Verify the Integrity of a Downloaded ISO with md5sum

Introduction

This article offers guidance to verify the integrity of a downloaded ISO file. Check the integrity of larger files, such as ISO files for distros with md5sum. If you are using a common Debian* based distro, mdsum will be installed on the system and ready to use. Due to the size of an ISO (often several gigabytes), the integrity of the files should be checked for any potential edits or possible errors. Distros will often list the md5sum for a particular ISO. To check the ISO, run md5sum against that ISO file.

md5sum - What is it?

The man page description:

       Print or check MD5 (128-bit) checksums.

MD5  is a 128 bit:

• Message-Direct algorithm 5
• hash - 128 bit encryption
• checksum

This is represented by 32 hexadecimal digits.

How It Works

Use a md5sum to validate the integrity of a file. What does that mean?  A file or files can be corrupted or edited. Files can become corrupted during downloading, for example. The md5sum is compared to the downloaded file. If the checksums match, no corruption is present.

Create a checksum

If you want to create a checksum, use md5sum.

• md5sum can generate a MD5 (128-bit) checksum or verify a checksum.
• md5sum can also create a BSD-style checksum.

Verify checksum

Verify the integrity of a file using md5sum. See the section Use md5sum to check the ISO file.

Use md5sum to check the ISO file

Integrity

• A MD5 hash comparison would indicate if there were any changes in files to cause errors.
• Running a md5sum against an ISO is a good idea

Usage

md5sum [OPTION]... [FILE]...

To use md5sum, run the following command:

md5sum ubuntuisoname.iso

The md5sum output for the specified file displays.

Check this output against the list of distro hashes. For example, the Ubuntu* hashes for 18.04.3 are located here:

http://old-releases.ubuntu.com/releases/bionic/MD5SUMS

Security

MD5 algorithm is no longer used for security related purposes as SHA-2 is typically used over MD5.

Resources

For more information about md5sum, see the man page:

man md5sum

     or

md5sum --help

For the complete  texinfo manual for coreutils:

info coreutils aqmd5sum invocationaq