Communicating with the System

Overview

The IBM i operating system (OS) is one of the most sophisticated on the market today. To a new user, the apparent complexity may seem like a huge jigsaw puzzle waiting to be solved. What we hope to provide with this first chapter is simply a place to start collecting critical pieces of the puzzle.

This chapter provides initial exposure to several topics necessary for a basic understanding of how to communicate with the IBM i OS using the different types of screens and menus. The chapter also introduces concepts related to system organization and a few basic work management ideas (e.g., how jobs enter, run in, and leave the system).

As in any other technical field, you will need to master a number of terms and concepts to be successful using the OS. Although the IBM i OS will provide comprehensive help as you learn, you are strongly encouraged to ask questions of your instructor or mentor.

Objectives

Students will be able to

• Sign on to the IBM i OS system, properly entering a user profile and password

• Explain the difference between system and subsystem

• Describe the two most common types of jobs

• List several attributes of a user profile

• List several features of the IBM i OS

• Explain the function of IBM i Control Language (CL) and enter a CL command on a command line using proper syntax

• Explain the purpose of system values and how to check them

• Describe four types of displays, their use, and their components

• Explain the relationship between CL commands and IBM i OS menu paths

The System

The IBM i OS is a complex and rich set of programs that not only controls traditional functions such as data access, storage, and task management but also incorporates features that normally would require separate software components on other systems — features such as communications support, database management, security, and interactive support.

A new system running IBM i OS comes with a standard basic configuration, which includes predefined system settings for work management functions that allow interactive and batch jobs to run without need for a customized installation. Later, subsystems can be created and system resources allocated to optimize workload distribution and throughput according to the special needs of a particular business.

IBM i is a multiuser, multitasking OS (a system on which two or more people can perform two or more tasks concurrently) optimized for the efficient execution of business applications. The basic unit of work is a job. The term job refers generally to a unit of work that includes all programs, files, and instructions necessary to perform that work. Examples of a job would be an interactive user session for updating a customer master file, or a program compilation running unobtrusively in the background.

The older IBM AS/400 systems used terminals and hardwired (twinaxial, or "twinax") connections to access the system. Today, most users connect to the system using 5250 emulators or Web interfaces. In this book, we present a number of ways to connect to the system, including 5250 emulators, Remote System Explorer (RSE)/Rational Developer for Power (RDP)-based, and IBM i Access for Web and Access for Windows. The IBM i OS has evolved to become one of the most advanced OSs available today.

IBM I Objects

The IBM i OS is an object-based OS. An object is anything on the system that has a name and takes up space in storage. IBM supplies a large number of objects through the IBM i OS and licensed program products. These objects typically have names beginning with Q. Programmers and operators create other objects and name them according to their organizations' naming conventions.

The system can locate an object by its name; once located, the object can further identify itself to the system by functional attributes that are a part of the object. Objects are grouped into types. An object type determines how the object is used on the system (i.e., the actions that one can take when using the object). Common object types include programs, files, and commands. Object types also include user-profile objects, which contain information about users, and subsystem-description objects, which contain the characteristics of subsystems. Object type is always assigned by the system and is determined by the command used to create the object. We continue to explore this concept of objects throughout this book.

Subsystems

All jobs in the IBM i OS are run in subsystems. A subsystem is a predefined operating environment the system uses to coordinate workflow and system resources. The system uses a subsystem description to define the required resources to process work. The components of a subsystem description determine how the system uses resources to process jobs within the subsystem. When the base IBM i OS is installed, several different subsystems are already defined and active, and each one has a separate subsystem description.

Attributes of subsystems are defined in the subsystem description; these include the subsystem name (e.g., QCTL for the controlling subsystem, QINTER for the interactive subsystem, QBATCH for the batch subsystem), how many jobs can run in the subsystem at one time, which storage pools the subsystem will use (IBM i main storage is divided into a number of different storage pools), and which job queues the subsystem will use.

Different subsystems are necessary because there are many different types of jobs with different characteristics and often-conflicting needs. If we treated all of these various jobs equally, the overall performance of the system would suffer. As system administrators, we can change the existing subsystem descriptions and create new subsystems when necessary. In this way, we can tailor subsystems to efficiently handle the needs of different jobs — for example, to ensure that long-running jobs that require no user interaction but significant CPU time do not interfere with high-priority interactive jobs that need fast response time. Within subsystems, we can prioritize individual jobs to begin execution sooner or later; and, after they begin execution, we can give them a higher or lower runtime priority.

Types of Jobs

IBM i OS jobs can originate from several sources and are classified by how they originate on the system. In...