Shell Programming and Scripting

I think I read that by entering "disconnect <script_name>" somewhere in pppd, that when ppp connection is lost that the named script will be executed. I also see that something similar can be (if I read correctly) in ip-down. Which is correct or are both correct. I want to set off the system alarm on my Linux machine whenever the "carrier" signal is lost. Has someone done this?

The usual thing is a ping, not too often, of a host out there but nearby, like the ISP DNS or MAIL server. If you cannot ping their dns server, your connection is not very useful. In fact, nslookup test-addr dns-server-ip could do the same thing! Stick it in the cron. This does not complicate anything else, and does not stop checking for any reason.

I can see that would work and I thought about using a separate terminal or cron but those increase overhead and are a pain to set up/down each time whereas a disconnect/ip-down script "IF" it would be executed after a carrier loss is only used if needed which is what I want. Just don't know about when/if either of those kicks in, hence my query.

Well, you need to set an externall visible marker before you request a dial in and reset it when you request a disconnect. Then the ping or nsloopup monitor skips until the next connect. Horsepower is cheap, but the wrong approach can be partial or fragile: possibly necessary but not sufficient, where a better approach can finess all the problems and limitations. Heck, I think I need it for my VPN connection, which seems to wink out now and then and leave ie and outlook all confused.

Too bad what you have is not like Always On ISDN -- the folly of the phone company was so overpriced that we call it I Smell Dollars Now, but it had a nice enhancement where you could always get 1200 bytes per second through the D=dialer channel to support email and other low BW apps, so you were virtually always on. It acquired more B=Basic POTS = 56-64KBit channels temporarily for higher BW.

I ran a test using ip-down in /etc/ppp. I have problems with system beep and the system flipping my sound device cards via whimsy so have not used a beep to alert me when the connection gets lost but I was able to write to a file immediately when I switched off my 56K modem. Now I will try to add an alarm sound. I should try using the disconnect script but maybe later.

Yes, if you can reliably do something quick and simple like a status file, you might let a watcher script take care of the rest.