# dpkg-gensymbols

## NAME



           dpkg-gensymbols - generate symbols files (shared library
           dependency information)
    


## SYNOPSIS



           **dpkg-gensymbols**[_option_...]
    


## DESCRIPTION



           **dpkg-gensymbols** scans a temporary build tree (debian/tmp by
           default) looking for libraries and generates a _symbols_ file
           describing them.  This file, if non-empty, is then installed in
           the DEBIAN subdirectory of the build tree so that it ends up
           included in the control information of the package.
    
           When generating those files, it uses as input some symbols files
           provided by the maintainer.  It looks for the following files (and
           uses the first that is found):
    
           •   debian/_package_.symbols._arch_
    
           •   debian/symbols._arch_
    
           •   debian/_package_.symbols
    
           •   debian/symbols
    
           The main interest of those files is to provide the minimal version
           associated to each symbol provided by the libraries.  Usually it
           corresponds to the first version of that package that provided the
           symbol, but it can be manually incremented by the maintainer if
           the ABI of the symbol is extended without breaking backwards
           compatibility.  It's the responsibility of the maintainer to keep
           those files up-to-date and accurate, but **dpkg-gensymbols** helps
           with that.
    
           When the generated symbols files differ from the maintainer
           supplied one, **dpkg-gensymbols** will print a diff between the two
           versions.  Furthermore if the difference is too significant, it
           will even fail (you can customize how much difference you can
           tolerate, see the **-c** option).
    
           This program was introduced in dpkg 1.14.8.
    


## MAINTAINING SYMBOLS FILES



           The base interchange format of the symbols file is described in
           deb-symbols(5), which is used by the symbols files included in
           binary packages.  These are generated from template symbols files
           with a format based on the former, described in deb-src-symbols(5)
           and included in source packages.
    
           The symbols files are really useful only if they reflect the
           evolution of the package through several releases.  Thus the
           maintainer has to update them every time that a new symbol is
           added so that its associated minimal version matches reality.
    
           The diffs contained in the build logs can be used as a starting
           point, but the maintainer, additionally, has to make sure that the
           behaviour of those symbols has not changed in a way that would
           make anything using those symbols and linking against the new
           version, stop working with the old version.
    
           In most cases, the diff applies directly to the
           debian/_package_.symbols file.  That said, further tweaks are
           usually needed: it's recommended for example to drop the Debian
           revision from the minimal version so that backports with a lower
           version number but the same upstream version still satisfy the
           generated dependencies.  If the Debian revision can't be dropped
           because the symbol really got added by the Debian specific change,
           then one should suffix the version with ‘**~** ’.
    
           Before applying any patch to the symbols file, the maintainer
           should double-check that it's sane.  Public symbols are not
           supposed to disappear, so the patch should ideally only add new
           lines.
    
           Note that you can put comments in symbols files.
    
           Do not forget to check if old symbol versions need to be
           increased.  There is no way **dpkg-gensymbols** can warn about this.
           Blindly applying the diff or assuming there is nothing to change
           if there is no diff, without checking for such changes, can lead
           to packages with loose dependencies that claim they can work with
           older packages they cannot work with.  This will introduce hard to
           find bugs with (partial) upgrades.
    
       **Good library management**
           A well-maintained library has the following features:
    
           •   its API is stable (public symbols are never dropped, only new
               public symbols are added) and changes in incompatible ways
               only when the SONAME changes;
    
           •   ideally, it uses symbol versioning to achieve ABI stability
               despite internal changes and API extension;
    
           •   it doesn't export private symbols (such symbols can be tagged
               optional as workaround).
    
           While maintaining the symbols file, it's easy to notice appearance
           and disappearance of symbols.  But it's more difficult to catch
           incompatible API and ABI change.  Thus the maintainer should read
           thoroughly the upstream changelog looking for cases where the
           rules of good library management have been broken.  If potential
           problems are discovered, the upstream author should be notified as
           an upstream fix is always better than a Debian specific work-
           around.
    


## OPTIONS



           **-P** _package-build-dir_
               Scan _package-build-dir_ instead of debian/tmp.
    
           **-p** _package_
               Define the package name.  Required if more than one binary
               package is listed in debian/control (or if there's no
               debian/control file).
    
           **-v** _version_
               Define the package version.  Defaults to the version extracted
               from debian/changelog.  Required if called outside of a source
               package tree.
    
           **-e** _library-file_
               Only analyze libraries explicitly listed instead of finding
               all public libraries.  You can use shell patterns used for
               pathname expansions (see the File::Glob manual page for
               details) in _library-file_ to match multiple libraries with a
               single argument (otherwise you need multiple **-e**).
    
           **-l** _directory_
               Prepend _directory_ to the list of directories to search for
               private shared libraries (since dpkg 1.19.1).  This option can
               be used multiple times.
    
               **Note** : Use this option instead of setting **LD_LIBRARY_PATH** , as
               that environment variable is used to control the run-time
               linker and abusing it to set the shared library paths at
               build-time can be problematic when cross-compiling for
               example.
    
           **-I** _filename_
               Use _filename_ as reference file to generate the symbols file
               that is integrated in the package itself.
    
           **-O**[_filename_]
               Print the generated symbols file to standard output or to
               _filename_ if specified, rather than to
               **debian/tmp/DEBIAN/symbols**(or _package-build-dir_**/DEBIAN/symbols**
               if **-P** was used).  If _filename_ is pre-existing, its contents
               are used as basis for the generated symbols file.  You can use
               this feature to update a symbols file so that it matches a
               newer upstream version of your library.
    
           **-t** Write the symbol file in template mode rather than the format
               compatible with deb-symbols(5).  The main difference is that
               in the template mode symbol names and tags are written in
               their original form contrary to the post-processed symbol
               names with tags stripped in the compatibility mode.  Moreover,
               some symbols might be omitted when writing a standard
               deb-symbols(5) file (according to the tag processing rules)
               while all symbols are always written to the symbol file
               template.
    
           **-c** _[0-4]_
               Define the checks to do when comparing the generated symbols
               file with the template file used as starting point.  By
               default the level is 1.  Increasing levels do more checks and
               include all checks of lower levels.
    
               Level 0
                   Never fails.
    
               Level 1
                   Fails if some symbols have disappeared.
    
               Level 2
                   Fails if some new symbols have been introduced.
    
               Level 3
                   Fails if some libraries have disappeared.
    
               Level 4
                   Fails if some libraries have been introduced.
    
               This value can be overridden by the environment variable
               **DPKG_GENSYMBOLS_CHECK_LEVEL**.
    
           **-q** Keep quiet and never generate a diff between generated symbols
               file and the template file used as starting point or show any
               warnings about new/lost libraries or new/lost symbols.  This
               option only disables informational output but not the checks
               themselves (see **-c** option).
    
           **-a** _arch_
               Assume _arch_ as host architecture when processing symbol files.
               Use this option to generate a symbol file or diff for any
               architecture provided its binaries are already available.
    
           **-d** Enable debug mode.  Numerous messages are displayed to explain
               what **dpkg-gensymbols** does.
    
           **-V** Enable verbose mode.  The generated symbols file contains
               deprecated symbols as comments.  Furthermore in template mode,
               pattern symbols are followed by comments listing real symbols
               that have matched the pattern.
    
           **-?** , **--help**
               Show the usage message and exit.
    
           **--version**
               Show the version and exit.
    


## ENVIRONMENT



           **DEB_HOST_ARCH**
               Sets the host architecture if the **--arch** option has not be
               specified.
    
           **DPKG_GENSYMBOLS_CHECK_LEVEL**
               Overrides the command check level, even if the **-c** command-line
               argument was given (note that this goes against the common
               convention of command-line arguments having precedence over
               environment variables).
    
           **DPKG_COLORS**
               Sets the color mode (since dpkg 1.18.5).  The currently
               accepted values are: **auto**(default), **always** and **never**.
    
           **DPKG_NLS**
               If set, it will be used to decide whether to activate Native
               Language Support, also known as internationalization (or i18n)
               support (since dpkg 1.19.0).  The accepted values are: **0** and **1**
               (default).
    


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