Creating Shared Libraries in Linux - Part 2

Check the PART1 of this article.

4. Making the library available at run-time

Using LD_LIBRARY_PATH
We have to create or set the environment variable "LD_LIBRARY_PATH" to the directory containing the shared libraries.

export LD_LIBRARY_PATH=/home/cf/lib

If in current directory you can give the following command

export LD_LIBRARY_PATH=.

If we have to append a new directory to the existing paths then add the directories separated by colons to environment variable "LD_LIBRARY_PATH".

export LD_LIBRARY_PATH=/opt/lib:$LD_LIBRARY_PATH

Now recompile the main program

gcc -o test main.c -lcalc_mean -L/home/cf/slib

Now check the ldd command output

$ ldd test
 linux-gate.so.1 =>  (0x007ad000)
 libcalc_mean.so => ./libcalc_mean.so (0x0081e000)
 libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0x005ff000)
 /lib/ld-linux.so.2 (0x00e19000)

It seems now linker is able to locate our shared library as we can see in above output. Now run the program

$./test

LD_LIBRARY_PATH is good for quick tests and for systems on which you don’t have admin privileges. As a downside, however, exporting the LD_LIBRARY_PATH environment variable  might screw up with other programs you run that also rely on LD_LIBRARY_PATH if you don’t reset it to its previous state when you’re done.