Fix the SSH "Connection reset by peer" Error

What the error means

"Connection reset by peer" means the other side of the connection closed it. Typical causes:

1. Network problems: lost packets, heavy traffic or a firewall.
2. Server problems: low resources, a stopped SSH service or limits in the SSH settings.
3. Client problems: a wrong SSH config or old software.

Step 1: Check the network

ping server_address

If there is no reply or many packets are lost, the problem is in the network.

Step 2: Check the SSH service

On the server (use the console if you cannot log in):

sudo systemctl status ssh

On CentOS and Red Hat the service is called sshd. If it is not running, start it:

sudo systemctl start ssh

Read the log for hints (/var/log/secure on CentOS, /var/log/auth.log on Ubuntu):

sudo tail -f /var/log/secure

Step 3: Check the client config

Look at your SSH client file for wrong settings:

nano ~/.ssh/config

Step 4: Check the firewall

Allow SSH in the firewall:

sudo ufw allow 22/tcp

or:

sudo ufw allow ssh

If you changed the SSH port, allow that port instead.

Step 5: Check the SSH server settings

Open the server config:

sudo nano /etc/ssh/sshd_config

Check or change these values:

MaxAuthTries 6

ClientAliveInterval 60
ClientAliveCountMax 3

MaxStartups 10:30:100
MaxSessions 100

Restart the service:

sudo systemctl restart sshd

Step 6: Ask SSH to explain

Run the client in verbose mode. It prints each step of the connection:

ssh -v user@server

Add more v letters (-vvv) for more detail.

Good to know

• SSH keys are safer than passwords.
• Keep the SSH client and server updated.
• Check CPU, memory and disk use of the server. A busy server may drop connections.
• Try another user account to see if the problem is about one account.

Quick recap

• Test the network, the SSH service and the firewall first.
• Adjust ClientAliveInterval, MaxStartups and MaxSessions.
• Use ssh -v to see where the connection fails.