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<h1 class="topictitle1">How a subsystem starts</h1>
<div><p>When a subsystem starts, the system allocates several items and
starts autostart and prestart jobs before the subsystem is ready for work.</p>
<div class="p">The subsystem description is used to determine how items are allocated.
The following list represents the sequence of events that occur when the subsystem
starts:<ol><li><strong>Request to start subsystem is issued.</strong> The Start Subsystem (<span class="cmdname">STRSBS</span>)
command is issued. Key startup information is located in the subsystem description.</li>
<li><strong>Memory pools are allocated.</strong> Memory is allocated to the pools defined
in the subsystem description. The memory that is allocated to each defined
pool is taken from the Base memory pool. The system does not allocate memory
to a pool if the amount of memory available to the Base storage pool is less
than the minimum size specified by the Base memory pool minimum size system
value QBASPOOL. If the system cannot allocate all of the requested memory,
it allocates as much memory as is available and allocates all the other as
memory becomes available.</li>
<li><strong>Prestart jobs are started.</strong> This information comes from the prestart
job entries.</li>
<li><strong>Autostart jobs are started.</strong> This information comes from the autostart
jobs entries.</li>
<li><strong>Display stations are allocated (signon displays are up).</strong> If there
are workstation entries and the device is varied on and has not been allocated
by any other subsystem, the subsystem can allocate it and display the signon
display. If the device is varied on and has been allocated by another subsystem
and is at the signon display (the signon display was displayed before the
second subsystem was started), a second subsystem can allocate the device
from the first subsystem and display the signon display. If the device is
not varied on, the subsystem cannot allocate it. The system arbiter (QSYSARB)
and the QCMNARB jobs hold locks on all varied-off devices. Workstation entries
provide the information about what devices to check for allocation.<div class="p"><div class="note"><span class="notetitle">Note:</span> For
virtual display devices, the signon prompt is displayed when the device becomes
fully varied on. This happens when a user connects to the iSeries™ using
that device description (assuming the connection request does not carry the
data that is used to bypass the signon prompt processing). A device can be
taken from a pool of previously created device descriptions and varied on
as part of that connection processing, or a device can be created and varied
on. At a subsystem start, the subsystem will pend a lock for any of the previously
created device descriptions that it wants.</div>
</div>
</li>
<li><strong>Job queues are allocated.</strong> The subsystem will not be able to allocate
a job queue if it is already allocated to another active subsystem. This information
comes from the job queue entries.</li>
<li><strong>Communications devices are allocated.</strong> Requests are sent to the
QLUS (LU services) system job, which handles device allocation for all communications
devices. This information comes from the communication entries.</li>
<li><strong>The Environment is ready for work.</strong></li>
</ol>
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<div>
<ul class="ullinks">
<li class="ulchildlink"><strong><a href="rzakswrkstationallocationa.htm">How workstation devices are allocated</a></strong><br />
Subsystems attempt to allocate all workstation devices in its subsystem description for AT(*SIGNON) workstation entries.</li>
<li class="ulchildlink"><strong><a href="rzakswrkstatnallocationexmpl.htm">Scenario: Workstation allocation</a></strong><br />
The following is an example of how two workstations are allocated to two different subsystems.</li>
</ul>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaksaboutsbs.htm" title="The subsystem is where work is processed on the iSeries server. A subsystem is a single, predefined operating environment through which the system coordinates the work flow and resource use. The system can contain several subsystems, all operating independently of each other. Subsystems manage resources.">Subsystems</a></div>
</div>
<div class="reltasks"><strong>Related tasks</strong><br />
<div><a href="rzaksstartsbs.htm" title="The Start Subsystem (STRSBS) command starts a subsystem using the subsystem description specified in the command. When the subsystem is started, the system allocates the necessary and available resources (storage, workstations, and job queues) that are specified in the subsystem description. You can start a subsystem by using the iSeries Navigator interface or the character-based interface.">Start a subsystem</a></div>
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