Understanding Package Managers and "systemctl" in Linux

Package Manager:

A package manager is a software tool that automates the process of installing, updating, configuring, and removing software packages on a Linux distribution. It simplifies the software management process and handles dependencies, which are other software packages required for a particular application to work correctly.

Common package managers in various Linux distributions are:

APT (Advanced Package Tool): Used in Debian and Debian-based distributions like Ubuntu.
DNF (Dandified YUM): Used in Fedora and Red Hat Enterprise Linux (RHEL) 8 and later versions.
YUM (Yellowdog Updater Modified): Used in RHEL 7 and earlier versions.
Pacman: Used in Arch Linux and Arch-based distributions.

With a package manager, you can install new software packages, update existing ones to the latest versions, remove unnecessary packages, and search for available packages in the distribution's software repositories.

Let's explore some of the most commonly used package managers along with examples:

APT (Advanced Package Tool) - Debian/Ubuntu:
- Install a package:
```
  sudo apt-get install package_name
```
- Update package information (repository metadata):
```
  sudo apt-get update
```
- Upgrade all installed packages:
```
  sudo apt-get upgrade
```
- Remove a package:
```
  sudo apt-get remove package_name
```
DNF (Dandified YUM) - Fedora/RHEL 8 and later:
- Install a package:
```
  sudo dnf install package_name\
```
- Update all installed packages:
```
  sudo dnf update
```
- Remove a package:
```
  sudo dnf remove package_name
```
YUM (Yellowdog Updater Modified) - RHEL 7 and earlier:
- Install a package:
```
  sudo yum install package_name
```
- Update all installed packages:
```
  sudo yum update
```
- Remove a package:
```
  sudo yum remove package_name
```

Pacman - Arch Linux:

Install a package:
```
  sudo pacman -S package_name
```
Update all installed packages:
```
  sudo pacman -Syu
```
Remove a package:
```
  sudo pacman -R package_name
```

These package managers provide more than just basic installation and removal capabilities. They handle dependencies, automatically resolving and installing any required packages for the software you want to use. Additionally, you can search for packages, list installed packages, and perform many other package-related tasks with these tools.

You have to install Docker and Jenkins in your system from your terminal using package managers

To install Docker and Jenkins on Ubuntu, you can use the apt-get package manager. Here are the steps:

Install Docker on Ubuntu:

ubuntu@ip-172-31-92-36:~$ sudo apt-get update -y
ubuntu@ip-172-31-92-36:~$ sudo apt-get install docker.io

Check if the docker service is up and running:

ubuntu@ip-172-31-92-36:~$ sudo service docker status
● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2023-07-27 17:06:23 UTC; 15s ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 16758 (dockerd)
      Tasks: 7
     Memory: 28.8M
        CPU: 262ms
     CGroup: /system.slice/docker.service
             └─16758 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

Enable the service to start when the system reboots up:

ubuntu@ip-172-31-92-36:~$ sudo systemctl enable docker

Add your user to the "docker" group to avoid using "sudo" with Docker commands:

ubuntu@ip-172-31-92-36:~$ sudo usermod -aG docker ubuntu
ubuntu@ip-172-31-92-36:~$ cat /etc/group | grep -i ubuntu
ubuntu:x:1000:
docker:x:122:ubuntu

systemctl and systemd:

Systemctl and systemd are essential components in modern Linux systems that play a crucial role in managing services and processes. Let's explore each of them:

systemd is a system and service manager for Linux operating systems. It is designed to replace the traditional SysV init system and brings several advantages, including faster boot times, parallel startup of services, and better management of system resources.
systemctl is a command-line tool that interacts with the systemd service manager. It allows users to control and manage services, view their status, enable or disable them at boot, and more.

Common systemctl Commands:

systemctl start service_name: Start a service.
systemctl stop service_name: Stop a service.
systemctl restart service_name: Restart a service.
systemctl enable service_name: Enable a service to start automatically at boot.
systemctl disable service_name: Disable a service from starting automatically at boot.
systemctl status service_name: View the status of a service.

service:
- service is a legacy command that works with the older SysV init system, which was used by many Linux distributions before the widespread adoption of systemd.
- While service can still be found on many systems, it is essentially a compatibility command for managing SysV-style init scripts.
- service is simpler in functionality compared to systemctl and lacks some of the more advanced features provided by systemd

Understanding Package Managers and "systemctl" in Linux

Table of contents

Package Manager:

Common package managers in various Linux distributions are:

You have to install Docker and Jenkins in your system from your terminal using package managers

systemctl and systemd: