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<title>Berkeley DB Reference Guide: Dynamic shared libraries</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Building Berkeley DB for UNIX systems</dl></h3></td>
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<h1 align=center>Dynamic shared libraries</h1>
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<p><b>Warning</b>: the following information is intended to be generic and
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is likely to be correct for most UNIX systems. Unfortunately, dynamic
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shared libraries are not standard between UNIX systems, so there may be
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information here that is not correct for your system. If you have
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problems, consult your compiler and linker manual pages, or your system
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<p>The Berkeley DB dynamic shared libraries are created with the name
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libdb-<b>major</b>.<b>minor</b>.so, where <b>major</b> is the major
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version number and <b>minor</b> is the minor version number. Other
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shared libraries are created if Java and Tcl support are enabled --
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specifically, libdb_java-<b>major</b>.<b>minor</b>.so and
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libdb_tcl-<b>major</b>.<b>minor</b>.so.
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<p>On most UNIX systems, when any shared library is created, the linker
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stamps it with a "SONAME". In the case of Berkeley DB, the SONAME is
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libdb-<b>major</b>.<b>minor</b>.so. It is important to realize that
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applications linked against a shared library remember the SONAMEs of the
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libraries they use and not the underlying names in the filesystem.
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<p>When the Berkeley DB shared library is installed, links are created in the
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install lib directory so that libdb-<b>major</b>.<b>minor</b>.so,
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libdb-<b>major</b>.so, and libdb.so all refer to the same library. This
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library will have an SONAME of libdb-<b>major</b>.<b>minor</b>.so.
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<p>Any previous versions of the Berkeley DB libraries that are present in the
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install directory (such as libdb-2.7.so or libdb-2.so) are left unchanged.
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(Removing or moving old shared libraries is one drastic way to identify
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applications that have been linked against those vintage releases.)
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<p>Once you have installed the Berkeley DB libraries, unless they are installed
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in a directory where the linker normally looks for shared libraries,
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you will need to specify the installation directory as part of compiling
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and linking against Berkeley DB. Consult your system manuals or system
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administrator for ways to specify a shared library directory when
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compiling and linking applications with the Berkeley DB libraries. Many
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systems support environment variables (for example, LD_LIBRARY_PATH or
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LD_RUN_PATH), or system configuration files (for example, /etc/ld.so.conf)
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<p><b>Warning</b>: some UNIX installations may have an already existing
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<b>/usr/lib/libdb.so</b>, and this library may be an incompatible
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version of Berkeley DB.
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<p>We recommend that applications link against libdb.so (for example, using
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-ldb). Even though the linker uses the file named libdb.so, the
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executable file for the application remembers the library's SONAME
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(libdb-<b>major</b>.<b>minor</b>.so). This has the effect of
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marking the applications with the versions they need at link time.
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Because applications locate their needed SONAMEs when they are executed,
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all previously linked applications will continue to run using the
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library they were linked with, even when a new version of Berkeley DB is
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installed and the file <b>libdb.so</b> is replaced with a new
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<p>Applications that know they are using features specific to a particular
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Berkeley DB release can be linked to that release. For example, an application
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wanting to link to Berkeley DB major release "3" can link using -ldb-3, and
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applications that know about a particular minor release number can specify
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both major and minor release numbers; for example, -ldb-3.5.
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<p>If you want to link with Berkeley DB before performing library installation,
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the "make" command will have created a shared library object in the
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<b>.libs</b> subdirectory of the build directory, such as
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<b>build_unix/.libs/libdb-major.minor.so</b>. If you want to link a
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file against this library, with, for example, a major number of "3" and
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a minor number of "5", you should be able to do something like the
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<p><blockquote><pre>cc -L BUILD_DIRECTORY/.libs -o testprog testprog.o -ldb-3.5
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env LD_LIBRARY_PATH="BUILD_DIRECTORY/.libs:$LD_LIBRARY_PATH" ./testprog</pre></blockquote>
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<p>where <b>BUILD_DIRECTORY</b> is the full directory path to the directory
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where you built Berkeley DB.
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<p>The libtool program (which is configured in the build directory) can be
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used to set the shared library path and run a program. For example,
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the following runs the gdb debugger on the db_dump utility after setting
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the appropriate paths:
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<p><blockquote><pre>libtool gdb db_dump</pre></blockquote>
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<p>Libtool may not know what to do with arbitrary commands (it is hardwired
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to recognize "gdb" and some other commands). If it complains the mode
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argument will usually resolve the problem:
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<p><blockquote><pre>libtool --mode=execute my_debugger db_dump</pre></blockquote>
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<p>On most systems, using libtool in this way is exactly equivalent to
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setting the LD_LIBRARY_PATH environment variable and then executing the
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program. On other systems, using libtool has the virtue of knowing about
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any other details on systems that don't behave in this typical way.
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