Operating Systems

How often have you wasted time reconfiguring your Linux systems using a line-mode terminal? How often have you struggled using “ed” to correct configuration files; for example, replacing the Internet Protocol (IP) address in the network configuration?

Terminal connections over the z/VM Inter-User Communication Vehicle (IUCV) let you run your favorite editor. The terminal server using z/VM IUCV helps you connect to your Linux instances even when they aren’t connected to an IP network.

This article introduces you to the Linux on System z terminal server and the concept of terminals over z/VM IUCV. It will guide you through the components of an IUCV terminal environment, describe how to enable Linux instances for IUCV terminal connections, and explain how you can increase availability and security.

Benefits of Terminal Connections Over z/VM IUCV

Terminals are input and output devices through which users interact with operating systems and programs. Early terminals were separate physical devices connected to a computer system. Today, separate terminals are rarities. Instead, terminals are emulated by software programs, called terminal emulators. On Linux systems, typical terminal emulators are xterm, kconsole, and gnome-terminal. On Linux on System z, you work with two different types of terminals. The 3215 line-mode or 3270 block-mode terminals are the traditional mainframe interfaces. The terminal capabilities of 3215 and 3270 are limited compared to standard Linux terminals. Have you ever tried using vi to edit configuration files in a 3215 terminal? Administrating Linux systems using 3215 or 3270 terminals is a cumbersome task.

Is there an alternative? Yes! The alternative comprises new tools and a Linux kernel device driver that supports full-screen Linux terminals accessible through z/VM IUCV. Terminals with full-screen capabilities allow resizing terminal windows, displaying colors, and positioning the cursor in the terminal window. You can also run screen-based programs; for example vi, emacs, or top.

The z/VM IUCV provides communication between two z/VM guest virtual machines. The device driver uses IUCV to ensure communication even if Linux instances aren’t connected to an IP network.

Suppose you need to correct the network configuration for a Linux instance, LXGUEST1. Instead of working from a 3270 session with LXGUEST1, you first start a Linux terminal session with a dedicated Linux instance on the same z/VM system. This Linux instance is your terminal server. From the session on the terminal server, you then establish, over IUCV, a terminal session with the Linux instance in the LXGUEST1 guest virtual machine. After the terminal session is established, all the usual Linux programs are at your disposal to make the required changes. The example might look like Figure 1.

 

What an IUCV Terminal Environment Looks Like

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