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Linux Shell Scripting Cookbook

You're reading from   Linux Shell Scripting Cookbook Do amazing things with the shell and automate tedious tasks

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Product type Paperback
Published in May 2017
Publisher
ISBN-13 9781785881985
Length 552 pages
Edition 3rd Edition
Tools
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Authors (3):
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Clif Flynt Clif Flynt
Author Profile Icon Clif Flynt
Clif Flynt
Sarath Lakshman Sarath Lakshman
Author Profile Icon Sarath Lakshman
Sarath Lakshman
Shantanu Tushar Shantanu Tushar
Author Profile Icon Shantanu Tushar
Shantanu Tushar
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Toc

Table of Contents (20) Chapters Close

Title Page
Credits
About the Authors
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface
1. Shell Something Out FREE CHAPTER 2. Have a Good Command 3. File In, File Out 4. Texting and Driving 5. Tangled Web? Not At All! 6. Repository Management 7. The Backup Plan 8. The Old-Boy Network 9. Put On the Monitors Cap 10. Administration Calls 11. Tracing the Clues 12. Tuning a Linux System 13. Containers, Virtual Machines, and the Cloud

Tracing packets with tcpdump


Just knowing which applications are using a given port may not be sufficient information to trace down a problem. Sometimes you need to check the data that is being transferred as well.

Getting ready

You need to be a root user to run tcpdump. The tcpdump application may not be installed in your system by default. So install it with your package manager:

$ sudo apt-get install tcpdump
$ sudo yum install libpcap tcpdump

How to do it...

The tcpdump application is the frontend to Wireshark and other network sniffer programs. The GUI interface supports many of the options we'll describe shortly.

This application's default behavior is to display every packet seen on the primary Ethernet link. The format of a packet report is as follows:

TIMESTAMP SRC_IP:PORT > DEST_IP:PORT: NAME1 VALUE1, NAME2 VALUE2,...

The name-value pairs include:

  • The term S stands for SYN (Start Connection)
  • The term F stands for FIN (Finish Connection)
  • The term P stands for PUSH (Push data)
  • The term R stands...
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