Overview

These exercises give you practice managing:

• Dynamically and statically linked programs
• Shared object library cache
• Shared object library paths
• Link shared objects

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Prerequisites

To get the most from the practice exercises in this series, you should have a basic knowledge of Linux and a working Linux system on which you can practice the exercises covered in this article.

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Exercise 1. List dynamically linked shared objects

Imagine you are a systems administrator for a Linux file server. You are working to create a new directory, and suddenly, the popular mkdir command returns an error. This error could be the result of a missing dynamically linked library. You've probably used the mkdir tool numerous times. It is just one example of a program that depends on external shared objects to function properly.

• Use the appropriate command to properly identify the shared libraries mkdir calls externally.

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Exercise 2. Find statically linked executables

You have now found shared libraries dynamically linked to the mkdir command.

• Locate an executable in the /bin directory that doesn't use external shared libraries.

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Exercise 3. Find information about library caching

Linux caches library location information for dynamically linked programs to improve performance.

• Locate the caching directory on your Linux computer, and use the appropriate command to find a library that mkdir needs.

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Exercise 4. Set an alternative shared library path

Commonly used Linux executables such as mkdir typically use a common path that your Linux distribution sets. Suppose the organization you are working for requires the use of a third-party program that is dynamically linked to shared libraries not included in a typical Linux computer's library search path. In such cases, you might consider creating a separate directory for the libraries. However, the program needs to locate the libraries when executed. For this task, assume that the third-party application foo has been provided, but an older version uses a shared library not installed on your Linux computer.

1. Create a directory with the path /opt/foo/lib.
2. Create a file in the /opt/foo/lib directory, and name it foo.so.
3. Use the export command to set the library path variable that will enable the application to find foo.so at run time.

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Exercise 5. Create a symbolic link to a shared library

Consider the possibility that foo software has been updated and documented to use the latest /lib/libcat.so library in place of foo.so. Even though the new software has backward compatibility to use foo.so, you can experiment using the new library by creating a symbolic link:

1. Rename the original foo.so to foo.so.old.
2. Create a symbolic link from /lib/libcat.so to /opt/foo/lib/foo.so.

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Exercise solutions

Follow these solution steps to check your work.

Resources

• The developerWorks article "Learn Linux,101: Manage shared libraries" (developerWorks, March 2010) describes the commands required to complete these exercises.
  
  
• At the LPIC Program site, find detailed objectives, task lists, and sample questions for the three levels of the LPI's Linux systems administration certification. In particular, look at the LPI-101 detailed objectives and the sample questions.
  
  
• Review the entire LPI exam prep series on developerWorks to learn Linux fundamentals and prepare for systems administrator certification based on LPI exam objectives prior to April 2009.
  
  
• Exam Preparation Resources for Revised LPIC Exams provides a list of other certification training resources that LPI maintains.
  
  

About the author

Tracy Bost is a seasoned software developer and systems engineer. He is also a lecturer and trainer for the Linux operating system. Tracy has been certified as both a Red Hat Certified Engineer (RHCE) and a Microsoft Certified Systems Engineer (MCSE), along with being an active member of the Linux Foundation. He has worked in several industries, including mortgage, real estate, and the nonprofit sector.

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Table of contents

• Overview
• Prerequisites
• Exercise 1. List dynamically linked shared objects
• Exercise 2. Find statically linked executables
• Exercise 3. Find information about library caching
• Exercise 4. Set an alternative shared library path
• Exercise 5. Create a symbolic link to a shared library
• Exercise solutions
• Resources
• About the author
• Comments

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