User Communication

If you are running a multiuser system like Linux, you should expect to find other users on your system. (I guess that's why it is a multi-user system.) Although there are many built-in mechanisms to keep users separated, sometimes you will want to communicate with other users.

Linux provides several tools to do this, depending on exactly what you want to accomplish. If you simply want to send a quick message to someone, for example, to remind him or her of a meeting, you might use the write program, which sends (writes) a message to his or her terminal.

In contrast to some other systems (say, the winpop mechanism under Windows), each line is sent when you press Enter. If you are on the receiving end of the message, the system lets you know who sent you the message.

If the person you are trying to contact is logged in more than once, you need to specify the terminal to which you want to send the message. So, if I wanted to talk to the user jimmo on terminal tty6, the command would look like this:

write jimmo tty6

If you omit the terminal, write is kind enough to let you select which terminal to which you want to send the message.

It might happen that someone tries the above command and receives the following message:

This message means that jimmo has used the mesg command to turn off such messages. The syntax for this command is

mesg n

to turn it off and

mesg y

to turn it on. Unless the system administrator has decided otherwise, the command is on by default. I have worked on some systems in which the administrator changed the default to off.

An extension of write is the wall command. Instead of simply writing the message to a single user, wall writes as if it were writing on a (where else) wall. That is, everyone can see the message when it is written on a wall, and so can every user. The wall command is often used by root to send messages about system status (e.g. when the system is about to be shutdown. Even if a user has disabled messages, the root user can still send them messages using wall.

If you want to have an interactive session, you could send write messages back and forth. On the other hand, you could use the talk program that was designed to do just that. When talk first connects to the other user, that other user sees on his or her screen

As the message indicates, to respond, you would enter

You might have noticed that you can use talk to communicate with users on other machines. If you omitted the machine name, talk would try to contact the user on the local machine (localhost). The preceding message would simply say

You can also disable talk by using the mesg command.

It is common practice to use a couple of terms from radio communication when using talk. Because you cannot always tell when someone is finished writing, it is common to end the line with -o (or use a separate line) to indicate that your turn is "over." When you are finished with the conversation and wish to end it, use oo (over and out).

Both of these mechanisms have some major problems if the user is not logged in: they don't work! Instead, there's mail or, more accurately, electronic mail (or e-mail).

On most UNIX systems (including Linux), e-mail is accessed through the mail command. Depending on your system, the mail program may be linked to something else. On my system, the default was to link to /usr/bin/mail.

There are several different programs for sending and viewing mail. You could use one mail program (or mailer) to send the message and another to read it. Often the program that you use to read your mail is called a mail reader or, simply, reader. Before we go on to the more advanced mail programs, I want to talk about the most common mail program and the one that is most likely to be on your system. (From here on, I will be referring to e-mail simply as mail.)

Mail comes in units called messages. Whether you use UUCP or the Internet, mail is sent back and forth in messages. However, once the message has reached its destination, it is usually tacked onto the end of an existing mail file. There is usually one mail file per user, but that single file contains all of a user's messages (that is, all those that haven't yet been deleted).

To read your mail, you can use three primary character-based programs: elm, pine, and the default reader, mail. Actually, you can use all three programs to send mail as well as read it. Each program has its own advantages and disadvantages. Although the mail interface looks menu-driven, it simply scrolls the information across the screen. Both elm and pine have much more complex menuing systems. Because of this, mail is easier to learn, but you can do much more with the other two programs.

All three programs understand the concept of a "folder" in which you can store messages. This allows you to develop a hierarchy of files that is no different from the normal file system. How the folders are created and managed depends on the program you are using. Therefore, I would suggest that once you decide to use a specific program, stick with it because the files may not be compatible.

In keeping with the basic premise of this book, I must treat these programs as applications. Therefore, I won't go into any more detail about them. Instead, I suggest that you install all three and see which one suits your needs best. If you have the space, you may consider providing all three for your users. The man-pages provide a great deal of information and each program has its own on-line help.

If you are using the X-Windowing System and a desktop environment such as the KDE, you have a much larger and varied choice, such as my favorite Kmail. Prior to using kmail, I was using Netscape Communicator. Although the Netscape Communicator has many useful features, Kmail had the features I really need. Plus, I use the KDE as my desktop environment and Kmail fits into the KDE architecture. (I will talk more about the KDE and many of the programs when I get the time.)

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