The Mysteries of Rosetta Housekeeping

| How-To

Rosetta is a software technology that allows Intel-based Macs to run most, but not all, of native PowerPC applications. This How-to explains some details of using, enabling, disabling and status checking Rosetta.

The first thing you need to know is that Rosetta is a very small piece of code, about 2.1 MB. It's not at all like the Classic environment of old, so any obsession with eradicating it from your system is unwarranted. It just waits in stand-by mode and is only invoked when a native PPC application is launched.

Second, if you didn't have it loaded in Leopard, the Snow Leopard upgrade won't install it by default. What happens is, when the OS sees that you're trying to launch a native PPC app, it will open a dialog box and invite you to install Rosetta -- even if it's already installed. (You'll need a network connection for that.) If you aren't on the Internet, you can use the Snow Leopard DVD to install manually. Our Jeff Gamet explained the complete installation back in early September.

Rosetta Install

Dialog box for install of Rosetta

So that's one reason why it's a waste of time to try to delete a functioning install of Rosetta. Some day, you may need it for just a few minutes, so once you have it, just let it lie dormant, doing nothing most of the time, and taking up about a much disk space as a two minute MP3.

How can you tell if an app is native PowerPC only? Select the app and do a Get Info (CMD + i). If it's PPC only, the Kind field will say, simply, "Application."

Kinds of apps

The Three Kinds of apps

That's in contrast to: Application (Universal) which has code for both. Or Application (Intel) which is Intel only.

Disabling Rosetta

Removing Rosetta requires some UNIX expertise, and, as I said above, it isn't really worth it. It's just a microscopic piece of code that's utilized by the OS only when needed.

I have seen some websites that provide a command line sequence to enable and disable Rosetta. If you disable Rosetta, the only practical outcome is that when you do launch a native PPC app, you'll be notified with the dialog box above, and the system will want to download and install Rosetta all over again. This can only be useful if you really, really need to know that an app you've launched is native PPC and want to set about the business of replacing it with a more modern version, say, a Universal app. But you could have checked that, if in doubt, with the Get Info function as well before launching.

For the sake of completeness, here's the command to disable Rosetta:

$ sudo sysctl -w kern.exec.archhandler.powerpc=/usr/libexec/oah/RosettaNonGrata

You'll need to be logged on as administrator because the Administrator of the Mac is in the "sudoers list" (/etc/sudoers) and can manage files owned by root.

Here's the command to enable Rosetta:

$ sudo sysctl -w kern.exec.archhandler.powerpc=/usr/libexec/oah/translate

To determine the current status of your Rosetta, enabled or disabled, enter this on the command line:

$ sudo sysctl kern.exec.archhandler.powerpc

If Rosetta is enabled, you'll see a line that includes "translate." If not, then the line will include "RosettaNonGrata."

Unless you have a specific, expert need to disable Rosetta, it can safely be left "enabled."

OS Practicalities

My advice is that once you have Rosetta installed, just forget about it. Don't try to delete it or disable it. That is, unless you really, really need to be alerted when a native PPC app tries to launch. Mostly, Mac IT managers will watch for that, not casual users at home.

Apple is all about gentle, methodical translations. At some point in the future, Rosetta won't even be included in the OS, or be available, and it will quietly disappear, just as the Classic environment has. By now, you should have identified any critical apps that are PPC only and found an upgrade or substitute. That's a more important task than a false sense of aesthetics for those who just don't want Rosetta on their Mac anymore.

Rosetta, by the way, is not a panacea. It translates G3, G4 and AltiVec instructions into Intel native code, but not any special, G5 only instructions. There are other software components that can't be handled by Rosetta, for example screen savers and kernel extensions. See this article for more background information. Fortunately, as part of your migration over the years, any software that had those limitations has been upgrade or removed.

In summary, if you never launch a native PPC app, you'll never encounter Rosetta. But if it does get installed, just leave it there. It'll quietly do its job for you when needed. As Apple says, it's "The most amazing software you'll never see."

Popular TMO Stories



Grammar police:

let it LIE dormant


A more pro-active approach to locating PowerPC applications would be to use System Profiler (located in the /Applications/Utilities directory).

Under “Software” choose “Applications”. After a moment, you will have a list of every application installed on your system.

The “Kind” column will indicate “Intel”, “PowerPC”, or “Universal”. This allows you to do your seek-and-destroy to upgrade what you can to Intel versions.

Another column of interest is the one titled “64-Bit (Intel)”. You’ll be able to find which applications have yet to be compiled for 64-bit mode.

There is also a command-line version located in /usr/sbin/system_profiler which could help for remote administration.

John Martellaro

My thanks to the grammar police.


You can also open Activity Monitor and see a column indicating PPC or Intel for running applications.

There seems to be a rare bug with Rosetta. Once in a while (for me anyway) using Rosetta causes an instant logout. The system doesn’t crash but you are instantly back at the login screen and unsaved work is lost. This has only happened about three times for me but it has been worse for others.

Log in to comment (TMO, Twitter or Facebook) or Register for a TMO account