Linux md5sum Command with Practical Examples

Introduction

In this lab, you will learn how to use the Linux md5sum command to generate and verify the MD5 checksums of files. The md5sum command is a useful tool for ensuring the integrity of downloaded files, as it can be used to detect any changes or corruption that may have occurred during the download process. You will start by understanding the purpose of the md5sum command, then learn how to generate MD5 checksums for files, and finally, how to use those checksums to verify the integrity of the files.

The lab covers the following steps:

1. Understand the Purpose of the md5sum Command
2. Generate MD5 Checksums for Files
3. Verify File Integrity Using MD5 Checksums

Linux Commands Cheat Sheet

Skills Graph

Understand the Purpose of the md5sum Command

In this step, you will learn about the purpose of the md5sum command in Linux. The md5sum command is used to generate and verify the MD5 checksum of a file. The MD5 checksum is a 128-bit hash value that can be used to uniquely identify a file and ensure its integrity.

The MD5 checksum is commonly used to verify the integrity of downloaded files, such as software packages or disk images. If the MD5 checksum of a downloaded file matches the expected checksum, it indicates that the file has been downloaded correctly and has not been corrupted during the transfer.

Let's start by running the md5sum command on a file:

cd ~/project
echo "This is a test file." > test.txt
md5sum test.txt

Example output:

e10adc3949ba59abbe56e057f20f883e  test.txt

The output shows the MD5 checksum of the test.txt file, which is e10adc3949ba59abbe56e057f20f883e. You can use this checksum to verify the integrity of the file later.

Generate MD5 Checksums for Files

In this step, you will learn how to generate MD5 checksums for files using the md5sum command.

First, let's create a few sample files to work with:

cd ~/project
echo "This is file1.txt" > file1.txt
echo "This is file2.txt" > file2.txt
echo "This is file3.txt" > file3.txt

Now, let's generate the MD5 checksums for these files:

md5sum file1.txt file2.txt file3.txt

Example output:

e10adc3949ba59abbe56e057f20f883e  file1.txt
c778c38f1bf5b425c468a45e316d71d2  file2.txt
5d41402abc4b2a76b9719d911017c592  file3.txt

The output shows the MD5 checksum for each file. You can use these checksums to verify the integrity of the files later.

You can also generate the checksums for all files in a directory using the following command:

md5sum *

This will generate the checksums for all files in the current directory.

Verify File Integrity Using MD5 Checksums

In this step, you will learn how to use the md5sum command to verify the integrity of files by comparing their MD5 checksums.

First, let's create a new file and generate its MD5 checksum:

cd ~/project
echo "This is a test file." > test.txt
md5sum test.txt

Example output:

e10adc3949ba59abbe56e057f20f883e  test.txt

Now, let's say you have received a file from a different source, and you want to verify its integrity. You can do this by comparing the MD5 checksum of the received file with the expected checksum.

Suppose the expected MD5 checksum for the test.txt file is e10adc3949ba59abbe56e057f20f883e. You can verify the integrity of the file by running the following command:

md5sum -c <(echo "e10adc3949ba59abbe56e057f20f883e  test.txt")

Example output:

test.txt: OK

The output shows that the MD5 checksum of the test.txt file matches the expected value, indicating that the file has not been corrupted.

If the checksum does not match, the output will show an error:

echo "This is a modified file." > test.txt
md5sum -c <(echo "e10adc3949ba59abbe56e057f20f883e  test.txt")

Example output:

test.txt: FAILED
md5sum: test.txt: FAILED

In this case, the MD5 checksum of the modified test.txt file does not match the expected value, indicating that the file has been corrupted or modified.

Summary

In this lab, you learned about the purpose of the md5sum command in Linux, which is used to generate and verify the MD5 checksum of a file. The MD5 checksum is a 128-bit hash value that can be used to uniquely identify a file and ensure its integrity. You generated MD5 checksums for files and learned how to use these checksums to verify the integrity of downloaded files. Finally, you explored how to verify file integrity using MD5 checksums, which is commonly used to ensure the correctness of downloaded software packages or disk images.

Linux Commands Cheat Sheet