Day 7: Understanding Package Manager and Systemctl

What is a Package Manager in Linux?

In simpler words, a package manager is a tool that allows users to install, remove, upgrade, configure and manage software packages on an operating system. The package manager can be a graphical application like a software center or a command line tool like apt-get or pacman.

What is Package?

A package contains all the necessary data required for the installation and maintenance of the software package. These packages are created by someone known as a package maintainer. A package maintainer takes care of the packages. They ensure active maintenance, bug fixes if any, and the final compilation of the package.

Different Kinds of Package Managers

There are different package managers for different Linux distributions. Here I have shown some of the popular package managers:

1. Advanced Packaging Tool (APT)

   The APT package manager is used in the Debian-based Linux distribution and its derivatives. APT package manager handles the .deb format packages. It install, remove, upgrade packages, and resolve dependencies automatically. It uses the apt, apt-get command line.

2. Yellow-Dog Updater Modified (YUM)

   YUM package manager is used in the RedHat-based Linux distribution and its derivatives. It is the default common package manager in RedHat and handles the .rpm formatted packages. Yum checks the dependencies with header files and package metadata and resolves dependencies while installing or updating packages.

3. Dandified YUM (DNF)

   DNF package manager is the successor and the top of the yum package manager. It is is also used in Red Hat-based distribution. Dnf also uses the .rpm file extension. Dnf provides faster performance, Parallel downloading, a rich command line interface, and enhanced dependency resolution by using a dependency solver.

4. Pacman

   Pacman is a utility that is used in Arch Linux distribution for managing software packages. Using simple compressed files, it maintains a text-based database. The file extension for the Pacman package manager is .pkg.tar.xz. Pacman is lightweight, fast, and high-speed packaging, it provides two types of repositories and automatically upgrades the package.

TASKS

How to install Docker and Jenkins using package managers on Ubuntu and CentOS.

DOCKER INSTALLATION ON UBUNTU

1. Update Packages:

    sudo apt-get update
   

2. Install Docker:

    sudo apt install docker.io -y
   

3. Verify the installation:

    docker --version
   

   ON CENTOS

4. Set up the repository:

    sudo yum install -y yum-utils
    sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
   

5. Install Docker Engine, containerd, and Docker Compose:

    sudo yum install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
   

6. Verify the installation:

    docker --version
   

JENKINS INSTALLATION ON UBUNTU

1. Update package list:

    sudo apt-get update
   

2. Install Java (Jenkins requires Java):

    sudo apt-get install openjdk-11-jdk -y
   

3. Add the Jenkins repository key:

    curl -fsSL https://pkg.jenkins.io/debian/jenkins.io.key | sudo tee /usr/share/keyrings/jenkins-keyring.asc > /dev/null
   

4. Add the Jenkins repository:

    echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] https://pkg.jenkins.io/debian-stable binary/ | sudo tee /etc/apt/sources.list.d/jenkins.list > /dev/null
   

5. Update the package list again:

    sudo apt-get update
   

6. Install Jenkins:

    sudo apt-get install jenkins -y
   

7. Check the status:

    sudo systemctl status jenkins
   

ON CENTOS 9

1. Install java:

    sudo dnf install java-11-openjdk-devel -y
   

2. Install wget:

    sudo yum install wget
   

3. Install Jenkins:

    sudo wget -O /etc/yum.repos.d/jenkins.repo https://pkg.jenkins.io/redhat-stable/jenkins.repo
   
    sudo rpm --import https://pkg.jenkins.io/redhat-stable/jenkins.io.key
   
    sudo dnf upgrade
   
    sudo dnf install jenkins
   

4. Start Jenkins:

    sudo systemctl start jenkins
   

5. Check Status:

    sudo systemctl status jenkins
   

Systemctl and Systemd

systemd gives us the systemctl commands suite which is mostly used to enable services to start at boot time. We can also start, stop, reload, restart and check status of services with the help of systemctl .

We can do, for example, sudo systemctl enable service_name, and service_name will automatically start at boot time. We can also disable services not to start at boot time.

Tasks

1. Check Docker Service Status:

   • Check the status of the Docker service on your system (ensure you have completed the installation tasks above).

    sudo systemctl status docker

2. Manage Jenkins Service:

   • Stop the Jenkins service and post before and after screenshots.

Before stopping the jenkins service:

After stopping the jenkins service:

3. Systemctl vs. Service:

   • Differences between the systemctl and service commands.

Systemctl:- It works with systemd, the newer and more modern system and service manager. Provides detailed information about the service, including logs. Manages more than just services (e.g., system states like shutdown, reboot).

The syntax for systemctl is 'systemctl [command] [service_name]'. For example- To check the status of Docker: 'system status docker'

Service:- It works with older service managers like SysVinit and Upstart. Simpler and more traditional command structure. Simpler and more traditional command structure.

The syntax for service is 'service [service_name] [command]'. For example- To check the status of Docker: 'service docker status'

Additional Tasks

4. Automate Service Management:

   • Write a script to automate the starting and stopping of Docker and Jenkins services.

1. Make a file script.sh:

vim script.sh

2. Write a script:

#!/bin/bash

# Function to start services
start_services() {
    echo "Starting Docker and Jenkins services..."
    sudo systemctl start docker
    sudo systemctl start jenkins
    echo "Services started."
}

# Function to stop services
stop_services() {
    echo "Stopping Docker and Jenkins services..."
    sudo systemctl stop docker
    sudo systemctl stop jenkins
    echo "Services stopped."
}
# Check if the user provided an argument
if [ $# -eq 0 ]; then
    usage
fi

# Handle the input argument
case "$1" in
    start)
        start_services
        ;;
    stop)
        stop_services
        ;;
esac

3. Make the file executable:

chmod 700 script.sh

4. Run the script:

./script.sh start
OR
./script.sh stop

5. Enable and Disable Services:

   • Use systemctl to enable Docker to start on boot and disable Jenkins from starting on boot.

     Enable Docker to start on boot:

       sudo systemctl enable docker
     

     Disable Jenkins from starting on boot:

       sudo systemctl disable jenkins
     

6. Analyze Logs:

   • Use journalctl to analyze the logs of the Docker and Jenkins services.

1. Analyze Docker logs:

    sudo journalctl -u docker
   

2. Analyze Jenkins logs:

    sudo journalctl -u jenkins
   

Conclusion

Linux package managers and systemd (with systemctl) form the backbone of software and service management in modern Linux distributions. Package managers ensure that software installations are handled smoothly and consistently, managing dependencies and updates efficiently. Meanwhile, systemd and systemctl provide robust tools for controlling and managing system services, enhancing system reliability and maintainability. Understanding these tools is crucial for effective Linux system administration.

HAPPY LEARNING!