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CompTIA® Linux+ Certification, Powered by LPI, Student Manual by Axzo Press

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620 CompTIA Linux+ Certification, Powered by LPI
Topic B: Managing shared libraries
This topic covers the following CompTIA exam objectives for Linux+ [Powered by
LPI] Certification, LX0-101 and LX0-102 exams.
# Objective
102.3 Manage shared libraries
Identify shared libraries
Identify the typical locations of system libraries
Load shared libraries
The following is a partial list of the used files, terms, and utilities:
ldd
ldconfig
/etc/ld.so.conf
LD_LIBRARY_PATH
Libraries
Explanation
A programmer writing an application for Linux rarely writes every single piece of
functionality from scratch. Programmers frequently reuse existing bits of code in their
applications. They might use functions they themselves wrote for other programs. Or
just as likely, they might use common functions written and shared by other
programmers. Collections of shared functions are called libraries, and in Linux, there
are three types:
Static libraries
Shared libraries
Dynamically loaded (DL) libraries
Static libraries
A static library is associated with a single program, and a single version of that
program. The files associated with such libraries are named with the .a extension. Static
libraries are mostly of historical interest, as few modern programs use this type. Static
library files are distributed with a program and kept together with the rest of the
applications files or with its configuration files.
Shared libraries
Shared libraries, as the name suggests, can be shared between programs and versions of
programs. This makes them much more flexible for both their originator and other
programmers who want to use the libraries in their programs. Various techniques are
used to enable users to upgrade shared library versions without breaking compatibility
with existing programs that use those libraries.
Dynamically loaded libraries
DL libraries are similar to shared libraries, except that they can be loaded or unloaded
by a program as needed. A shared library is loaded when the application is launched. A
DL library is loaded by a plug-in, module, or feature of the program on an as-needed

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