New answers tagged web-development
You can use nmap as mentioned by the previous response. sudo nmap -sV -T4 -O -F --version-light <your_server> NOTE: If you run a nmap against a server that you don't own, prepare to explain when a call from network security admin asking you what are you trying to do. In other words, don't do it if it is not your server.
Your best option, without SSH access would be nmap's OS detection. It's not going to be totally reliable, but it's probably better than nothing, which seems to be your other option. Here's a page with a little run down on how the OS detection works, which should give you an idea of its limitations.
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