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How To Fix “Read from socket failed: Connection reset by peer” SSH Error

Ubuntu 8

In the world of system administration, encountering errors is a common occurrence. One such error that you may come across while using SSH (Secure Shell) is “Read from socket failed: Connection reset by peer”. This error can be quite frustrating, but with the right approach, it can be resolved. In this article, we will walk you through several methods to fix this SSH error.

Understanding the Error

Before we dive into the solutions, it’s important to understand what this error means. “Read from socket failed: Connection reset by peer” is a network-related error that occurs when one device (the peer) sends a TCP reset packet to another device. This typically happens when the peer device is not able to handle the data it’s receiving, leading to a connection reset.

Check Network Configuration

The first thing you should do when you encounter this error is to check your network configuration. Make sure both computers are connected to the same network, and there are no firewall or router settings that could be blocking the SSH connection. You can also try pinging the server from the client machine to ensure network connectivity.

Verify SSH Daemons

SSH daemons are background services that listen for incoming SSH connections. If these daemons are not running on your machines, you will not be able to establish an SSH connection. Use the command ps -ef | grep sshd to check if the SSH daemon is running. If it’s not, you can start it using the service sshd start command on most Linux distributions.

Regenerate Missing Keys

SSH relies on RSA and DSA keys for secure communication. If these keys are missing on the server, you might encounter the “Read from socket failed: Connection reset by peer” error. To regenerate these keys, use the following commands:

ssh-keygen -t rsa1 -f /etc/ssh/ssh_host_rsa_key
ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key

The -t option specifies the type of key to create (rsa1 or dsa), and the -f option specifies the filename of the key file.

Reinstall SSH

Sometimes, reinstalling the SSH server and client packages can resolve this issue. On a Debian-based system, you can use the following command:

sudo apt-get --reinstall install openssh-server openssh-client

The --reinstall option tells apt-get to reinstall the specified packages, and openssh-server and openssh-client are the names of the SSH server and client packages, respectively.

Check File Permissions

Incorrect file permissions in the /etc/ssh directory can also lead to this error. The permissions should be set as follows:

chmod 644 ssh_config
chmod 600 moduli

The chmod command changes the permissions of a file, and the numbers (644 and 600) specify the new permissions. In this case, ssh_config should be readable and writable by the owner and readable by others, and moduli should be readable and writable only by the owner.

Configure SSH Options

You may need to modify the /etc/ssh/ssh_config file on the client machine. This file contains various settings that control the behavior of the SSH client. Here are some lines that you might need to add or modify:

Host *
SendEnv LANG LC_*
HashKnownHosts yes
GSSAPIAuthentication yes
GSSAPIDelegateCredentials no
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc
HostKeyAlgorithms ssh-rsa,ssh-dss
MACs hmac-md5,hmac-sha1,hmac-ripemd160

Each line in this file represents a different setting. For instance, Ciphers specifies the ciphers allowed for SSH connections, and HostKeyAlgorithms specifies the host key algorithms that the client is willing to use.

Protect Against SSH Attacks

If the error is caused by multiple attempted SSH attacks, you might want to install the “fail2ban” package. This tool can slow down brute force attacks and block malicious IP addresses. To install fail2ban on a Debian-based system, use the following command:

sudo apt-get install fail2ban

Remember, the solutions provided in this article may not apply to every situation. Depending on the specific configuration of your system and network, further troubleshooting may be required. However, these steps should provide a good starting point for resolving the “Read from socket failed: Connection reset by peer” SSH error.

What is SSH?

SSH stands for Secure Shell, and it is a cryptographic network protocol that allows secure remote login and file transfer between computers. It provides a secure channel over an unsecured network by encrypting the data sent between the client and the server.

How can I check if SSH daemon is running on my machine?

You can check if the SSH daemon is running on your machine by using the command ps -ef | grep sshd. This command will show you a list of running processes that contain the term "sshd". If you see any results, it means the SSH daemon is running.

How can I start the SSH daemon if it is not running?

To start the SSH daemon on most Linux distributions, you can use the command service sshd start. This command will start the SSH daemon and allow incoming SSH connections.

What are RSA and DSA keys in SSH?

RSA and DSA are cryptographic algorithms used in SSH for secure communication. RSA (Rivest-Shamir-Adleman) is an asymmetric algorithm that uses a pair of public and private keys for encryption and decryption. DSA (Digital Signature Algorithm) is also an asymmetric algorithm used for digital signatures and key exchange.

How can I regenerate missing SSH keys?

To regenerate missing SSH keys, you can use the ssh-keygen command. For example, to regenerate the RSA key, you can use ssh-keygen -t rsa1 -f /etc/ssh/ssh_host_rsa_key. Similarly, you can regenerate the DSA key using ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key. These commands will recreate the missing keys.

How can I reinstall SSH on my system?

To reinstall the SSH server and client packages on a Debian-based system, you can use the command sudo apt-get --reinstall install openssh-server openssh-client. This command will reinstall the SSH packages and can help resolve any issues with the SSH installation.

What file permissions should be set in the /etc/ssh directory?

The file permissions in the /etc/ssh directory should be set as follows: chmod 644 ssh_config and chmod 600 moduli. These commands will set the permissions of the ssh_config file to be readable and writable by the owner and readable by others, and the moduli file to be readable and writable only by the owner.

How can I install the “fail2ban” package to protect against SSH attacks?

To install the "fail2ban" package on a Debian-based system, you can use the command sudo apt-get install fail2ban. This tool can help protect against SSH attacks by slowing down brute force attacks and blocking malicious IP addresses.

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