Setting Dynamic Library Paths via Command Line

To configure the dynamic linker search path at runtime, use:

export LD_LIBRARY_PATH=$(pwd)/library_dir:$LD_LIBRARY_PATH

This command prepends the current directory's library_dir subdirectory to the existing library search path. Key components:

• export: Makes the variible available to child processes
• LD_LIBRARY_PATH: Colon-separated list of directories for shared libraries (.so files)
• $PWD/library_dir: Path to additional library directory
• :$LD_LIBRARY_PATH: Appends existing paths

Useful for temporary/test environments but avoid permanent usage due to potential version conflicts.

LD_LIBRARY_PATH Deep Dive

A colon-delimited environment variable specifying additional directories for dynamic linker searches beyond standard locations (/lib, /usr/lib).

Configuration Syntax

export LD_LIBRARY_PATH=/custom/lib/path:$DYNAMIC_LIB_PATH

Replace /custom/lib/path with actual directory. Multiple paths require colon separation.

Practical Example

For libraries in /home/user/project_libs:

export LD_LIBRARY_PATH=/home/user/project_libs:$DYNAMIC_LIB_PATH

The dynamic linker checks this directory first before standard paths.

Caveats

1. Security: Risk of loading malicious/unintended libraries
2. Portability: Environment-dependent execution failures
3. Maintenance: Complex dependency management in multi-user systems

Prefer standard installation paths or compiler-level configurations where possible.

Alternative Approaches

Stendard System Paths

Install libraries to default locations (/usr/lib, /lib) requiring administrative privileges.

Compiler-Level Path Specification

Embed paths directly in binaries using linker options:

RPATH (Hard-coded paths):

gcc -o application main.c -L/custom/lib/dir -lcoollib -Wl,-rpath,/custom/lib/dir

• -L: Compilation-time library search path
• -l: Library name
• -Wl,-rpath: Embeds runtime search path

RUNPATH (Environment-overridable):

gcc -o application main.c -L/custom/lib/dir -lcoollib -Wl,--enable-new-dtags,-rpath,/custom/lib/dir

Prioritizes LD_LIBRARY_PATH over embedded paths.

Selection Guidance

• Use RPATH for immutable deployment paths
• Choose RUNPATH when runtime flexibility is required

CMake Implementation

RPATH Configuration

Modern approach avoiding environment variables:

cmake_minimum_required(VERSION 3.10)
project(SampleApp)

set(CMAKE_CXX_STANDARD 17)
add_executable(sample_exe source.cpp)
target_link_libraries(sample_exe coollib)

# Build-tree RPATH
set(CMAKE_BUILD_RPATH "/custom/build/lib")
# Install-tree RPATH
set(CMAKE_INSTALL_RPATH "/custom/install/lib")
set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)

Target-Specific Properties

set_target_properties(application PROPERTIES
    BUILD_RPATH "${CMAKE_SOURCE_DIR}/build_libs"
    INSTALL_RPATH "${CMAKE_SOURCE_DIR}/install_libs"
    INSTALL_RPATH_USE_LINK_PATH TRUE
)

Configures runtime search paths for specific targets during build/installation.

Custom Build Commands (Legacy Approach)

add_custom_command(TARGET sample_exe POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E env LD_LIBRARY_PATH="/custom/runtime/libs" $<TARGET_FILE:sample_exe>
)

Sets temporary environment during post-build execution.

Recommendations

1. Prefer system package managers for library management
2. Use RPATH/RUNPATH for self-contained deployments
3. Reserve LD_LIBRARY_PATH for development/testing scenarios
4. Document all non-standard library dependencies