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Internet Related/Filtering/Firewall Thread, How website identifies client OS in Technical; Hi all, How does a website identify a client OS version? For example, when I go to download Google Chrome ...
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    How website identifies client OS

    Hi all,

    How does a website identify a client OS version? For example, when I go to download Google Chrome from Google's website, it automatically knows which version of Mac OS X I am running. How does it do this? Where on the client OS does this information come from?

    Thanks in advance!

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    nickbro's Avatar
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    The browser sends this information in the HTTP request, as part of the HTTP Header. List of HTTP header fields - Wikipedia, the free encyclopedia See User Agent String

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    MarsRed (8th February 2011)

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    CESIL's Avatar
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    As a developer you can usually trust the agent string...but some browsers allow users to change this...why you would (apart from testing your own sites) I don't know

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    MarsRed (8th February 2011)

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    Quote Originally Posted by CESIL View Post
    As a developer you can usually trust the agent string...but some browsers allow users to change this...why you would (apart from testing your own sites) I don't know
    Most often? Because the developer a) doesn't realise I may want to use Windows to download the OSX / Linux version and b) doesn't provide a "pick a version for another OS" link. Biggest culprit who used to do this? Apple for the quicktime downloads (since fixed). Still doing this? Google for chrome downloads.

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    Quote Originally Posted by pete View Post
    Most often? Because the developer a) doesn't realise I may want to use Windows to download the OSX / Linux version and b) doesn't provide a "pick a version for another OS" link. Biggest culprit who used to do this? Apple for the quicktime downloads (since fixed). Still doing this? Google for chrome downloads.
    Thanks, this is very helpful! Now, without intentionally/manually changing the user agent string, why would a site think I'm running a different OS?

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    webman's Avatar
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    Bad code on their behalf? You're using an obscure User Agent? The User Agent header is being stripped out somewhere between you and the website?

    You can check your user agent here: Whats My User Agent?

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    MarsRed (1st March 2011)

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    Quote Originally Posted by pete View Post
    Most often? Because the developer a) doesn't realise I may want to use Windows to download the OSX / Linux version and b) doesn't provide a "pick a version for another OS" link. Biggest culprit who used to do this? Apple for the quicktime downloads (since fixed). Still doing this? Google for chrome downloads.
    Good point...I hate websites that try to be clever and 'guess' what I want to download...

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    Just returning to this issue now...

    Where does the OS info for the user agent string come from (on a Mac, if that makes a difference)? The machines exhibiting this issue show the correct OS version in System Profiler.

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