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<title>Berkeley DB Reference Guide: Dynamic shared libraries</title>
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<td><dl><dt>Berkeley DB Reference Guide:<dd>Building Berkeley DB for UNIX/POSIX systems</dl></td>
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Dynamic shared libraries
Warning: the following information is intended to be generic and
is likely to be correct for most UNIX systems. Unfortunately, dynamic
shared libraries are not standard between UNIX systems, so there may be
information here that is not correct for your system. If you have
problems, consult your compiler and linker manual pages, or your system
administrator.
The Berkeley DB dynamic shared libraries are created with the name
libdb-major.minor.so, where major is
the major version number and minor is the minor version number.
Other shared libraries are created if Java and Tcl support are enabled:
specifically, libdb_java-major.minor.so
and libdb_tcl-major.minor.so.
On most UNIX systems, when any shared library is created, the linker
stamps it with a "SONAME". In the case of Berkeley DB, the SONAME
is libdb-major.minor.so. It is important to
realize that applications linked against a shared library remember the
SONAMEs of the libraries they use and not the underlying names in the
filesystem.
When the Berkeley DB shared library is installed, links are
created in the install lib directory so that
libdb-major.minor.so,
libdb-major.so, and libdb.so all refer to the
same library. This library will have an SONAME of
libdb-major.minor.so.
Any previous versions of the Berkeley DB libraries that are
present in the install directory (such as libdb-2.7.so or
libdb-2.so) are left unchanged. (Removing or moving old shared
libraries is one drastic way to identify applications that have been
linked against those vintage releases.)
Once you have installed the Berkeley DB libraries, unless they are
installed in a directory where the linker normally looks for shared
libraries, you will need to specify the installation directory as part
of compiling and linking against Berkeley DB. Consult your system
manuals or system administrator for ways to specify a shared library
directory when compiling and linking applications with the
Berkeley DB libraries. Many systems support environment variables
(for example, LD_LIBRARY_PATH or LD_RUN_PATH), or system configuration
files (for example, /etc/ld.so.conf) for this purpose.
Warning: some UNIX installations may have an already existing
/usr/lib/libdb.so, and this library may be an incompatible
version of Berkeley DB.
We recommend that applications link against libdb.so (for example,
using -ldb). Even though the linker uses the file named
libdb.so, the executable file for the application remembers the
library's SONAME (libdb-major.minor.so). This
has the effect of marking the applications with the versions they need
at link time. Because applications locate their needed SONAMEs when
they are executed, all previously linked applications will continue to
run using the library they were linked with, even when a new version of
Berkeley DB is installed and the file libdb.so
is replaced with a new version.
Applications that know they are using features specific to a particular
Berkeley DB release can be linked to that release. For example, an
application wanting to link to Berkeley DB major release "3" can link
using -ldb-3, and applications that know about a particular
minor release number can specify both major and minor release numbers;
for example, -ldb-3.5.
If you want to link with Berkeley DB before performing library
installation, the "make" command will have created a shared library
object in the .libs subdirectory of the build directory, such
as build_unix/.libs/libdb-major.minor.so. If you want
to link a file against this library, with, for example, a major number
of "3" and a minor number of "5", you should be able to do something
like the following:
<blockquote><pre>cc -L BUILD_DIRECTORY/.libs -o testprog testprog.o -ldb-3.5
env LD_LIBRARY_PATH="BUILD_DIRECTORY/.libs:$LD_LIBRARY_PATH" ./testprog</pre></blockquote>
where BUILD_DIRECTORY is the full directory path to the directory
where you built Berkeley DB.
The libtool program (which is configured in the build directory) can be
used to set the shared library path and run a program. For example,
the following runs the gdb debugger on the db_dump utility after setting
the appropriate paths:
<blockquote><pre>libtool gdb db_dump</pre></blockquote>
Libtool may not know what to do with arbitrary commands (it is hardwired
to recognize "gdb" and some other commands). If it complains the mode
argument will usually resolve the problem:
<blockquote><pre>libtool --mode=execute my_debugger db_dump</pre></blockquote>
On most systems, using libtool in this way is exactly equivalent to
setting the LD_LIBRARY_PATH environment variable and then executing the
program. On other systems, using libtool has the virtue of knowing about
any other details on systems that don't behave in this typical way.
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