IBM Power 720 Overview page 191

The modes are as follows:
Service mode
This mode requires a service mode boot of the system and enables the checking of
system devices and features. Service mode provides the most complete self-check of the
system resources. All system resources, except the SCSI adapter and the disk drives
used for paging, can be tested.
Concurrent mode
This mode enables the normal system functions to continue while selected resources are
being checked. Because the system is running in normal operation, certain devices might
require additional actions by the user or diagnostic application before testing can be done.
Maintenance mode
This mode enables the checking of most system resources. Maintenance mode provides
the same test coverage as service mode. The difference between the two modes is the
way that they are invoked. Maintenance mode requires that all activity on the operating
system be stopped. The
system and put the operating system into maintenance mode.
The System Management Services (SMS) error log is accessible on the SMS menus. This
error log contains errors that are found by partition firmware when the system or partition is
booting.
The service processor's error log can be accessed on the ASMI menus.
You can also access the system diagnostics from a Network Installation Management (NIM)
server.
Alternate method: When you order a Power System, a DVD-ROM or DVD-RAM might be
optional. An alternate method for maintaining and servicing the system must be available if
you do not order the DVD-ROM or DVD-RAM.
The IBM i operating system and associated machine code provide dedicated service tools
(DST) as part of the IBM i licensed machine code (Licensed Internal Code) and System
Service Tools (SST) as part of the IBM i operating system. DST can be run in dedicated mode
(no operating system loaded). DST tools and diagnostics are a superset of those available
under SST.
The IBM i End Subsystem (ENDSBS *ALL) command can shut down all IBM and customer
applications subsystems except the controlling subsystem QTCL. The Power Down System
(PWRDWNSYS) command can be set to power down the IBM i partition and restart the
partition in DST mode.
You can start SST during normal operations, which keeps all applications running, by using
the IBM i Start Service Tools (STRSST) command (when signed onto IBM i with the
appropriately secured user ID).
With DST and SST, you can look at various logs, run various diagnostics, or take several
kinds of system dumps or other options.
Depending on the operating system, the following service-level functions are what you
typically see when you use the operating system service menus:
Product activity log
Trace Licensed Internal Code
Work with communications trace
command is used to stop all activity on the operating
shutdown -m
Chapter 4. Continuous availability and manageability
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