General Information

Additional SSH options.

The following virtual machines will be used:

• server1.example.com (192.168.1.150) → The SSH client
• server2.example.com (192.168.1.151) → The SSH server

Install package and generates system keys (should almost always be installed)

yum install openssh-server

• openssl is a dependency

Enable and start sshd

systemctl enable sshd
systemctl start sshd

Allow through firewall

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

• SSH Daemon config file: /etc/ssh/sshd_config
  • Configure additional options here
  • See man sshd_config

Some useful options

• Port → TCP listening port for sshd
• PermitRootLogin → Allow/disallow root login
• MaxAuthTries → Number of authentication tries. When 1/2 the number is reached, failures are logged.
• MaxSessions → Max number of ssh sessions from one IP address
• AllowUsers → Space-separated list of users allowed to connect
• DenyUsers → Space-separated list of users to deny conections
• PasswordAuthentication → Whether to allow password authentication or not.
• GSSAPIAuthentication → Authentication through GSSAPI enabled or disabled. Used for kerberos
• ClientAliveInterval → Interval in seconds packets are sent to the client to see if the client is still alive.
• ClientAliveCountMax → Number of client alive packets to send.
• UseDNS → Use DNS name lookup to match an incoming IP address to name. (if on)