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It will be assumed that we have installed the essential
networking software modules from your Linux distribution, 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: LOCAL
Or if you insist:
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 .
nameserver 193.212.1.0
<nidx>nameserver
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, each on a separate line.
They will be requested in the sequence in which they are listed.
If you want to be able to use names like somemachine as
an abbreviation for somemachine.acme.xz , you must
replace the first line with:
search acme.xz
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 that.
Likewise, a minimum
/etc/networks is:
loopback 127.0.0.0
localnet 0.0.0.0
You should also set your external mail domain in
/etc/mailname:
acme.xz
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 a prompt that ends with
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:
tail /var/adm/messages
or
dmesg
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
/usr/lib/ppp/README.linux-chat
Finally, an additional word about security 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 minor issue: 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 fortunate 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.sol.no/user/bjorn/Linux-offline.tgz
The TERM program is also an option. Refer to the
Term-HOWTO.
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