This creates a SharedLibrary file __libfoo.so.1.0.1__, with shared object name ("soname") __libfoo.so__, dependent on __libquux__. To make __libfoo__ usable, you need to put it someplace ldconfig(8) will find it, and SymLink it to __libfoo.so.1__ and __libfoo.so__. 

  

 So long as you don't change the call signature of one of the functions (or what they do, in a way that would break programs), you can just bump the minor version of the library and programs using the SharedLibrary will just work. If you do change call signatures on existing functions or change their semantics, bump the version, try to recompile the programs, and check that they work correctly once they pass. Another way to make it usable is to put it in a directory refered to in your __LD_LIBRARY_PATH__ environment variable. 

  

 For more information, see Ulrich Drepper's [How to write shared libraries | http://people.redhat.com/drepper/dsohowto.pdf]. 

  

 !! Creating a SharedLibrary using libtool(1)