Lead Image © sgame, fotolia.com

Improving performance with environment variables

Trick or No Trick

Article from ADMIN 64/2021

By Jeff Layton

By using the LD_PRELOAD environment variable, you can improve performance without making changes to applications.

A topic that system administrators learn as they gain experience is called the "LD_PRELOAD Trick." This trick can help fix misbehaving applications, upgrade applications, and even improve application performance. Of course, it is not really a trick, just the use of a feature in *nix operating systems.

Have you ever installed an application on Linux and tried to run it only to be told the application can't be found? To debug the issue, probably the first thing to check is your PATH [1], which is "an environment variable … that tells the shell which directories to search for executable files." In short, the path tells Linux where to look for applications. If the application is not in the path, then Linux "thinks" it does not exist.

Fortunately, environment variables in Linux can be changed. If Linux cannot find an application, you can change the environment variable, edit the environment variable, or add to the environment variable. Linux uses other environment variables for defining other aspects of the operating system beyond the location of executables. Many times, applications define and use their own environment variables. Users can even define their own environment variables.

In addition to PATH, which helps locate applications, the LD_LIBRARY_PATH environment variable tells Linux where to search for the shared libraries used by applications, which allows you to control which libraries are "available." Like PATH, this variable can be changed, and each shell can have its own value.

The variable can be useful when debugging a new library because you can simply change LD_LIBRARY_PATH to the new library, test it, and then change it back. You can also use it when upgrading libraries. If there is little or no change to the APIs in the new library, then a simple change to LD_LIBRARY_PATH allows you to use the new library without changing anything

...

Use Express-Checkout link below to read the full article (PDF).