dpkg-gensymbols(1) dpkg suite dpkg-gensymbols(1)
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
-Ppackage-build-dir
Scan package-build-dir instead of debian/tmp.
-ppackage
Define the package name. Required if more than one binary package
is listed in debian/control (or if there's no debian/control file).
-vversion
Define the package version. Defaults to the version extracted from
debian/changelog. Required if called outside of a source package
tree.
-elibrary-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).
-ldirectory
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.
-Ifilename
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).
-aarch
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).
SEE ALSO
<https://people.redhat.com/drepper/symbol-versioning>,
<https://people.redhat.com/drepper/goodpractice.pdf>,
<https://people.redhat.com/drepper/dsohowto.pdf>, deb-src-symbol(5),
deb-symbols(5), dpkg-shlibdeps(1).
1.22.21 2025-06-30 dpkg-gensymbols(1)
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