After having installed the ISDN system I felt a bit uneasy since the
system can initiate connections by itself. In fact, I have seen
spontaneous connections when Netscape was running.
For this reason I wanted a monitor that does not consume too much CPU
resource and displays the connection status in a concise way. Further,
I wanted an easy method to control the ISDN connection, which means
shutting down the ISDN subsystem or starting it up -- by clicking on
Using the Xbiff program as a source of inspiration I implemented a tool
that has the functionality described above.
2. Monitoring the ISDN Subsystem
The state of the ISDN subsystem is displayed in a small window showing
- the ISDN subsystem is inactive: one solid terminal in the foreground,
another dashed terminal in the background
- the ISDN subsystem is active, but there is no network connection over
the ISDN line: two terminals connected by dashed arrows
- there is an incoming ISDN network connection or the ISDN system is dialing:
two terminals connected by solid arrows
- there is an outgoing ISDN network connection: two terminals connected
by fat arrows in reverse video.
When an outgoing connection is established or when the ISDN subsystem
hangs up, the program beeps to signal this important state change.
3. Controlling the ISDN Subsystem
Pressing button 2 in the window while the ISDN system is inactive
executes the command "/sbin/isdnnet start &" and pressing button 3
executes "/sbin/isdnnet stop". Provided /sbin/isdnnet is a
shell-script that can start and stop the ISDN subsystem and provided
you are in the dialout group (and the ISDN devices in /dev are also
in the dialout group) you can startup and stop the ISDN system in
An alternative is to install xmonisdn as setuid root, but that may
have serious security problems, so that is strongly discouraged.
If you insist on using xmonisdn as setuid root, read the manual
page on info how to do that. You could also install xmonisdn as
setgid dialout, but that too is not without possible problems.
4. Compilation and Installation
After having installed the source directory type
which compiles and installs all files.
Now you only have to setup the shell-script /sbin/isdnnet, which could
simply be a link to the appropriate initialization script. I wrote a
new script that includes a call to "sendmail -q" in order to deliver
all mail that has been queued while the ISDN system was inactive.
Bernhard Nebel, December 9, 1996
Modified August 3, 1999 by Paul Slootman <email@example.com>