Uninstalling items installed by an .app when user deletes it, including SMJobBless helpers

Question

The short version: is it possible to delete helper tools which were set up by the app (SMJobBless() etc.) when the app is deleted? If so, how?

The long version:

The Mac app we are developing unfortunately requires admin privileges to perform an occasional operation, and it also requires a background task to be live for other apps' plugins to connect to even when the app itself isn't running (this one can be unprivileged). The app will be signed with a Developer ID certificate, and distributed only outside the App Store.

We'd like the app to be a "good citizen" as far as possible, also on uninstall.

For the background task, we're using a login item, created using SMLoginItemSetEnabled(). This isn't amazing, because XPC messaging doesn't seem to work (we're using CFMessagePort instead - alternative suggestions welcome), but if the user deletes the app, the login item at least doesn't get loaded anymore on next login. I suspect there's still a trace of it somewhere in the system, but the executable inside the .app bundle is used, and when that disappears, the login item no longer runs.

For the occasional operation requiring admin rights, we've got a privileged helper tool which our app installs using SMJobBless(), and which implements a named XPC service, so the task spins up on demand when it receives a message from the main app. This is what Apple recommends and describes in its Even Better Authorization Sample.

The helper executable is copied to /Library/PrivilegedHelperTools/ by SMJobBless(), and the embedded launchd.plist ends up in /Library/LaunchDaemons/. Even though the OS has the information on which app "owns" the helper, it doesn't seem to uninstall it when the user deletes the app. Apple's sample is silent on uninstalling, other than the uninstall.sh script which is apparently intended to be used during development only. We don't need this helper while the app isn't running, so installing it as a full-blown launch daemon is slightly overkill, but we'd also like to avoid repeatedly annoying the user with the password prompt too. Besides, Apple advises against other forms of running code with admin privileges than SMJobBless() these days - for example SMJobSubmit() is marked deprecated.

So how do we clean up after ourselves?

I've found SMJobRemove(), but (a) when would we call that in our case - you can't run code on .app bundle deletion, or can you? and (b) it doesn't actually seem to clean up.

The only 2 things I can think of are not terribly satisfying:

1. Some kind of uninstaller app or script. But that seems pretty ugly too.
2. Don't worry about it and just leave a mess behind when the user deletes our app.

Answer 1

Update:

There have been some changes in this area with macOS 13.0 Ventura; there's an introduction to the new mechanism in the WWDC22 session 'What’s new in privacy'. The new SMAppService APIs support automatic cleanup for daemons, agents and login items. Unfortunately you'll of course still have to find a workaround for any older macOS versions you support.

Original answer:

There has been a similar question on the Apple Developer Forums at https://forums.developer.apple.com/thread/66821 - the recommendation by Apple is a manual uninstall mechanism, and consuming as few resources as possible if the user does not do this.

Apple DTS staff further recommended implementing a self-uninstall mechanism in the privileged launch daemon, to be triggered from the app via XPC. This is what we're going with.

Answer 2

I think the only solution you have right now is to use the uninstall shell code that you mentioned in order to physically remove the privileged helper from disk or to build an uninstaller for it. Either way you will have to ask the user to enter his/her password. This what all installers / uninstallers that require privileged access to the system do, and for a very good reason. That's why I avoid like the plague to use privileged helpers, but I understand that sometimes you really have to. I don't think it is good that you leave such a helper in the user's system, because it will reload next time the user starts up the computer.

I just checked ServiceManagement.h header and they state that SMJobRemove will be replaced by an API that will be made available through libxpc in the future. (Sometimes you really need to go to the headers to get extra info that the documentation does not give you.) Hopefully this promised replacement will uninstall it for us. However, I'd file a bug report and ask for that enhancement.

Answer 3

One solution you could consider is to include an uninstaller script or program in your .app bundle.

You can then pass the path of this small tool to your helper tool (via IPC) and have the execute the the uninstaller, thereby deleting itself. You will have to be careful that components are removed in the right order but it can be made to work.

Answer 4

You're correct that Apple does not provide an API to uninstall a helper tool installed with SMJobBless nor do they do so automatically. As for why macOS doesn't automatically do an uninstall, my educated guess is because macOS fundamentally doesn't have a unified concept of "install". While it's convention for apps to be located in /Applications (and a few other locations), it's perfectly valid for apps to be located and run from anywhere on the system including external drives and network drives. For example should macOS uninstall helper tools when apps disappear because the drive they're on is disconnected?

In terms of how to uninstall, doing so requires root permission and so realistically have the helper tool itself do the uninstall is the easiest option. You can have your app via XPC tell the helper to uninstall itself. Here's an example in Swift of how to do this; it's part of SwiftAuthorizationSample. The basic idea is:

• Use the launchctl command line tool to unload the helper tool
• Delete the helper tool executable
• Delete the helper tool launchd plist

But there's a bit of additional complexity involved because launchctl won't let you unload a running process.