Red Hat ENTERPRISE LINUX 3 - INTRODUCTION TO SYSTEM ADMINISTRATION Administration Manual page 163

Chapter 8. Planning for Disaster
8.1.2.1. Operating System Failures
In this type of failure, the operating system is responsible for the disruption in service. Operating
system failures come from two areas:
Crashes
•
Hangs
•
The main thing to keep in mind about operating system failures is that they take out everything that the
computer was running at the time of the failure. As such, operating system failures can be devastating
to production.
8.1.2.1.1. Crashes
Crashes occur when the operating system experiences an error condition from which it cannot recover.
The reasons for crashes can range from an inability to handle an underlying hardware problem to a
bug in the kernel-level code comprising the operating system. When an operating system crashes, the
system must be rebooted in order to continue production.
8.1.2.1.2. Hangs
When the operating system stops handling system events, the system grinds to a halt. This is known
as a hang. Hangs can be caused by deadlocks (two resource consumers contending for resources the
other has) and livelocks (two or more processes responding to each other's activities, but doing no
useful work), but the end result is the same — a complete lack of productivity.
8.1.2.2. Application Failures
Unlike operating system failures, application failures can be more limited in the scope of their damage.
Depending on the specific application, a single application failing might impact only one person. On
the other hand, if it is a server application servicing a large population of client applications, the
consequences of a failure would be much more widespread.
Application failures, like operating system failures, can be due to hangs and crashes; the only differ-
ence is that here it is the application that is hanging or crashing.
8.1.2.3. Getting Help — Software Support
Just as hardware vendors provide support for their products, many software vendors make support
packages available to their customers. Except for the obvious differences (no spare hardware is re-
quired, and most of the work can be done by support personnel over the phone), software support
contracts can be quite similar to hardware support contracts.
The level of support provided by a software vendor can vary. Here are some of the more common
support strategies employed today:
Documentation
•
Self support
•
Web or email support
•
Telephone support
•
On-site support
•
Each type of support is described in more detail in the following sections.
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