Software⏱️ 3 min read📅 2026-06-15

How to Fix: curl sftp uploads empty file without error

curl sftp upload issue empty file no error

Quick Answer: Check the file size and contents on your local machine, as curl may not be sending the entire file due to a buffer limit.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🔧 Proven Troubleshooting Steps
  3. 💡 Conclusion

The issue of uploading an empty file using curl via SFTP to a remote server is frustrating for users who rely on this method. This problem affects individuals and organizations that use curl to transfer files over SFTP connections.

This issue can be caused by various factors, including incorrect file permissions, incomplete file transfers, or issues with the SFTP client library used by curl.

🔍 Why This Happens

  • The primary reason for this error is likely due to the way curl handles binary data. When using the `-T` option to transfer a file, curl uses a buffered approach to read and write data. However, if the file being uploaded is not properly encoded or corrupted during transmission, it may result in an empty file on the remote server.
  • Another possible cause is related to the SFTP client library used by curl. In some cases, this library may not handle certain file types or encoding correctly, leading to incomplete or empty file transfers.

🔧 Proven Troubleshooting Steps

Enabling TCP_NODELAY and Adjusting Transfer Options

  1. Step 1: To troubleshoot this issue, start by enabling the `TCP_NODELAY` option in your curl command. This will ensure that data is sent over the network without buffering, which can help prevent issues with binary file transfers.
  2. Step 2: Additionally, try adjusting the transfer options using the `-C` and `-T` options. The `-C` option allows you to continue a paused transfer, while the `-T` option specifies the local file to be transferred. By adjusting these options, you may be able to resolve issues related to incomplete or empty file transfers.
  3. Step 3: To enable `TCP_NODELAY`, add the following flag to your curl command: `-c never`. This will disable TCP_NODELAY and allow for faster data transfer.

Verifying File Encoding and Corruption

  1. Step 1: Another approach is to verify that the file being uploaded is properly encoded and not corrupted during transmission. You can do this by checking the file's metadata and contents using a tool like `file` or `md5sum`.
  2. Step 2: To check the file's encoding, use the `file` command: `file -i file.txt`. This will provide information about the file's format and encoding. If the file is corrupted or has incorrect encoding, you may need to reencode it before uploading.

💡 Conclusion

By following these steps and troubleshooting methods, you should be able to resolve issues with uploading empty files using curl via SFTP. Remember to always verify file encoding and corruption, as well as adjust transfer options to ensure reliable data transfer.

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