When sac is invoked, it first looks for the per-system configuration script /etc/saf/_sysconfig. sac interprets _sysconfig to customize its own environment. The modifications made to the SAC environment by _sysconfig are inherited by all the children of the SAC. This inherited environment may be modified by the children.

After it has interpreted the _sysconfig file, the sac reads its administrative file /etc/saf/_sactab. _sactab specifies which port monitors are to be started. For each port monitor to be started, sac forks a child (see fork(2)) and creates a utmpx entry with the type field set to LOGIN_PROCESS. Each child then interprets its per-port monitor configuration script /etc/saf/pmtag/_config , if the file exists. These modifications to the environment affect the port monitor and will be inherited by all its children. Finally, the child process execs the port monitor, using the command found in the _sactab entry. (See sacadm; this is the command given with the -c option when the port monitor is added to the system.)

The -t option sets the frequency with which sac polls the port monitors on the system. This time may also be thought of as half of the maximum latency required to detect that a port monitor has failed and that recovery action is necessary.

The Service Access Controller represents the administrative point of control for port monitors. Its administrative tasks are explained below.

When queried (sacadm with either -l or -L), the Service Access Controller returns the status of the port monitors specified, which sacadm prints on the standard output. A port monitor may be in one of six states:

ENABLED

The port monitor is currently running and is accepting connections. See sacadm(1M) with the -e option.

DISABLED

The port monitor is currently running and is not accepting connections. See sacadm with the -d option, and see NOTRUNNING, below.

STARTING

The port monitor is in the process of starting up. STARTING is an intermediate state on the way to ENABLED or DISABLED.

FAILED

The port monitor was unable to start and remain running.

STOPPING

The port monitor has been manually terminated but has not completed its shutdown procedure. STOPPING is an intermediate state on the way to NOTRUNNING.

NOTRUNNING

The port monitor is not currently running. (See sacadm with -k.) This is the normal "not running" state. When a port monitor is killed, all ports it was monitoring are inaccessible. It is not possible for an external user to tell whether a port is not being monitored or the system is down. If the port monitor is not killed but is in the DISABLED state, it may be possible (depending on the port monitor being used) to write a message on the inaccessible port telling the user who is trying to access the port that it is disabled. This is the advantage of having a DISABLED state as well as the NOTRUNNING state.

When a port monitor terminates, the SAC removes the utmpx entry for that port monitor.

The SAC receives all requests to enable, disable, start, or stop port monitors and takes the appropriate action.

The SAC is responsible for restarting port monitors that terminate. Whether or not the SAC will restart a given port monitor depends on two things:

• The restart count specified for the port monitor when the port monitor was added by sacadm; this information is included in /etc/saf/pmtag/_sactab.
• The number of times the port monitor has already been restarted.

sac  session   required   pam_unix_session.so.1