Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Administering a System: Booting and Shutdown
Shutting Down Systems
Chapter 5526
Many HP-UX systems can be equipped with uninterruptible power
supplies (UPSs) to allow you to maintain power to your systems for a
short while following the failure of your computer’s primary power
source. If the power failure is brief, systems equipped with UPSs will not
be affected by the power failure at all. If the power failure appears as
though it will last for a long time, you can use the buffer period provided
by an uninterruptible power supply to perform a normal shutdown. See
“Normal (Planned) Shutdown” on page 522.
Computers equipped with HP PowerTrust uninterruptible power
supplies can also be monitored by a special daemon called upsmond,
which, when running, always resides in memory (is not swappable).
upsmond communicates with the power supplies, and when power has
been off for longer than a pre-configured time period, upsmond will
perform a clean shutdown of your system automatically.
Not all HP-UX systems are equipped with uninterruptible power
supplies. If yours is not, an unclean shutdown is the likely result of a
power failure. No memory dump will be performed, and it is possible that
buffers of recent disk changes still reside in memory, and have not been
written to disk by the sync program. See “Unclean Shutdowns” on
page 526 for details.
When a power failure occurs, it is good practice to turn off the power
switches to your computer and its peripherals. This will reduce the
chances of a power surge harming your equipment when the power
comes back on. After the power is restored, follow normal boot
procedures. See “A Standard Boot” on page 466.
Unclean Shutdowns
When a system is properly shut down, all memory-based file system
changes are written to disk and the file systems on disk are marked as
being clean. However, if an improper shutdown (for example, a power
failure) occurs, the memory-based information might not be written to
disk and therefore certain file systems will not have their “clean” flag set
(because, in fact, they might have structural problems as a result of the
memory-based information not being written to disk).
When this happens, a special activity occurs during the boot process. The
file system consistency checker (fsck), when checking for clean flags on
all file systems represented in the file /etc/fstab, will detect that file
systems exist that do not have clean flags set. For these file systems,
fsck will perform a check/repair operation to locate and fix any problems