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TL:DR

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 192.168.1.0/24, edit it as follows:

-A RH-Firewall-1-INPUT -s 192.168.1.0/24 -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