Docker Crash Course for DevOps Engineers

 

Introduction to Docker:

            Containerization is a lightweight method of running applications in isolated environments using shared OS kernels, while virtualization uses full virtual machines with separate operating systems to achieve isolation.

Containerization:

    Running applications in isolated user spaces (containers) on the same operating system kernel.

• Technology: Docker, Podman, containerd
• Isolation Level: Process-level isolation using namespaces and cgroups
• Resource Usage: Lightweight — shares OS kernel, faster startup, lower overhead
• Portability: Highly portable across environments (dev, test, prod)
• Use Case: Microservices, CI/CD pipelines, cloud-native apps.

Virtualization:

    Running multiple operating systems on a single physical machine using a hypervisor.

• Technology: VMware, VirtualBox, KVM, Hyper-V
• Isolation Level: Full OS-level isolation — each VM has its own OS and kernel
• Resource Usage: Heavy — requires more CPU, RAM, and disk space
• Portability: Less portable due to OS dependencies
• Use Case: Legacy applications, multi-OS testing, infrastructure-level isolation

Nagios Full Course | That will actually makes your life better

Nagios Full Course 

 Nagios Installation In Linux :

Nagios Installation Article: https://server-computer.com/how-to-install-nagios-in-linux/
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Step1: Disable SELinux
# sed -i 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/selinux/config
# setenforce 0
Step2: Allow Required Ports
# firewall-cmd --permanent --add-service=http
# firewall-cmd --permanent --add-service=https
# firewall-cmd –reload
Step3: Install Required Packages
# yum install -y wget httpd php gcc glibc glibc-common gd gd-devel make
net-snmp perl perl-devel openssl
Step4: Download package
# wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-
4.4.3.tar.gz

 

Step5: Create User and Group
Extract the package
# tar –xvf Nagios-4.4.3.tar.gz
# ./configure --with-command-group=nagcmd
https://server-computer.com Nagios Installation In Linux
Nagios Installation Article: https://server-computer.com/how-to-install-nagios-in-linux/
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Compile the package
https://server-computer.com Nagios Installation In Linux
Nagios Installation Article: https://server-computer.com/how-to-install-nagios-in-linux/
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Step6: Install package
# make install
https://server-computer.com Nagios Installation In Linux
Nagios Installation Article: https://server-computer.com/how-to-install-nagios-in-linux/
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# make install-init
# make install-config
# make install-webconf
# make install-classicui
Create nagiosadmin user and password for web console access. Enable and
Start Services.
https://server-computer.com Nagios Installation In Linux
Nagios Installation Article: https://server-computer.com/how-to-install-nagios-in-linux/
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Login to Web console
Services
Step7: Download and install Nagios Plugins
cd nagios-plugins-2.2.1
./configure --with-nagios-user=nagios --with-nagios-group=nagcmd
make
make install
Done.
https://server-computer.com Nagios Installation In Linux
Nagios Installation Article: https://server-computer.com/how-to-install-nagios-in-linux/
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After successful installation of plugins, you can see all service checks completes
normally. 

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monitoring tools, nagios, rmm, prtg network monitor, icinga, network monitoring tools, 

tac command in Linux with Examples

                                             Tac Command

    tac command in Linux is used to print files in reverse. When no file is specified then this command will read the standard input.

 Example for tac command

1. Create a file by using cat command.

[root@localhost ~]# cat > file1
welcome to linux
Thanks for visiting our channel

2. Check the file the data is available are not.

[root@localhost ~]# cat file1
welcome to linux
Thanks for visiting our channel

3. tac command will print the output in reverse.

[root@localhost ~]# tac file1
Thanks for visiting our channel
welcome to linux 

     

    You can use this tac command in all Linux flavors like redhat, ubuntu, kali linux, linux mint, debian, manjaro, arch linux, opensuse, centos, etc.

Cat Command in Linux / Unix

                                 Cat Command

Cat means "concatenate files and print on the standard output"

• By using cat command you can create, read, append the data to the file.

• You can use this cat command in all Linux flavors like redhat, ubuntu, kali linux, linux mint, debian, manjaro, arch linux, opensuse, centos, etc. 

  Some examples for cat command
  
  1. Create a file by using cat command.
  
  [root@localhost ~]# cat > file1
  welcome to linux
  
  Note: to save the file use Ctrl + d
  
  2. Read a file by using cat command.
  
  [root@localhost ~]# cat file1
  welcome to linux
  
  3. Append the data to a file by using cat command.
  
  [root@localhost ~]# cat >> file1
  Thanks for visiting our channel
  
  4. Check the file the data is available are not.
  
  [root@localhost ~]# cat file1
  welcome to linux
  Thanks for visiting our channel
  

FHS (filesystem hierarchy standard) in Linux & Unix

Filesystem Hierarchy Standard :-

Here you can find some directory's

/ (slash)

In Linux  /  is treated as Top level directory.all directory's  comes under / only.

when you install linux OS in PC or Server  operating system is stored in / directory and OS will create some Default Directory's


/ , /bin, /boot, /dev, /etc, /home,  /media, /mnt, /opt,  /root, /run, /sbin, /usr, /var

They are

/bin 

/bin is called as binary. This Directory contains  all user commends.

/root

/root is called as root home directory or Admin home directory and it contains some default properties. 

/boot 

/boot  is contains boot loader files like grub,efi,....

latest version of boot loader is grub2

GRUB means GRand Unified Bootloader.
  

/dev 

/dev is device file or special files.it contains device information.

/etc 

/etc  is called as et cetera. it Contains system-wide configuration files and system databases.

/home  

it is called as user home directory and it is contains all user's information.

/media

/media directory is shows external devices information like pen-drives,cd,dvd,external hard drives in Some linux flavors 

/mnt 

/mnt stands for mount. This directory is used as a default mount point and it is a empty directory.


/opt 

/opt stands for optional.This directory contains local installed software information.

/run 

/run is contains all external device information in RHEL7

/sbin 

/sbin is called as system binary or superuser binary and it contains admin level commends like start service and stop service create & delete partitions etc..
 
/usr 

/usr stands for Unix System Resource  it contains system programs.

/var

/var stands for variable and it contains variables information.

Linux introduction & Basic Linux Commands

Linux Introduction.

[sas@localhost ~]$


here sas is normal user , localhost is a system name ,"~" this symbol indicates Home Directory of login user or admin and $ indicates normal user.

[root@localhost ~]#

Here # indicates admin user or root user.