The sshd (Secure Shell Daemon) service is part of the OpenSSH implementation for Linux that provides authenticated, end-to-end encrypted networked communication. For example, a user on one host can log in to another system without using a password because the sshd service can be configured to use alternate authentication techniques such as exchanging shared-key information.
The openssh-server RPM package provides the /usr/sbin/sshd daemon and its configuration files
Two versions of the SSH communication protocol exist, version 1 and version 2. Connections between the client and the sshd daemon are made on TCP/IP port 22 by default, using either UDP or TCP protocols.
To manage the sshd service on demand, use the service tool or run the /etc/init.d/sshd script directly:
# /sbin/service sshd help
Usage: /etc/init.d/sshd {start|stop|restart|reload|condrestart|status}
# /etc/init.d/sshd help
Usage: /etc/init.d/sshd {start|stop|restart|reload|condrestart|status}
/etc/ssh/sshd_config