Introduction
Network Attached Storage (NAS) devices have become a staple in modern home and business networks, offering a centralized location for storing and sharing data. Synology, a leader in the NAS market, provides users with robust and user-friendly devices that can be managed through a graphical interface or via command-line using Secure Shell (SSH). However, users may sometimes encounter the frustrating “Permission Denied” error when trying to access their Synology NAS via SSH. This article delves into the causes of this issue and provides comprehensive solutions to regain access to your Synology NAS using SSH.
Understanding SSH and Its Role in Synology NAS
What is SSH?
Secure Shell (SSH) is a cryptographic network protocol used for secure data communication, remote command-line login, remote command execution, and other secure network services between two networked computers. It is widely used by system administrators for managing systems and applications remotely, allowing them to log into another computer over a network, execute commands in a remote machine, and move files from one machine to another.
SSH in Synology NAS
Synology NAS devices support SSH access, which allows advanced users to manage their systems using the command line. SSH access can be particularly useful for performing administrative tasks, automating processes through scripts, and accessing the NAS in situations where the graphical user interface is not accessible.
Common Causes of SSH Permission Denied in Synology NAS
- User Authentication Issues: Incorrect username or password, disabled user accounts, or SSH not enabled for the user.
- SSH Service Configuration: SSH service not enabled on the NAS, incorrect SSH port, or firewall restrictions.
- File Permissions: Improper file permissions on the SSH directory or key files.
- Public Key Authentication Problems: Issues with the public/private key pair or incorrect file permissions on the authorized_keys file.
- SSH Daemon Configuration: Misconfiguration in the SSH daemon settings, such as the sshd_config file.
Troubleshooting SSH Permission Denied on Synology NAS
Verifying User Credentials and SSH Access
The first step in troubleshooting is to ensure that the user credentials are correct and that the user account has SSH access enabled. This can be done through the Synology DSM interface under Control Panel > Terminal & SNMP > Enable SSH service. Additionally, verify that the account is not disabled or restricted.
Checking SSH Service and Network Configuration
If user credentials are correct, the next step is to check whether the SSH service is running on the NAS. This can be done by accessing the Synology DSM and navigating to Control Panel > Terminal & SNMP. Ensure that the SSH service is enabled and that the correct port is specified. Also, check any network firewalls or routers to ensure that they are not blocking the SSH port.
Inspecting File Permissions
File permissions can cause access issues if not set correctly. Use the DSM File Station or SSH as an admin user to check the permissions of the .ssh directory and the authorized_keys file within it. The .ssh directory should have 700 permissions, and the authorized_keys file should have 600 permissions.
Public Key Authentication Checks
If you are using public key authentication, ensure that the public key is correctly placed in the authorized_keys file and that the private key matches the public key. Also, verify that the permissions for the .ssh directory and the authorized_keys file are set correctly.
SSH Daemon Configuration
Misconfiguration in the SSH daemon can also lead to permission denied errors. Access the sshd_config file located in /etc/ssh/ and check for any incorrect settings that may be preventing access. Ensure that the configuration allows for password or public key authentication as required.
Advanced Solutions for Resolving SSH Access Issues
Resetting User Permissions and Passwords
In some cases, resetting the user permissions and passwords through the DSM interface can resolve access issues. This can be done by editing the user’s profile and reapplying the permissions or resetting the password.
Reconfiguring SSH Daemon Settings
If the sshd_config file has been modified, it may be necessary to restore it to its default settings or adjust specific parameters to align with security policies and access requirements. After making changes, restart the SSH service to apply the new configuration.
Using Verbose Mode for Debugging
Connecting to the Synology NAS using SSH with verbose mode enabled can provide additional information about the connection attempt. Use the command ssh -vvv user@nas_ip to initiate a connection with verbose output, which can help identify where the process is failing.
Case Studies and Examples
To illustrate the troubleshooting process, consider the following case study:
- A user attempts to SSH into their Synology NAS and receives a “Permission Denied” error.
- They verify their username and password are correct and that SSH access is enabled for their account.
- Upon checking the SSH service, they discover that the port was changed during a recent network reconfiguration.
- After updating their SSH client with the correct port, they successfully gain access to the NAS.
Frequently Asked Questions
How do I enable SSH on my Synology NAS?
To enable SSH on your Synology NAS, log into the DSM interface, navigate to Control Panel > Terminal & SNMP, and check the option to “Enable SSH service.”
What are the default file permissions for the .ssh directory and authorized_keys file?
The default file permissions should be 700 for the .ssh directory and 600 for the authorized_keys file.
Can I use SSH to access my Synology NAS from the internet?
Yes, you can access your Synology NAS from the internet using SSH, but it is recommended to use a VPN or set up port forwarding with caution to ensure security.
What should I do if I’m locked out of my Synology NAS?
If you are locked out of your Synology NAS, you can reset the admin password using the reset button on the device or contact Synology support for assistance.
Conclusion
Troubleshooting “Permission Denied” errors when accessing a Synology NAS via SSH can be a complex process, but by methodically checking user credentials, SSH service configuration, file permissions, and SSH daemon settings, access can typically be restored. It’s crucial to maintain security best practices when enabling SSH access, especially when accessible over the internet. With the right approach, your Synology NAS will continue to serve as a secure and reliable hub for your data storage needs.
References
For further reading and advanced troubleshooting, refer to the following resources:
- Synology Knowledge Base: https://www.synology.com/en-global/knowledgebase
- OpenSSH Manual Pages: https://man.openbsd.org/sshd
- SSH Command Usage: https://www.ssh.com/ssh/command/
