Software⏱️ 4 min read📅 2026-06-15

How to Fix: mount error(5): Input/output error on mount using CIFS

Troubleshooting CIFS mount error on Ubuntu with ntlm credentials.

Quick Answer: Check the SMB credentials and ensure the correct version is used (vers=3.0).

📋 Table of Contents

  1. 💡 Why You Are Getting This Error
  2. 🔧 Proven Troubleshooting Steps
  3. 🎯 Final Words

The 'mount error(5): Input/output error' issue affects users who attempt to mount network drives from a Windows host onto their Ubuntu Virtual Machine (VM). This problem can be frustrating as it prevents users from accessing important files and data stored on the remote server. In this guide, we will walk through the steps to troubleshoot and resolve this common issue.

Resolving the 'mount error(5): Input/output error' requires a systematic approach to identify and address potential causes. By following these steps, users can successfully mount their network drive and access the files they need.

💡 Why You Are Getting This Error

  • The primary reason for this error is due to an incorrect or missing SMB protocol version in the CIFS settings. The 'vers=3.0' parameter specifies the SMB protocol version used for mounting the network drive. If this parameter is set incorrectly, it can cause input/output errors during the mount process.
  • Another potential cause of this error is related to the authentication mechanism. If the NTLM authentication method is not properly configured or if the credentials are incorrect, it can lead to input/output errors when attempting to mount the network drive.

🔧 Proven Troubleshooting Steps

Verify and adjust SMB protocol version

  1. Step 1: Open a terminal on your Ubuntu VM and edit the CIFS settings in /etc/fstab by using the following command: `sudo nano /etc/fstab`.
  2. Step 2: Locate the line with the network drive configuration (e.g., `//xx.xx.xxx.xx/datacom /home/ubuntu/test cifs`) and update the 'vers' parameter to a valid SMB protocol version. For example, you can use 'vers=3.1' or 'vers=4.0'.
  3. Step 3: Save and close the file using Ctrl+X, then exit the nano editor by pressing Enter.
  4. Step 4: Restart the network service to apply the changes: `sudo service nmbd restart`.

Verify and adjust NTLM authentication settings

  1. Step 1: Open a terminal on your Ubuntu VM and edit the /etc/samba/smb.conf file using the following command: `sudo nano /etc/samba/smb.conf`.
  2. Step 2: Locate the 'security' section and update the 'ntlmv2 = yes' parameter to ensure NTLM authentication is enabled. For example, you can add the following line: `security = user`.
  3. Step 3: Save and close the file using Ctrl+X, then exit the nano editor by pressing Enter.
  4. Step 4: Restart the network service to apply the changes: `sudo service nmbd restart`.

🎯 Final Words

By following these steps, you should be able to resolve the 'mount error(5): Input/output error' issue and successfully mount your network drive onto your Ubuntu VM. Remember to verify your CIFS settings and NTLM authentication configuration to ensure a smooth and secure connection to your remote server.

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