Shared library versions and naming (cont.)

soname

Format: libname.so.major-id

soname includes the same major version identifier as corresponding real name, but does not include minor version identifier.

Purpose: run-time loading is dependent only on major version number of the library

soname is created as a symbolic link (usually in same directory as real name).

The soname for each major library version points to most recent minor version.
Since it is the soname (not the real name) that is embedded in executable by linker:
1. At any time, we can change soname symbolic link to point to a newer minor version.
2. Different major versions can co-exist and be accessed by the programs that require them.

Examples of sonames (along with the real names to which they might be symbolically linked):

libdemo.so.1        -> libdemo.so.1.0.2
libdemo.so.2        -> libdemo.so.2.0.1
libreadline.so.4    -> libreadline.so.4.0