Environment Variables for Shared Libraries

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The environment variable that overrides or extends the list of directories holding shared libraries in Linux is LD_LIBRARY_PATH. This variable is used to specify a list of directories that the system's dynamic linker should search for shared libraries when running an executable.

When a program is executed, the dynamic linker needs to find all the shared libraries that are required by the program. By default, it searches for these libraries in a set of standard directories, such as /lib and /usr/lib. However, if a program requires a shared library that is not located in one of these standard directories, the dynamic linker will not be able to find it.

To solve this problem, the LD_LIBRARY_PATH variable can be used to specify additional directories where the dynamic linker should search for shared libraries. The variable should be set to a colon-separated list of directories, for example:

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export LD_LIBRARY_PATH=/usr/local/lib:/opt/mylibs 

This command would add the directories /usr/local/lib and /opt/mylibs to the list of directories searched by the dynamic linker.

Note that setting LD_LIBRARY_PATH can be a security risk if not used carefully, as it allows users to potentially load malicious libraries that could compromise the system. It is recommended to only use this variable when absolutely necessary, and to avoid setting it globally for all users.