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Linux Tutorials

- Herong's Tutorial Examples

1.20, 2020

Dr. Herong Yang

2020 Dr. Herong Yang. All rights reserved.

This book is a collection of notes and sample codes written by the author while he was learning Linux systems. Topics include using network configuration and security firewall; managing Linux file systems; installing CentOS systems; using SELinux (Security-Enhanced Linux) system; DNF/YUM software package manager; managing MySQL server; developing Python and PHP scripts; using GCC C/C++ compilers; managing vsftpd - Very Secure FTP daemon; running Conda - Environment and Package Manager. Updated in 2020 (Version 1.20) with SELinux tutorials. For latest updates and free sample chapters, visit http://www.herongyang.com/Linux.

Table of Contents

Keywords: Linux, CentOS, macOS, Tutorials

About This Book

This section provides some detailed information about this book - Linux Tutorials - Herong's Tutorial Examples.

Title: Linux Tutorials - Herong's Tutorial Examples

Author: Dr. Herong Yang - Contact by email via herong_yang@yahoo.com.

Category: Programming

Version/Edition: 1.20, 2020

Number of pages in PDF format: 157

Description: This book is a collection of notes and sample codes written by the author while he was learning Linux systems. Topics include using network configuration and security firewall; managing Linux file systems; installing CentOS systems; using SELinux (Security-Enhanced Linux) system; DNF/YUM software package manager; managing MySQL server; developing Python and PHP scripts; using GCC C/C++ compilers; managing vsftpd - Very Secure FTP daemon; running Conda - Environment and Package Manager. Updated in 2020 (Version 1.20) with SELinux tutorials.

Keywords: C/C++, File System, Linux, MySQL, PHP, Python, SELinux, Unix.

Copyright:

• This book is under Copyright 2020 Dr. Herong Yang. All rights reserved.
• Material in this book may not be published, broadcasted, rewritten or redistributed in any form.
• Code examples are provided as-is, with no warranty of any kind.

Revision history:

• Version 1.20, 2020. Added SELinux tutorials.
• Version 1.00, 2019. Completed first edition.

Web version: http://www.herongyang.com/Linux - Provides free sample chapters, latest updates and readers' comments. The Web version of this book has been viewed a total of:

• 0 times as of December 2019.

PDF/EPUB version: http://www.herongyang.com/Linux/PDF-Full-Version.html - Provides information on how to obtain the full version of this book in PDF, EPUB, or other format.

Introduction to Linux Systems

Provides introductions and tutorial on Linux operating systems. Topics include 'uname' to display operating system information.

Takeaways:

• "uname command can be used to display operating system information.

"uname" - Display System Information

Provides a tutorial example on how to display operating system information using the 'uname' command on Linux systems.

The first thing you should do on a new Linux computer is to gather its system information as shown in this tutorial.

1. The most commonly used command to display Linux operating system information is the "uname" command.

(on my CentOS 8 computer)
centos8$ uname -mprsv
Linux 4.18.0-147.el8.x86_64
#1 SMP Wed Dec 4 21:51:45 UTC 2019 x86_64 x86_64
(on my CentOS 6 computer)
centos6$ uname -mprsv
Linux 2.6.32-696.20.1.el6.i686 #1 SMP Fri Jan 26 18:13:32 UTC 2018
i686 i686 i386 GNU/Linux i386
(on my macOS 10 computer)
macos$ uname -mnprsv
Darwin 16.7.0 Darwin Kernel Version 16.7.0:
Sun Jun 2 20:26:31 PDT 2019; root:xnu-3789.73.50~1/RELEASE_X86_64
x86_64 i386

2. On most Linux systems, the operating system information is accessible via a special file called /proc/version. You can use the "cat" command to display it:

(on my CentOS 8 computer)
centos8$ cat /proc/version
Linux version 4.18.0-147.el8.x86_64
(mockbuild@kbuilder.bsys.centos.org)
(gcc version 8.3.1 20190507 (Red Hat 8.3.1-4) (GCC))
#1 SMP Wed Dec 4 21:51:45 UTC 2019
(on my CentOS 6 computer)
centos6$ cat /proc/version
Linux version 2.6.32-696.20.1.el6.i686
(mockbuild@x86_64_01.bsys.centos.org)
(gcc version 4.4.7 20120313 (Red Hat 4.4.7-18) (GCC))
#1 SMP Fri Jan 26 18:13:32 UTC 2018

3. The CPU architecture is a key parameter when installing Linux systems and applications. You can use the "arch" command to display it:

(on my CentOS 8 computer)
centos8$ arch
x86_64
(on my CentOS 6 computer)
centos6$ arch
i686
(on my macOS 10 computer)
macOS$ arch
i386

"free" - Display Free and Used Memory

Provides a tutorial example on how to display free and used memory information using the 'free' command on Linux systems.

Another important information about your Linux system is the memory. You can use the "free" command to display memory statistics including free and used memory sizes. Here are some examples of "free" command output on my CentOS computer.

1. Display memory information using "free" with default options. The memory counts are displayed in kibibytes (1,024 bytes). Note that a kibibyte (1,024 bytes) is slightly different than a kilobyte (1,000 bytes).

herong$ free
total used free shared buff/cache available
Mem: 7789220 2047412 677256 297448 5064552 5145248
Swap: 8085500 0 8085500

2. To control the unit, you can use "free -b|k|m|g" options.

herong$ free -m
total used free shared buff/cache available
Mem: 7606 1999 661 290 4945 5024
Swap: 7895 0 7895

3. Or you can use "free -h" to display counts in human readable formats.

herong$ free -h
total used free shared buff/cache available
Mem: 7.4Gi 2.0Gi 661Mi 290Mi 4.8Gi 4.9Gi
Swap: 7.7Gi 0B 7.7Gi

The output columns are defined as:

• total - Total installed memory (MemTotal and SwapTotal in /proc/meminfo)
• used - Used memory (calculated as total - free - buffers - cache)
• free - Unused memory
• shared - Memory used (mostly) by tmpfs
• buffers - Memory used by kernel buffers (Buffers in /proc/meminfo)
• cache Memory used by the page cache and slabs
• buff/cache - Sum of buffers and cache
• available - Estimation of how much memory is available for starting new applications, without swapping. Unlike the data provided by the cache or free fields, this field takes into account page cache and also that not all reclaimable memory slabs will be reclaimed due to items being in use

Process Management

Provides introductions and tutorial on managing processes on Linux systems. Topics include 'ps' to display processes; 'jobs' and other commands to manage background jobs; 'tmux' tool to manage multiple shells and keep them in background.

Takeaways:

• "ps command can be used to display processes running on the system.
• "jobs" command can be used to display your background jobs that are running with inputs detached from keyboards.
• "ctrl-z" can be used to stop a foreground job and send it to the background.
• "bg" command can be used to resume a background job.
• "fg" command can be used to bring a background job to the foreground.
• "tmux" tool can be used to manage multiple shells in a single terminal window.
• "tmux" tool automatically keeps its shells running when the terminal is disconnected.

"ps" - Display Current Processes

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