Troubleshoot Connection Reset by Peer Error in SSH on Linux

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SSH Connection Reset by Peer

Troubleshooting SSH Connection Reset by Peer may be difficult, particularly if you run into the ssh_exchange_identification: read: Connection reset by peer error. This error usually appears when you attempt to set up an SSH connection to a remote server. This situation indicates that the remote host abruptly closed the connection attempt.

This is frustrating for the user that’s initiating the connection to the target system.

In this tutorial, we will discuss ssh_exchange_identification: read: Connection reset by peer error, its triggers, and how to fix it.

Table of Contents

  1. What is ssh_exchange_identification: read: Connection reset by peer Error?
  2. What Triggers the ssh_exchange_identification: read: Connection reset by peer Error?
    1. Network Issues
    2. Firewall Restrictions
    3. SSH Misconfigurations
    4. Server Issues
  3. The Prerequisites
  4. Troubleshoot the ssh_exchange_identification: read: Connection reset by peer Error
    1. Method #1: Restart sshd Daemon on Server
    2. Method #2: Check DenyUsers and AllowUsers Directives
    3. Method #3: Verify MaxStartups
    4. Method #4: Adjust MaxAuthTries
    5. Method #5: Check hosts.allow and hosts.deny
    6. Method #6: Review Server Logs
    7. Method #7: Firewall and Network Issues
    8. Method #8: Server Resource Limits
    9. Method #9: Client-Side Issues
  5. Conclusion
  6. FAQs

What is ssh_exchange_identification: read: Connection reset by peer Error?

The error ssh_exchange_identification: read: Connection reset by peer occurs during an SSH connection attempt where the connection is abruptly terminated by the server.

ssh_exchange_identification refers to the stage in the SSH connection process where crucial identification details are exchanged between the SSH client and server. This information is essential to set up a secure encrypted connection.

The other half, read: Connection reset by peer indicates that the server unexpectedly terminated the connection while the client was waiting to receive its identification data.

This problem could stem from a variety of reasons ranging from firewall settings blocking the connection, issues with the SSHD service on the remote server, or improper SSH configuration settings.

In addition, factors like the blocked IP address, incompatible version string used by the SSH server, or a strict compatibility mode for protocol handling, could trigger the error.

Let us now understand some of the possible reasons for ssh_exchange_identification: read: Connection reset by peer error.

What Triggers the ssh_exchange_identification: read: Connection reset by peer Error?

The ssh_exchange_identification: read: Connection reset by peer error occurs when attempting to create an SSH connection to a remote server. Here are some factors that trigger this error.

Network Issues

Unstable or high-latency network connections can abruptly terminate the SSH session. If the server doesn’t receive the information it needs within a specific timeframe, it resets the connection.

Firewall Restrictions

Firewalls either on the client or server side might block the necessary communication for proper SSH identification, leading to the ssh_exchange_identification: read: Connection reset by peer error.

SSH Misconfigurations

Incorrect SSH settings, authentication issues, or incompatible key exchange scenarios can result in a connection reset error.

Server Issues

Problems on the remote server, like issues with the SSH service (SSHD) or configuration errors, can cause the server to unexpectedly reset the connection.

In many cases, reconfiguring SSH or rebooting the remote server resolves temporary outages or connectivity problems. Understanding how to troubleshoot and identify the root cause of the issue will help you prevent it in the future.

Now that you have a basic understanding of ssh_exchange_identification: read: Connection reset by peer error, and the causes, let us discuss how to troubleshoot them. However, before that, let us take a quick look at the prerequisites.

The Prerequisites

Before moving in, ensure you have the following:

  • A system running any popular Linux distro
  • You have OpenSSH installed
  • A user account with sudo or administrative privileges

Troubleshoot the ssh_exchange_identification: read: Connection reset by peer Error

Encountering the ssh_exchange_identification: read: Connection reset by peer error can be frustrating when you attempt to initiate an SSH connection. This issue can stem from various causes, ranging from server-side configuration problems to network issues.

Method #1: Restart sshd Daemon on Server

The sshd daemon is a background service that runs on a server. It handles incoming SSH connection requests and manages secure communication.

The SSH Daemon (SSHD) configuration can have errors or restrictions, leading to ssh_exchange_identification: read: Connection reset by peer error.

Therefore, as a simple fix, restart the sshd daemon on the server by running the following command:

# sudo systemctl restart sshd

 

Verifying the status of your SSH server is a crucial step in troubleshooting SSH-related issues. For this, run the following command to check the status of the SSHD service:

# sudo systemctl status ssh

Method #1: Restart sshd Daemon on Server

If this does not resolve, try the rest of the methods mentioned below.

Method #2: Check DenyUsers and AllowUsers Directives

The ssh_exchange_identification: read: Connection reset by peer error can occur if the SSHD configuration file is under DenyUsers directive.

Check the SSHD configuration file (/etc/ssh/sshd_config) for any misconfigurations or restrictions that might be causing the issue.

Run this command that uses Nano to access DenyUsers and AllowUsers directives.

# sudo nano /etc/ssh/sshd_config

Scroll through the file and verify that your username is not listed under DenyUsers directive and is appropriately configured under AllowUsers.

Method #3: Verify MaxStartups

This setting limits the number of concurrent unauthenticated SSH connection attempts the server can handle.

If the server is overloaded with connection attempts, adjusting this value (e.g., MaxStartups 10:30:60) might help.

Execute the following command to adjust the number of allowed server connection attempts.

# MaxStartups 10:30:60

Method #3: Verify MaxStartups

 

 

 

Method #4: Adjust MaxAuthTries

Having multiple SSH keys on your system might cause you to exceed the MaxAuthTries limit on the server. This setting controls the maximum number of authentication attempts allowed for a user. The default value is 6.

To resolve this, increase the MaxAuthTries value in the SSH server’s configuration file using a text editor like Nano and restart the SSH daemon.

# sudo nano /etc/ssh/sshd_config

Method #4: Adjust MaxAuthTries

Method #5: Check hosts.allow and hosts.deny

The hosts.allow and hosts.deny files on the server can be used to manage access restrictions for SSH connections based on the IP addresses of the incoming connections.

We recommend opening the hosts.deny file using a text editor like Nano to check if these files are contributing to the ssh_exchange_identification: read: Connection reset by peer error.

# sudo nano /etc/hosts.deny

Look for any lines that might be blocking specific IP addresses. These lines typically start with sshd: followed by the IP address or subnet to be denied SSH access.

If you find a line blocking your IP, remove it or comment it out by adding a # symbol at the beginning of the line.

 

Alternatively, if you do not find lines, check if the hosts.allow file is contributing to the error.

Method #5: Check hosts.allow and hosts.deny

Run the following command to open the file in your preferred text editor like Nano or Vim.

# sudo nano /etc/hosts.allow

Look for lines starting with sshd: followed by allowed IP addresses or subnets.

Method #5: Check hosts.allow and hosts.deny

If hosts.allow is being used for vetting connections, and your IP isn’t present, consider adding a line with sshd: your_IP_address to allow access from your system.

Method #6: Review Server Logs

Server logs can provide insights into what is causing the connection reset. Examining these logs can help pinpoint the root cause of the ssh_exchange_identification: read: Connection reset by peer error

We recommend combining the tail command to check the latest entries in the SSH server log file.

# sudo tail -f /var/log/auth.log

Check for any errors or messages related to SSH connections.

Method #7: Firewall and Network Issues

Firewalls and network configurations can block or restrict SSH connections.

If you suspect that this is the underlying cause, start by checking the current firewall rules. Firewalls act as security barriers, controlling incoming and outgoing traffic. If firewall rules are configured to block SSH traffic, it could lead to connection reset errors.

Use iptables to check the current firewall rules by running the following command:

# sudo iptables -L

Ensure that port 22 (the standard SSH port) is open for incoming connections.

Network issues can also disrupt the connection between the SSH client and the server. Therefore, check for any network issues or changes that might be affecting the connection.

Method #8: Server Resource Limits

In some cases, the ssh_exchange_identification: read: Connection reset by peer error can stem from limitations on the available server resources.

Ulimits define the maximum number of resources a particular user or process can utilize. In this context, we suggest checking the Ulimits settings for the server’s SSH processes.

If the server is running low on available resources due to high utilization, it might reject new SSH connections.

Use the ulimit -a command to view the current ulimit settings on the server.

# ulimit -a

Ensure the server is not hitting limits on the number of processes or open files. If these values are set very low, the server might be reaching its capacity.

Method #9: Client-Side Issues

The ssh_exchange_identification: read: Connection reset by peer error can sometimes originate from problems on the SSH client system.

Check SSH client configuration and ensure your SSH client configuration (~/.ssh/config) is correct.

If you have access to another system, try connecting to the server using SSH from that client. This can help isolate whether the problem lies with your client machine’s configuration or the server itself.

By systematically checking these potential causes, you can identify and resolve the ssh_exchange_identification: read: Connection reset by peer error.

Conclusion

Encountering the ssh_exchange_identification: read: Connection reset by peer error can be frustrating, but understanding its root causes and solutions can help you quickly resolve the issue and maintain seamless access to your server via SSH. By systematically checking your SSH configurations, log files and network settings, you can identify and fix the underlying problems that trigger this error.

FAQs

Q. What does the Connection Reset by Peer error mean in SSH on Linux?

When you attempt to connect over SSH and the remote server suddenly quits the connection, you get the Connection Reset by Peer error. Firewall regulations, incorrect server configuration, or network outages can all cause this.

Q. How can I troubleshoot the Connection Reset by Peer error in SSH on Linux?

To troubleshoot this error, you can start by checking the SSH logs on the server to gather information about the connection setup. Additionally, inspect the server’s firewall settings, SSH configuration, and any load balancers that might affect the connection.

Q. Why does the Connection Reset by Peer error happen when I try to connect to the server?

When there are problems with connectivity between your client and the server, an error may appear. This can be due to network problems, SSH port configurations, or server SSH service issues.

Q. In Linux SSH, how can I fix the Connection Reset by Peer error?

You may need to check the outgoing and incoming SSH traffic, ensure that the correct options are applied when establishing the connection, and verify that no restrictions are blocking the connection at either end. Restarting SSH services or the server itself may also be necessary.

Q. How can I debug the Connection Reset by Peer error when connecting to a remote machine over SSH?

Type -1 debug1 in the SSH command to enable verbose debugging output. This will provide more information about the connection process and any errors encountered.

Q. What information should I look for in the SSH logs when troubleshooting the Connection Reset by Peer error?

Look for details about the connection established, reading configuration data, and any attempts to connect to the server. This information can help pinpoint where the issue is occurring.

Q. How does the Connection Reset by Peer error impact my SSH connection with a remote server?

The error disrupts the communication between your client and the server, causing the connection to be abruptly terminated. This can prevent you from establishing a stable connection and accessing the remote machine.

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