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Mastering Bash

You're reading from   Mastering Bash A Step-by-Step Guide to working with Bash Programming and Shell Scripting

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Product type Paperback
Published in Jun 2017
Publisher Packt
ISBN-13 9781784396879
Length 502 pages
Edition 1st Edition
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Author (1):
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 Zarrelli Zarrelli
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Zarrelli
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Table of Contents (22) Chapters Close

Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface
1. Let's Start Programming FREE CHAPTER 2. Operators 3. Testing 4. Quoting and Escaping 5. Menus, Arrays, and Functions 6. Iterations 7. Plug into the Real World 8. We Want to Chat 9. Subshells, Signals, and Job Controls 10. Lets Make a Process Chat 11. Living as a Daemon 12. Remote Connections over SSH 13. Its Time for a Timer 14. Time for Safety 1. Use in Real World Application

Double fork and setsid


There are a couple of methods to daemonize a process, maybe less but really interesting ones; and these are the double fork and setsid.

Double fork is the way a process is usually and implies a fork, a duplication of the parent process to create a child one. In the case of double forking applied to daemonization, the parent process forks off a child process, then terminates it. Then, the child process forks its own child process and terminates. So, at the end of the chain, the two parent processes die and only the grandchild is alive and running but as a daemon. The reason for this resides in how a controlling terminal for a session is allocated since the child processes that are forked inherit the controlling terminal from their parent process.

In an interactive session, the shell is the first processed to be executed, so it is the controlling process for the terminal and the session leader from which all forked processes in the session inherit their controlling terminal...

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