Book Image

Mastering Bash

By : Giorgio Zarrelli
Book Image

Mastering Bash

By: Giorgio Zarrelli

Overview of this book

System administration is an everyday effort that involves a lot of tedious tasks, and devious pits. Knowing your environment is the key to unleashing the most powerful solution that will make your life easy as an administrator, and show you the path to new heights. Bash is your Swiss army knife to set up your working or home environment as you want, when you want. This book will enable you to customize your system step by step, making your own real, virtual, home out of it. The journey will take you swiftly through the basis of the shell programming in Bash to more interesting and challenging tasks. You will be introduced to one of the most famous open source monitoring systems—Nagios, and write complex programs with it in any languages. You’ll see how to perform checks on your sites and applications. Moving on, you’ll discover how to write your own daemons so you can create your services and take advantage of inter-process communication to let your scripts talk to each other. So, despite these being everyday tasks, you’ll have a lot of fun on the way. By the end of the book, you will have gained advanced knowledge of Bash that will help you automate routine tasks and manage your systems.
Table of Contents (15 chapters)

Becoming a daemon

A life as a daemon is not an easy life and requires a lot of gruesome deaths of parent processes.

The first thing needed for a process to become a daemon is to fork as a new process so the parent can exit, and the the prompt is returned to the invoking shell. This ensures that the new process is not a process group leader, since a process group leader cannot create a new session calling setsid. So, the new child process can now be promoted to process group leader and session leader by calling setsid. So far, the new session has no controlling terminal, and so does the new child. So, we fork again to be sure that the session and group leader can exit. Now, the grandchild is not a session, so the terminal it is going to open cannot be its controlling terminal. This is how things work in the hard life of a Linux process; if it is not a session leader, the terminal...