What's the unit of keep-alive in http?

Keep-Alive  115
Connection  keep-alive

The above appears in most request sent from m开发者_运维技巧y firefox,what's its unit?

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From the documentation:

Amount of time in seconds to keep keep-alive connections alive

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That header is actually invalid; see https://bugzilla.mozilla.org/show_bug.cgi?id=643352

That said, the unit is seconds.