Linux

What is Linux?

Most people think of Linux as another operating system, just like Windows or Mac OS, that must be installed on a computer, rather than as a Kernel or a family of operating systems. This is an easy explanation, abstract enough to bring some sense and understanding to people.

What is a Kernel?

The kernel is the essential foundation of a computer's operating system (OS). It is the core that provides basic services for all other parts of the OS. It is the main layer between the OS and underlying computer hardware, and it helps with tasks such as process and memory management, file systems, device control and networking.

Summary

Linux is basically a Kernel. But in simpler terms, Linux is a technology.

To make it clearer, you can comparing operating systems with cars:

Windows | It is a complete car, with motorcycles, wheels, windows and steering wheel. You use this car to make all your activities, travelling, commuting to work (it is a popular car) and almost everyone that you know has a similar model. Microsoft do that car from the beginning to the end (all components), and Microsoft has an absolute control over all features and how it will looks like. Microsoft will lease that car for you through a license, and from time to time it launches some new models.
Mac OS | It is a very similar car, but free. The difference is you can only use the card if you live in a determined city, that Apple controls (Apple's devices). Living in this city can be very expensive, despite the car is free. You can do all your activities with this car in that city, but everytime you try to leave that city with the car, you will face some difficulties.

In both cases, you would be a customer of Microsoft and Apple, driving their cars.

Linux | Linux wouldn't be a complete car, but an essential component, like an engine. It can be used to create different types of cars. You don't need to pay for your Linux engine, so you are not a Linux's customer and nobody will tell you what you can do with the engine. If you transform this engine in a motorcycle, that's up to you. With the engine you receives a manual, explaining how it works and how to assemble it. The Linux engine is assemble for many companies around the world.

But now you are thinking that it's not possible to drive a engine, you need all the other components to make a car. And that where systems based on Linux are born, or distribution (distros). A very common Linux-based operating system is Ubuntu.

Linux was created by "Linus Torvalds", a Finnish developer, in 1991.

Linux Distros (Distributions Full List)

This is a list of the most relevant Linux distributions categorized by distros-based and their respective variants.

Linux Distros	Distributions Based / Variants	Description
BlackArch	Pacman-based > Arch Linux-based	A cybersecurity-focused OS based on Arch Linux. It is designed to test security and run penetration tests. It includes window managers preconfigured, but no desktop environment.
EndeavourOS	Pacman-based > Arch Linux-based	Continuation of Antergos, featuring a graphical installer capable of installing KDE Plasma (default, offline), Budgie, Cinnamon, Deepin, GNOME, i3, Xfce, LXQt, and MATE.
Garuda Linux	Pacman-based > Arch Linux-based	A distribution based on gaming.[106]
Hyperbola GNU/Linux-libre	Pacman-based > Arch Linux-based	An Arch and Debian derivative without any blobs, without systemd support and with OpenRC as its default init system. Packages are built for i686 and x64. Unlike Arch, Hyperbola uses the long-term support model like Debian.
LinHES	Pacman-based > Arch Linux-based	LinHES (Linux Home Entertainment Server) designed for use on home theater PCs (HTPCs), providing applications for recording TV and acting as a sound and video center.
Manjaro	Pacman-based > Arch Linux-based	Based on Arch Linux, using its own repositories and ships with either Xfce, Plasma, GNOME, or the CLI as the default desktop environment. Additional community-driven editions are available that use MATE, Cinnamon, Openbox, Awesome, i3, BSPWM, or Budgie as a base.
Parabola GNU/Linux-libre	Pacman-based > Arch Linux-based	An Arch derivative without any blobs, plus various added packages. Packages are also built for ARMv7 in addition to i686 and x64. MATE and text-mode distributions available.
SteamOS	Pacman-based > Arch Linux-based	Arch-based and gaming-focused distribution developed by Valve and designed for the Steam digital distribution platform and Steam Deck. Before version 3.0, was previously based on Debian.
SystemRescue	Pacman-based > Arch Linux-based	Linux System rescue toolkit. Previously based on Gentoo, it has been based on Arch Linux since version 6.0.0
Chakra Linux	Pacman-based > Other Variants	Originally derived from Arch Linux, with the latest KDE. For now uses the Pacman utility for package management. Strives to be Qt-only. Discontinued.[107]
Frugalware Linux	Pacman-based > Other Variants	A general purpose Linux distribution designed for intermediate users. Has some influences from Slackware, and uses a heavily modified version of pacman, Pacman-G2, a fork of a cvs version of the complete rewrite of Pacman-G1 by Aurelien Foret (the old monolithic Pacman-G1 is written by Judd Vinet). The packages are tar archives compressed using xz.[108]
KaOS	Pacman-based > Other Variants	An independent 64-bit only rolling-release Linux distribution inspired by Arch that features the latest KDE Plasma environment and the Qt toolkit.[109]
RPM (Red Hat Package Manager)	RPM-based	Red Hat Linux and SUSE Linux were the original major distributions that used the .rpm file format, which today is used in several package management systems. Both of these were later divided into commercial and community-supported distributions. Red Hat Linux was divided into a community-supported but Red Hat-sponsored distribution named Fedora, and a commercially supported distribution called Red Hat Enterprise Linux, whereas SUSE Linux was divided into openSUSE and SUSE Linux Enterprise.
Fedora	RPM-based	Fedora is a community supported distribution. It aims to provide the latest software while maintaining a completely Free Software system
RHEL (Red Hat Enterprise Linux)	RPM-based > Fedora-based	Red Hat Enterprise Linux is a commercial open-source Linux distribution developed by Red Hat for the commercial market.
AlmaLinux	RPM-based > Fedora-based > RHEL-based	A 100% community owned and governed alternative CentOS as a Red Hat Enterprise Linux rebuild. Governed by the AlmaLinux OS Foundation.
Asianux	RPM-based > Fedora-based > RHEL-based	A Linux distribution co-developed between Red Flag Software Co., Ltd., Miracle Linux Corp. and Haansoft, INC., focused on Chinese, Japanese and Korean support.
ClearOS	RPM-based > Fedora-based > RHEL-based	A Linux distribution designed for use in small and medium enterprises.
Fermi Linux LTS	RPM-based > Fedora-based > RHEL-based	Based on Scientific Linux.[111]
Miracle Linux	RPM-based > Fedora-based > RHEL-based	A Linux distribution developed by Cybertrust Japan Co., Ltd., aims to be compatible with Red Hat Enterprise Linux.
Oracle Linux	RPM-based > Fedora-based > RHEL-based	Supported by Oracle. Aims to be fully compatible with Red Hat Enterprise Linux.
Red Flag Linux	RPM-based > Fedora-based > RHEL-based	A Linux distribution developed in China and optimized for the Chinese market. Based on Asianux.
Rocks Cluster Distribution	RPM-based > Fedora-based > RHEL-based	A Linux distribution for building a High-Performance Computing computer cluster, with a recent release supporting Cloud computing. It is based on Red Hat Enterprise Linux but with extensions to support large multi-node heterogeneous systems for clusters (HPC), Cloud, and Data Warehousing (in development).
Rocky Linux	RPM-based > Fedora-based > RHEL-based	A Linux distribution that is currently in development by the CentOS founder, Gregory Kurtzer, aims to be compatible with Red Hat Enterprise Linux.
Scientific Linux	RPM-based > Fedora-based > RHEL-based	A discontinued Linux distribution co-developed by Fermi National Accelerator Laboratory and the European Organization for Nuclear Research (CERN), which aims to be compatible with and based on Red Hat Enterprise Linux.
Asahi Linux	RPM-based > Fedora-based > Other Variants	Port of Linux to Apple silicon-powered Macs.
Amazon Linux 2	RPM-based > Fedora-based > Other Variants	Amazon Linux 2 is available as an Amazon Machine Image (AMI) for use on Amazon Elastic Compute Cloud (Amazon EC2). It is also available as a Docker container image and as a virtual machine image for use on Kernel-based Virtual Machine (KVM), Oracle VM VirtualBox, Microsoft Hyper-V, and VMware ESXi
Berry Linux	RPM-based > Fedora-based > Other Variants	A medium-sized Fedora-based distribution that provides support in Japanese and English.
BLAG Linux and GNU	RPM-based > Fedora-based > Other Variants	A completely free software distribution.
CentOS Stream	RPM-based > Fedora-based > Other Variants	Community-supported Linux distribution originally based on RHEL and well suited for servers. Now sponsored by Red Hat.[112]
EnGarde Secure Linux	RPM-based > Fedora-based > Other Variants	Server-only Linux distribution designed to be secure.[113]
Fuduntu	RPM-based > Fedora-based > Other Variants	Designed to fit in somewhere between Fedora and Ubuntu.
Hanthana	RPM-based > Fedora-based > Other Variants	Designed to cater the needs of Sri Lankan computer users who are unable to access Internet frequently, with many most-wanted applications built in.
Korora	RPM-based > Fedora-based > Other Variants	Initially aimed at easy installation of a Gentoo system by using install scripts instead of manual configuration. Now based on Fedora.
Linpus Linux	RPM-based > Fedora-based > Other Variants	Focused on the Chinese market, along with Linpus Lite focused on the netbook market.
Linux XP	RPM-based > Fedora-based > Other Variants	Fedora-based shareware distribution designed to imitate the Windows environment using GNOME.
MeeGo	RPM-based > Fedora-based > Other Variants	Built by Intel and Nokia, intended for mobile phones (mainly Nokia N9) and tablets. It is based on Moblin together with Maemo.
Moblin	RPM-based > Fedora-based > Other Variants	Built around the Intel Atom processor; supplanted by Meego when Intel and (temporarily) Nokia combined activities
Network Security Toolkit	RPM-based > Fedora-based > Other Variants	A live CD/DVD with security and networking tools to perform routine security and networking diagnostic and monitoring tasks.
Qubes OS	RPM-based > Fedora-based > Other Variants	Focused on security for desktop users. Based on an "ancient" Fedora release which is said to be upgraded under YUM.

Debian Operating System

Debian had a long history. Founded in 1993 by Ian Murdock, it is one of the early Linux distributions and one that is the basis for many other Linux distributions.

Debian releases are named for characters from the Toy Story movies.

Debian 1.1 Buzz (June 17th, 1996): Named for the Buzz Lightyear.
Debian 1.2 Rex (December 12th, 1996): Named for the plastic dinosaur in the Toy Story movies.
Debian 1.3 Bo (June 5th, 1997): Named for Bo Peep, the shepherdess.
Debian 2.0 Hamm (July 24th, 1998): Named for the piggy-bank in the Toy Story movies.
Debian 2.1 Slink (March 9th, 1999): Named for the slinky-dog in the movie.
Debian 2.2 Potato (15 August 2000): Named for "Mr Potato Head" in the Toy Story movies.
Debian 3.0 Woody (19 July 2002): Named for the main character the Toy Story movies: "Woody" the cowboy.
Debian 3.1 Sarge (6 June 2005): Named for the sergeant of the Green Plastic Army Men.
Debian 4.0 Etch (8 April 2007): Named for the sketch toy in the movie.
Debian 5.0 Lenny (February 2009): Named for the wind up binoculars in the Toy Story movies.
Debian 6.0 Squeeze (February 2011): Named for the green three-eyed aliens.
Debian 7.0 Wheezy (May 2013): Named for the rubber toy penguin with a red bow tie.
Debian 8 Jessie (April 2015): Named for the cow girl doll who first appeared in Toy Story 2.
Debian 9 Stretch (June 2017): Named for the toy rubber octopus with suckers on her eight long arms that appeared in Toy Story 3.
Debian 10 Buster (July 2019): Named for Andy's pet dog, received as Christmas present in the end of Toy Story.
Debian 11 Bullseye (August 14th, 2021): Named for Woody's wooden toyhorse that appeared in Toy Story 2.

User Interface (UI) | CLI vs GUI

Usually there are two different interfaces available in all operating systems. These interfaces are Command Line Interface (CLI) and Graphical User Interface (GUI).

What are the different types of UIs (User Interfaces)?

CLI (Command-Line Interface) | A command-line interface is a means of interacting with a computer program by inputting lines of text called command-lines. Command-line interfaces emerged in the mid-1960s, on computer terminals, as an interactive and more user-friendly alternative to the non-interactive interface available with punched cards.
GUI (Graphical User Interface) | A graphical user interface is a form of user interface that allows users to interact with electronic devices through graphical icons and visual indicators such as secondary notation. In many applications, GUIs are used instead of text-based UIs, which are based on typed command labels or text navigation.

Linux GUI | Graphical User Interface

Linux provides variety of GUI known as desktop environment. Each desktop environment has peculiar features. The most popular and widely used desktop environments available on Linux are:

GNOME | GNOME is bundled as the default desktop environment for many distributions, including RHEL, Fedora, CentOS, SUSE Linux Enterprise, and Debian. GNOME has menu-based navigation
KDE | KDE is another popular desktop environment, KDE is often used in SUSE and openSUSE
XFCE | XFCE is a free and open-source desktop environment for Linux and other Unix-like operating systems. Xfce aims to be fast and lightweight while still being visually appealing and easy to use. It embodies the traditional Unix philosophy of modularity and re-usability
LXDE | LXDE (Lightweight X11 Desktop Environment) is a free, open-source desktop environment for Linux that is designed to be fast, energy-efficient, and lightweight. It's a good choice for older or resource-constrained computers, such as netbooks, mobile devices, or cloud computers
Unity | In Unity, the graphical user interface (GUI) is a subset of the user interface (UI) that includes graphical representations like images, animations, and icons

SSH (Secure Shell) | Remote Access

Secure Shell (SSH) is a network protocol that allows users to securely connect to and access computers, routers, and servers over an unsecured network. SSH is often used for remote logins, file transfers, and managing applications.

Key Features

Encryption: SSH encrypts communication between computers, making it suitable for use on insecure networks
Remote access: SSH allows users to remotely log in to and perform operations on other computers
File transfer: SSH enables users to securely transfer files between computers
Tunneling: SSH also enables tunneling
Automated access: SSH tools can be used by non-human entities to access other devices with little to no human intervention

SSH Design: The first version of SSH designed in 1995 by Tatu Ylönen, a researcher at Helsinki University of Technology in Finland.

How to access Linux terminal remotely through Windows

It is possible to access the Linux terminal remotely using Windows PowerShell through SSH (Secure Shell).

Installing SSH on Linux

For non-root users, use the command "sudo" to perform administrative tasks
Update the list of available packages and their versions stored | Command: apt update
Install SSH | Command: apt install openssh-server

Accessing SSH

On Windows, open "Powershell"
Establish connection | Command: SSH <username>@<linux ip>
- Example: SSH johnsmith@10.10.1.217
When connection question pops up, choose "Yes"
Insert your "Password"
The Linux Terminal will be connected

Accessing SSH using "Root" User

On Linux machine, open the Terminal
For non-root users, use the command "sudo" to perform administrative tasks
(Optional) If you've never used "root" user before, change password | Command: sudo passwd root
Inform your password to elevate your "sudo" rights, than inform the "root" password, and confirm it
Edit the SSH config to "Permit Root Login" | Command: nano /etc/ssh/sshd_config
Find the line "#PermitRootLogin prohibit-password" and change to "PermitRootLogin yes"
Press "Ctrl+X", yes to save it
Restart the SSH service
- 1 Option | Restart only the SSH service | Command: systemctl restart ssh
- 2 Option | Restart the Linux machine | Command: shutdown -r now
Try to access again with "root" user (see all steps above) | Command: ssh root@<linux ip>

Installing Packages

How to install packages on Ubuntu with one command line.

Preparing to install the packages

For non-root users, use the command "sudo" to perform administrative tasks
It is recommended run the update command (if your system is not updated) | Command: apt update
Than, check if you already have the package | Command: <package> --version

Installing the desired packages

Netstat | Command: apt install net-tools
- Netstat derived from the words network and statistics and it is a command-line utility used by system administrators for analyzing network statistics. It displays a whole manner of statistics such as open ports and corresponding addresses on the host system, routing table, and masquerade connections
NMap | Command: apt install nmap
- Nmap is a powerful network discovery and security auditing utility that is free, open-source, and easy to install. Nmap scans for vulnerabilities on your network, performs inventory checks, and monitors host or service uptime, alongside many other useful features.
Snap | Command: apt install snapd
- Snap is a software packaging and deployment system developed by Canonical for operating systems that use the Linux kernel and the systemd init system
Curl | Command: apt install curl
- Curl (Client URL) is a command-line tool used for transferring data with various protocols, including HTTP, HTTPS, FTP, and many more. Ubuntu, being one of the most popular Linux distributions, often has curl available in its software repositories. This allows users to easily install and update curl using Ubuntu’s package management tools like apt
Crontab | Command: apt install cron
- The cron command-line utility is a job scheduler on Unix-like operating systems. Users who set up and maintain software environments use cron to schedule jobs, also known as cron jobs, to run periodically at fixed times, dates, or intervals.

Hostname

How to check and manage hostname

For non-root users, use the command "sudo" to perform administrative tasks
Check your current Hostname | Command: hostname
Check additional Hostname information | Command: hostnamectl
Change the Hostname | Command: hostnamectl set-hostname <New-Hostname>
- Example: hostnamectl set-hostname ubuntu

Linux | Timezone

How to check and manage timezone

For non-root users, use the command "sudo" to perform administrative tasks
Check your current Timezone | Command: timedatectl
Verify the list of all timezones | Command: timedatectl list-timezones
Or you can find the right timezone per city | Command: timedatectl list-timezones | grep <city>
- Example: timedatectl list-timezones | grep London
Change the Timezone | Command: timedatectl set-timezone <timezone>
- Example: timedatectl set-timezone Europe/London
Check your new Timezone | Command: timedatectl

Linux | Mounting an SMB Drive

How to Mount an SMB Drive on Ubuntu

Mount an SMB Password-Protected Share Drive

Open your Linux Terminal
For non-root users, use the command 'sudo' to perform administrative tasks
Install CIFS | Command: apt install cifs-utils
Create the Mount Directory | Command: mkdir <local-directory>
- Example: mkdir /mnt/smb-media
(Optional) Check details about file systems | Command: stat <local-directory>
- Example: stat /mnt/smb-media
- File System Info | Access: (0777/drwxrwxrwx) UID: (0/root) GID: (0/root)
- Changing Directory Permission | If you need change the directory permission | Check it here
Mount the SMB Drive | Command: mount -t cifs -o username=<user>,password=<password>,uid=0,gid=0,rw,nounix,iocharset=utf8,file_mode=0777,dir_mode=0777 //<smb-ip-address>/<sharedrive-name> <local-directory>
- Example: mount -t cifs -o username=JohnSmith,password=Secret123,uid=0,gid=0,rw,nounix,iocharset=utf8,file_mode=0777,dir_mode=0777 //192.168.0.115/storage /mnt/smb-media
- (Optional) If you want to mount a specific directory inside the SMB drive | //<smb-ip-address>/<sharedrive-name>/<directory> | Example: //192.168.115/storage/media
Verify that SMB is mounted correctly | Command: ls <local-directory>
- Example: ls /mnt/smb-media

Auto-mount on boot an SMB Password-Protected Share Drive Permanently

Open your Linux Terminal
For non-root users, use the command 'sudo' to perform administrative tasks
Install CIFS | Command: apt install cifs-utils
Create the Mount Directory | Command: mkdir <local-directory>
- Example: mkdir /mnt/smb-media
Edit the 'fstab' file | Command: nano /etc/fstab
Add this line | //<smb-ip-address>/<sharedrive-name> <local-directory> cifs username=<user>,password=<password> 0 0
- Example: //192.168.0.115/storage /mnt/smb-media cifs username=JohnSmith,password=Secret123 0 0
- (Optional) If you want to mount a specific directory inside the SMB drive | //<smb-ip-address>/<sharedrive-name>/<directory> | Example: //192.168.115/storage/media
Reload the new 'fstab' version | Command: systemctl daemon-reload
Mount the SMB Drive | Command: mount <local-directory>
- Example: mount /mnt/smb-media

Verify that SMB is mounted correctly | Command: ls <local-directory>
- Example: ls /mnt/smb-media

Unmount the SMB Drive

1 Option | Unmount the drive
- (Optional) If you are inside the drive, leave the directory or it will be currently busy | Command: cd
- Unmount the Drive| Command: umount -i <local-drive>
  - Example: umount -i /mnt/smb-media

2 Option | Unmount the permanent drive
- Edit the 'fstab' file| Command: nano /etc/fstab
- Remove the previous added line | //<smb-ip-address>/<sharedrive-name> <local-directory> cifs username=<user>,password=<password> 0 0
- Reload the new 'fstab' version | Command: systemctl daemon-reload
- (Optional) If you are inside the drive, leave the directory or it will be currently busy | Command: cd
- Unmount the Drive| Command: umount -i <local-drive>
  - Example: umount -i /mnt/smb-media
3 Option | Unmount the drive if the target is busy or currently in use (be careful) | Laze Unmount
- (Optional) Verify the processes | Command: lsof | grep <local-drive>
  - Example: lsof | grep /mnt/smb-media
- Leave the directory | Command: cd
- Unmount the Drive (laze unmount)| Command: umount -l <local-drive>
  - Example: umount -l /mnt/smb-media

Linux | Change Mode (chmod) | Access Permission

Purpose

The chmod, or change mode, command allows an administrator to set or modify a file’s permissions. Every UNIX/Linux file has an owner user and an owner group attached to it, and every file has permissions associated with it.

The permissions are as follows: Read, Write, or Execute.

Application

UNIX/Linux systems have many users. In this context, a user may refer to an individual or a system operation. UNIX/Linux identifies each user with a UID, and users may be organized into groups.

Syntax

Chmod Syntax for Files| Command: chmod <mode/access-code> <file>
- Example: chmod 720 readme.txt

Chmod Syntax for Directories| Command: chmod <mode/access-code> <directory>
- Example: chmod 777 /mnt/sharedfolder

Each number in the mode parameter represents the permissions for a user or group of users:

The first number represents the file’s owner
The second number represents the file’s group
The third number represents everyone else

The Change Mode (chmod) Parameters Reference Table below shows the eight numbers that can be used within the chmod parameter.

The RWX specifies Read, Write, and Execute access, offering a binary value for each operation.

1 = "Yes"
0 = "No"

If RWX reads 110, then that permission may Read and Write, but not Execute.

Parameters Reference

Number 0 | None | RWX 000

Number 1 | Execute Only | RWX 001

Number 2 | Write Only | RWX 010

Number 3 | Write and Execute | RWX 011

Number 4 | Read Only | RWX 100

Number 5 | Read and Execute | RWX 101

Number 6 | Read and Write | RWX 110

Number 7 | Read, Write, and Execute | RWX 111

Example 1

Access Code = 720
- 7 = File’s owner may Read, Write and Execute the file
- 2 = File’s group may only Write the file
- 0 = All others cannot access the file

Example 2

Access Code = 600
- 6 = File’s owner may Read and Write the file
- 0 = File’s group cannot access the file
- 0 = All others cannot access the file

Linux | File Hierarchy Structure

Linux file hierarchy structure describes the directory structure and it's contents in Unix and Unix-like Operating systems. It is maintained by Linux Foundation.

/bin
- /bin | This directory contains executable programs which are needed in single user mode and to bring the system up or repair it
- /usr/X11R6/bin | Binaries which belong to the X-Window system; often, there is a symbolic link from the more traditional /usr/bin/X11 to here.
- /usr/bin | This is the primary directory for executable programs. Most programs executed by normal users which are not needed for booting or for repairing the system and which are not installed locally should be
- /usr/local/bin | Binaries for programs local to the site. It contains binaries of the third-party apps we install. Any local executable that didn't come with the Linux install may get it's place here
/boot
/dev
/etc
/lib
/media
/mnt
/opt
/home
/var
/usr
/tmp
/sys
/proc
/root
/sbin | It contains the binaries for root users

/etc/ssl/certs/

/etc/ssh/sshd_config

/etc/passwd

Linux | SAMBA (SMB)

Samba is an open-source software package that allows users to share files and print services across a network, including between Linux and Windows systems. It's a common way to network Ubuntu and Windows computers.

Samba uses the Server Message Block (SMB) and Common Internet File System (CIFS) protocols, making it available to clients running Linux, macOS, and Windows. It's a useful service for organizations that support multiple operating systems, and can also be useful on networks that are homogeneous.

Here are some things Samba can do:

File sharing: Samba allows users to share files, directories, and print services across a network
Access permissions: Samba allows users to grant read, write, and anonymous access permissions on a shared directory
Authentication and authorization: Samba supports authentication and authorization
Name resolution: Samba supports name resolution, such as DNS
Service announcements: Samba supports service announcements between Linux/Unix servers and Windows clients

Install and Configure Samba on Ubuntu

Open your Linux Terminal
For non-root users, use the command "sudo" to perform administrative tasks
Install Samba | Command: apt install samba
(Optional) Check the installation | Command: whereis samba
- Output Example: samba: /usr/sbin/samba /usr/lib/samba /etc/samba /usr/share/samba /usr/share/man/man7/samba.7.gz /usr/share/man/man8/samba.8.gz
(Optional) Create a directory to share | Command: mkdir /home/public
Configuring Samba File, open the CONF file | Command: nano /etc/samba/smb.conf
- Copy and paste the lines below in the bottom of the file and save it:
  - Lines:

[share]
comment = Ubuntu File Server Share
path = /home/public
browsable = yes
guest ok = yes
read only = no
create mask = 0755

Restart the service | Command: service smbd restart
(Optional) Maybe you need to adjust your firewall | Command: ufw allow samba

* Warning: Your directory maybe not showing in the Windows Network, but it is there, and you can map it as network drive

Linux | Certificates

How to add a Certificate on Ubuntu

Issue your Certificate
Open your Linux Terminal
For non-root users, use the command "sudo" to perform administrative tasks
(Optional) If your system id not updated | Update Ubuntu | Command: apt update
(Optional) If you don't have the CA-Certificate | Command: apt install ca-certificates -y
1 Option | If you already have your Certificate file in the system
- Go to certificate directory | Command: cd <directory-of-certificate>
- Copy the certificate to right directory | Command: cp local-ca.crt /usr/local/share/ca-certificates
2 Option | Create the certificate ".crt" file direct in the directory
- Go to Certificate directory | Command: cd /usr/local/share/ca-certificates
- Create the file ".crt" | Command: nano <FileName>.crt
  - Example: nano myCert.crt
- Copy and Past you Certificate key to the file, exit "Ctrl+X" and Save it
Update the Certificates | Command: update-ca-certificates
The CA trust store (as generated by update-ca-certificates) will be available, as a single file (PEM bundle), at /etc/ssl/certs/ca-certificates.crt
You can check the file | Command: nano /etc/ssl/certs/ca-certificates.crt

Linux | Unattended Upgrades

Check the Debian Unattended Upgrades page: https://wiki.debian.org/UnattendedUpgrades

Install Unattended Upgrades on Ubuntu

Open your Linux Terminal
For non-root users, use the command "sudo" to perform administrative tasks
Install Unattended-Upgrades package | Command: apt-get install unattended-upgrades apt-listchanges

Configuring Unattended Upgrades

Copy file | Command: cp /etc/apt/apt.conf.d/50unattended-upgrades /etc/apt/apt.conf.d/52unattended-upgrades-local
Configure the unattended upgrades | Command: nano /etc/apt/apt.conf.d/52unattended-upgrades-local
- This '50' file will be overwritten by '52': /etc/apt/apt.conf.d/50unattended-upgrades
Configure '20auto-upgrades' | Command: dpkg-reconfigure unattended-upgrades
- Confirm with 'yes'
- This file is modified (you can also configure directly) | File: /etc/apt/apt.conf.d/20auto-upgrades
Configure 'apt-listchanges' | Command: nano /etc/apt/listchanges.conf

Changing Schedules

Update Schedule | Command: systemctl edit apt-daily.timer
- Restart Schedule | Command: systemctl restart apt-daily.timer
- (Optional) Checking Status | Command: systemctl status apt-daily.timer
- Original schedule file | File: /lib/systemd/system/apt-daily.timer
  - Recommended to not change the original, but if you do, reload it | Command: systemctl daemon-reload
- Gets overridden by | File: /etc/systemd/system/apt-daily.timer.d/override.conf
Upgrade Schedule | Command: systemctl edit apt-daily-upgrade.timer
- Restart Schedule | Command: systemctl restart apt-daily-upgrade.timer
- (Optional) Checking Status | Command: systemctl status apt-daily-upgrade.timer
- Original schedule file | File: /lib/systemd/system/apt-daily-upgrade.timer
  - Recommended to not change the original, but if you do, reload it | Command: systemctl daemon-reload
- Gets overridden by| File: /etc/systemd/system/apt-daily-upgrade.timer.d/override.conf

Verifying Unattended Upgrades

(Optional) Manual Run | Command: unattended-upgrade -d
(Optional) Check Unattended Upgrades Log | Command: nano /var/log/unattended-upgrades/unattended-upgrades.log

Warnings

Email: To receive emails, you need to set up email first (using postfix for example) and then set up unattended updates
Schedule: You only check the agenda correctly the next day, after the calendar is reset correctly

Config Files

Example of how to override the download time via 'apt-daily.timer'

[Unit]

Description=Daily apt download activities

[Timer]

OnCalendar=

OnCalendar=*-*-* 6,18:00

RandomizedDelaySec=12h

Persistent=true

[Install]

WantedBy=timers.target

Example of how to override the download time via 'apt-daily-upgrade.timer'

[Unit]

Description=Daily apt upgrade and clean activities
After=apt-daily.timer

[Timer]

OnCalendar=

OnCalendar=*-*-* 06:00

RandomizedDelaySec=2h

Persistent=true

[Install]

WantedBy=timers.target

Example of 'listchanges.conf'

[apt]
frontend=pager
which=both
email_address=root
email_format=text
confirm=false
headers=false
reverse=false
save_seen=/var/lib/apt/listchanges.db

Bash Scripting

How to Create and Execute Bash scripts

Script naming conventions

By naming convention, bash scripts end with ".sh". However, bash scripts can run perfectly fine without the "sh" extension.

Adding the Shebang

Bash scripts start with a "shebang". Shebang is a combination of "bash #" and "bang !" followed by the bash shell path. This is the first line of the script. Shebang tells the shell to execute it via bash shell. Shebang is simply an absolute path to the bash interpreter.

Bash Shell Path | Command: which bash

Examples of the shebang statement:

#! /bin/bash
#! /user/bin/bash

Creating your Bash Script

For non-root users, use the command "sudo" to perform administrative tasks
Creating a directory to your script | Command: mkdir <directory>
- Example: mkdir /home/script
Creating the file name with "touch" | Command: touch <filename>
- Example: touch /home/script/update.sh
Assign execution rights to your user, to make the script executable | Command: chmod u+x <filename>
- Example: chmod u+x /home/script/update.sh
- "chmod" modifies the ownership of a file for the current user "u"
- "+x" adds the execution rights to the current user. This means that the user who is the owner can now run the script
- "update.sh" is the file we wish to run
Open with editor "nano" to create your script | Command: nano <filename>
- Example: nano /home/script/update.sh
Write your Script | Check the example below to update your Ubuntu
When you finish it, press Ctrl+X and Save
To run your script | Command: bash <filename>
- Example: bash /home/script/update.sh
- Other example: sh /home/script/update.sh

Example to run the update

---

#! /bin/bash

# Update and Upgrade

apt-get update; apt-get dist-upgrade -y

# Remove and Clean

apt-get autoremove; apt-get autoclean

#Write a Log

echo "Update Run: `date`" >> /home/script/update.log

# End

exit

---

Executing Bash Scripts on Multiple Remote Servers

How to access a remote server bypassing the password prompt

You can use a RSA Keypair to bypass the password request.

Open your Linux Terminal on Local Server
For non-root users, use the command "sudo" to perform administrative tasks
Generating a RSA Keypair | Command: ssh-keygen
- Enter file in which to save the key: Blank
- Passphrase: Blank
- Confirm Passphrase: Blank
Two files will be created
- Example: "id_rsa" ans "id_rsa.pub"
- You can see the files in the ssh directory | Command: cd ~/.ssh
Copy the keypair to the Remote Server | Command: ssh-copy-id <userid>@<hostname>
- Example: ssh-copy-id root@ubuntu.home.arpa
- You can see the rsa keypair copied | Command: cat ~/.ssh/authorized_keys
Now you can log in without a password | Command: ssh <userid>@<hostname>
- Example: ssh root@ubuntu.home.arpa

How to run a local script on a remote server

You can use the options below to run a local script on a remote server without having the script on your remote server.

Option 1 | Command: ssh user@remote_server 'bash -s' < localfile
Option 2 | Command: ssh user@remote_server "$(< localfile)"

Option 3 | Command: cat localfile | ssh user@remote_server

How to run a local script on multiple remote servers

You can create a script to run a script on multiple remote servers.

Username = This is the username of your remote server

Hosts = This is your remote servers

Script = This is your command to run your script (see options above)

Example:

---

#! /bin/bash
USERNAME="root"
HOSTS="ubuntu1.home.arpa ubunt2.home.arpa"
SCRIPT="bash -s < /home/update.sh"
for HOSTNAME in ${HOSTS}
do
ssh -l ${USERNAME} ${HOSTNAME} "${SCRIPT}"
done

---

Linux | Commands

ssh - Secure Shell command in Linux
sudo - Command to escalate privileges in Linux
ls - The most frequently used command in Linux to list directories
pwd - Print working directory command in Linux
cd - Linux command to navigate through directories
mkdir - Command used to create directories in Linux
mv - Move or rename files in Linux
cp - Similar usage as mv but for copying files in Linux
rm - Delete files or directories
touch - Create blank/empty files
ln - Create symbolic links (shortcuts) to other files
cat - Display file contents on the terminal
clear - Clear the terminal display
echo - Print any text that follows the command
less - Linux command to display paged outputs in the terminal
man - Access manual pages for all Linux commands
uname - Linux command to get basic information about the OS
whoami - Get the active username
tar - Command to extract and compress files in Linux
grep - Search for a string within an output
head - Return the specified number of lines from the top
tail - Return the specified number of lines from the bottom
diff - Find the difference between two files
cmp - Allows you to check if two files are identical
comm - Combines the functionality of diff and cmp
sort - Linux command to sort the content of a file while outputting
export - Export environment variables in Linux
zip - Zip files in Linux
unzip - Unzip files in Linux
service - Linux command to start and stop services
ps - Display active processes
kill and killall - Kill active processes by process ID or name
df - Display disk filesystem information
mount - Mount file systems in Linux
chmod - Command to change file permissions
chown - Command for granting ownership of files or folders
ifconfig - Display network interfaces and IP addresses
traceroute - Trace all the network hops to reach the destination
wget - Direct download files from the internet
ufw - Firewall command
iptables - Base firewall for all other firewall utilities to interface with
apt, pacman, yum, rpm - Package managers depending on the distro
cal - View a command-line calendar
alias - Create custom shortcuts for your regularly used commands
dd - Majorly used for creating bootable USB sticks
whereis - Locate the binary, source, and manual pages for a command
whatis - Find what a command is used for
top - View active processes live with their system usage
useradd and usermod - Add new user or change existing users data
passwd - Create or update passwords for existing users

Command	Description	Type	Example	Comments
netstat -v	Check the version of netstat installed	Netstat		If you don't have the Netstat, you just need install it
pacman -S net-tools	Install netstat	Netstat	sudo pacman -S net-tools	Netstat is command-line utility to analyze network and statistics
yum install net-tools	Install netstat	Netstat	sudo yum install net-tools	Netstat is command-line utility to analyze network and statistics
zypper install net-tools	Install netstat	Netstat	sudo zypper install net-tools	Netstat is command-line utility to analyze network and statistics
curl <url>	Download data from url	Network
curl <url> -o <filename>	Download data from url to local file	Network
ifconfig	List network configuration	Network
netstat -an	List all ports opened	Network
ping	Ping network connectivity	Network	ping 8.8.8.8
apt install <package-name>[=<version>]	Install packages	Packages
apt-get --purge remove <package-name>	Uninstall packages	Packages
apt-get update	Update the apt package index	Packages	sudo apt-get update

References: Wikipedia (www.wikipedia.org); Google (www.google.com); Oracle (www.oracle.com); Raspberry PI (www.raspberrypi.org); Microsoft (www.microsoft.com); CloudFlare (www.cloudflare.com)