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Linux and Dialup ISP

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  Egil Kvaleberg, [email protected]
  v1.26, 5 March 1998

  This document describes how to use Linux to connect to an Internet
  Service Provider via a dial-up modem TCP/IP connection.  As well as
  the basic dial-up procedure and IP establishment, email and news han-
  dling is covered.

  Table of Contents

  1. Introduction

     1.1 Copyright
     1.2 Disclaimer
     1.3 Translations
     1.4 New versions of this document
     1.5 Feedback

  2. How do I connect to the rest of the world?

     2.1 The basic configuration

  3. How do I

  4. How do I send and receive

  5. News

     5.1 How do I set up an online news-reader?
     5.2 How do I set up an offline news-reader?
     5.3 How do I set up C News?
     5.4 How do I set up Leafnode?

  6. How do I automate the connection procedure?

  7. Final words

     7.1 Other things I should know about?

  8. ISP specific information

     8.1 How do I learn more?
     8.2 Thanks to


  1.  Introduction

  This description has been made to answer a few questions about how
  dial-up ISP (Internet Service Provider) subscribers may configure and
  use Linux.

  To aid those who will connect their Linux based machines to an ISP for
  the first time, an attempt has been made to cover most issues
  encountered.  This quite unavoidably will create a certain degree of
  overlap with other Linux Howto-documents and LDP books.  Reference
  should be made to these documents to provide better understanding and

  Much of the existing documentation is targeted towards users with a
  certain degree of experience, and first time users will often have
  trouble sorting out the relevant information.

  To simplify, the examples given will assume the following:

  o  User name: dirk

  o  Password: PrettySecret

  o  Internet service provider: acme.xz

  o  Email server: mail.acme.xz

  o  News server: news.acme.xz

  o  Name server:

  o  Phone number: 12345678

  Our dirk will be calling his machine roderick.

  All references in the table above should naturally be replaced by
  whatever is valid for the ISP one is using.  Often, just a minimum of
  changes will otherwise be required for users with different ISPs.  I
  would like to be informed about what problems you encounter on this

  1.1.  Copyright

  Copyright (c) 1996,1997,1998 by Egil Kvaleberg. This document may be
  distributed under the terms set forth in the LDP license at

  1.2.  Disclaimer

   No liability for the contents of this documents can be accepted.  Use
  the concepts, examples and other content at your own risk.

  One of many possible setups will be described. In the Linux world,
  there is usually a number of ways in which to accomplish things.
  Paragraphs containing hints to alternatives are marked by ALT: Please
  also note that FTP-references often will change slightly as new
  versions of programs arrive.

  As far as I know, only programs that under certain terms may be used
  or evaluated for personal purposes will be described. Most of the
  programs will be available complete with source under GNU-like terms.

  1.3.  Translations

  This document has been translated to the following languages:

  German, by Cristoph Seibert:

  Korean, by Kidong Lee:

  French, by Eric Jacoboni:

  Polish, by Piotr Pogorzelski: URL TBA


  1.4.  New versions of this document

  New versions of this document will be periodically posted to
  comp.os.linux.answers.  They will also be added to the various
  anonymous FTP sites who archive such information, including:

  In addition, you should generally be able to find this document on the
  Linux Documentation Project page via:

  The very latest version of this document should also be available in
  various formats from:

  1.5.  Feedback

  All comments, error reports, additional information and criticism of
  all sorts should be directed to:

  [email protected]

  2.  How do I connect to the rest of the world?

  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

  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.

  2.1.  The basic configuration

  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:


  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 con-
  nection, 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:


  The next step is to set up the name server in

       search .

  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 dif-
  ferent 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

       search acme.xz

  A certain minimum of configuration will also be required in be able to
  manage with:       localhost         roderick

  obviously replace with that.

  Likewise, a minimum /etc/networks is:


  You should also set your external mail domain in


  The username and password at the ISP must be specified in

       dirk * PrettySecret

  For those ISPs using CHAP instead of PAP the filename is

  Finally, the nitty gritty regarding the connection procedure itself
  must be specified before PPP can be initiated.  This is done in

       TIMEOUT 5
       "" ATZ
       OK ATDT12345678
       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 tai-
  lored 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 proce-

  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

  until the program is killed by typing a ctrl-C.  CAny messages con-
  cerning the connection will be appended to the system logs. To read
  them, try:

       tail /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:



  Finally, an additional word about security The file all services that
  your machine will offer externally. With the have made, no external
  access will be allowed.  For those who need it, access must be allowed
  explicitly in 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 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

  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:

  The TERM program is also an option. Refer to the Term-HOWTO.

  3.  How do I surf ?

  If you think that text is the most important, you might want to use
  the Lynx web browser. It is available from:

  If you have installed the X window system, you can also use one of the
  many graphical browsers.  Chimera may be found at:


  Netscape (aka.  Mozilla

  These browsers are constantly available in new and in various ways
  exciting versions.

  Use and evaluation of these programs is subject to certain terms.
  Please observe them.

  4.  How do I send and receiveemail

  First of all, ensure that sendmail is installed.  Sendmail sorts
  internal and out-bound mail, and will buffer out-bound mail until such
  time it is possible to forward it.

  Sendmail is based on a configuration found in example suitable for ISP
  users can be found in: This is based on delivery
  agent but may easily be changed to use

  It is if course required to have an official domain address for out-
  bound mail, something which is specified in

       # who I masquerade as (null for no masquerading)

  have the same user name locally as you have at your ISP. If it is dif-
  ferent, just specify the full name instead:

       [email protected]

  Sendmail is now configured for sending directly to the recipient.  To
  avoid long and repeated connections in those cases where the connec-
  tion to the receiving end is slow and irregular, is is usually nice to
  use ones ISP as a buffer store.  This can be specified by the DS spec-

       # "Smart" relay host (may be null)

  Beware that sendmail is somewhat sensitive to handling of tab stop
  characters in  You might want to use the characters are
  retained unchanged.

  Email reception can often be performed via the POP3 protocol, which
  can be initiated every time the connection is brought up.  A script
  for testing this is:

       sendmail -q
       popclient -3 -v mail.acme.xz -u dirk -p "PrettySecret" \
              -k -o /usr/spool/mail/dirk

  connection has been established.  Beware that this script is just for
  testing, so ensure that the local mailbox is left untouched while it
  runs.  The -k option means that the mail is kept in the ISP mailbox,
  and you are simply given a copy of the mail.  You would of course want
  to remove this option once you are confident that your setup is work-

  Beware that the password will show on the command line.  Also note
  that popclient is getting old fashioned, and that you should consider
  using instead.

  A more secure and better version of this script may be found at:

  This version of the script requires that procmail is installed, but
  that is something you'll never regret anyway. Most distributions
  include it, otherwise you may try:

  Procmail is a simple and flexible tool that can sort incoming email
  based on a large range of criteria. In addition to being able to
  handle automated tasks like vacation messages and such.

  Note that when we use procmail directly as in this case, the situation
  is somewhat different from what is described in the procmail
  documentation.  A .forward is not required, and we also don't need a
  .procmailrc.  The latter is only required if we want to sort the mail.

  The user interface for reading and sending of email can be found in
  programs like

  ALT: Fetchmail has recently become an improved alternative to
  popclient.  The latest version is available from:

  ALT: For an ordinary dial-up ISP user it is not really necessary to
  have the sendmail daemon active.  To reduce resource usage, and
  possibly other problems, one may thus comment out any startup of
  sendmail, as is usually found in /etc/rc.d/rc.M (this varies from
  distribution to distribution).

  ALT: In place of sendmail one might use the simpler description of it
  (as well as most other things mentioned here) in the Linux Network
  Administrator's Guide.

  ALT: There is also an m4 macro package for making a fresh
  /etc/  For a simple installation it might be just as well
  to modify an existing configuration.

  ALT: There are also simpler although less flexible alternatives for
  handling email.  Pine may run stand-alone as long as it is configured
  properly, for instance.  It might even be possible to use newer
  versions of some web-browsers.

  ALT: Many are very enthusiastic regarding the Emacs companion Gnus as
  an email and news handler. Further information can be found at:

  ALT: An alternative to popclient is pop-perl5.  It is available from:

  5.  News

  5.1.  How do I set up an online news-reader?

  possible to read news online.  There are lots of available programs,
  two simple alternatives being trn.

  To start reading news, the only thing required in terms of
  configuration in most cases is to set NNTPSERVER (usually once and for
  all in the file .profile):

       export NNTPSERVER=news.acme.xz

  To get the From-address correct in postings, some programs may

       export NNTP_INEWS_DOMAIN=acme.xz

  5.2.  How do I set up an offline news-reader?

  offline and thus reduce phone bills and give greater flexibility, one
  must set up a local news-spool of one sort or the other.  This
  requires some configuration, and there will also be a certain amount
  of disk space involved.  After initial setup, things should run more
  or less by themselves, with only some attention needed from time to

  Two different solutions will be described here.

  5.3.  How do I set up C News?

  The solution described here is based on the news-server C News and the
  NNTP protocol.  C News was originally targeted towards another sort of
  configuration, but is flexible enough to handle our situation too.
  One might also use the more recent INN news server but it might
  require a bit more in terms of resources. Either way, be careful not
  to install both; they don't live together easily.

  It is crucial that all maintenance of news is done while logged in as
  user news, and that all configuration files is placed in
  /usr/lib/news.  One way of handling this is, while logged in as root
  to write su news; cd.

  The most important files in the configuration are:

  o   over active newsgroups.  It is updated as required by the command
     comp.os.linux.networking y.

  o   simply contain whatever you want in the Organization: header
     field, in our case:

       Dirk Gently's Holistic Detective Agency

  o   case be set to acme.xz.

  o   of your site in the Path: thread.  In a setup as described here,
     using newsx, this name will never leave the machine, so you can set
     this to whatever you like as long as you are pretty sure it is
     unique. In this case roderick.

  o  The file fetching and further distribution of news.  We will assume
     the ISP in our case adds acme.xz to the Path, and that this is the
     only news source we have.  The example given really tells that we
     will accept everything that arrives, and that we will only post
     news to acme.xz that it hasn't seen before, and is originally
     posted at our own site.  In this simplified setup we assume that
     the all groups will come from a single source.  /all specifies the
     distribution, and must be included.  The letter F says that
     (pointers to) outgoing news articles will be collected in a file.


  o  A subdirectory for the outgoing news must be created, in our case:

       mkdir /var/spool/news/out.going/acme

  o   posting in moderated groups, although this task may usually be
     left to the ISP.

  C News needs a certain degree of daily maintenance, but this can be
  specified once and for all via the command crontab -e setup follows;
  it can be tuned as required:

       # maintain incoming and outgoing batches
       10,40 *  * * * /usr/lib/newsbin/input/newsrun

       # expire C News, once a day
       30 0  * * * /usr/lib/newsbin/expire/doexpire

       # monitor and report if needed
       00 2  * * sat /usr/lib/newsbin/maint/addmissing
       40 3  * * * /usr/lib/newsbin/maint/newswatch
       50 3  * * * /usr/lib/newsbin/maint/newsdaily

  out (twice every hour), doexpire will delete articles as they get old
  (every night at 00:30), and the three last commands does various
  supervisory and error correcting tasks.

  One should also ensure that things are cleaned up when starting the
  machine. As user root, add the following line to /etc/rc.d/rc.local:

       su news -c /usr/lib/newsbin/maint/newsboot

  News may be collected via the program NewsX, The program can be found

  Setting up NewsX is quite simple.  Installation is a classic case of:

       make install

  With the setup outlined here, all you have to do is to create the
  groups you want to read using the addgroup command.

  To fetch articles, user news issues the following commands (assuming
  communication via PPP or similar is up):

       newsx acme news.acme.xz

  The option -d gives continuous printout to the screen.  Refer to the
  NewsX documentation for further information.

  NewsX will also take care of posting of outgoing news.

  To control disposal of articles as they get old, a file explist is
  required.  The comments in this example should explain what we want to

       # hold onto history lines 14 days, nobody gets >120 days
       /expired/                       x       14      -
       /bounds/                        x       0-1-120 -

       # retain these for 2 months
       comp.sources,comp.os.linux.all  x       60      -

       # noise gets thrown away fast
       junk,control                    x       2       -

       # default:  14 days, no archive
       all                             x       14      -

  ALT: In a small news-spool, one will usually not need the newsgroup
  control.  The traffic is huge compared to the possible usefulness. The
  main point is that articles will be canceled, and that groups may be
  created automatically. To ensure that control messages containing
  newgroup not shall mess up things for us, a file called what we will

  comp.os.linux   [email protected]  yv
  all             any             nq

  In this example, all proper groups under comp.os.linux will be created
  (y), and the user news will be notified (v).  Everything else will be
  silently (q) ignored (n).  The last line is sufficient if you want to
  create all groups manually.

  ALT: An alternative to NewsX is suck.

  5.4.  How do I set up Leafnode?

  A different solution altogether is to install the integrated package
  handle all tasks required for a personal news spool, and is easy to
  configure.  It is available via:

  As for C News, all news maintenance really should be performed as user

  The home directory for leafnode is in /usr/lib/leafnode.  To install,

       cd /usr/lib/leafnode
       tar -xzvf leafnode-0.8.tgz
       cd leafnode-0.8
       make install

  Note in the following that the prefix /usr/local/sbin should be
  replaced with /usr/sbin if you installed leafnode from a package.

  While still being logged in as root, change the line that controls
  NNTP in /etc/inetd.conf:

       nntp  stream  tcp  nowait  news  /usr/sbin/tcpd /usr/local/sbin/leafnode

  Activate it by:

       killall -HUP inetd

  Return to user news by writing exit.  In /usr/lib/leafnode/config
  change the line that defines the NNTP server. In our case:

       server = news.acme.xz

  Leafnode will look after itself by adding the following command via
  crontab -e as user news:

       # expire Leafnode, once a day
       0 4 * * * /usr/local/sbin/texpire

  News exchange is also done as user news by the following command
  (assuming PPP is up and running):


  Users who wants to read news should then use the recipe in How do I
  set up an online news-reader?, except that they configure for the
  local machine, i.e:

       export NNTPSERVER=localhost

  That should be all there is to it.  The first fetch will transfer a
  list of available newsgroups.  Leafnode will then monitor what groups
  the users are requesting, and adapt to this the next time it is

  Note that leafnode does not seems to work in cases where NNTP
  authorization is required.  +.LP

  ALT: An alternative to leafnode is nntpcache, available from: ALT: Another
  alternative is to use the newsreader pullslrn-pull package. The
  newsreader must be compiled with the spool feature set.

  6.  How do I automate the connection procedure?

  Automated handling of news and email is quite easy to implement in

  First and foremost one should make a that initiates the ISP
  connection.  Often, this file will simply contain the following:


  connect "/usr/lib/ppp/chat -v -f /etc/ppp/chatscript"
  asyncmap 00000000
  user dirk
  /dev/modem 38400

  To end a connection, use the supplied version of /usr/lib/ppp/ppp-off.

  Having tested the functionality of these two scripts, one must then
  write scripts that perform the various tasks. The script to collect
  email has been described before, and we will here assume it is located
  at /home/dirk/pop.

  A script for exchange of email can then be produced in /root/mail:

       #! /bin/sh
       # exchange mail
       # 10 minutes timeout:

       # kick sendmail:
       sendmail -q &

       # retrieve mail:
       su dirk -c /home/dirk/pop

       # wait for sendmail to terminate:
       while ! mailq | grep -q "Mail queue is empty"; do
           if [ $t -gt $TIMEOUT ] ; then
            echo "sendmail -q timeout ($TIMEOUT).."
            exit 1
           sleep $DT

       exit 0

  The script to exchange news may be placed in /usr/lib/news/news:

  # exchange news
  # must be run as news:
  cd /usr/lib/news

  #update the outgoing batch (C News):
  /usr/lib/newsbin/input/newsrun < /dev/null

  #exchange news:
  /usr/lib/newsbin/newsx acme news.acme.xz

  #and flush the incoming batch:
  /usr/lib/newsbin/input/newsrun < /dev/null

  A script to connect the various bits and pieces remains, and can be
  placed in /root/news+mail:

       # exchange news and email
       # must be run as root
       if ! /usr/lib/ppp/ppp-on; then
           exit 1
       trap "/usr/lib/ppp/ppp-off" 1 2 3 15

       #exchange news+mail:
       /root/mail &
       su news -c ~news/news


       #update the incoming batch (C News):
       su news -c /usr/lib/newsbin/input/newsrun < /dev/null &

       exit 0

  It is quite easy to make an extension to the above that only will
  establish a connection if outgoing email and news is present.  Lets
  call it /root/news+mail.cond, and keep in mind that the name of the
  outgoing news-spool must be updated to suit:

       # exchange news and email, only if outgoing news or mail
       # (C News spool)
       if [ -s /var/spool/news/out.going/acme/togo ] ||
           ! ( mailq | grep -q "Mail queue is empty"); then

  The only thing remaining is to specify when all this is going to
  happen.  This is done using the command crontab -e to exchange news
  and mail at 07:00 in the morning, and after that every 4th hour
  assuming there are outgoing email and news:

       00 7            * * *   /root/news+mail
       00 11,15,19,23  * * *   /root/news+mail.cond

  Ensure that every component is tested well before you connect them
  together. One may later add several other tasks, such as adjustment of
  the time of day (using ntpdate), and automatic update (mirroring) of
  locally maintained WWW and FTP files up to the ISP (using make and

  ALT: Depending on ones preferences, it is also possible to turn the
  process upside down. Every time a PPP link is initiated, the script
  /etc/ppp/ip-up will be started.  One may here add whatever magic is
  required to start exchange of email and news.  See man pppd for
  further detail.

  ALT: It is also possible to automatically connect PPP whenever network
  traffic is detected.  This is in many ways the more elegant solution,
  but it is quite dependent on a good configuration to avoid frequent
  (and costly) connections being made.  More information can be found

  The diald utility is available from:

  At the same location one will also find other variations on the theme
  PPP connections.

  7.  Final words

  7.1.  Other things I should know about?

  o  Various error messages in the system will normally be issued as
     internal email. To ensure that these will actually be read, one
     should create an /etc/aliases.  Remember the command newaliases
     every time you change this.  An example that should cover most
     eventualities is:

       PostMaster: root
       ftp: root
       news: root
       usenet: root
       FaxMaster: root
       fax: root
       WebMaster: root
       MAILER.DAEMON: root

  o  Many programs for Linux may be found at Sunsite, many mirrors and
     every time there is a reference to one should try to use a mirror
     close to home, e.g.

  o  If you happen to be migrating from Yarn it should be possible to
     convert these to standard folders using the yarn2mf available at:

  8.  ISP specific information

  More specific information for certain ISPs is available from a variety
  of sources:

  Demon Internet


  PowerTech, Telenor Online, Telia




  AOL is not possible since AOL uses a proprietary protocol.

  If you can supply ISP specific information not listed here, please get
  in touch.

  8.1.  How do I learn more?

  The Linux Documentation Project book called Linux Network
  Administrator's Guide by Olaf Kirch is pretty mandatory for anyone
  that will set up and maintain anything involving TCP/IP and Internet

  The documentation that follows each software package will normally
  give you all the detailed information you need, if not always the
  overview. The man-pages will be the first place to look. Try for

       man pppd

  You will also find some documentation about certain programs in the
  this is not always well structured.

  The following HOWTOs will be highly relevant:

  o  Installation-HOWTO will get the basics sorted.

  o  NET-2-HOWTO is a very thorough description of installation and
     setup of the NET code.  Much of this should already have been done
     if you use a standard Linux distribution (e.g. Slackware, Red Hat,
     Debian).  But many sections on setup and troubleshooting will be
     very worthwhile.

  o  Mail-HOWTO explains how to configure various tools.  Again, much of
     this will already have been done for you when you install a
     standard Linux distribution.

  o  News-HOWTO is for setting up a (conventional) news spool.

  o  Tiny-News covers yet another alternative for collecting news.

  o  PPP-HOWTO is a good description of problems you may encounter when
     setting up a PPP connection.

  o  Serial-HOWTO contains everything you need to know about setting up
     serial ports.

  o  Mail-Queue tells you how to send up sendmail to always queue remote
     mail but deliver local mail at once.

  Red Hat has a mailing list for PPP issues; to join send an email to

  redhat-ppp-list-request with the subject line


  8.2.  Thanks to

  Information here is collected from many sources. Thanks to the
  following that either indirectly or directly have contributed:

  Adam Holt <[email protected]>
  Arne Coucheron <[email protected]>
  Arne Riiber <[email protected]>
  Arnt Gulbrandsen <[email protected]>
  Bjorn Steensrud <[email protected]>
  Gisle Hannemyr <[email protected]>
  Hans Amund Rosbach <[email protected]>
  Hans Peter Verne <[email protected]>
  Harald T Alvestrand <[email protected]>
  Harald Terkelsen  <[email protected]>
  Haavard Engum <[email protected]>
  James Youngman <[email protected]>
  Johan S. Seland <[email protected]>
  John Phillips <[email protected]>
  Jorn Lokoy <[email protected]>
  Kenneth Tjostheim <[email protected]>
  Kjell M. Myksvoll <[email protected]>
  Kjetil T. Homme <[email protected]>
  Michael Meissner <[email protected]>
  N J Bailey <[email protected]>
  Nicolai Langfeldt <[email protected]>
  Ove Ruben R Olsen <[email protected]>
  R. Bardarson <[email protected]>
  Steinar Fremme <[email protected]>
  Sverre H. Huseby <[email protected]>
  Trond Eivind Glomsrod <[email protected]>
  Tommy Larsen <[email protected]>
  Yves Bellefeuille <[email protected]>