DRD-Safe Concepts for HP-UX 11i v2 and Later

1 Introduction
1.1 Abstract
System administrators often want to upgrade software and apply patches to their HP-UX systems in as
short a maintenance window as possible. In addition, they also need a quick and reliable way to
return to the pre-updated system in the event that the modifications do not work as expected.
The Dynamic Root Disk (DRD) utilities create and manage the inactive copy of the HP-UX operating
system (or inactive system image). Utilization of DRD allows for the installation of patches and
products to the inactive system image while the booted system image continues to run.
Note:
The installation of HP-UX that is currently in use is known as
the booted system image. The booted system image
includes all aspects of the HP-UX installation, including the
file system layout, kernel definition, configuration
information, installed software, processes, memory layout,
and daemons servicing the system.
The other installation of HP-UX that is not currently in use is
known as the inactive system image. Because the inactive
system image is not running, processes, memory layout, and
daemons are not part of it. However, the inactive system
image does include the file system layout, kernel definition,
installed software, configuration information, and all other
parts of the operating system that persist across boots of the
system.
A system administrator can reduce a maintenance window by applying patches and software updates
to the inactive system image that has been produced as a clone of the booted system image.
Because the booted system image remains unchanged, this use model is known as hot maintenance
.
When the software changes have been successfully applied, the system administrator boots the
inactive system image, making it the booted system image. The interruption to application availability
is thus reduced to the time needed to boot the system, rather than the entire period needed to
upgrade the software.
In addition, if a (newly) booted system image has a problem with disk hardware or an incompatibility
in installed software, the system administrator can resolve the issue by booting the inactive system
image, making it the booted system image. This use model is known as hot recovery
. Hot recovery
eliminates the need for a time-consuming restore from a tape or network backup.
The core functionality in the DRD utilities is the ability to modify the inactive system image while the
booted system image is active, yet keep the changes isolated to the inactive system image. There are
three basic methods that are all employed to ensure the inactive system is isolated:
• drd runcmd – With drd runcmd, DRD runs a command in a special modification
environment. This environment is called the runcmd environment. The runcmd tool uses
chroot(1M) to create an environment where it runs software management commands such as