1. Introduction to Linux Instructor: Bennett M. Tanyag PART – 2 Unit 2

2. UNIX COMMUNICATIONS COMMUNICATING WITH OTHER USERS IN A UNIX SYSTEM In a multi-user system like UNIX, it is possible for a particular user to communicate with other users within the system.

3. In fact, sending messages electronically is a more efficient alternative to traditional means of communication such as the telephone and memos. UNIX COMMUNICATIONS

4. UNIX has four different facilities for communication among users: 1.The xsend and xget Commands 2.The mail Command 2.The write Command 3.The talk Command UNIX COMMUNICATIONS

5. ELECTRONIC MAIL One tool in UNIX that can facilitate communications among users is the electronic mail. A user can electronically send messages to other users in the system (whether the users concerned are logged-in or not).

6. In a multi-computer environment (such as the Internet), users may even send messages to users of other computers. Electronic mail is faster than written memos and more efficient than making telephone call in the sense that the user does not have to be physically in his office in order for someone to send him a message. ELECTRONIC MAIL

7. The major requirements for this to work properly are that the intended recipient of the message is a recognized user of the UNIX system and that he uses the system regularly (a user cannot read his messages if he does not log-in regularly). ELECTRONIC MAIL

8. CONFIDENTIAL ELECTRONIC MAIL All users who intend to send (and receive) private or confidential electronic mail should first execute the enroll command. This is done by typing enroll at the UNIX prompt followed by the Enter key: $ enroll  Enter encryption key:

9. UNIX will require the user to enter an encryption key. This is the user's password for the private electronic mail facility. Before a user can read his confidential messages, UNIX will again ask for this encryption key. Without this, UNIX users cannot read their private messages. Like the UNIX password, the encryption key is not echoed back (printed on the screen) to the user as he is typing it. CONFIDENTIAL ELECTRONIC MAIL

10. In sending confidential electronic mail, the user should use the xsend command. Format : xsend user_name Where: xsendis the name of the command to send confidential electronic mail user_nameis the user or account name of the intended recipient of the message CONFIDENTIAL ELECTRONIC MAIL

11. After typing xsend, the sender may now proceed in entering the text of the message. Once the user finishes typing, he should then press Control-D to send message. Example: $ xsend Linus  Dear Linus,   Hi Sir Linus, I have already sent you a detailed report on our sales.  Please send me a note if you have comments on my report.  Thank you very much,  Bill Gates  ^D $ _ CONFIDENTIAL ELECTRONIC MAIL

12. When the recipient logs-in into the system, the user will be prompt that he/she has a new email. Notice the [YOU HAVE NEW MAIL] message before the prompt. This tells the user that he has a pending mail. CONFIDENTIAL ELECTRONIC MAIL

13. In order for the recipient to read his private mail, he should execute the xget command. After typing xget, UNIX will ask for the encryption key. After typing the encryption key, the message is displayed together with pertinent information such as the user name of the sender, the date and the time the message was sent. CONFIDENTIAL ELECTRONIC MAIL

14. Example : $ xget  Enter encryption key : From Bill Gates Sat Oct 25 09:08:34 2003 Dear Linus, Hi Sir Linus, I have already sent you a detailed report on our sales. Please send me a note if you have comments on my report. Thank you very much, Bill Gates ? CONFIDENTIAL ELECTRONIC MAIL

15. Notice also that UNIX displays a question mark “?” after the message. This is the xget prompt. Whenever the user sees this prompt, he can type in commands related to the private electronic mail facility. To get a list of commands available, simply type h (help) at the ? prompt followed by Enter key. CONFIDENTIAL ELECTRONIC MAIL

16. ? h  Commands are: qquit leaving unread language n delete current message, display next d same as above CRsame as above !execute shell commands ssave message in named file or mbox wsame as above ?print this list CONFIDENTIAL ELECTRONIC MAIL

17. If the user wants to save the current private mail, he should type s or w to save the message in a file called mbox located in his home directory (/home/Linus). If the user wants to save the current mail to a different file, then he should type s or w followed by the filename: ? s message.from.Gates  $ _ CONFIDENTIAL ELECTRONIC MAIL