Introduction

Knowing the exact Ubuntu version inside a Docker container matters for package compatibility, security patching, and debugging. Docker images are often tagged with version labels like ubuntu:22.04, but the actual OS version inside the container can differ from the tag if the image was built from a custom base. There are several commands to check the version — from inside a running container, from outside using docker exec, or by inspecting the image without running it.

Method 1: cat /etc/os-release

The most reliable method. This file exists on all modern Ubuntu images and contains structured version data:

1# From inside the container
2cat /etc/os-release
3
4# From outside (running container)
5docker exec my-container cat /etc/os-release

Output:

1PRETTY_NAME="Ubuntu 22.04.3 LTS"
2NAME="Ubuntu"
3VERSION_ID="22.04"
4VERSION="22.04.3 LTS (Jammy Jellyfish)"
5VERSION_CODENAME=jammy
6ID=ubuntu
7ID_LIKE=debian
8HOME_URL="https://www.ubuntu.com/"
9SUPPORT_URL="https://help.ubuntu.com/"
10BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
11PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
12UBUNTU_CODENAME=jammy

The key fields are VERSION_ID (e.g., 22.04) and VERSION_CODENAME (e.g., jammy).

Method 2: lsb_release -a

The lsb_release command gives a clean summary, but it is not installed in minimal Docker images:

docker exec my-container lsb_release -a

Output:

1Distributor ID: Ubuntu
2Description:    Ubuntu 22.04.3 LTS
3Release:        22.04
4Codename:       jammy

If the command is not found, install it:

docker exec my-container bash -c "apt-get update && apt-get install -y lsb-release && lsb_release -a"

For minimal images, cat /etc/os-release is preferred since it requires no extra packages.

Method 3: cat /etc/lsb-release

A simpler file that exists on most Ubuntu images:

docker exec my-container cat /etc/lsb-release

Output:

1DISTRIB_ID=Ubuntu
2DISTRIB_RELEASE=22.04
3DISTRIB_CODENAME=jammy
4DISTRIB_DESCRIPTION="Ubuntu 22.04.3 LTS"

Method 4: /etc/issue

A short one-liner that shows the version:

docker exec my-container cat /etc/issue

Output:

Ubuntu 22.04.3 LTS \n \l

The \n and \l are escape codes for hostname and terminal line — they appear literally in Docker since there is no login session.

Method 5: Without Running the Container

You can inspect the image metadata or run a throwaway container:

1# Run a temporary container just to check the version
2docker run --rm ubuntu:latest cat /etc/os-release
3
4# Inspect image labels (if the image was built with version labels)
5docker inspect ubuntu:22.04 | grep -i version
6
7# Check the image tag you pulled
8docker images ubuntu

REPOSITORY   TAG       IMAGE ID       CREATED       SIZE
ubuntu       22.04     6b7dfa7e8fdb   2 weeks ago   77.8MB
ubuntu       latest    6b7dfa7e8fdb   2 weeks ago   77.8MB

Note that ubuntu:latest may point to the same image as a specific version tag.

Method 6: From a Dockerfile

During a build, you can verify the base image version:

1FROM ubuntu:22.04
2
3# Print version during build (appears in build output)
4RUN cat /etc/os-release
5
6# Or store it as an environment variable
7RUN . /etc/os-release && echo "Building on Ubuntu $VERSION_ID"

Scripting Version Checks

Extract specific fields for use in scripts or CI pipelines:

1# Get just the version number
2docker exec my-container grep VERSION_ID /etc/os-release | cut -d'"' -f2
3# Output: 22.04
4
5# Get the codename
6docker exec my-container grep VERSION_CODENAME /etc/os-release | cut -d= -f2
7# Output: jammy
8
9# Use in a shell variable
10UBUNTU_VERSION=$(docker exec my-container grep VERSION_ID /etc/os-release | cut -d'"' -f2)
11echo "Container is running Ubuntu $UBUNTU_VERSION"

Ubuntu Version Reference

LTS releases receive five years of standard support and up to ten years with Extended Security Maintenance (ESM).

Common Pitfalls

• Trusting the image tag: docker pull ubuntu:latest does not always mean the latest LTS. The latest tag is set by the image maintainer and may not update immediately. Always verify inside the container.
• Missing lsb_release in minimal images: Docker Ubuntu images are stripped down. Use /etc/os-release instead of installing lsb-release just to check the version.
• Confusing host and container versions: cat /etc/os-release on the host shows the host OS, not the container. Always use docker exec to run the command inside the container.
• Assuming all Ubuntu-based images are Ubuntu: Images built FROM ubuntu:22.04 may install packages that change /etc/issue or add custom /etc/os-release entries. Check the Dockerfile or image history with docker history <image>.
• Alpine or Debian images mistaken for Ubuntu: Some Docker images use Debian or Alpine as the base. /etc/os-release will show the actual distribution. Check ID=ubuntu to confirm it is actually Ubuntu.

Summary

• /etc/os-release is the most reliable method — works on all Ubuntu Docker images without extra packages
• lsb_release -a gives a clean summary but requires the lsb-release package
• Use docker exec <container> cat /etc/os-release to check from outside the container
• Use docker run --rm <image> cat /etc/os-release to check an image without starting a persistent container
• Do not trust image tags blindly — always verify the actual version inside the container
• Extract specific fields with grep and cut for scripting and CI pipelines