HP-UX

Note that I said "I would use cron to schedule it to run every five minutes". If an error occurs no more than 5 minutes later, cron will run the script. I think that an average wait of 2.5 minutes is acceptable.

What is difference between a script running continuosly looping forever (but with a "sleep 300" statement in the loop) and cron running a script every 5 minutes? The only one I can think of is that if your script dies, you lose monitoring if it was looping but not if cron is running it.

You could even have cron run the script once a minute. Will a one minute maximum wait (30 seconds average) really kill you?

When I send an sms message to my phone, it can take several minutes to arrive. How fast is sms for you? And how fast can you read the message and take corrective action?

It does not make sense to require your script to notice an error in a millisecond and then use sms to notify someone.

If your application is that critical, I suggest sending the error messages to a terminal. Arrange to have someone onsite 24 hours a day, 7 days a week staring intently at the terminal. When the error message occurs, the person can respond in seconds.

We actually do that, except that the person is monitoring about 30 terminals. He has procedures to handle some things, but most problems involve calling someone...and he must actually talk to someone, he does not simply send a page or email.

And even then, the scripts that send the error messages to most of those terminals do indeed involve a delay of a minute ot two.

Many thanks for your advise. You definitely got the points.

Do you mean that i can run the cron for every one minutes?
And i am actually able to receive the error from the machine out to my PC in less than a minute? The time for the information to be SMS will depend on the transsmion network itself, right?

If my SMS application is written with Visual Basic.net, do you think it is possible to integrate with Unix/Linux?

I'd be surprised if you can run visual basic on Unix. But you will need a Microsoft expert to be sure.

Yes, cron can run a script once a minute.

To unix, the sms is just a mail message. It will get passed from computer to computer until it reaches your phone companies computer. Only then does it become sms in a true sense. And mail is seldom treated as a high priority. Your local computer will try to contact your local mailhost. If your mailhost is too busy, it will reject the connection. Then your local computer will just queue the mail. One an hour or once a half hour, your computer will try to send stuff in the queue. It typically will take days before it gives up and returns the mail to sender. You can adjust your own settings. But you cannot adjust everyone else's. Mail really should not be used for emergencies.

When I use sms, it is for messages like "part 2 of the big rsync job is done". As long as the messages arrive, I know that my job is progressing. If a message is overdue, then I can check the status.