It will be assumed that we have installed the essential networking software modules (e.g. essential parts of the Slackware N-series), and that you have set up which serial port that is to be used for the /dev/modem.
The default configuration will usually only allow direct access to "/dev/modem" as user "root".
To connect to ISP shell accounts directly, and to experiment with connection sequences, you may use the "minicom" program. It is pretty straight forward to use.
Configuration of the machine for use on the net should be done as user "root". Before proceeding any further, ensure that the file "/etc/hosts.deny" contains the following line:
ALL: ALL
You would normally want to allow yourself, so add the following
line to "/etc/hosts.allow":
ALL: 127.0.0.1
For the following, note that it is meant for those connected via
PPP and with a dynamic IP address. If you have the benefit of a
fixed connection, there will be some differences.
It is nice to have a name connected to the machine, a name that the dynamic IP user really can select as he or she pleases. Put the name in "/etc/HOSTNAME":
roderick
The next step is to set up the name server in "/etc/resolv.conf":
search acme.com
nameserver 193.212.1.0
The name server must be specified by a numeric IP address, and
will be different from ISP to ISP. If required, you can have up
to three different servers. They will be requested in the
sequence in which they are listed. A "search" statement has been
added to allow abbreviation of names like "news.acme.com" to
"news".
A certain minimum of configuration will also be required in "/etc/hosts". Most users will be able to manage with:
127.0.0.1 localhost
0.0.0.0 roderick
Those with a fixed IP-address will obviously replace 0.0.0.0 with
this.
Likewise, a minimum "/etc/networks" is:
loopback 127.0.0.0
localnet 0.0.0.0
The username and password at the ISP must be specified in
"/etc/ppp/pap-secrets"
dirk * PrettySecret
For those ISPs using CHAP instead of PAP, the filename is "/etc/ppp/chap-secrets".
Finally, the nitty gritty regarding the connection procedure itself must be specified before PPP can be initiated. This is done in "/etc/ppp/chatscript":
TIMEOUT 5
'' ATZ
OK ATDT12345678
ABORT 'NO CARRIER'
ABORT BUSY
ABORT 'NO DIALTONE'
ABORT WAITING
TIMEOUT 45
CONNECT ""
TIMEOUT 5
"name:" ppp
Details here may have to be tuned somewhat. The phone number in
the third line must of course be set as required. Some users may
need to replace the "ATZ" modem initialization string with
something more tailored for the modem being used. The last line
specifies that one is expecting the prompt "name:", and that the
response should be "ppp" when it arrives. Other systems may have
other login procedures.
To actually initiate a call, the PPP-protocol may be initiated by issuing the following command:
exec pppd connect \
'chat -v -f /etc/ppp/chatscript' \
-detach crtscts modem defaultroute \
user dirk \
/dev/modem 38400
We should now be on-air, and stay up until the program is killed
by typing a Ctrl-C. Any messages concerning the connection will
be appended to the system logs. To read them, try:
trail /var/adm/messages
As long as PPP is up, you will have direct access to the Internet, and may use programs like ftp, ncftp, rlogin, telnet, finger etc. All these programs should be part of the network package.
Further information concerning PPP is also available from:
/usr/lib/ppp/README.linux-chat
Finally, an additional word about safety. The file "/etc/inetd.conf" lists all services that your machine will offer externally. With the "/etc/hosts.deny" file we have made, no external access will be allowed. For those who need it, access must be allowed explicitly in "/etc/hosts.allow". Local traffic may be allowed by:
ALL: LOCAL
See also "man 5 hosts_access".
A final little thing. A certain confusion exists regarding the names of the POP-protocols. A definition in "/etc/services" compatible with just about everything is:
pop2 109/tcp pop-2 # PostOffice V.2
pop3 110/tcp pop-3 pop # PostOffice V.3
ALT Instead of "chatscript", one might use the much more flexible "dip". But not in connection with "diald".
ALT Those lucky enough to have a permanent TCP/IP connection via e.g. an Ethernet may safely ignore anything about PPP, and rather start concentrating about setting up their network card.
ALT Others may not have the possibility of using PPP, but may be able to use SLIP instead, for which there is support in much the same manner as for PPP. Another possibility is UUCP. Others again may have to rely on exchange of news and email be means of SOUP. A description for the latter case may be found in:
ftp://ftp.sn.no/user/bjorn/Linux-offline.tgz
The TERM program is also an option. Refer to the "Term-HOWTO".