SAC(1M)             RISC/os Reference Manual              SAC(1M)



NAME
     sac - service access controller

SYNOPSIS
     sac -t sanity_interval

DESCRIPTION
     The Service Access Controller (SAC) is the overseer of the
     server machine.  It is started when the server machine
     enters multiuser mode.  The SAC performs several important
     functions as explained below.

     Customizing the SAC environment.  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.

     Starting port monitors.  After it has interpreted the _sys-
     config 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 [fork(2)] and creates a utmp 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 modifi-
     cations to the environment affect the port monitor and will
     be inherited by all its children.  Finally, the child pro-
     cess 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.)

     Polling port monitors to detect failure.  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.

     Administrative functions.  The Service Access Controller
     represents the administrative point of control for port mon-
     itors.  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.



                        Printed 11/19/92                   Page 1

SAC(1M)             RISC/os Reference Manual              SAC(1M)



     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.  STOP-
               PING 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 run-
               ning'' 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 utmp
     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

SEE ALSO
     sacadm(1M), pmadm(1M).




 Page 2                 Printed 11/19/92

SAC(1M)             RISC/os Reference Manual              SAC(1M)



FILES
     /etc/saf/_sactab
     /etc/saf/_sysconfig
     /var/adm/utmp
     /var/saf/_log


















































                        Printed 11/19/92                   Page 3