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I am some what new to access_log and just started monitoring it for one of my new sites. The questions I have, is when viewing via -f tail, this is the average output: - - [22/Jun/2011:08:23:11 -0500] "GET /groups/ HTTP/1.1" 200 12526 "" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0.1) Gecko/20100101 Firefox/4.0.1"

I wanted to know if someone could explain what the different info means. I know most of it and know - means missing info.

My question is, why are there 2 user agents listed? What do they each mean? Mozilla/5.0 and Firefox/4.0.1.

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up vote 1 down vote accepted

Very simple answer : Firefox reports itself as that.

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Oh ok, thank you. – ATLChris Jun 22 '11 at 14:08

User agent strings are a mess. Everything between the "'s is one user agent. It's up to individual bits of software to decide how they describe themselves and some of it is there for historical reasons. So basically, you only have 1 user agent string (one thing between the last pair of "'s), it's just that the string in question is made up of multiple components. As mfinni said, that's how Firefox reports itself. Other agents use similar structures.

The site linked by mfinni can be used to break the strings up and explain the bits.

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