|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | MAINTAINING SYMBOLS FILES | OPTIONS | ENVIRONMENT | SEE ALSO | COLOPHON |
|
|
|
dpkg-gensymbols(1) dpkg suite dpkg-gensymbols(1)
dpkg-gensymbols - generate symbols files (shared library
dependency information)
dpkg-gensymbols [option...]
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.
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.
-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.
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).
<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).
This page is part of the dpkg (Debian Package Manager) project.
Information about the project can be found at
⟨https://wiki.debian.org/Teams/Dpkg/⟩. If you have a bug report
for this manual page, see
⟨http://bugs.debian.org/cgi-bin/pkgreport.cgi?src=dpkg⟩. This
page was obtained from the project's upstream Git repository ⟨git
clone https://git.dpkg.org/git/dpkg/dpkg.git⟩ on 2025-08-11. (At
that time, the date of the most recent commit that was found in
the repository was 2025-08-06.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
1.22.6-77-g86fe7 2024-03-10 dpkg-gensymbols(1)
Pages that refer to this page: dh_makeshlibs(1), dpkg-buildtree(1), dpkg-shlibdeps(1), deb-src-symbols(5), deb-symbols(5), debhelper-compat-upgrade-checklist(7)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|