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Application for monitoring all applications that are using the internet in Mac OS X

I use Menu Meters to show me how much data is being sent and received by my Mac as a whole.

But (as far as I can tell), it doesn’t break it down by application. If there’s a lot of data being sent or received, it’d be nice to see which app is doing it.

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My bounty is for any free application which does show the amount of bandwidth per application. (I made this as a separate question but it was closed as a duplicate to this one and I was told to start a bounty here instead; so here it is). –  Albert Nov 2 '10 at 22:07
    
@Albert: some Stack Exchange users are a bit heavy on the “no duplication” thing — applying programming principles too literally into real life. Hope you get some useful answers. –  Paul D. Waite Nov 3 '10 at 15:23
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marked as duplicate by slhck Aug 25 '12 at 16:17

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Take a look at Little Snitch. It monitors which applications are using the network and also tracks usage. From its website:

Keep an eye on your traffic

Little Snitch 2 introduces a new Network Monitor, showing detailed information of all incoming and outgoing network traffic.

A status icon in the menu bar provides a summary of current network activity, and a monitor window with more comprehensive information pops up automatically in case of new traffic events.

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Perfect, that’s spot on. You can assign a keyboard shortcut to the network monitor too, if you don’t want it to come up every time something accesses the network. –  Paul D. Waite Sep 28 '09 at 19:56
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There is the lsof terminal command. This has a size field (7th field by default). This has a plethora of switches. Can probably tell you all you need to know about data connections.

sudo lsof -i : this will give you a complete list of all open network connections. Does not appear to give you the amount of data written or read from each socket though.

When searching for well-known ports, such as 8080 which is listed as http-alt due to its mapping in /etc/services, it might be easier to use lsof -i -P to suppress conversion of port numbers to port names. Alternatively, explicitly specify the port one's looking for, like lsof -i tcp:8080. When just trying to figure out what services are actually listening, use lsof -i -P | grep LISTEN.

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