You need to install the following packages (which are installed by default until and unless you removed it or skipped it while installing CentOS)

  • openssh-clients : The OpenSSH client applications
  • openssh-server : The OpenSSH server daemon

OpenSSH Installations under CentOS Linux

To install the server and client type:
# yum -y install openssh-server openssh-clients
Start the service:
# chkconfig sshd on
# service sshd start

Make sure port 22 is opened:
# netstat -tulpn | grep :22

Firewall Settings

Edit /etc/sysconfig/iptables (IPv4 firewall),
# vi /etc/sysconfig/iptables
Add the line
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
If you want to restict access to, edit it as follows:
-A RH-Firewall-1-INPUT -s -m state --state NEW -p tcp --dport 22 -j ACCEPT
If your site uses IPv6, and you are editing ip6tables, use the line:
-A RH-Firewall-1-INPUT  -m tcp -p tcp --dport 22 -j ACCEPT
Save and close the file. Restart iptables:
# service iptables restart

OpenSSH Server Configuration

Edit /etc/ssh/sshd_config, enter:
# vi /etc/ssh/sshd_config
To disable root logins, edit or add as follows:
PermitRootLogin no
Restrict login to user tom and jerry only over ssh:
AllowUsers tom jerry
Change ssh port i.e. run it on a non-standard port like 1235
Port 1235
Save and close the file. Restart sshd:
# service sshd restart