When green was a colour ...
Cast your mind back to 1990 (if you were born - otherwise indulge your Aussie Grandpa as he strolls down Memory Lane). The "data centre" is the main office. The IBM RS/6000 is under the coffee urn table and both get turned off at 5 o'clock each afternoon. When the RS/6000 gets turned on the next morning - while the urn is heating up - a whole lot of messages scroll off a terminal (look it up, Junior) with a green screen. (In computing back then, "green" had nothing to do with saving electricity. It was a colour.) That green screen (although often more grey with dust) was called the system console.
That console was your lifeline. It displayed error messages and if you lost your network connectivity because someone borrowed a cable, you could still log on to the system, which would display "Welcome to AIX 3."
Well, time has moved on (more's the pity!) and physical consoles have now been replaced with virtual ones.
"All very interesting, Pop, but ... "
Don't interrupt me! You're wondering why you'd ever need to know about a console. You never see the inside of a data centre and you always log in via the network. Well, here are some times when a console is your best (and often only) option:
- you are installing AIX or migrating to a new version
- you are restoring a mksysb after accidentally cleaning up your system
- you need to run diagnostics in stand-alone mode or maybe some file system checks (fsck)
- you have to crack the root password
- you don't have the network configured on your LPAR yet, or you've lost your last good network connection
- security restricts root access to the console
Sometimes you just have to connect via the system console.
How you connect to the console will depend on your system configuration.
If you're on a small or old standalone system, you'll probably use the ASCII screen I was reminiscing about. But if you're on a larger or newer system - one that is partitioned (LPARs) - you'll either use the Integrated Virtualization Manager (IVM), or a Hardware Management Console (HMC).
Console connection via IVM and HMC
With IVM you can open a virtual terminal session to a partition. Of course, the HMC itself serves as a console for one or several physical servers, but here we're only speaking of making a console connection to a single LPAR. You can select a single LPAR, then Console Window > Open Terminal Window
If you get a message "A terminal session is already open ... " then someone else is logged in. You can have the fun of working out what Close Terminal Window is for.
The HMC console is a bit of a clunky terminal. Using Putty is much more pleasant (cut and paste, colours, scroll history). To use a terminal emulator and still connect as a console, you'll need to use Remote Virtual Terminal. If you connect to the HMC via a browser, you can check if you can do this remote console thing by selecting HMC Management > Administration > Remote Command Execution and Remote Virtual Terminal. Here's what those screens look like.
Once that's done, you can ssh to the HMC and run the command vtmenu. That should display a menu of the managed systems which the HMC is connected to. From there you should be given a selection of LPARs. More details are available on the HMC hints wiki.
Be a local anywhere
When you set up a new user through smit, you get a question "User can LOGIN?" and another one "User can LOGIN REMOTELY(rsh,tn,login)?" The first one refers to connecting via the console or a directly connected terminal. The second is across the network. As we have seen, you can connect via the console through the HMC. That's a local connection. You could login "locally" over the console from your PC in Uruguay, which connects to an HMC in Uzbekhistan that manages a Power system in Uganda. Local ain't what it used to be.
Bringing it all together
If you really need to connect via a console, there are all sorts of ways of doing it, which is consoling, but a bit odd, because the word "console" has nothing to do with "consolation." It's actually from the Latin con- (with) +solidare (make solid). A console is there to bring everything together when it's all fallen apart - even your network. Of course, in my day networks were a luxury ...