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# 26.3 Terminals

Contributed by Sean Kelly.

Terminals provide a convenient and low-cost way to access your FreeBSD system when you are not at the computer's console or on a connected network. This section describes how to use terminals with FreeBSD.

## 26.3.1 Uses and Types of Terminals

The original UNIX® systems did not have consoles. Instead, people logged in and ran programs through terminals that were connected to the computer's serial ports. It is quite similar to using a modem and terminal software to dial into a remote system to do text-only work.

Today's PCs have consoles capable of high quality graphics, but the ability to establish a login session on a serial port still exists in nearly every UNIX style operating system today; FreeBSD is no exception. By using a terminal attached to an unused serial port, you can log in and run any text program that you would normally run on the console or in an `xterm` window in the X Window System.

For the business user, you can attach many terminals to a FreeBSD system and place them on your employees' desktops. For a home user, a spare computer such as an older IBM PC or a Macintosh® can be a terminal wired into a more powerful computer running FreeBSD. You can turn what might otherwise be a single-user computer into a powerful multiple user system.

For FreeBSD, there are three kinds of terminals:

- Dumb terminals

- PCs acting as terminals

- X terminals

The remaining subsections describe each kind.

### 26.3.1.1 Dumb Terminals

Dumb terminals are specialized pieces of hardware that let you connect to computers over serial lines. They are called “dumb” because they have only enough computational power to display, send, and receive text. You cannot run any programs on them. It is the computer to which you connect them that has all the power to run text editors, compilers, email, games, and so forth.

There are hundreds of kinds of dumb terminals made by many manufacturers, including Digital Equipment Corporation's VT-100 and Wyse's WY-75. Just about any kind will work with FreeBSD. Some high-end terminals can even display graphics, but only certain software packages can take advantage of these advanced features.

Dumb terminals are popular in work environments where workers do not need access to graphical applications such as those provided by the X Window System.

### 26.3.1.2 PCs Acting as Terminals

If a dumb terminal has just enough ability to display, send, and receive text, then certainly any spare personal computer can be a dumb terminal. All you need is the proper cable and some terminal emulation software to run on the computer.

Such a configuration is popular in homes. For example, if your spouse is busy working on your FreeBSD system's console, you can do some text-only work at the same time from a less powerful personal computer hooked up as a terminal to the FreeBSD system.

There are at least two utilities in the base-system of FreeBSD that can be used to work through a serial connection: cu(1) and tip(1).

To connect from a client system that runs FreeBSD to the serial connection of another system, you can use:

    # cu -l serial-port-device

Where “serial-port-device” is the name of a special device file denoting a serial port of your system. These device files are called `/dev/cuad`N``.

The “N”-part of a device name is the serial port number.

> Note: Note that device numbers in FreeBSD start from zero and not one (like they do, for instance in MS-DOS®-derived systems). This means that what MS-DOS-based systems call `COM1` is usually `/dev/cuad0` in FreeBSD.

> Note: Some people prefer to use other programs, available through the Ports Collection. The Ports include quite a few utilities which can work in ways similar to cu(1) and tip(1), i.e. `comms/minicom`.

### 26.3.1.3 X Terminals

X terminals are the most sophisticated kind of terminal available. Instead of connecting to a serial port, they usually connect to a network like Ethernet. Instead of being relegated to text-only applications, they can display any X application.

We introduce X terminals just for the sake of completeness. However, this chapter does not cover setup, configuration, or use of X terminals.

## 26.3.2 Configuration

This section describes what you need to configure on your FreeBSD system to enable a login session on a terminal. It assumes you have already configured your kernel to support the serial port to which the terminal is connected--and that you have connected it.

Recall from Chapter 12 that the `init` process is responsible for all process control and initialization at system startup. One of the tasks performed by `init` is to read the `/etc/ttys` file and start a `getty` process on the available terminals. The `getty` process is responsible for reading a login name and starting the `login` program.

Thus, to configure terminals for your FreeBSD system the following steps should be taken as `root`:

1. Add a line to `/etc/ttys` for the entry in the `/dev` directory for the serial port if it is not already there.

2. Specify that `/usr/libexec/getty` be run on the port, and specify the appropriate `getty` type from the `/etc/gettytab` file.

3. Specify the default terminal type.

4. Set the port to “on.”

5. Specify whether the port should be “secure.”

6. Force `init` to reread the `/etc/ttys` file.

As an optional step, you may wish to create a custom `getty` type for use in step 2 by making an entry in `/etc/gettytab`. This chapter does not explain how to do so; you are encouraged to see the gettytab(5) and the getty(8) manual pages for more information.

### 26.3.2.1 Adding an Entry to `/etc/ttys`

The `/etc/ttys` file lists all of the ports on your FreeBSD system where you want to allow logins. For example, the first virtual console `ttyv0` has an entry in this file. You can log in on the console using this entry. This file also contains entries for the other virtual consoles, serial ports, and pseudo-ttys. For a hardwired terminal, just list the serial port's `/dev` entry without the `/dev` part (for example, `/dev/ttyv0` would be listed as `ttyv0`).

A default FreeBSD install includes an `/etc/ttys` file with support for the first four serial ports: `ttyd0` through `ttyd3`. If you are attaching a terminal to one of those ports, you do not need to add another entry.

Example 26-1. Adding Terminal Entries to `/etc/ttys`

Suppose we would like to connect two terminals to the system: a Wyse-50 and an old 286 IBM PC running Procomm terminal software emulating a VT-100 terminal. We connect the Wyse to the second serial port and the 286 to the sixth serial port (a port on a multiport serial card). The corresponding entries in the `/etc/ttys` file would look like this:

    ttyd1  "/usr/libexec/getty std.38400"  wy50  on  insecure
    ttyd5   "/usr/libexec/getty std.19200"  vt100  on  insecure

  The first field normally specifies the name of the terminal special file as it is found in `/dev`.
  The second field is the command to execute for this line, which is usually getty(8). `getty` initializes and opens the line, sets the speed, prompts for a user name and then executes the login(1) program.

  The `getty` program accepts one (optional) parameter on its command line, the `getty` type. A `getty` type configures characteristics on the terminal line, like bps rate and parity. The `getty` program reads these characteristics from the file `/etc/gettytab`.

  The file `/etc/gettytab` contains lots of entries for terminal lines both old and new. In almost all cases, the entries that start with the text `std` will work for hardwired terminals. These entries ignore parity. There is a `std` entry for each bps rate from 110 to 115200. Of course, you can add your own entries to this file. The gettytab(5) manual page provides more information.

  When setting the `getty` type in the `/etc/ttys` file, make sure that the communications settings on the terminal match.

  For our example, the Wyse-50 uses no parity and connects at 38400 bps. The 286 PC uses no parity and connects at 19200 bps.

  The third field is the type of terminal usually connected to that tty line. For dial-up ports, `unknown` or `dialup` is typically used in this field since users may dial up with practically any type of terminal or software. For hardwired terminals, the terminal type does not change, so you can put a real terminal type from the termcap(5) database file in this field.

  For our example, the Wyse-50 uses the real terminal type while the 286 PC running Procomm will be set to emulate at VT-100.

  The fourth field specifies if the port should be enabled. Putting `on` here will have the `init` process start the program in the second field, `getty`. If you put `off` in this field, there will be no `getty`, and hence no logins on the port.
  The final field is used to specify whether the port is secure. Marking a port as secure means that you trust it enough to allow the `root` account (or any account with a user ID of 0) to login from that port. Insecure ports do not allow `root` logins. On an insecure port, users must login from unprivileged accounts and then use su(1) or a similar mechanism to gain superuser privileges.

  It is highly recommended that you use “insecure” even for terminals that are behind locked doors. It is quite easy to login and use `su` if you need superuser privileges.

### 26.3.2.2 Force `init` to Reread `/etc/ttys`

After making the necessary changes to the `/etc/ttys` file you should send a SIGHUP (hangup) signal to the `init` process to force it to re-read its configuration file. For example:

    # kill -HUP 1

> Note: `init` is always the first process run on a system, therefore it will always have PID 1.

If everything is set up correctly, all cables are in place, and the terminals are powered up, then a `getty` process should be running on each terminal and you should see login prompts on your terminals at this point.

## 26.3.3 Troubleshooting Your Connection

Even with the most meticulous attention to detail, something could still go wrong while setting up a terminal. Here is a list of symptoms and some suggested fixes.

### 26.3.3.1 No Login Prompt Appears

Make sure the terminal is plugged in and powered up. If it is a personal computer acting as a terminal, make sure it is running terminal emulation software on the correct serial port.

Make sure the cable is connected firmly to both the terminal and the FreeBSD computer. Make sure it is the right kind of cable.

Make sure the terminal and FreeBSD agree on the bps rate and parity settings. If you have a video display terminal, make sure the contrast and brightness controls are turned up. If it is a printing terminal, make sure paper and ink are in good supply.

Make sure that a `getty` process is running and serving the terminal. For example, to get a list of running `getty` processes with `ps`, type:

    # ps -axww|grep getty

You should see an entry for the terminal. For example, the following display shows that a `getty` is running on the second serial port `ttyd1` and is using the `std.38400` entry in `/etc/gettytab`:

    22189  d1  Is+    0:00.03 /usr/libexec/getty std.38400 ttyd1

If no `getty` process is running, make sure you have enabled the port in `/etc/ttys`. Also remember to run `kill -HUP 1` after modifying the `ttys` file.

If the `getty` process is running but the terminal still does not display a login prompt, or if it displays a prompt but will not allow you to type, your terminal or cable may not support hardware handshaking. Try changing the entry in `/etc/ttys` from `std.38400` to `3wire.38400` (remember to run `kill -HUP 1` after modifying `/etc/ttys`). The `3wire` entry is similar to `std`, but ignores hardware handshaking. You may need to reduce the baud rate or enable software flow control when using `3wire` to prevent buffer overflows.

### 26.3.3.2 If Garbage Appears Instead of a Login Prompt

Make sure the terminal and FreeBSD agree on the bps rate and parity settings. Check the `getty` processes to make sure the correct `getty` type is in use. If not, edit `/etc/ttys` and run `kill -HUP 1`.

### 26.3.3.3 Characters Appear Doubled; the Password Appears When Typed

Switch the terminal (or the terminal emulation software) from “half duplex” or “local echo” to “full duplex.”

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