Administering an IBM i: how the system works

Coming to an AS/400 from Linux or Windows means meeting a machine that seems to speak another language, and partly it does: the words are different — library, subsystem, output queue, library list — and the ideas beneath the words are genuinely different, not out of historical quirk but because the system is built on a model that does not exist elsewhere.

This guide explains that model. It is not a list of commands to memorise: commands get looked up when needed, and this site already has the reference for that. It is the mental map that makes those commands predictable — which is the difference between administering a machine and repeating procedures somebody else wrote.

Who it is for

Anyone handed an IBM i who has to start answering for its nights: the sysadmin at a company that has had the machine for twenty years and has just lost the person who looked after it, the developer who has always worked inside the application and now has to understand what sits underneath, the consultant walking into an environment they did not build.

No RPG required. What is required is access to a system, even read-only, because almost everything written here can be seen with your own eyes in thirty seconds.

How it is organised

Read the chapters in order the first time: each one uses terms defined in the ones before. After that they work on their own, which is why they are separate chapters rather than one long text.

It starts with how the machine is built, moves to how data is organised, then to how it works — jobs and subsystems — then to who may do what, and ends with the three things a sysadmin genuinely answers for: that the work runs, that printing does not fill the disk, and that there is a backup to restart from.

A note on names

The machine was called System/38, then AS/400, then iSeries, then System i. The operating system was called OS/400, then i5/OS, and today IBM i. They are the same line, and in the average company people still say "the AS/400" about a machine bought last year.

This guide uses IBM i for the operating system and AS/400 where that is the name the thing actually goes by on site. It is not a distinction worth defending: it is useful only so you know that, when searching for documentation, all four names lead to the same place.