system administration

    How to correctly use LD_LIBRARY_PATH

    RyanBy Updated:12 Comments2 Mins Read

    The LD_LIBRARY_PATH environment variable contains a colon separated list of paths that the linker uses to resolve library dependencies of ELF executables at run-time. These paths will be given priority over the standard library paths /lib and /usr/lib. The standard paths will still be searched, but only after the list of paths in LD_LIBRARY_PATH has been exhausted.

    The best way to use LD_LIBRARY_PATH is to set it on the command line or script immediately before executing the program. This way you can keep the new LD_LIBRARY_PATH isolated from the rest of your system.

    $ export LD_LIBRARY_PATH="/list/of/library/paths:/another/path"
$ ./program

    In general it is not a good practice to have LD_LIBRARY_PATH permanently set in your environment. This could lead to unintended side effects as programs can link to unintended libraries producing strange results or unexpectedly crashing. There is also the possibility introducing potential security threats.

    All those warnings aside, if you are using BASH you can set it permanently by placing a line similar to this in your .bashrc in your home directory.

    export LIBRARY_PATH="/list/of/library/paths:/another/path"

    A common case for setting LD_LIBRARY_PATH is when you have an application that requires dynamic libraries which were not installed in the standard library locations.

    You can check if the linker can locate all the required libraries by running the ldd command.

    $ ldd ~/myprogram
    	librt.so.1 => /lib/librt.so.1 (0x00002b4eca08e000)
	libc.so.6 => /lib/libc.so.6 (0x00002b4eca49f000)
	libpthread.so.0 => /lib/libpthread.so.0 (0x00002b4eca7df000)
	/lib64/ld-linux-x86-64.so.2 (0x00002b4ec9e72000)
	libmylib.so.1 => not found

    The linker cannot find libmylib.so.1.

    Let’s assume this library exists here “~/myprogdir/lib/libmylib.so.1”. We have to set LD_LIBRARY_PATH to include this path for the application to successfully run.

    $ export LD_LIBRARY_PATH="~/myprogdir/lib/:$LD_LIBRARY_PATH"
$ ldd ~/myprogram
    	librt.so.1 => /lib/librt.so.1 (0x00002b4eca08e000)
	libc.so.6 => /lib/libc.so.6 (0x00002b4eca49f000)
	libpthread.so.0 => /lib/libpthread.so.0 (0x00002b4eca7df000)
	/lib64/ld-linux-x86-64.so.2 (0x00002b4ec9e72000)
	libmylib.so.1 => ~/myprogdir/lib/libmylib.so.1 (0x00002b4eca9fa000)

    The linker has now found all the required libraries.

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