Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Understanding Serviceguard Software Components
Serviceguard Architecture
Chapter 3 41
This daemon is started by xinetd. Parameters are in the
/etc/xinetd.d/hacl-probe file. The path for this daemon is
$SGLBIN/cmomd.
This daemon may not be running on your system; it is used only by
clients of the object manager.
Service Assistant Daemon: cmsrvassistd
This daemon forks and execs any script or processes as required by the
cluster daemon, cmcld. There are two type of forks that this daemon
carries out:
• Executing package run and halt scripts
• Launching services
For services, cmcld monitors the service process and, depending on the
number of service retries, cmcld either restarts the service through
cmsrvassistd or it causes the package to halt and moves the package to
an available alternate node. The path for this daemon is:
$SGLBIN/cmsrvassistd.
Quorum Server Daemon: qs
Using a quorum server is one way to break a tie and establish a
quorum when the cluster is re-forming; the other way is to use a Lock
LUN. See “Cluster Quorum to Prevent Split-Brain Syndrome” and the
sections that follow it, starting on page 46.
The quorum server, if used, runs on a system external to the cluster. It is
normally started from /etc/inittab with the respawn option, which
means that it automatically restarts if it fails or is killed. It can also be
configured as a Serviceguard package in a cluster other than the one(s) it
serves; see Figure 3-4 on page 49.
All members of the cluster initiate and maintain a connection to the
quorum server; if it dies, the Serviceguard nodes will detect this and
then periodically try to reconnect to it. If there is a cluster re-formation
while the quorum server is down and tie-breaking is needed, the
re-formation will fail and all the nodes will halt (system reset). For this
reason it is important to bring the quorum server back up as soon as
possible.