<p>
Note that a package should <em>not</em> modify a <code>dpkg</code>-handled
conffile in its maintainer scripts.  Doing this will lead to <code>dpkg</code>
giving the user confusing and possibly dangerous options for conffile update
when the package is upgraded.
</p>

<hr>

<h2><a name="sE.2"></a>E.2 Fully-featured maintainer script configuration handling</h2>

<p>
For files which contain site-specific information such as the hostname and
networking details and so forth, it is better to create the file in the
package's <code>postinst</code> script.
</p>

<p>
This will typically involve examining the state of the rest of the system to
determine values and other information, and may involve prompting the user for
some information which can't be obtained some other way.
</p>

<p>
When using this method there are a couple of important issues which should be
considered:
</p>

<p>
If you discover a bug in the program which generates the configuration file, or
if the format of the file changes from one version to the next, you will have
to arrange for the postinst script to do something sensible - usually this will
mean editing the installed configuration file to remove the problem or change
the syntax.  You will have to do this very carefully, since the user may have
changed the file, perhaps to fix the very problem that your script is trying to
deal with - you will have to detect these situations and deal with them
correctly.
</p>

<p>
If you do go down this route it's probably a good idea to make the program that
generates the configuration file(s) a separate program in
<code>/usr/sbin</code>, by convention called
<code><var>package</var>config</code> and then run that if appropriate from the
post-installation script.  The <samp><var>package</var>config</samp> program
should not unquestioningly overwrite an existing configuration - if its mode of
operation is geared towards setting up a package for the first time (rather
than any arbitrary reconfiguration later) you should have it check whether the
configuration already exists, and require a <samp>--force</samp> flag to
overwrite it.
</p>

<hr>

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</p>

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<p>
Debian Policy Manual
</p>

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<br>
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