Port monitor requirements

To implement a port monitor, several requirements must be met. These are summarized here. In addition to the port monitor itself, an administrative command must be supplied.

Initial environment

When a port monitor is started, it expects an initial execution environment in which:

• it will have no file descriptors open

• it will not be a process group leader

• it will have an entry in /etc/utmp of type LOGIN_PROCESS

• an environment variable, ISTATE, will be set to ``enabled'' or ``disabled'' to show the port monitor's correct initial state

• an environment variable, PMTAG, will be set to the port monitor's assigned tag

• the directory that contains the port monitor's administrative files will be its current directory

• the port monitor will be able to create private files in the directory /var/saf/pmtag, where pmtag is the port monitor's tag

• the port monitor will be running with user ID 0 (root)

Important files

Relative to its current directory, the following key files exist for a port monitor:

_config

The port monitor's configuration script. The port monitor configuration script is run by the SAC. The SAC is started by init(1M) as a result of an entry in /etc/inittab that calls sac(1M).

_pid

The file into which the port monitor writes its process ID.

_pmtab

The port monitor's administrative file. This file contains information about the ports and services for which the port monitor is responsible.

_pmpipe

The FIFO through which the port monitor will receive messages from the SAC.

svctag

The per-service configuration script for the service with the tag svctag.

../_sacpipe

The FIFO through which the port monitor will send messages to the SAC.

Responsibilities

A port monitor is responsible for performing the tasks described below in addition to its port monitor-specific function.

A port monitor must perform the following miscellaneous tasks during its normal operation:

• Write its process id into the file _pid and place an advisory lock on the file.

• Terminate gracefully on receipt of the signal SIGTERM.

• Follow the protocol for message exchange with the SAC.

A port monitor must perform the following tasks during service invocation:

• Create a utmp entry if the requested service has the u flag set in _pmtab.

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  NOTE: Port monitors may ignore this flag if creating a utmp entry for the service does not make sense because of the manner in which the service is to be invoked. On the other hand, some services may not start properly unless utmp entries have been created for them.

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• Interpret the per-service configuration script for the requested service, if it exists, by calling the doconfig(3iac) library routine.