A simpler method to load shared libraries without root

Question

I am trying to compile and run a C++ program on a server where I don't have root access. I am having trouble linkingboost_iostreams library.

I can successfully compile my program by pointing to the boost installation directory using the -L flag as: g++ -I path/to/boost/build/include -o out prog1.cpp prog2.cpp -L path/to/boost/build/lib -lboost_iostreams

However, if I run the program as ./out I get the error error while loading shared libraries: libboost_iostreams.so.1.67.0: cannot open shared object file: No such file or directory since the linker is not able to locate libboost_iostreams.so.1.67.0 (which DOES exist under path/to/boost/build/lib)

Thanks to this answer, I was able to explicitly specify LD_LIBRARY_PATH and run the program as

LD_LIBRARY_PATH="path/to/boost/build/lib" ./out.

Since I am not root, I can't run ldconfig either. I was wondering if there is a way to load dynamic libraries without having to prefix LD_LIBRARY_PATH when you run the program and no root access.

Answer 1

I have figured out a way to solve this using the method explained here https://amir.rachum.com/blog/2016/09/17/shared-libraries/. The solution is to use rpath during compilation.

According to the article The only difference between rpath and runpath is the order they are searched in. Specifically, their relation to LD_LIBRARY_PATH - rpath is searched in before LD_LIBRARY_PATH while runpath is searched in after. The meaning of this is that rpath cannot be changed dynamically with environment variables while runpath can.

In short once you compile with -rpath path/to/boost/build/lib, the directory containing the library libboost_iostreams.so.1.67.0 is searched at runtime without having to prefix LD_LIBRARY_PATH="path/to/boost/build/lib" ./out.

After compiling with g++ -I path/to/boost/build/include -o out prog1.cpp prog2.cpp -L path/to/boost/build/lib -lboost_iostreams -rpath path/to/boost/build/lib

I was able to run ./out without any issues.

EDIT 1

As pointed by Nikos in the comments, alternatively you can set your LD_LIBRARY_PATH by export LD_LIBRARY_PATH=path/to/boost/build/lib. Add this line to .~/.bashrc file so that it is not lost when you log out.