Manage RPATHs

The rpath is encoded inside dynamic libraries and executables and helps the linker to find its required shared libraries.

If we have an executable, my_exe, that requires a shared library, shared_lib_1, and shared_lib_1, in turn, requires another shared_lib_2.

So the rpaths values are:

File	rpath
my_exe	/path/to/shared_lib_1
shared_lib_1	/path/to/shared_lib_2
shared_lib_2

In Linux if the linker doesn’t find the library in rpath, it will continue the search in system defaults paths (LD_LIBRARY_PATH… etc) In OSX, if the linker detects an invalid rpath (the file does not exist there), it will fail.

Default Conan approach

The consumer project of dependencies with shared libraries needs to import them to the executable directory to be able to run it:

conanfile.txt

[requires]
Poco/1.9.0@pocoproject/stable

[imports]
bin, *.dll -> ./bin # Copies all dll files from packages bin folder to my "bin" folder
lib, *.dylib* -> ./bin # Copies all dylib files from packages lib folder to my "bin" folder

On Windows this approach works well, importing the shared library to the directory containing your executable is a very common procedure.

On Linux there is an additional problem, the dynamic linker doesn’t look by default in the executable directory, and you will need to adjust the LD_LIBRARY_PATH environment variable like this:

LD_LIBRARY_PATH=$(pwd) && ./mybin

On OSX if absolute rpaths are hardcoded in an executable or shared library and they don’t exist the executable will fail to run. This is the most common problem when we reuse packages in a different environment from where the artifacts have been generated.

So for OSX, Conan, by default, when you build your library with CMake, the rpaths will be generated without any path:

File	rpath
my_exe	shared_lib_1.dylib
shared_lib_1.dylib	shared_lib_2.dylib
shared_lib_2.dylib

The conan_basic_setup() macro will set the set(CMAKE_SKIP_RPATH 1) in OSX.

You can skip this default behavior by passing the KEEP_RPATHS parameter to the conan_basic_setup macro:

include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup(KEEP_RPATHS)

add_executable(timer timer.cpp)
target_link_libraries(timer ${CONAN_LIBS})

If you are using autotools Conan won’t auto-adjust the rpaths behavior. if you want to follow this default behavior you will probably need to replace the install_name in the configure or MakeFile generated files in your recipe to not use $rpath:

replace_in_file("./configure", r"-install_name \$rpath/", "-install_name ")

Different approaches

You can adjust the rpaths in the way that adapts better to your needs.

If you are using CMake take a look to the CMake RPATH handling guide.

Remember to pass the KEEP_RPATHS variable to the conan_basic_setup:

include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup(KEEP_RPATHS)

Then, you could, for example, use the @executable_path in OSX and $ORIGIN in Linux to adjust a relative path from the executable. Also, enabling CMAKE_BUILD_WITH_INSTALL_RPATH will build the application with the RPATH value of CMAKE_INSTALL_RPATH and avoid the need to be relinked when installed.

if (APPLE)
    set(CMAKE_INSTALL_RPATH "@executable_path/../lib")
else()
    set(CMAKE_INSTALL_RPATH "$ORIGIN/../lib")
endif()

set(CMAKE_BUILD_WITH_INSTALL_RPATH ON)

You can use this imports statements in the consumer project:

[requires]
Poco/1.9.0@pocoproject/stable

[imports]
bin, *.dll -> ./bin # Copies all dll files from packages bin folder to my "bin" folder
lib, *.dylib* -> ./lib # Copies all dylib files from packages lib folder to my "lib" folder
lib, *.so* -> ./lib # Copies all so files from packages lib folder to my "lib" folder

And your final application can follow this layout:

bin
 |_____ my_executable
 |_____ mylib.dll
 |
lib
 |_____ libmylib.so
 |_____ libmylib.dylib

You could move the entire application folder to any location and the shared libraries will be located correctly.