SSH, The Secure Shell: The Definitive Guide, 2nd Edition

Using the OpenSSH Server

Before you can use sshd on Mac OS X, you’ll need to enable the server and possibly open up the Mac’s firewall. In addition, you’ll want to know about some configuration differences as compared to most other OpenSSH installations.

15.2.1 Enabling the Server

SSH server startup is controlled from the Sharing pane in System Preferences, under Services, as in Figure 15-1. To enable sshd, select Remote Login and click the Start button.

Figure 15-1. Enabling the SSH server in System Preferences

15.2.2 Opening the Firewall

By default, the Mac OS X personal firewall will block SSH connections from the outside world. If you have this firewall enabled, you must manually permit SSH traffic through it. This is done from the Sharing pane in System Preferences, under Firewall, as in Figure 15-2.

Figure 15-2. Opening a firewall hole for SSH in System Preferences

15.2.3 Control by xinetd

In most Unix-like operating systems, the OpenSSH server runs as a daemon, listening for SSH connections. On Mac OS X, however, sshd is controlled by the super-server daemon, xinetd. [5.3.3.2] Whenever an SSH client attempts to contact sshd on TCP port 22, xinetd notices the attempt and invokes a single instance of sshd (specifically, sshd -i) to serve that connection.

The xinetd configuration file for ...