Welcome to Linux Knowledge Base and Tutorial
"The place where you learn linux"
Child Fund

 Create an AccountHome | Submit News | Your Account  

Tutorial Menu
Linux Tutorial Home
Table of Contents

· Introduction to Operating Systems
· Linux Basics
· Working with the System
· Shells and Utilities
· Editing Files
· Basic Administration
· The Operating System
· The X Windowing System
· The Computer Itself
· Networking
· System Monitoring
· Solving Problems
· Security
· Installing and Upgrading
· Linux and Windows

Glossary
MoreInfo
Man Pages
Linux Topics
Test Your Knowledge

Site Menu
Site Map
FAQ
Copyright Info
Terms of Use
Privacy Info
Disclaimer
WorkBoard
Thanks
Donations
Advertising
Masthead / Impressum
Your Account

Communication
Feedback
Forums
Private Messages
Surveys

Features
HOWTOs
News Archive
Submit News
Topics
User Articles
Web Links

Google
Google


The Web
linux-tutorial.info

Who's Online
There are currently, 74 guest(s) and 0 member(s) that are online.

You are an Anonymous user. You can register for free by clicking here

  

callback



SYNOPSIS

       callback  [-x<debuglevel>] [-V] [-l<modemlines>] [-m<init­
       string>] [-s<speed>] [-d] [-S] [phone-number]


DESCRIPTION

       Call the given phone number (if none is given on the  com­
       mand  line,  ask user for one), and if a CONNECT is estab­
       lished, hand over control to  mgetty(8)  to  present  user
       with a login name prompt.

       callback is used for various purposes:

       *  security:  make sure your users are who they pretend to
       be by calling a well-known phone number.

       * cost savings: make your company call you back.

       callback can be called directly from the command line (but
       you  must  be  "root" to do this, otherwise callback can't
       signal mgetty), or from mgetty's "login.config".  See  the
       login.config file shipped with mgetty for an example.


OPTIONS

       -x <debug level>
              Use the given level of verbosity for logging
              - 0 means no logging, 5 is really noisy.

       -V     Print version number and quit.

       -d     Do not go into the background. This is help­
              ful for debugging.

       -l <modem lines>
              Use  the  given  modem lines. Multiple lines
              can be separated by ":", as with sendfax(8).
              Example: callback -l tty1a:tty2a

       -m <init sequence>
              Set  the  modem  initialization sequence (as
              usual: expect send expect ...).  This can do
              nearly  everything, as long as it leaves the
              modem command responses on (that is, no ATQ1
              here!)  and  switches the modem to data mode
              (AT+FCLASS=0) if  it  is  used  in  data/fax
              mode.

       -s <speed>
              This is the bit rate that should be used for
              the   machine-modem   connection.    Usually
              you'll  set  this  via  the  "speed  <nnnn>"
              option in "callback.config".


DIAGNOSTICS

       In  most cases, callback can't print any error mes­
       sages to the console, because it must detach itself
       immediately  from  the  terminal,  in  case someone
       wants to be called back on the modem line he called
       in. So, nothing to print messages to...

       Because  of this, all callback errors are logged to
       a protocol file (the extent of the data written  is
       controlled  by the "-x" option), especially includ­
       ing the reason why a call was  not  made,  or  what
       exactly failed.

       Just  two messages are printed on stdout, and those
       are self-explaining, a call from a  non-root  user,
       and an invalid option.


INTERNALS

       How does it work?

       This  is  a  bit tricky, because of the way init(8)
       handles the utmp(5) file.  You can't just have  any
       program  ask  the  user  for a login name, and then
       start a "login shell", it won't work (this  is  for
       the  same  reason  mgetty(8) has to be started from
       /etc/inittab).

       So, mgetty has to do the "asking for  login  name".
       But  I do not want to have all that dialout code in
       mgetty, bloating it even more.

       The way it works is this: callback dials out  on  a
       modem device. It will only take a modem device that
       has a mgetty watching over it (!). When the connec­
       tion is established (CONNECT), callback will send a
       signal SIGUSR1 to mgetty, which, in turn, will send
       the same signal back to signal "I got your signal".
       callback then exits,  and  mgetty  takes  over  the
       existing  connection,  prompts the user for a login
       name, and forks off /bin/login.

       Conclusion: this will not work with mgetty versions
       before  February 04, 1996 (no support for this sig­
       nalling), and if it doesn't work  for  you,  please
       send  me BOTH the mgetty and the callback log file,
       otherwise it's very hard to find the bugs.


BUGS

       callback is "alpha" code,  not  very  stable  right
       callback is Copyright (C) 1993-1996 by  Gert  Doer­
       ing, <gert@greenie.muc.de>.

greenie                     27 Oct 93                 callback(8)

An undefined database error occurred. SELECT distinct pages.pagepath,pages.pageid FROM pages, page2command WHERE pages.pageid = page2command.pageid AND commandid =


  
Help us cut cost by not downloading the whole site!
Use of automated download sofware ("harvesters") such as wget, httrack, etc. causes the site to quickly exceed its bandwidth limitation and therefore is expressedly prohibited. For more details on this, take a look here

Login
Nickname

Password

Security Code
Security Code
Type Security Code


Don't have an account yet? You can create one. As a registered user you have some advantages like theme manager, comments configuration and post comments with your name.

Help if you can!


Amazon Wish List

Did You Know?
You can choose larger fonts by selecting a different themes.


Friends



Tell a Friend About Us

Bookmark and Share



Web site powered by PHP-Nuke

Is this information useful? At the very least you can help by spreading the word to your favorite newsgroups, mailing lists and forums.
All logos and trademarks in this site are property of their respective owner. The comments are property of their posters. Articles are the property of their respective owners. Unless otherwise stated in the body of the article, article content (C) 1994-2013 by James Mohr. All rights reserved. The stylized page/paper, as well as the terms "The Linux Tutorial", "The Linux Server Tutorial", "The Linux Knowledge Base and Tutorial" and "The place where you learn Linux" are service marks of James Mohr. All rights reserved.
The Linux Knowledge Base and Tutorial may contain links to sites on the Internet, which are owned and operated by third parties. The Linux Tutorial is not responsible for the content of any such third-party site. By viewing/utilizing this web site, you have agreed to our disclaimer, terms of use and privacy policy. Use of automated download software ("harvesters") such as wget, httrack, etc. causes the site to quickly exceed its bandwidth limitation and are therefore expressly prohibited. For more details on this, take a look here

PHP-Nuke Copyright © 2004 by Francisco Burzi. This is free software, and you may redistribute it under the GPL. PHP-Nuke comes with absolutely no warranty, for details, see the license.
Page Generation: 0.14 Seconds