System Administration Guide
Appendix B, Using the system console and non-graphical displays

Using serial multiscreens with mscreen

Using serial multiscreens with mscreen

The multiscreen(M) feature provides many separate login screens on the console. It is possible to use a similar feature on a terminal. Terminals that have multiple pages of screen memory can be used as separate screens, each with a different login session, as if you had several terminals at your service instead of one.

On a Wyse 60 terminal, the contents of two entire screens of activity can easily be saved. The use of a third screen on the Wyse 60 is discussed below. Using two screens is very much like having more than one terminal. The complete functionality of a login session is provided on each screen, and previously executed commands (or their results) are displayed on each screen when it is in use. This section uses the Wyse 60 as an example. (See the mscreen(M) manual page for a technical explanation.)

You can also limit the number of mscreens available. The mscreen utility provides access to multiple terminal sessions, much like logging in on more than one terminal. These sessions are provided on ``pseudo-ttys'' rather than the tty devices usually used by terminals or modems. A tty is a special file associated directly with a particular hardware device used for communication with equipment such as terminals or printers. ttys can be seen in the /dev directory as files with the name ``tty'' followed by a number and a letter. Use the mkdev pttys command to add pseudo-ttys for use with mscreen. As a general guideline, the recommended number is two or three per user -- so if you plan to accommodate 8 serial terminal users, you should create 16-24 pseudo-ttys. Refer to ``Adding or removing pseudo-ttys'' in the Networking Guide for more information.

Adding more mscreen capability to your system should increase the productivity of the users. However, too much of a good thing can slow your system down. A system with 10 users, each of whom uses two screens, could perform as though it is servicing 20 users. Keep system performance in mind when deciding how many mscreens should be allowed system-wide, and who should be able to use them.

NOTE: When using the who command, each user mscreen session is listed. If you wish to list only the master logins, use the who -f command.

No terminal known contains enough screen memory to save the material displayed during the use of all 20 logins that mscreen is capable of. However, any terminal should allow the user to switch between as many as 20 screens, providing the keyboard has enough extra keys to indicate the switch between screens. The user will probably not find multiple screens very useful without multiple pages of screen memory. It is inconvenient, for example, to have to redraw the terminal's screen each time one switches screens when using a spreadsheet on one screen and vi on the other. Most people who use terminals with minimal screen memory prefer shell layers shl(C) to mscreen for multiple login sessions. For more information, see the shl(C) manual page.