AIX Version 4.3 Differences Guide

6.10 System Resource Controller Subsystem Enhancements (4.3.2)
Two major enhancements have been introduced to the System Resource
Controller (SRC) subsystem in AIX 4.3.2. They are aimed at increasing the
reliability and scalability of both the various subsystems that are controlled by
SRC and the SRC itself. The following sections explain these enhancements:
6.10.1 Recoverable SRC Daemon
The SRC is a subsystem controller that facilitates the management and control of
complex subsystems. The SRC provides a single set of commands to start, stop,
trace, refresh, and query the status of a subsystem. If a subsystem should fail for
any reason, the SRC can automatically restart it.
If the SRC itself were to fail for any reason, it would be restarted due to its entry
in /etc/inittab, as shown in the following example:
srcmstr:2:respawn:/usr/sbin/srcmstr # System Resource Controller
The respawned SRC is, however, unable to control or monitor the subsystems
started by the previous instance of SRC since they will have been inherited by the
init process when the original SRC terminated. As a result, the lssrc command
will show such a subsystem as inoperative, even though it is still running. In
addition, the startsrc command can be used to start a second instance of the
subsystem, even though the subsystem definition explicitly forbids multiple
instances.
The SRC in AIX 4.3.2 has been enhanced to allow a respawned srcmstr daemon
to monitor and control the subsystems started by the previous instance of the
daemon. This has been achieved using the following enhancements.
The SRC now keeps an external list of the subsystems under its control in the file
/var/adm/SRC/active_list. This file is for use by the SRC system only, therefore
the format is unpublished. A respawned srcmstr daemon will read the contents of
this file to update its internal list of the currently running subsystems. This will
allow the lssrc command to correctly determine the status of the running
subsystems, even though they were not necessarily started by the current
instance of the srcmstr daemon.
A respawned srcmstr daemon uses a new kernel extension to register interest in
the termination of certain processes. This allows a respawned srcmstr daemon to
be informed of the termination of subsystems started by the previous instance of
the daemon. A child process is created to communicate with the kernel extension.
The child process in turn communicates with the srcmstr daemon. The presence
of the child process, called srcd, indicates that the srcmstr daemon has been
restarted.
# ps -ef | grep src
root 4650 1 0 Aug 21 - 0:00 /usr/sbin/srcmstr
root 24680 4650 0 Aug 21 - 0:00 srcd
root 25894 7030 2 10:03:38 pts/1 0:00 grep src
#
If a subsystem fails for any reason while under the control of a respawned srcmstr
daemon, it will be restarted if the subsystem policy requires it. In this case the exit
code of the subsystem is not available to SRC due to the method used by the
132 AIX Version 4.3 Differences Guide