SSH connection configurations - Parthaaaaa/practicelinux GitHub Wiki

Server

• In order to check the version of your SSH utility, you can run the following command:

  ssh -V

• In order to install a SSH server,run the following command:

  CentOS 7,8:

  sudo yum install openssh-server

  sudo apt install openssh-server (for ubuntu)

  sudo dnf install openssh-server (centos 8)

• Check if the ssh-server is running or not (replace sshd with ssh during ubuntu command):

  systemctl status sshd

• Start it by

  systemctl start sshd

• Automatic start in bootup enable by:

  systemctl enable sshd

• To check whether ssh service is enable or not by:

  systemctl list-unit-files | grep enabled | grep ssh

Firewall might not allow SSH connections by default.So,it should be configured by following:

• In order to check SSH services configured in firewall to run following command:

  firewall-cmd --list-all | grep services

output:

services: cockpit dhcpv6-client

• If the service in the list run following command to listing:

  firewall-cmd --permanent --zone=public --add-service=ssh firewall-cmd --reload

• And verify again:

  firewall-cmd --list-all | grep services

output:

services: cockpit dhcpv6-client ssh

• Configure SSH Server;

  cd /etc/ssh

  vim sshd_config

• change

  port 22 to 2244 (or your wish)

  permitrootlogin no

  PasswordAuthentication no(Do this after you configured key based login which is described in the last)

Save the file and quit.

• Restart ssh by:

  systemctl restart sshd

If SELinux is running then ssh restart will not work.Run following command reconfigure

• SELinux for SSH:

  semanage port -a -t ssh_port_t -p tcp 2244(or your entered port)

• check if SELinux enabled by:

  sestatus

• Disable SELinux permanently by:

  vim /etc/sysconfig/selinux

change to SELINUX=disable

save file

• Allow changed port on firewall:

  firewall-cmd --zone=public --permanent --add-port=2244/tcp

  firewall-cmd --reload

• To see the port list:

  firewall-cmd --zone=public --permanent --list-all

Now,connect from user-client by:

ssh -p 2244 username@YourServerIPAddress

Enter the user password and thats it !

Setup Passwordless SSH Login to get more secured connection:

User-client

• Check for existing SSH key pair.

  ls -al ~/.ssh/id_*.pub

• Generate a keypair by:

  ssh-keygen -t rsa -b 4096 -C "[email protected] or writesomthing"

• To be sure that the SSH keys are generated you can list your new private and public keys by:

  ls -al ~/.ssh/id_*.pub or /home/user/.ssh

  id_rsa

  id_rsa.pub

• copy the public key to the server by:

  ssh-copy-id -p 2244 -i .ssh/id_rsa.pub username@YourServerIPAddress

• A folder named 'authorized_keys' with public key will be created in your server under following location:

  cd /home/user/.ssh

If 'ssh-copy-id' command doesn't work,then run the following:

1.scp ~/.ssh/id_rsa.pub username@YourServerIPAddress:/home/user/.ssh/uploadedkey.pub

• Now go to your server and run following:

  cat ~/.ssh/uploadedkey.pub >> ~/.ssh/authorized_keys

  chmod 700 ~/.ssh chmod 600 ~/.ssh/*

or

2.cat ~/.ssh/id_rsa.pub | ssh remote_username@server_ip_address "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"

Thats all ! This time your will not have to enter your password.Enjoy!!!