Linux HowTo: Library Files

Almost all of Linux programs depend on some thing called library files. 

-the idea behind library files:

            . to simplify programmers lives by providing a repository for commonly used shared program fragments.

            . this reduces the main program size as you only need to invoke the libraries as a reference link (eg #include xyz.so)

            . shared library files usually have a '.so' filename extension; '.so' = shared object

-note: besides shared libraries, there are static libraries which have a '.a' filename extn. they are used for backward compatibility to older programs.

-eg:         libc.so              - the library for C programs.

              Gimp toolkit      - the library for onscreen widgets (buttons, scrollbars, menubars etc) in Gnome

              Qt                     - the library for onscreen widgets (buttons, scrollbars, menubars etc) in KDE

-the library path for the system is set in the file /etc/ld.so.conf or in the env variables LIBPATH or LD_LIBRARY_PATH

-displaying libraries that a program depends upon:

-eg:         # ldd  /bin/ls       [ shows the library dependencies for the /bin/ls binary ]

-display config info for libraries, currently loaded in memory:

              # ldconfig