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