monitor when server back online [closed]

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http://serverfault.com – My day is being severely impacted by the downtime on trac-hacks.org. Judging by previous server failures, it could be up to 48 hours before this is fixed. I'd like to know the minute trac-hacks.org is back up. However, most server monitoring services are set up to send alerts when a server goes down. Is there a free server monitoring service that will allow me to easily (i.e. not require a sign-up with password, although OpenID login or gathering a contact e-mail is OK) monitor a server and alert me when it comes back online? The fallback is to run this in my OS X Terminal ping -q -o -i 30 (HowTos)