Book Image

Learning Linux Shell Scripting

By : Ganesh Sanjiv Naik
Book Image

Learning Linux Shell Scripting

By: Ganesh Sanjiv Naik

Overview of this book

Linux is the one of the most powerful and universally adopted OSes. Shell is a program that gives the user direct interaction with the operating system. Scripts are collections of commands that are stored in a file. The shell can read this file and act on the commands as if they were typed on the keyboard. Shell scripting is used to automate day-to-day administration, and for testing or product development tasks. This book covers Bash, GNU Bourne Again SHell, preparing you to work in the exciting world of Linux shell scripting. We start with an introduction to the Shell environment and explain basic commands used in Shell. Next we move on to check, kill, and control the execution of processes in Linux OS. Further, we teach you about the filter tools available in Linux and explain standard output and standard errors devices. Then we will ensure you understand Shell’s interpretation of commands and get a firmer grasp so you use them in practice. Next, you’ll experience some real-world essentials such as debugging and perform Shell arithmetic fluently. Then you’ll take a step ahead and learn new and advanced topics in Shell scripting, such as starting up a system and customizing a Linux system. Finally, you’ll get to understand the capabilities of scripting and learn about Grep, Stream Editor, and Awk.
Table of Contents (20 chapters)
Learning Linux Shell Scripting
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Process monitoring tools – top, iostat, and vmstat


We can view the native performance of various processes in OS using tools which will be discussed further. To view a dynamic real-time view of the top running processes in OS, use the following command:

$top

An explanation of the top command generated output is as follows:

The $top command displays a lot of information about the running system.

The first line of the display is shown as follows:

The description of fields in the first line is as follows:

  • Current time

  • System uptime

  • Number of users logged in

  • Load average of 5, 10, and 15 minutes, respectively

The second line is shown as follows:

This line shows the summary of tasks or processes. It shows the total number of all the processes, which includes the total number of running, sleeping, stopped, and zombie processes.

The third line is shown as follows:

This line shows information about CPU usage in % in different modes as follows:

  • * us (user): CPU usage in % for running (un-niced) the user processes...