Shared Library Issues In Linux

[ Thanks to Jeremy Mack Wright for this link. ]

"Shared libraries are one of the many strong design features of Linux, but can lead to headaches for inexperienced users, and even experienced users in certain situations. Shared libraries allow software developers keep the size of their application storage and memory footprints down by using common code from a single location. The glibc library is a good example of this. There are two standardized locations for shared libraries on a Linux system, and these are the /lib and /usr/lib directories. On some distributions /usr/local/lib is included, but check the documentation for your specific distribution to be sure. These are not the only locations that you can use for libraries though, and I’ll talk about how to use other library directories later. According to the Filesystem Hierarchy Standard (FHS), /lib is for shared libraries and kernel modules that are required for startup and running in the root filesystem (/bin and /sbin), and /usr/lib holds most of the internal libraries that are not meant to be executed directly by users or shell scripts. The /usr/local/lib directory is not defined in the latest version of the FHS, but if it exists on a distribution it normally holds libraries that aren’t a part of the standard distribution, including libraries that the system administrator has compiled/installed after the initial setup. There are some other directories like /lib/security that holds PAM modules, but for our discussion we’ll focus on /lib and /usr/lib.

"The counterpart to the dynamically linked (shared) library is the statically linked library. Whereas dynamically linked libraries are loaded and used as they are needed by the applications, statically linked libraries are either built into, or closely associated with a program at the time it is compiled."

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