Recently there was a tweet from Hannes Juutilainen about a new tool in macOS 10.12.4 called AssetCacheActivatorUtil. Charles Edge recently wrote a blog post on some new tools that came with the macOS 10.12.4 update. This update introduced AssetCacheActivatorUtil along with a few other related tools: AssetCache, AssetCacheLocatorUtil, AssetCacheTetheratorUtil.

The man page has some basic options on how to use this tool:

NAME

AssetCacheActivatorUtil — control the macOS caching server

 

SYNOPSIS

AssetCacheActivatorUtil activate

AssetCacheActivatorUtil deactivate

AssetCacheActivatorUtil isActivated

AssetCacheActivatorUtil canActivate

AssetCacheActivatorUtil status

 

DESCRIPTION

The caching server built-in to macOS is deactivated by default.  In its first three forms, AssetCacheActivatorUtil activates the built-in caching server, deactivates it, or reports its activation status.  In its fourth form, AssetCacheActivatorUtil reports whether the built-in caching server is eligible for activation.  Installing macOS Server prevents the built-in caching server from activating.  In its fifth form, AssetCacheActivatorUtil reports the built-in caching server’s status.

The benefit to having this baked into macOS is that you no longer need to have the macOS Server app installed. You could take any Mac in your organization and have this service running. For example, if you have Mac Minis in conference rooms, you can have them running this service without having to place a Mac in your server room.

The first thing that came to mind was how exactly do we set the cache limit or manage any other preferences. Thanks to a tip from Clayton Burlison I was able to figure out how to set the Cache Limit.

To activate the caching service, simply enter AssetCacheActivatorUtil activate in the command line. That’s right, no sudo required. AssetCacheActivatorUtil will write its preferences to /Library/Preferences/com.apple.AssetCache.plist and places its cache in /Library/Caches/com.apple.AssetCache. You can also get certain information by running AssetCacheActivatorUtil status. The one caveat here is that if you want to manage the preferences for the caching service, you will need to deactivate the service. Simply type, AssetCacheActivatorUtil deactivate. Once you’ve done this, you can now write to the preference list file.

To set the caching limit simply enter a command like: defaults write /Library/Preferences/com.apple.AssetCache.plist CacheLimit -int 15000000000 where the integer appears to be in bytes (e.g. 15000000000 bytes = 15 gigabytes). I’ve gathered this from some of the values you get when you run AssetCacheActivatorUtil status: TotalBytesDropped, TotalBytesImported, TotalBytesReturned, TotalBytesStored, TotalBytesStoredFromOrigin, TotalBytesStoredFromPeers (these all appear towards the end if the output from this command).

There may be other keys of interest in this plist (note: there are more than these keys, but these are just the ones that stood out to me):
Key = ReservedVolumeSpace; Type = Int
Key = DataPath; Type = String
Key = LocalSubnetsOnly; Type = Bool
Key = PeerLocalSubnetsOnly; Type = Bool
Key = SavedCacheDetailsOrder; Type = Array of Strings which would seem to allow you to pick the data you want to cache: Mac Software, iOS Software, Apple TV Software, iCloud, Books, iTunes U, Movies, Music, Other

The one other thing I did test was to see the ReservedVolumeSpace key could be higher than the CacheLimit key. This would make sense. The ReservedVolumeSpace would be the space on the volume that you want to reserve specifically for caching and the CacheLimit would be how much of that reserved space is allocated to caching. What ends up happening if you try to make the CacheLimit key higher than ReservedVolumeSpace is that the CacheLimit will be set to equal the ReservedVolumeSpace value.

The last thing I want to note is that trying to manage these values with a configuration profile did not work in my testing. You need to write to the plist because that’s where this tool reads from.

I have not tested the the other keys, but feel free to report back in the comments what they do if you’ve tested it.

Lastly, please consider speaking to your networking team if you do decide to turn this service on. When they see so much traffic coming from one Mac, they might start to wonder what’s going on. Communication is important and no one likes surprises.