Fix the 'Failed to Start Docker.Service: Unit Docker.Service Not Found' Error: A Comprehensive Guide

If you are a developer working with Docker, you might have encountered the error message Failed to start docker.service: Unit docker.service not found. This issue can be quite frustrating, especially if you are not sure what is causing it or how to fix it. In this comprehensive guide, we will walk you through the process of troubleshooting and resolving this error, step-by-step.

Table of Contents

1. Prerequisites
2. Understanding the Error
3. Step-by-Step Solution
4. Check Docker Installation
5. Reinstall Docker
6. Enable and Start Docker Service
7. Check Docker Service Status
8. FAQs

Prerequisites {#prerequisites}

Before diving into the guide, make sure you have the following prerequisites:

• A Linux-based system (Ubuntu, CentOS, or another distribution)
• Basic knowledge of command-line interface and Linux system administration
• Access to an administrator or sudo user account on your system

Understanding the Error {#understanding-the-error}

The error message Failed to start docker.service: Unit docker.service not found typically occurs when you try to start the Docker service, but the system cannot find the service definition or the Docker package is not properly installed on your system. This could be due to several reasons, including:

• Docker is not installed or not installed correctly
• The Docker service is disabled or not running
• System configuration issues, such as missing files or incorrect permissions

Step-by-Step Solution {#step-by-step-solution}

Check Docker Installation {#check-docker-installation}

The first step in troubleshooting this error is to verify that Docker is installed on your system. You can do this by running the following command:

docker --version

If Docker is installed, you should see the version number in the output. If not, proceed to the next step to reinstall Docker.

Reinstall Docker {#reinstall-docker}

If Docker is not installed or not installed correctly, you need to reinstall it. The installation process varies depending on your Linux distribution. You can find the specific instructions for your distribution in the official Docker documentation.

For example, to install Docker on Ubuntu, you can follow these steps:

1. Update your package index:

sudo apt-get update

1. Install Docker dependencies:

sudo apt-get install apt-transport-https ca-certificates curl software-properties-common

1. Add Docker's official GPG key:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

1. Add the Docker repository:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

1. Update your package index again:

sudo apt-get update

1. Install Docker:

sudo apt-get install docker-ce

Enable and Start Docker Service {#enable-and-start-docker-service}

Once Docker is installed, you need to enable and start the Docker service. You can do this using the following commands:

1. Enable the Docker service:

sudo systemctl enable docker

1. Start the Docker service:

sudo systemctl start docker

Check Docker Service Status {#check-docker-service-status}

After enabling and starting the Docker service, you should check its status to ensure it is running without any issues. You can do this using the following command:

sudo systemctl status docker

If the Docker service is running properly, you should see an output similar to this:

● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2021-11-01 10:00:00 UTC; 10min ago
     Docs: https://docs.docker.com
 Main PID: 12345 (dockerd)
    Tasks: 16
   Memory: 50.0M
      CPU: 10.123s
   CGroup: /system.slice/docker.service
           └─12345 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

If you see active (running) under the Active field, the Docker service is running, and the error should be resolved.

FAQs {#faqs}

Why does the 'Failed to start docker.service: Unit docker.service not found' error occur? {#faq1}

This error occurs when the system cannot find the Docker service definition or the Docker package is not properly installed on your system.

How do I check if Docker is installed on my system? {#faq2}

You can check if Docker is installed by running the following command:

docker --version

How do I enable the Docker service? {#faq3}

You can enable the Docker service using the following command:

sudo systemctl enable docker

How do I start the Docker service? {#faq4}

You can start the Docker service using the following command:

sudo systemctl start docker

How do I check the status of the Docker service? {#faq5}

You can check the status of the Docker service using the following command:

sudo systemctl status docker

Related: How to Install Docker on Ubuntu 20.04

Related: Docker Commands Cheat Sheet