Bash script to detect when my server is down or offline

Question

Background : I need to receive an alert when my server is down. When the server is down, maybe the Sysload collector will not be able to send any alert. To receive an alert when the server is down, I have an external source (server) to detect it.

Question : Is there any way (i prefer bash script) to detect when my server is down or offline and sends an alert message (Email + SMS)?

Answer 1

If you have a separate server to run your check script on, something like this would do a simple Ping test to see if the server is alive:

#!/bin/bash
SERVERIP=192.168.2.3
NOTIFYEMAIL=test@example.com

ping -c 3 $SERVERIP > /dev/null 2>&1
if [ $? -ne 0 ]
then
   # Use your favorite mailer here:
   mailx -s "Server $SERVERIP is down" -t "$NOTIFYEMAIL" < /dev/null 
fi

You can cron the script to run periodically.

If you don't have mailx, you'll have to replace that line with whatever command line email program you have and probably change the options. If your carrier provides an SMS email address, you can send the email to that address. For example, with AT&T, if you send an email to phonenumber@txt.att.net, it will send the email to your phone.

Here's a list of email to SMS gateways:

http://en.wikipedia.org/wiki/List_of_SMS_gateways

If your server is a publicly accessible webserver, there are some free services to monitor your website and alert you if it's down, search the web for free website monitoring to find some.

Answer 2

Pinging is an option, but on many occasions a machine will be able to send a ping reply, while the actual server that it is all about is down. It is better do an end-to-end test. In the below example a page is requested from the webserver.

If it is a webserver, it would look something like this:

#!/bin/bash
wget -qO /dev/null 'http://webserver/some_existing_short_document.html' || {
    echo "Webserver down"
    # another mailer example
    sendemail -s mailserverip -f 'from@localhost' -t 'user@localhost' -u 'Webserver down' -m 'The webserver is down'
}

If you change the html document into a php document, and make de php script test things like the database connection, filesystems etc., you can even test more aspects of the server. That way you can start proactive monitoring of the machine (see problems before they make the server crash).

Similar with checking a mailserver, but instead of requesting a web page, you simply send an email through the mailserver and see if you receive it in your mailbox