Why do I have to define LD_LIBRARY_PATH with an export every time I run my application?

Question

I have some code that uses some shared libraries (c code on gcc). When compiling I have to explicitly define the include and library directories using -I and -L, since they aren't in the standard places. When I try to run the code, I get the following error:

./sync_test 
./sync_test: error while loading shared libraries: libsync.so: cannot open shared object file: No such file or directory

However, do the following, everything works just fine:

export LD_LIBRARY_PATH="/path/to/library/"
./sync_test

Now, the strange part is, this only works once. If I try and run sync_test again I get the same error unless I run the export command first. I tried adding the following to my .bashrc, but it made no difference:

LD_LIBRARY_PATH="/path/to/library/"

Answer 1

You should avoid setting LD_LIBRARY_PATH in your .bashrc. See "Why LD_LIBRARY_PATH is bad" for more information.

Use the linker option -rpath while linking so that the dynamic linker knows where to find libsync.so during runtime.

gcc ... -Wl,-rpath /path/to/library -L/path/to/library -lsync -o sync_test

EDIT:

Another way would be to use a wrapper like this

#!/bin/bash

LD_LIBRARY_PATH=/path/to/library sync_test "$@"

If sync_test starts any other programs, they might end up using the libs in /path/to/library which may or may not be intended.