LD_LIBRARY_PATH

http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html

 

You can temporarily substitute a different library for this particular execution. In Linux, the environment variable LD_LIBRARY_PATH is a colon-separated set of directories where libraries should be searched for first, before the standard set of directories; this is useful when debugging a new library or using a nonstandard library for special purposes. The environment variable LD_PRELOAD lists shared libraries with functions that override the standard set, just as /etc/ld.so.preload does. These are implemented by the loader /lib/ld-linux.so. I should note that, while LD_LIBRARY_PATH works on many Unix-like systems, it doesn't work on all; for example, this functionality is available on HP-UX but as the environment variable SHLIB_PATH, and on AIX this functionality is through the variable LIBPATH (with the same syntax, a colon-separated list).

LD_LIBRARY_PATH is handy for development and testing, but shouldn't be modified by an installation process for normal use by normal users; see ``Why LD_LIBRARY_PATH is Bad'' at http://www.visi.com/~barr/ldpath.html for an explanation of why. But it's still useful for development or testing, and for working around problems that can't be worked around otherwise. If you don't want to set the LD_LIBRARY_PATH environment variable, on Linux you can even invoke the program loader directly and pass it arguments. For example, the following will use the given PATH instead of the content of the environment variable LD_LIBRARY_PATH, and run the given executable:

/lib/ld-linux.so.2 --library-path PATH EXECUTABLE

Just executing ld-linux.so without arguments will give you more help on using this, but again, don't use this for normal use - these are all intended for debugging.

3.3.2. LD_DEBUG

Another useful environment variable in the GNU C loader is LD_DEBUG. This triggers the dl* functions so that they give quite verbose information on what they are doing. For example:

export LD_DEBUG=files command_to_run

displays the processing of files and libraries when handling libraries, telling you what dependencies are detected and which SOs are loaded in what order. Setting LD_DEBUG to ``bindings'' displays information about symbol binding, setting it to ``libs'' displays the library search paths, and setting ti to ``versions'' displays the version depdendencies.

Setting LD_DEBUG to ``help'' and then trying to run a program will list the possible options. Again, LD_DEBUG isn't intended for normal use, but it can be handy when debugging and testing.