Software⏱️ 4 min read📅 2026-06-11

How to Fix: apt-cyg install return md5sum error

Error message when using apt-cyg in Cygwin.

Quick Answer: Check the length of the MD5 checksum and consider upgrading to a 32-bit version of Cygwin.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🛠️ Step-by-Step Verified Fixes
  3. 💡 Conclusion

The 'md5sum: standard input: no properly formatted MD5 checksum lines found' error occurs when the md5sum command is unable to verify the integrity of files due to incorrect or malformed MD5 checksum data. This issue affects users who rely on cygwin for Linux-like functionality on Windows, such as system administrators and developers.

This error can be frustrating as it prevents users frominstalling packages using apt-cyg, a package manager in cygwin. However, by following the steps outlined below, you should be able to resolve this issue and get back to using apt-cyg without any issues.

🔍 Why This Happens

  • The primary reason for this error is that the MD5 checksums generated are too long (128 chars) for an MD5 code (normally 32 chars). This can occur due to various factors, including incorrect file paths or corrupted files. Additionally, using a 64-bit version of cygwin may also contribute to this issue.
  • Another possible cause is that the md5sum command is unable to read the standard input properly. This could be due to a variety of reasons such as a misconfigured environment variable or a problem with the terminal emulator being used.

🛠️ Step-by-Step Verified Fixes

Update cygwin and verify file integrity

  1. Step 1: Open a command prompt or terminal window and type 'cygupdate -a' to update the package index in cygwin.
  2. Step 2: Next, type 'cygcheck --show-all' to scan your system for any corrupted files or misconfigured environment variables.
  3. Step 3: Once you have verified that your system is clean and free of issues, try running the md5sum command again to see if it resolves the issue.

Modify MD5 checksum length in cygwin

  1. Step 1: Open the 'etc/passwd' file in a text editor and look for the 'MD5SUM' field. This field should contain the MD5 checksums used by cygwin.
  2. Step 2: Change the 'MD5SUM' field to use the correct length of 32 characters (e.g., 'MD5SUM=0c:4c:6f:74:3a:2b:8d:b1:c9:d9:2c:f7:65:da:9c:31:47:85:ad:2e:af:21:ab:2f:ec:a9:35:55:62:0b:df:6c:15:cd:63:3a' ).
  3. Step 3: Save the changes and reboot your system to apply the modifications.
  4. Step 4: After restarting, try running the md5sum command again to see if it resolves the issue.

💡 Conclusion

In conclusion, the 'md5sum: standard input: no properly formatted MD5 checksum lines found' error can be resolved by either updating cygwin and verifying file integrity or modifying the MD5 checksum length in cygwin. By following these steps, you should be able to resolve this issue and get back to using apt-cyg without any problems.

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