Overview of the Service Access Facility

The manner in which a port monitor monitors and manages access ports is specific to the port monitor and not to any other component of the Service Access Facility. Users may therefore extend their systems by developing and installing their own port monitors. This is one of the important features of the Service Access Facility.

From the point of view of the Service Access Facility, a service is a process that is started. There are no restrictions on the functions a service may provide.

The Service Access Facility consists of a controlling process, the Service Access Controller (SAC), and two administrative levels corresponding to two levels in the supporting directory structure. The top administrative level is concerned with port monitor administration, the lower level with service administration.

From an administrative point of view, the Service Access Facility consists of the following components:

• The Service Access Controller (SAC)

• A per-system configuration script

• The SAC administrative file, _sactab

• The SAC administrative command, sacadm(1M)

• Port monitors

• Optional per-port monitor configuration scripts

• An administrative file for each port monitor, _pmtab

• The administrative command pmadm(1M)

• Optional per-service configuration scripts

The Service Access Controller

The Service Access Controller is the Service Access Facility's controlling process. The SAC is started by init(1M) by means of an entry in /etc/inittab. Its function is to maintain the port monitors on the system in the state specified by the system administrator.

The administrative command sacadm is used to tell the SAC to:

• change the state of a port monitor

• add or remove a port monitor from SAC supervision

• list information about port monitors known to the SAC.

The SAC's administrative file contains a unique tag for each port monitor known to the SAC and the pathname of the command used to start each port monitor.

The SAC performs three main functions:

• customizes its own environment

• starts the appropriate port monitors

• polls its port monitors and initiates recovery procedures when necessary