How do library files (*.so) resolve shared dependencies?

Question

If I invoke the following command:

ldd mylib.so

this then yields something along the lines of:

libopencv_features2d.so.4.1 => /usr/local/lib/libopencv_features2d.so.4.1 (0x00007f83dee6b000)

If I copy /usr/local/lib/libopencv_features2d.so.4.1 into my current working directory, I would then expect ldd to show => ./libopencv_features2d.so.4.1 (0x00007f83dee6b000)

Instead, it still resolves it to /usr/local/lib. Why is that? And how do system dependencies like this get resolved? Is there also a way to influence the way dependencies are resolved? Can I force it to resolve it to my local directory?

Answer 1

The dynamic linker looks for libraries in a variety of places, but those don’t include the current directory by default. On Linux, the list is

• the paths defined in the binary’s rpath, if any;
• the paths listed in LD_LIBRARY_PATH, if any;
• the paths defined in the binary’s runpath, if any;
• the libraries known in /etc/ld.so.cache;
• the system’s library paths (/usr/lib etc.).

The link above provides more detail.

You can influence the way dependencies are resolved by exporting LD_LIBRARY_PATH; specifically in your case:

export LD_LIBRARY_PATH=.

(Don’t leave it set to that value.)