How to Use the md5sum Command in Linux

Introduction

When you download a file from the internet, it is a good safety practice to check whether you received the original version. Comparing checksums you received from the file creator with the ones you obtain by checking the file yourself is a reliable way to confirm your download’s integrity.

The md5sum command in Linux helps create, read, and check file checksums.

In this tutorial, you will learn how to use the md5sum command to validate the files you receive.

Prerequisites

• A system running Linux
• Access to the command line

The md5sum Command with Examples

When used on a file without any options, the md5sum command displays the file’s hash value alongside the filename. The syntax is:

md5sum [filename]

After obtaining the hash value, compare it with the MD5 value provided by the file creator.

Read in Binary Mode

To read the file in binary mode, use the -b option (--binary):

md5sum -b [filename]

The * character before the file name means that md5sum read it in binary mode.

Read in Text Mode

Use the -t option (--text) to read the file in text mode:

md5sum -t [filename]

Text mode is the default mode for reading files with md5sum.

Create a BSD-Style Checksum

Using the --tag option outputs the hash value in the BSD-style format:

md5sum --tag [filename]

Validate md5 Checksum with a File

To check a file by comparing its hash value with the value provided in a hash file, use the -c option.

1. As an example, create a hash file containing the md5sum output:

md5sum [filename] > [file-containing-hashes]

2. Use the following syntax to compare the hash value from the file you created against the current hash value of the .txt file:

md5sum -c [file-containing-hashes]

3. If you change the contents of the file and repeat the check, a warning message is displayed:

Validate Multiple Files

Use the same md5sum -c procedure to check the integrity of multiple files:

md5sum [filename1] [filename2] [filename3] > [file-containing-hashes]

In the following example, the contents of example2.txt have changed, resulting in a warning message from md5sum:

Display Only Modified Files

The --quiet option displays only the files whose hash value has changed. It skips the output of validated files.

md5sum --quiet -c [file-containing-hashes]

Generate Status Only

The md5sum command with the --status option does not produce any output but returns 0 if there are no changes and 1 if it detects changes. This argument is useful for scripting, where there is no need for standard output.

The example script below illustrates the use of the --status option:

#!/bin/bash
md5sum --status -c hashfile
Status=$?
echo "File check status is: $Status"
exit $Status

When the script executes, it shows status 1, meaning that md5sum detected the change made earlier in example2.txt.

Check Improperly Formatted Checksum Lines

Add the --strict option to exit non-zero for improperly formatted hash values:

md5sum --strict -c [file-containing-hashes]

The example shows the output of md5sum --strict when you put invalid characters in the first line of the file containing hashes:

To display which line has an invalid hash, use -w (--warn):

md5sum -w -c [file-containing-hashes]

The example above shows the -w option displaying that the improperly formatted MD5 checksum line is line 1 of the file.

Skip Reporting Status for Missing Files

By default, md5sum shows warnings about the files it cannot find on the system. To override this behavior, use the --ignore-missing option:

md5sum --ignore-missing -c [file-containing-hashes]

In the example below, example1.txt was deleted before running the md5sum command. The output ignores the deleted file:

Show Help and Version Information

To get the official help for the md5sum command, type:

md5sum --help

To check md5sum version, type:

md5sum --version 

Conclusion

After completing this tutorial, you should know how to properly use the md5sum command to create, print, or check MD5 checksums.