HowTo: Install ssh In Linux

How do I install ssh under Linux operating systems?

Linux operating system comes with OpenSSH client and server as follows from OpenBSD project:
[a] ssh - SSH client act as remote login program.
[b] sshd - SSH server (Daemon) act as server which provide secure encrypted communications between two untrusted hosts over an insecure network. sshd listens for connections from clients (default ssh tcp port # 22). It is normally started at boot from /etc/init.d/ssh or /etc/init.d/sshd script. It forks a new daemon for each incoming connection. The forked daemons handle key exchange, encryption, authentication, command execution, and data exchange.

How do I install ssh under RHEL / SL (Scientific Linux) / CentOS / Fedora Linux?

Type the following yum command to install ssh client and server:
# yum -y install openssh-server openssh-clients
Start and enable sshd server:
# chkconfig sshd on
# service sshd start
Open port 22 for all IP address, enter:
# /sbin/iptable -A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
# service iptables save
You can set an appropriate network block/mask, representing the machines on your network which must be allowed to access this SSH server. In this example open port 22 to only subnet 192.168.1.0/24:
# /sbin/iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 22 -j ACCEPT
# service iptables save
To configure OpenSSH server edit /etc/ssh/sshd config file. Please go though these recommendations to improve security of SSHD server. You can also go through sshd_config(5) man page for more detailed information:
$ man 5 sshd_config