Ubuntu – Package Management

DPKG – Debian Package Manager used to install, uninstall, list and check the status of the package

It comes with .deb file.

DPKG does not honour dependecies hence we need to use APT for Ubuntu

APT stands for Advanced Packaging Tool and relies on DPKG

Use apt update command to refresh the repository-

sudo apt update

Use apt upgrade to upgrade exisitng package-

sudo apt upgrade

To install a package-

sudo apt install <package name>

To uninstall or remove package-

sudo apt remove <package name>

To search package e.g:- python-dev

sudo apt search python-dev

To list all the packages in repository-

sudo apt list

Linux Runlevels

A runlevel is a categorization number that determines what services are started and
what services are stopped

Runlevel #NameDescription
0HaltAll services are shut down and the server is stopped
1Single User ModeThe root account is automatically logged in to the server and other users cannot log in to the server
2Multiuser ModeUsers can log in to the server through CLI and network service are not started
3Extended Multiuser ModeUsers can log in to the server through CLI and network service are started
4User DefinedUser can cusomize the runlevel
5Graphical ModeUser can log in through CLI and GUI with network services started
6RebootThe server is rebooted

Check the current runlevel use following command-


To see the default target

systemctl get-default

To change the default target use following command

systemctl set-default multi-user.target

Install Docker on LINUX – Ubuntu

OS requirements

To install Docker Engine, you need the 64-bit version of one of these Ubuntu versions:

  • Ubuntu Hirsute 21.04
  • Ubuntu Groovy 20.10
  • Ubuntu Focal 20.04 (LTS)
  • Ubuntu Bionic 18.04 (LTS)

To check the OS version of Linux, use-

cat /etc/*release*

Check if you have already install docker on machine-

docker --version

Uninstall the older version of Docker if you have any, to do so-

sudo apt-get remove docker docker-engine docker.io containerd runc

Install Repository

Before the docker is installed setup the docker repository-

User Application Package Tool (APT) to install supporting packages for Docker. Use following commands-

sudo apt-get update
sudo apt-get install \
    apt-transport-https \
    ca-certificates \
    curl \
    gnupg \

Add Docker’s official GPG key:

GPG or GNU Privacy Guard is a public key cryptographic implementation and is used for allowing secure transmission of information between source and destination

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

Install Docker Engine

sudo apt-get update

sudo apt-get install docker-ce docker-ce-cli containerd.io

This installs the latest version of docker on OS.

Check the latest version of docker

docker --version

Reference documents- https://docs.docker.com/engine/install/ubuntu/

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