How to figure out server uptime?

[jewell]

I discovered that sites like netcraft.com can figure out your server uptime, how can they do that?
And more, is there a way to hidden such info?

[Geek-9pm]

I discovered that sites like netcraft.com can figure out your server uptime, how can they do that?
And more, is there a way to hidden such info? Shocked

Yes, for a fee. They  redirect the user to a backup server. If you don't get your server on line right away they will charge you for bandwidth.

[sharif934]

I recommend you reeading the post here:
http://1mum.geek-tools.org/2009/07/12/server-uptime-info/
it explains how to hide such info on a Linux box and also points you the info on how exactly sites like netcraft.com succeed in fetching this info from most of the web servers.