Fix: SSH Permission Denied Issue | Real Solution

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1. Verify SSH Command and Key Usage

Use the correct private key with -i:

ssh -i ~/.ssh/your_private_key user@host

Ensure the key is not passphrase-protected (or enter the passphrase correctly).

2. Check Key Generation and Deployment

Regenerate Keys (if unsure):

ssh-keygen -t ed25519 -C "your_email@example.com"  # Prefer ed25519

Ed25519 uses elliptic curve cryptography (Edwards-curve Digital Signature Algorithm) and provides 128-bit security (equivalent to RSA-3072 or RSA-4096) with a 256-bit key.

Copy the Public Key to the Server:

ssh-copy-id -i ~/.ssh/your_public_key user@host

If ssh-copy-id isn’t available, manually append the public key to ~/.ssh/authorized_keys on the server.

3. Fix File/Directory Permissions

On the Server:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
chmod go-w ~  # Home directory should not be world-writable

On the Client (Local Machine):

chmod 600 ~/.ssh/your_private_key

4. Check SSH Server Configuration

Edit /etc/ssh/sshd_config on the server:

PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
PasswordAuthentication no  # Optional but ensure keys work first

Restart SSH service:

sudo systemctl restart sshd

5. Inspect Logs and Debug Output

Client-Side Debugging:

ssh -vvv user@host  # Look for "Offering public key" or errors

Server Logs:

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

6. Check for SELinux Issues

Temporarily disable SELinux:

setenforce 0  # Revert with setenforce 1

Restore file contexts:

restorecon -Rv ~/.ssh

7. Miscellaneous Checks

  • Ensure the server has disk space (df -h).
  • Confirm AllowUsers or DenyUsers in /etc/ssh/sshd_config includes your user.
  • Verify the correct user owns the .ssh directory and files:
chown -R user:user ~/.ssh

8. Test Password Authentication (Temporarily)

Enable PasswordAuthentication yes in /etc/ssh/sshd_config, restart SSH, and test login: 

ssh user@host  # Use password to log in and fix key issues

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