Ubuntu 16.04遇Permission denied (publickey)错误，无法SSH登录求助

Hey there, sorry to hear you're suddenly locked out of your machine via SSH—let's work through the most likely fixes since you had access just yesterday.

Quick Local Checks #

• Fix your private key permissions: SSH is extremely strict about file permissions for security. Your private key (usually ~/.ssh/id_rsa or a custom-named key) must have 600 permissions. Run this to adjust it:

  chmod 600 ~/.ssh/your_private_key_file
  

  If you're using a non-default key, make sure to specify it when connecting:

  ssh -i /path/to/your/private/key user@your_server_ip
  

If You Can Access the Server Via Another Channel (Console/VNC/Admin Panel) #

If you can get into the server through a different method, check these critical server-side settings:

• Secure your authorized_keys setup: The ~/.ssh directory must be set to 700, and the ~/.ssh/authorized_keys file must be 600—SSH ignores keys if these permissions are too open. Fix with:

  chmod 700 ~/.ssh
  chmod 600 ~/.ssh/authorized_keys
  

• Verify your public key matches: Double-check that the entire content of your local public key (run cat ~/.ssh/your_key.pub on your machine) is exactly what's in the server's authorized_keys file—no extra newlines, typos, or truncated text.
• Check SSH daemon configuration: Open /etc/ssh/sshd_config and confirm:
  • PubkeyAuthentication yes (this enables public key login)
  • AuthorizedKeysFile .ssh/authorized_keys (the path matches where your keys are stored)
    After making changes, restart the SSH service to apply them:

  # For Debian/Ubuntu systems
  sudo systemctl restart sshd
  # For CentOS/RHEL systems
  sudo service ssh restart
  

Debug with Verbose Logs #

If you're still stuck, use verbose mode to see exactly where the connection fails:

ssh -vvv user@your_server_ip

This will output detailed step-by-step logs—look for lines about key loading or explicit server rejection messages to pinpoint the issue.

On the server side, check authentication logs for more context:

# Debian/Ubuntu
tail -f /var/log/auth.log
# CentOS/RHEL
tail -f /var/log/secure

Search for sshd entries—they'll tell you exactly why your key was rejected (e.g., permission issues, missing key, config mismatch).

Temporary Password Login (If Allowed) #

If password authentication wasn't fully disabled on the server, you can force password login to get in and fix the key issue:

ssh -o PreferredAuthentications=password user@your_server_ip

If none of these work, double-check if the server's user directory has overly open permissions (SSH rejects keys if your home directory is writable by others) or if your key was accidentally removed from the server.

内容的提问来源于stack exchange，提问作者kosta