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The shared library soname (cont.)

Here's how to use a soname:

1. Specify soname when creating shared library:

   $ gcc -fPIC -c -Wall -g mod1.c mod2.c mod3.c 
   $ gcc -shared -Wl,-soname,libbar.so -o libfoo.so \
              mod1.o mod2.o mod3.o
   

   -Wl,-soname,libbar.so instructs linker to mark the shared library libfoo.so with the soname libbar.so.

2. Create executable:

   $ gcc -g -Wall -o prog prog.c libfoo.so
   

   Linker detects that libfoo.so contains the soname libbar.so and embeds the latter name inside the executable.

3. Run the program:

   $ LD_LIBRARY_PATH=. ./prog
   ./prog: error in loading shared libraries: 
   libbar.so: cannot open shared object file: 
   No such file or directory
   

   Dynamic linker cannot find anything named libbar.so.

4. Create a symbolic link from the soname to the real name of the library:

   $ ln -s libfoo.so libbar.so
   $ LD_LIBRARY_PATH=. ./prog
   Called mod1-x1
   Called mod2-x2
   

At run-time this link can point to a version of the library which is different from the version against which linking was performed.

(C) 2006, Michael Kerrisk