47.5 Install Docker Engine on Ubuntu

Example 1: Show the version

Type this:

lsb_release -a

You will see:

Distributor ID: Ubuntu
Description:    Ubuntu 24.04.1 LTS
Release:        24.04
Codename:       noble

What it means: LTS means long term support, the version companies use on servers. Codename is noble.

Example 2: Read the same from a file

Type this:

grep VERSION_CODENAME /etc/os-release

You will see:

VERSION_CODENAME=noble

What it means: Scripts read this file because it exists on every Ubuntu machine.

Example 3: Check the CPU type

Type this:

dpkg --print-architecture

You will see:

amd64

What it means: amd64 means a normal Intel or AMD CPU. AWS Graviton servers print arm64. Docker supports both.

Example 4: Remove old packages

Type this:

for p in docker.io docker-doc docker-compose podman-docker containerd runc; do sudo apt-get remove -y $p; done

You will see:

Package 'docker.io' is not installed, so not removed
Package 'containerd' is not installed, so not removed

What it means: A loop runs the remove command once for each name. On a fresh server nothing is installed, so nothing is removed. That is fine.

Example 5: Check nothing is left

Type this:

dpkg -l | grep -E 'docker|containerd' || echo none

You will see:

none

What it means: dpkg -l lists installed packages. || echo none prints none when grep finds nothing.

Example 6: Refresh the package list

Type this:

sudo apt-get update

You will see:

Hit:1 http://archive.ubuntu.com/ubuntu noble InRelease
Reading package lists... Done

What it means: update downloads the latest list of packages. It does not install anything yet.

Example 7: Install the helpers

Type this:

sudo apt-get install -y ca-certificates curl

You will see:

ca-certificates is already the newest version.
curl is already the newest version.

What it means: On most images these are already present. -y answers yes automatically.

Example 8: Make the key folder

Type this:

sudo install -m 0755 -d /etc/apt/keyrings

You will see:

(no output)

What it means: install -d creates a folder; -m 0755 lets everyone read it, only root can change it. This is a safe permission.

Example 9: Check the folder

Type this:

ls -ld /etc/apt/keyrings

You will see:

drwxr-xr-x 2 root root 4096 Oct 25 09:40 /etc/apt/keyrings

What it means: The folder exists and is owned by root.

Example 10: Download Docker's key

Type this:

sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc

You will see:

(no output)

What it means: -fsSL means: fail on errors, be silent, show errors, follow redirects. -o saves to a file.

Example 11: Let apt read the key

Type this:

sudo chmod a+r /etc/apt/keyrings/docker.asc
ls -l /etc/apt/keyrings/docker.asc

You will see:

-rw-r--r-- 1 root root 3817 Oct 25 09:41 /etc/apt/keyrings/docker.asc

What it means: a+r adds read permission for all. Nobody except root can write it. Never use world-writable modes on key files.

Example 12: Look at the key's fingerprint

Type this:

gpg --show-keys /etc/apt/keyrings/docker.asc | head -2

You will see:

pub   rsa4096 2017-02-22 [SCEA]
      9DC858229FC7DD38854AE2D88D81803C0EBFCD88

What it means: This fingerprint should match the one on Docker's official docs page. If it does not, stop and check your download.

Example 13: Write the repository file

Type this:

echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu $(. /etc/os-release && echo $VERSION_CODENAME) stable" | sudo tee /etc/apt/sources.list.d/docker.list

You will see:

deb [arch=amd64 signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu noble stable

What it means: The $(...) parts fill in amd64 and noble for you. sudo tee writes the line to the file as root and prints it.

Example 14: Refresh with the new shelf

Type this:

sudo apt-get update | grep docker

You will see:

Get:5 https://download.docker.com/linux/ubuntu noble InRelease [48.8 kB]
Get:6 https://download.docker.com/linux/ubuntu noble/stable amd64 Packages [17.5 kB]

What it means: apt now reads Docker's shelf too.

Example 15: See which versions are offered

Type this:

apt-cache madison docker-ce | head -3

You will see:

docker-ce | 5:27.3.1-1~ubuntu.24.04~noble | https://download.docker.com/linux/ubuntu noble/stable amd64 Packages
docker-ce | 5:27.3.0-1~ubuntu.24.04~noble | ...

What it means: madison lists every available version. Teams at TCS often pin one exact version on all servers so they stay the same.

Example 16: Install everything

Type this:

sudo apt-get install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

You will see:

Setting up containerd.io (1.7.22-1) ...
Setting up docker-ce (5:27.3.1-1~ubuntu.24.04~noble) ...
Created symlink /etc/systemd/system/multi-user.target.wants/docker.service

What it means: The last line means Docker will start automatically every time the server boots.

Example 17: Install one exact version

Type this:

sudo apt-get install -y docker-ce=5:27.3.1-1~ubuntu.24.04~noble docker-ce-cli=5:27.3.1-1~ubuntu.24.04~noble containerd.io

You will see:

docker-ce is already the newest version (5:27.3.1-1~ubuntu.24.04~noble).

What it means: Put =version after the name to pin it. Useful when every server must match.

Example 18: Check the versions

Type this:

docker --version
docker compose version
docker buildx version

You will see:

Docker version 27.3.1, build ce12230
Docker Compose version v2.29.7
buildx v0.17.1 (docker-buildx-plugin)

What it means: All three tools are present. Compose is now a plugin, so it is docker compose with a space.

Example 19: Check status

Type this:

sudo systemctl status docker --no-pager | head -3

You will see:

● docker.service - Docker Application Container Engine
     Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled)
     Active: active (running) since Sun 2026-10-25 09:45:10 IST

What it means: "enabled" means it starts at boot. "active (running)" means it is on now.

Example 20: Enable both services

Type this:

sudo systemctl enable --now docker containerd

You will see:

Synchronizing state of docker.service with SysV service script...

What it means: --now starts and enables in one step. Safe to run even if already on.

Example 21: Run the proof

Type this:

sudo docker run --rm hello-world | head -2

You will see:

Hello from Docker!

What it means: Docker works. We used sudo because our user is not in the docker group yet. Next step fixes that.

Example 22: Add yourself to the group

Type this:

sudo usermod -aG docker $USER

You will see:

(no output)

What it means: -aG means add to this group and keep the old groups. Forgetting -a would remove your other groups.

Example 23: Load the new group

Type this:

newgrp docker
id -nG

You will see:

ubuntu adm sudo docker

What it means: newgrp starts a shell with the new group, so you do not need to log out. docker is now in your list.

Example 24: Run without sudo

Type this:

docker run --rm hello-world | head -2
docker ps

You will see:

Hello from Docker!
CONTAINER ID   IMAGE   COMMAND   STATUS   NAMES

What it means: No permission error any more. Your Ubuntu server is ready.

Example 25: Upgrade Docker

Type this:

sudo apt-get update && sudo apt-get install -y --only-upgrade docker-ce docker-ce-cli containerd.io

You will see:

docker-ce is already the newest version (5:27.3.1-1~ubuntu.24.04~noble).

What it means: --only-upgrade updates only if a newer version exists.

Example 26: Uninstall the packages

Type this:

sudo apt-get purge -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

You will see:

Removing docker-ce (5:27.3.1-1~ubuntu.24.04~noble) ...

What it means: purge removes packages and their config files.

Example 27: Remove images and containers too

Type this:

sudo rm -rf /var/lib/docker /var/lib/containerd
ls /var/lib | grep -c docker

You will see:

0

What it means: This deletes every image, container and volume. Do it only on a test server, never on a database server without a backup.