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30. Communications

You will almost certainly want to go "online," or otherwise communicate with other systems. Most systems today are sold with the necessary hardware that you need in order to be able to connect to other systems, such as a modem or a network card. You connect this hardware to the outside world via a telephone line or network connection.

This chapter includes recipes for connecting your Linux system to the Internet with an ISP, using fax services, and making serial connections with a modem.

For more information on this subject, see The Linux Network Administrator's Guide.

30.1 Connecting to the Internet  
30.2 Faxing  
30.3 Calling Out on a Modem  Dialing out on a modem.


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30.1 Connecting to the Internet

@sf{Debian}: `ppp'
@sf{WWW}: ftp://cs.anu.edu.au/pub/software/ppp/

There are several ways to connect a Linux box to the Internet. Digital Subscriber Line (DSL) service, cable modems, and dial-up connections with ISDN or analog modems are currently the most popular methods. Each of these services have their own hardware and software requirements.

For up-to-date, detailed instructions for using these services on Linux-based systems, the relevant HOWTOs published by the Linux Documentation Project remain the definitive guides (see section Reading System Documentation and Help Files):

The following recipes show how to set up and use a PPP ("Point-to-Point Protocol") dial-up connection, long the de facto means of connecting a computer to the Internet over a dial-up line.

30.1.1 Setting Up PPP  Setting up PPP.
30.1.2 Controlling a PPP Connection  Controlling PPP connections.


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30.1.1 Setting Up PPP

To configure PPP for a regular dial-up connection, where your system is assigned a dynamic IP address (the norm for home Internet access), you need to be root (the superuser) to edit the PPP configuration files, and you'll need the standard connection information from your ISP: the dial-up number to use, the IP addresses for their nameservers, and your username and password for accessing their system.

Use this information to customize the file `/etc/chatscripts/provider':

 
ABORT        BUSY
ABORT        "NO CARRIER"
ABORT        VOICE
ABORT        "NO DIALTONE"
""           "\p\p+++\p\p"
""           "at"
""           "at"
OK           "ath0"
""           atdt5551010,,
ost          ppp
ogin         smith
word         \qsecret\q

In this example, after eight lines of modem initialization strings, the modem is instructed to dial the ISP dial-up number, `5551010'. Some systems need one or two commas after the number to signify pauses for the modem; only do this if you can't get a good connection with just the telephone number in this space.

Next is the "host" line: this is an optional line used by some ISPs whose connection line contains a choice of services from which you must make a selection before entering your username and password (some ISPs offer SLIP and shell access along with the standard PPP, for example); customize this and the following lines as instructed by your ISP.

Finally, the username `smith' is given, and then the password of `secret'. The password appears between two `\q' strings, which--for security purposes--instruct ppp to display the question mark (`?') characters instead of the actual password in system log files or other places where an intruder might see it.

Next, edit the file `/etc/ppp/peers/provider' so that it contains these lines:

 
connect "/usr/sbin/chat -v -f /etc/chatscripts/provider"
defaultroute /dev/modem 115200 persist

The last line in this file should include the device name of the modem you are using and the maximum connect speed to try; the preceding example uses `/dev/modem' as the device name of the modem, and 115,200 bps as the maximum connect speed, which is a good value for a typical 56K modem (a rule of thumb is to use the highest connect speed your modem supports; you can always go lower when a connection is made, but you can never raise the speed above what is given here).

Finally, edit the file `/etc/resolv.conf' so that it contains the following, using the two nameserver IP addresses given to you by your ISP:

 
search .
nameserver      nameserver address 1
nameserver      nameserver address 2

For the two nameserver address values, use the IP address of the nameserver machines, as given to you by your ISP. The second is optional--most ISPs have more than one designated nameserver as a backup in the event that the first system becomes unavailable.

Make sure that your user account has membership to the dialout group; otherwise, you'll have to have the superuser account start and stop PPP, which is not recommended (see section Letting Users Access Hardware Peripherals).

Once you've done these things, you should be able to start and stop PPP connections to the Internet. Complete documentation for setting up PPP is in the `/usr/share/doc/ppp' directory.


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30.1.2 Controlling a PPP Connection

After PPP has been installed and configured, use the pon tool to start a PPP connection to the Internet. It calls the number of your ISP with your modem, sends the appropriate login information, and starts the PPP connection.

  • To start a PPP connection, type:

     
    $ pon RET
    

Once you have a PPP connection, you can connect to other systems on the Internet via the WWW or other network services, as described in the following chapters.

To make PPP automatically start when the system first boots, rename the file `/etc/ppp/no_ppp_on_boot' to `/etc/ppp/ppp_on_boot'. (you must be root, the superuser, to do this.)

To output the last few lines of the PPP log file, type plog. This is useful for checking the progress of your PPP connection when it first dials.

Use the poff tool to stop a PPP session. It disconnects your computer from your ISP and hangs up the modem.

  • To stop a PPP session, type:

     
    $ poff RET
    


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30.2 Faxing

@sf{Debian}: `efax'
@sf{WWW}: http://casas.ee.ubc.ca/efax/

If you have a Class 1 or 2 fax modem, you can send and receive fax ("facsimile") messages with your Linux system. The following subsections show how to do this with the efax package, which is designed for single user systems or relatively simple fax configurations (more complicated tools for faxing exist, but they are beyond the scope of this book).

To set up efax for faxing, edit the file `/etc/efax.rc' (you must be root to do this). The important things to specify in this file are the value for `DEV', which is the device name in `/dev' of the fax or modem device (this should almost always be `modem'), and the values for `FROM' and `NAME'---the fax number and organization name to appear on outgoing faxes.

NOTE: Unless you have membership to the dialout group, you must ask your system administrator for access to the modem hardware before you can use it (see section Letting Users Access Hardware Peripherals).

More information on faxing is contained in the Fax Server mini-HOWTO (see section Reading System Documentation and Help Files).

30.2.1 Sending a Fax  Sending a fax.
30.2.2 Receiving a Fax  Receiving a fax.
30.2.3 Receiving Faxes Automatically  Receiving faxes automatically.
30.2.4 Converting to and from Fax Format  Converting fax files.


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30.2.1 Sending a Fax

Use efax to send a fax. It dials the telephone number you give and faxes the contents of the file or files you specify. You can send plain text files or files in TIFF Group 3 format as they are. You can also send files in other formats, but you must convert them to `tiffg3' first--see Converting to and from Fax Format.

Use the `-d' option to specify the full path name of the fax device (usually `/dev/modem' if you are using the modem connected to your system) and the `-t' option followed by a telephone number to specify the number you are to send the fax to. To specify DTMF tone dialing, precede the phone number with a `T'; specify pauses in the dialing sequence with a comma (`,') character--this is useful for dialing out from a PBX or office phone system.

  • To fax a copy of the file `resume.txt' to the number `555-9099', using DTMF tone dialing, type:

     
    $ efax -d /dev/modem -t T555-9099 resume.txt RET
    

To send more than one file, specify them as arguments in the order they are to be sent. You can also specify them with a wildcard character, but be careful--they are sent in the order in which the shell expands the file names, which is alphabetical order. If you have a lot of files that should be sent in a particular order, rename them so their file names begin with the number of the page they correspond to. But be sure to number them with the same number of digits for each file--for example, if you have eleven files to fax, don't name them `1.fax', `2.fax', and so on, to `10.fax' and `11.fax', because the shell will expand them in the order of `1.fax', `10.fax', `11.fax', `2.fax', `3.fax', and so on up to `9.fax'. In this case, you would number them as `01.fax', `02.fax', and so on, so that files one through nine contain the same number of digits in their name as do `10.fax' and `11.fax'.

  • To fax all of the files with the `.fax' extension in the current directory to the number `555-9099', using DTMF tone dialing, type:

     
    $ efax -d /dev/modem -t T555-9099 *.fax RET
    

Another way to do this is to make a text file containing the list of files to fax, one file name per line, in the order you want them sent. If the files you want to send are not in the current directory, be sure to write the file names with path names relative to the current directory--so for example, if you want to send the file `header.fax', which is in your home directory, and the current directory is `~/documents/faxes', the file should be specified as `~/header.fax'.

  • To fax all of the files listed in the file `fax.list' to the number `555-9099', dialing `9' first to obtain an outside line, and using DTMF tone dialing, type:

     
    $ efax -d /dev/modem -t T9,555-9099 $(cat fax.list) RET
    

NOTE: efax doesn't delete the files it faxes.


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30.2.2 Receiving a Fax

To receive a fax, use efax with the `-w' option. You may also have to use `-iSO=1' to send an `S0=1' command to the modem to set it to auto answer, and use `-kZ' to send an `ATZ' reset request to the modem after efax exits.

As with sending a fax, specify the full path name of the device file to use with the `-d' option.

By default, efax outputs a "session log" to the standard error, containing information on the status of the fax messages received; use redirection to redirect it to a file (see section Redirecting Error Messages to a File).

  • To set up efax to receive an incoming fax, saving the session log to a file, `faxlog', type:

     
    $ efax -d /dev/modem -kZ -w -iS0=1 2>&1 >> faxlog RET
    

This command starts efax and sets up the modem to wait for an incoming fax. After a fax is received, efax exits. You can stop efax before it receives a fax by typing C-c or by killing the efax job (see section Stopping a Job).

When a fax is received, it is written to a file in the current directory whose base name consists of the current numeric date and a session number generated by efax; each page is written to a separate file whose three-digit file extension is the page number. The received fax files are in TIFF Group 3 fax format; use display to view them (see section Viewing an Image in X), or convert them to PostScript or another format for printing (see section Converting to and from Fax Format).


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30.2.3 Receiving Faxes Automatically

@sf{WWW}: http://dsl.org/comp/tinyutils/

The command described in the previous recipe can only receive one fax; once the fax is received, efax exits. To set up your system so that you automatically receive all incoming fax messages continually, until you interrupt it, use `faxon', part of the tinyutils package. It starts efax for receiving an incoming fax, as explained previously, but after a fax is received, it starts efax again and continues until you interrupt it.

  • To automatically receive any incoming fax messages, type:

     
    $ faxon RET
    efax: Wed Feb 24 08:38:52 1999 efax v 0.8a (Debian release 08a-6)
    Copyright 1996 Ed Casas 
    efax: 38:52 opened /dev/modem
    efax: 38:53 waiting for activity
    

Each time a fax is received and then saved, efax restarts, waiting for another fax. A session log is written to the file `faxlog' in your home directory.

Should an incoming facsimile message arrive, efax will receive it and write the message in files in the current directory, with a file name convention as described previously; then efax restarts, ready to receive another fax. Type C-c to stop the script and exit efax.


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30.2.4 Converting to and from Fax Format

In order to view or print a received fax, or to fax a file that you have, you must first convert the file to or from the TIFF Group 3 (`tiffg3') fax format, which is the standard format for sending fax files. (You can, however, view `tiffg3' files with the GIMP, or with display---see section Viewing an Image in X).

Use efix to convert (or "fix") files for faxing; it will convert a file you want to fax to the `tiffg3' format. You can also use it to convert received fax files to another format you can view or print. efax outputs to standard output, but you can redirect its output to a file to save it.

To convert a file for faxing, type efix followed by the name of the file to convert, and redirect standard output to the file you want to contain your fax image. efix can read plain text, PBM, and TIFF files.

  • To convert the file `chart.pbm' for faxing, type:

     
    $ efix -i pbm chart.pbm > chart.fax RET
    

This command converts a copy of the file `chart.pbm' to the `tiffg3' fax format, writing it to a file called `chart.fax'. The original PBM file is not altered.

To convert a PostScript file to fax format, use gs and specify tiffg3 as the output device to write to--see Preparing a PostScript File for Printing.

  • To convert the PostScript file `resume.ps' to fax format, type:

     
    $ gs -q -sDEVICE=tiffg3 -dSAFER -dNOPAUSE
    -sOutputFile=resume.fax resume.ps < /dev/null RET 
    

This command (typed all on one line) writes a copy of the file `resume.ps' to the file `resume.fax' in `tiffg3' format, which you can then send as a fax. The original PostScript file is not altered.

To convert a received fax file to a PostScript file that you can then preview (see section Previewing a PostScript File) or print (see section Sending a Print Job to the Printer), use the `-o ps' option.

  • To convert `19990325.001', a received fax file, to a PostScript file, type:

     
    $ efix -o ps 19990325.001 > received.ps RET
    

This command converts the fax file into a PostScript file called `received.ps'.


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30.3 Calling Out on a Modem

Use minicom to dial out with the modem and connect with another system--such as when you want to connect to a BBS ("Bulletin Board System"). It's a serial communications tool for X or the console; it resembles some of the communications tools of the DOS world, such as Telix and Procomm.

When you start minicom, the connection screen looks like this:

communications-minicom-01

The bottom line contains a status bar showing a message describing how to get help, the current modem settings (in this case, 57,600 bps, 8 data bits, no parity, one stop bit), whether or not cursor keys work (the mysterious `NOR' message), the version of the program (`1.82'), the kind of terminal emulation currently set (`VT102'), and whether or not an online connection is currently established. To get a help menu, type C-a z; from this menu, you can press P to set the communications parameters, T to set the terminal settings, O to configure minicom, or D to enter the dialing directory.

To dial a number from the main screen, type ATDT followed by the number to dial.

  • To dial the number `368-2208', type:

     
    ATDT3682208 RET
    

When you type RET, minicom will begin dialing the number; type any key to interrupt the dialing and hang up the line. Once connected, type C-a h to hang up the line and type C-a x to hang up the line and exit the program.

NOTE: minicom isn't really a way to connect your system to the Internet; to do that, you normally start a PPP connection, as described earlier in this chapter.(37)


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