HP-UX System Administrator's Guide: Overview HP-UX 11i v3 (B3921-90011, September 2010)

devices, get status of the devices, or to control those devices in some
other way.
There are two classes of device special files (based on how they are
used to transfer data):
• block special files (transfer data in blocks by means of the system’s
normal buffering mechanism, and are primarily used to mount
file systems)
• character special files (transfer data in an unbuffered stream, and
are used for nearly everything else)
In HP-UX 11i version 3 there are also three types of device special
files (based on how they refer to their associated devices):
• legacy device special files reference their corresponding devices
by the hardware paths to those devices. Legacy device special files
are the type of device special files that have always been part of
HP-UX. They are still supported in HP-UX 11i version 3 and
function as they always have.
• persistent device special files reference their corresponding
devices based on a world-wide unique identifier that is built
into, or associated with, the device. Because persistent device
special files are not dependent on specific hardware paths, they
allow for multiple hardware paths to be represented by a single
device special file. This opens up many new HP-UX features in
the areas of I/O performance, reliability, and flexibility.
• Device special files for pseudodevices. The majority of device
special files are not directly associated with actual hardware
devices but are instead used to access pseudodevices that allow
HP-UX to introduce a virtualization layer between processes
and disk storage (like those for LVM or VxVM), simulate
hardware devices like terminals (ptys), or provide useful
abstractions like /dev/null (a device file often referred to as
the "bit bucket", used to receive and discard output that is not
needed) There are many pseudo-devices in HP-UX, used for a
variety of purposes. Most of these are described in the manpages
of Section 7 of the HP-UX Reference Manual.
/etc The /etc directory stores system-wide configuration files including
files required for:
• customizing boot and shutdown activities
• networking configuration
• configuring which file systems to mount
• defining users and groups
• defining logical volumes
The previous list is only partial. For compatibility reasons, /etc also
contains a number of symbolic links to commands in other directories
(commands that once resided in the /etc directory).
/etc/opt/product
Some optional products, when added to a server, create subdirectories
under the directory /etc/opt to store product specific configuration
information.
/home The /home directory is the default location for the home directories
for user accounts. For example: If a user “Thomas” with user name
thomas is added to an HP-UX server (and if the home directory
The HP-UX Directory Structure 41