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Linux: See Bandwidth Usage Per Process With Nethogs Tool

I have Red Hat Enterprise Linux 6.x server. How do I find out and groups network bandwidth usage by process under Linux operating systems? How do I find out what programs are using network bandwidth under Linux operating systems? How can I see bandwidth usage per PID, command, and user on a Linux operating systems?
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Sysadmin because even developers need heroes!!!

HowTo: Firefox Disable Default PDF Viewer / Plugin

I recently updated my Mozilla Firefox. Firefox now includes a built-in PDF viewer that allows me to see PDF files found on the web without a plugin. The built-in PDF viewer is enabled by default. However, I found that this pdf viewer is not working properly with various web-sites, and it works slowly. How do disable the built-in PDF viewer so that I can use the Adobe PDF viewer or other PDF viewer that is shipped with my operating systems?
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Vi / Vim: Save And Quit The Editor Command

I am a new vi (vim) text editor user. How do I quit the vi editor and save my changes under Linux or Unix like operating systems?
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Linux/Unix: Cat Command Display Line Numbers

How do I use the cat command to display the line numbers for a file called myapp.c under Linux or Unix like operating systems?
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Vi / Vim: Quit Without Saving Command

I am a new vi / vim text editor user. How can I quit the vi / vim text editor without saving my changes to a file under Linux / Unix like operating systems?
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Squid Proxy Server Change Outgoing IP Address

I have Squid caching proxy server deployed on Rackspace based server in UK. This server has four IP address. I would like to change outgoing IP addresses from default 1.2.3.1 to 1.2.3.4. How do I change proxy server outgoing IP address under Linux or Unix operating systems?
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What Is SELinux?

What is SELinux? Why should I use SELInux on my CentOS or Red Hat Enterprise Linux server running on IBM hardware?
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Linux / Unix: Unicode and HTML Characters Lookup By Name or Number

I need to replace special characters with equivalent hexadecimal unicode under Linux or Unix like operating system. How do I list or find out unicodes for given characters?
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seinfo Command: Query SELinux Policy Under CentOS / RHEL / Linux

How do I query and get information about a policy under SELinux? How do I analyze a binary or a source policy file under SELinux?
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Linux / Unix Command To Optimize and Compress PNG Files In Bulk

I have lots of images in png format (over 250k+ png). Properly formatting and compressing png images can save many bytes of data. How do I compress and optimize png images on my amazon cloud account so that I can save bandwidth on cloudfront cdn account? How do I use an image compressor to create lossless compression on PNG files, with no effect on image quality in bulk using Red Hat Enterprise Linux bash shell?
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