How to force using local shared libraries over system libraries?

Question

How can I force using a local library over the system library in linux?

I linked my executable explicitly to some .so files in my project/lib directory e.g. (../lib/libluajit.so).

Running my executable under gdb or using ldd shows that it still uses the system libluajit-5.1.so.2

I then set LD_LIBRARY_PATH to my project/lib directory and exported it, then ran my executable. Somehow it's still picking up the system library (confirmed by both gdb and ldd)

I'd like to know how that's even possible, and what I can do to force it to use the local libluajit.so in my project/lib directory.

Answer 1

When you link, specify the directory of the library and also use an rpath:

-Wl,-rpath,/absolute/path/to/your/library -L/absolute/path/to/your/library -llibrary

-L tells the linker where to find your library at link time, and -rpath tells it where to search for the library at runtime.

Note that -L and -rpath need the directory that contains your .so file, not the actual path of the library file itself.

Answer 2

I have to question why you want to use your own version of a library over a system-provided version (having multiple different versions floating around is nothing but a recipe for trouble and user confusion).

However, you should be able to export LD_PRELOAD=<path_to_your_shared_obj> to force it to load your own version.

Note that no mechanism to override library versions will persist through any sort of privilege elevation (for example sudo).