MacOS – How to simulate slow internet connections on the mac

internetmacmacosNetworkperformance

What's a good software solution to slow down internet connections on the mac for testing and simulations?

My primary need is when testing code in the iPhone / iOS simulator, so slowing down the connection for specific applications or processes would be great.

Best Answer

Apple’s official tool to slow down the network connections on you Mac for testing purposes is Network Link Conditioner

Additional Tools for Xcode [version].

Additionally, iOS has similar function accessible from within Xcode and iOS 6 or later.

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Older versions of Xcode before version 4.3.2 embedded a copy of this tool. This SO thread documents some history of the tool in a similar manner to the iOS simulators and developer documentation.

There are 11 built in profiles from a Lossy Edge network with 400ms delay to a cable modem. If you need other limits, you can create custom profiles with your own settings or you can also use ipfw yourself as described in Craig Hockenberry's article slow ride, make it easy It also mentions the Speed Limit panel by Mike Schrag that is a smaller download than Xcode, but has fewer options than Apple's tool.

It slows down the entire network stack, so you can't throttle on a per app basis without doing things like install lion in a virtual machine and set that VM with a throttled stack.

Related Solutions

How to tell which application is using the network

You can try this dtrace one-liner:

sudo dtrace -n 'syscall::recvfrom:return { @[pid,execname] = sum(arg0); }'

Let it run for a while, then hit Control-C. It will print a summary of the number of bytes read from sockets, distributed among processes. For a more detailed view, replace sum by quantize. Or just to see a count of socket reads, replace sum by count.

Disclaimer: I have only tried this on Lion, but AFAIK no great changes in dtrace-ability have occured between SL and Lion.

MacOS – How to control (start/stop) applications and services that start up after reboot

Applications and Menu Bar items

Most of these can be easily configured in:
System Preferences → Users&Groups → Login Items

LaunchAgents and LaunchDaemons

Some applications are cannot be configured in the System Preferences (e.g. Sophos AV Scanner, HandsOff Firewall,...) It's best to configure them in their own application to assure that everything runs as designed and intended.

You can look for related LaunchAgents and LaunchDaemons in:

~/Library/LaunchAgents               ~/Library/LaunchDaemons
/Library/LaunchAgents                /Library/LaunchDaemons
/System/Library/LaunchAgents         /System/Library/LaunchDaemons

Startup Items

After I installed the multi-boot utility rEFIt, it copied a file rEFItBlesser which is run at startup. Items that run at startup can be found in the following locations:

~/Library/Startup Items
/Library/Startup Items