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md5sum – Utility program for calculating and verifying file message digests

md5sum is a command-line utility program that calculates and verifies the MD5 (Message Digest 5) hash values of files. The MD5 hash value is a 128-bit value that is used to check the integrity of files and to verify that they have not been tampered with. The md5sum command is commonly used to verify the integrity of downloaded files and to ensure that they have not been corrupted during the download process.

Overview

The basic syntax of the md5sum command is as follows:

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

To calculate the MD5 hash value of a file, simply specify the file name as an argument to the md5sum command. For example, to calculate the MD5 hash value of a file called myfile.txt, you would run the following command:

md5sum myfile.txt

This will output the MD5 hash value of the file in hexadecimal format, along with the file name:

3b3be63a4c2a439eac8c0f6d6c1ecf76  myfile.txt

To verify the integrity of a file, you can compare its MD5 hash value with the expected hash value. This is typically done by downloading the file and its associated MD5 hash value from a trusted source, and then running the md5sum command on the downloaded file to calculate its hash value. The calculated hash value can then be compared with the expected hash value to ensure that the file has not been tampered with.

For example, suppose you have downloaded a file called myfile.tar.gz and its associated MD5 hash value file called myfile.tar.gz.md5. To verify the integrity of the downloaded file, you would run the following command:

md5sum -c myfile.tar.gz.md5

This will read the MD5 hash value from the myfile.tar.gz.md5 file and compare it with the calculated hash value of the myfile.tar.gz file. If the two hash values match, the output will indicate that the file is OK:

myfile.tar.gz: OK

If the two hash values do not match, the output will indicate that the file is not OK:

myfile.tar.gz: FAILED

Options

The md5sum command supports the following options:

Option Description
-b, --binary Read files in binary mode (default is text mode)
-c, --check Read MD5 sums from the specified files and check them
-t, --text Read files in text mode (default)
-w, --warn Warn about improperly formatted MD5 checksum lines

Troubleshooting tips

  • If the calculated hash value does not match the expected hash value, try downloading the file again from a different source.
  • If the md5sum command reports that a file has failed verification, it is possible that the file has been tampered with or corrupted. Try downloading the file again from a trusted source.
  • If you encounter issues with the md5sum command, ensure that you are using the correct syntax and options. Refer to the command’s manual page (man md5sum) for more information.

Notes

  • MD5 is a cryptographic hash function that is no longer considered secure for certain applications. For more secure hash functions, consider using SHA-256 or SHA-512.
  • The md5sum command is part of the GNU Core Utilities package, which is typically included with most Linux distributions.

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