Database Reference
In-Depth Information
The entry point for the OHASD is when the node is started or restarted through
/etc/initab
. This executes the
/etc/init.d/ohasd
and
/etc/init.d/init.ohasd
control scripts. This Linux script is a run-level (RC) script and
contains controls to start, stop, enable, and disable actions. The control script in turn spawns the
ohasd.bin
executable.
Figure
16-2
illustrates several daemons involved in a clusterware startup. The figure illustrates how each daemon
is responsible for the startup and administration of the other lower-level daemon processes. Some of these daemons
are assocated with agents.
Agents are a new concept introduced in Oracle Clusterware 11g Release 2. These agents are multi-threaded,
meaning they are responsible for the startup of multiple resource types, which in turn spawn processes to perform
functions as required. Figure
16-2
illustrates two main agents, the
oraagent
and the
orarootagent
.
Figure
16-2
and Table
16-2
show the association of OHASD with various agent processes and other resources that
perform specific functions for the clusterware.
LINUX rUN LeVeLS
run levels are represented by a number value and indicate different states of the operating system. they indicate
entry points into the operating system kernel where different tasks are executed. Oracle enterprise linux(Oel) is
based off the red hat kernel and has the following run levels.
as listed in table
16-1
, run levels 0, 1, and 6 are reserved. run level 5 is the default run level for Oracle enterprise
linux operating system.
Table 16-1.
Linux run levels
Level
Description
0
Halt
1
Single-user mode
2
User definable (not used)
3
Multi-user mode
4
Not used
5
Full multi-user mode (default run level)
Graphical User Interface (GUI)
6
Reboot
the following command will list the current run level of the operating system.
[root@ssky3l11p1 ~]# runlevel
N 5
in the preceding output, ānā indicates that there is no previous run level and ā5ā indicates the current run level.
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