Using desktoppr in a managed environment

A few years back, I built and released a small tool to simplify the deployment of macOS desktop pictures (also known as “wallpapers” since macOS Ventura and on other platforms) without actually locking them down or needing privacy (PPPC) exemptions. The tool is desktoppr and is quite popular among Mac admins.

I haven’t updated desktoppr in the last three years, and even that last update was just a re-compile to make the binary universal. It was always meant to do one thing and it has done that well, so there was no need for updates.

Recently however, I have been thinking about the workflows to install and set a custom desktop picture or wallpaper in a managed environment.

Note: my thoughts here are for Macs that are owned and managed by organizations and given out to employees to work with. They do not really apply to shared devices in classrooms, carts, labs or kiosk style deployments or even 1:1 devices in an education setting. Other rules (figurative, literal, and legal) apply in these scenarios and you probably want to set and lock a desktop picture/wallpaper with a configuration profile.

Why do it at all?

This is a fair question. My general recommendation for Mac Admins regarding pre-configuring, or even locking down settings in user space is to only do it when you absolutely need to for compliance and security reasons.

I often get the argument that it makes the lives of Mac Admins and tech support easier when you pre-configure settings that “everyone wants anyway.” However, I believe, from my own experience, that “tech geeks” (and I include myself here) are poor judges for which settings should be a general preset and which are just our geeky personal habits and preferences.

This holds especially true when macOS updates change default settings. There have been examples for this throughout macOS history, such as the “natural scrolling” on trackpads, whether to use dark mode, or more recently, the “click to desktop” behavior in macOS Sonoma.

You may be able to generate the statistics from your support ticketing system that tells you which pre-configuration would cut down a significant number of incidents and then, by all means, apply those. (I’d be very interested in those stats and which settings those are.)

But generally, a more hands-off approach is less intrusive, and also less effort in management and maintenance.

So, why configure the wallpaper?

Given my lecture above, this is a fair question. The desktop picture/wallpaper is special. It gives you a chance for a great first impression.

The desktop picture/wallpaper is the first thing a user sees when they log in to a new Mac. Apple understands this, and creates new, beautiful images for each major release of macOS to emphasize its branding. Likewise, when you are managing Macs, this is a very compelling opportunity to present your organization’s branding. This will also demonstrate to end users that this Mac is different. This will identify this Mac as a managed Mac from your organization.

Of course, many users will go ahead and change the desktop picture/wallpaper immediately, or eventually. And so they should. The ability to configure and setup the device the way they like it will make it “theirs,” i.e. more personal, and also might encourage some to learn a bit more about macOS and the device they are working with. Limiting a power user in how they can configure “their” device and how they work with it will be a cause for much frustration, friction and complaints. This is why desktoppr exists: to set the desktop picture/wallpaper once, but then allow the user to change it later.

But first impressions are important. There are very few ways Apple lets Mac admins customize the first use experience. The desktop picture/wallpaper is fairly simple to manage and can leave a big impression.

Ok, but how?

That said, there a few considerations to get this first impression just right. In general, to set a customized wallpaper you need to:

  1. install the image file(s)
  2. install desktoppr
  3. run desktoppr to set the wallpaper

The challenge is to get the timing right on these steps. In this case the first two steps can (and should) happen right after enrollment. The third step configures user space, so it cannot happen before the user account is created and the user logs in. If you run it too late, the user will see the default macOS wallpaper for a while and then switch to the new one, which is not really ideal to create a good first impression.

In Jamf Pro (the management system I have most experience with) you can put the packages for the image file and desktoppr in the PreStage or enroll them with policies triggered at enrollmentComplete. Since these pkgs usually are not very large, the image files and the desktoppr binary are ready to go when the user finishes setting up their account and gets to the desktop for the first time.

Jamf Pro provides an option to run policies at login, but that also has few seconds delay before it actually runs, giving the user a “flash” of the default macOS wallpaper.

The good news is, that when you run desktoppr with a LaunchAgent, it runs early enough in the login process, that the user does not get “flashed” by Apple’s default wallpaper.

That extended our workflow to:

  1. install the image file(s)
  2. install desktoppr
  3. install LaunchAgent plist
  4. desktoppr runs as LaunchAgent at login to set the wallpaper

The LaunchAgent will run on every login, and reset the wallpaper even if the user changed a different one. This might be desirable for some deployments, but in general this goes against the notion to leave the user in control. There are workarounds to this. You can build a script that sets the wallpaper and creates a flag file somewhere in the user’s home directory. On subsequent runs, the script would check for that flag file and skip re-setting the wallpaper.

Also, since macOS Ventura, the system warns users about background items in the system. We can manage these warnings with a configuration profile. Since the desktoppr binary is signed, this works quite well. But if you insert a custom shell script as the LaunchAgent to perform all this extra logic, you need to sign this script and managing the background item profile gets a lot more messy.

This works, but now our workflow is:

  1. install the image file(s)
  2. install desktoppr
  3. install LaunchAgent plist
  4. install signed custom script
  5. configure and deploy managed Background Item profile
  6. script runs at login and sets the wallpaper, when necessary

If any of the pieces in step 1–5 change, you need to update at least one installation pkg, upload them to your management system and deploy them down to the clients. Neither of these are very complicated, but the number of moving pieces will make this very tedious quickly.

These workflow steps will not vary much from one deployment to another. So I thought it would be nice if I could integrate some of these steps in desktoppr and find some means to make the pieces less volatile.

Manage the arguments

The first moving piece I wanted to fix was the LaunchAgent plist file. This needs to contain the path to the image file as the first argument to the desktoppr binary, which will be different for every deployment. This value might even change over time for a single given deployment as the org wants to updated and “fresh” desktop pictures/wallpapers with new branding.

For a managed environment, we can also provide this information with a configuration profile. This separates the ‘data’ (the path to the image file) from the logic (the other information in the launchd plist file, that controls when it runs).

I added a new verb manage to desktoppr that tells it to get configuration from a preference domain or configuration profile instead of the arguments. Now, we can put desktoppr with the single argument manage in the LaunchAgent plist. This means the LaunchAgent will not have to change when you update image paths or other settings. Instead, the admin updates the configuration profile in the MDM server. The LaunchAgent plist file is still required, but it won’t need frequent updates any more. (Step 3 is now less volatile)

Setting once

The next step is some new logic in desktoppr to only set the wallpaper once. For that, desktoppr now “remembers” when it last set the wallpaper and to which file. When it is called again to set it to the same file, it does nothing, even if the user changed the desktop picture/wallpaper. Some deployments might still want to reset the wallpaper every time the LaunchAgent triggers, so I added a key to the configuration profile to enable or disable this behavior. This flag only takes effect when desktoppr manage is run, other invocations of desktoppr will set the desktop picture/wallpaper regardless.

This removes the requirement for a custom script that determines whether desktoppr should set the wallpaper or not. (Step 4) Since we are now running desktoppr manage directly from the LaunchAgent, and the desktoppr binary is signed, it is easy to create the PPPC profile to designate this as a managed background item. (Step 5 is less volatile)

There is a sample configuration profile in the repo which has the settings payload and the payload for the background item pre-approval.

Fetch image files

The last volatile bit is the image file itself. So far, you have to create an installation pkg for the image file and install that before desktoppr runs.

To avoid this, I taught desktoppr to download an image file from a URL and use that. So now, you can upload a file to a web server (or AWS, or some file sync service that can provide a static URL) and use that as your desktop.

Since images can be a vector for malware, we add the option to verify the downloaded file with an sha256 hash given in the configuration profile.

Since the download can take a few seconds, this re-introduces the “flash” of the default wallpaper. I don’t really see a way to avoid this and if this really upsets you, you will have to fall back to pre-installing an image file. Nevertheless, I found the option to have desktoppr download an image file to be useful and left it in there.

The new workflow

  1. create and deploy a desktoppr configuration profile
  2. install desktoppr with a LaunchAgent plist (these shouldn’t change very often)
  3. desktoppr runs, downloads the image file and sets the wallpaper, when necessary

All the custom configuration is now in the configuration profile. You will only need to update the desktoppr installation pkg when the binary is an updated.

New use cases

This shortened workflow enables some new workflows. First of all, since there is logic in desktoppr to only change when necessary, we don’t really have to wait until the next login any more. (Most users only “log in” after a reboot for a software update.) We can change the LaunchAgent plist to run in the background every few hours or so. That way, new settings in the configuration profile should be picked up by all the clients within a few hours after coming online and receiving the new profile from the MDM.

Introducing desktoppr 0.5beta

I have been playing around with this and testing for a bit now. It has been working well for me, but I know there will some edge cases and workflows out there that I am not anticipating. For this reason, I am releasing the new manage feature as a beta, so you can start testing it and reporting any improvements, issues, or challenges.

I am curious to see what you are going to do with it.

Installomator v10.5

We have released an update for installomator which brings it to v10.5. You can can see the details in its release notes page.

With an astounding 78 new labels and updates to 42 existing labels, this brings Installomator to 733 labels. The project has also reached 100 contributors who have put in at least one pull request!

Many thanks to everyone who contributed, whether through pull requests, or by filing issues or by joining in the discussion in the #installomator channel on the Mac Admins Slack.

Weekly News Summary for Admins — 2023-10-13

In my session at MacSysAdmin conference in Gothenburg last week, I announced that the name of this weekly news summary will be changing to “MacAdmins.news“.


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Why the change? This news summary has taken on a life of its own from my main Scripting OS X blog. I had been thinking it deserved a name and domain of its own, for a while, but I couldn’t think of one that I liked. When I realized that MacAdmins.news was available and I checked in with the MacAdmins Foundation if they would mind me using it.

I had already been double-posting to the new website for a few weeks to make sure that everything is working. Over the next few weeks, I will be updating everything else. Slowly and carefully, I don’t want to disrupt anything too badly.

If you are receiving this news summary by email and have mail rules by subject or sender you may have to update them, but I will announce the changes here before they take effect in the emails.

Go read this week’s news summary on MacAdmins.news!

If you would rather get the weekly newsletter by email, you can subscribe to the MacAdmins.news here!! (Same content, delivered to your Inbox once a week.)

Weekly News Summary for Admins — 2023-10-06

Just a short news summary this week, as I am busy presenting today at MacSysAdmin in Gothenburg!


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📰News and Opinion

⚙️macOS and iOS Updates

🔨Support and HowTos

🤖Scripting and Automation

🍏Apple Support

♻️Updates and Releases

🎧To Listen

🎈Just for Fun

📚Support

If you are enjoying what you are reading here, please spread the word and recommend it to another Mac Admin!

Weekly News Summary for Admins — 2023-09-29

Release week part 2! We got macOS Sonoma 14.0 release. If you were running the RC2, that is the same as the release. We also got the first round of iOS 17.1 and macOS Sonoma 14.1 betas! (It’ll be good to have the minor update numbers for iOS and macOS in sync for a change.


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macOS Sonoma

Reviews

MacAdmins

Security and Privacy

Support and HowTos

Scripting and Automation

Apple Support

Updates and Releases

To Watch

To Listen

Just for Fun

Support

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Weekly News Summary for Admins — 2023-09-22

Release week number one! We got iOS 17 and all the siblings. Next week, the updates will continue with the macOS Sonoma release on Sep 26, which Apple already set the stage for with security updates for iOS 16 and 17, and macOS Monterey and Ventura yesterday, as well as a second RC for macOS Sonoma.


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As expected, Big Sur did not get a security update. But there is a Safari update for Big Sur and Monterey. Apple’s productivity apps (Keynote, Numbers, Pages, iMovie and some of the Pro apps) also got updates.

The new iPhones 15 and Apple watches are shipping today. I am getting a new Series 9 watch, which will be an upgrade from my previous Series 5, where the battery has trouble lasting through my busier days. I am also considering upgrading from my iPhone 12 mini to the iPhone 15 Pro. My wife has the 14 Pro and I am very envious of the camera. But I want to go to the Apple Store and hold and feel the new phone first, and then decide whether to order or wait whether the mini form factor will see a revival in the next generation of the iPhone SE. (I don’t have much hope.)

Jamf Nation User Conference was this week, and from what I saw from afar, everyone had a great time. You can find a summary of the keynote on the Jamf blog.

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News and Opinion

iOS and iPad OS 17

macOS

Other Platforms

Applications

Community

Security and Privacy

Support and HowTos

Scripting and Automation

Updates and Releases

To Listen

Support

If you are enjoying what you are reading here, please spread the word and recommend it to another Mac Admin!

If you want to support me and this website even further, then consider buying one (or all) of my books. It’s like a subscription fee, but you also get a useful book or two extra!

Weekly News Summary for Admins — 2023-09-15

The Apple event this week, brought the expected iPhone 15 and Apple Watch updates. You can read all about them on Apple’s event page and the usual suspects.


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More importantly for Mac and iOS Admins: iOS 17, iPadOS 17, and watchOS 10 will be released September 18. macOS Sonoma 14.0 will be released September 26. This is four weeks earlier than the release of macOS Ventura. There were RC releases for all beta platforms this week.

JNUC is next week, safe travel and a fun conference for everyone who is going!

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Focus

News and Opinion

macOS Sonoma and iOS 17

macOS and iOS Updates

Social Media

  • David Nelson: “When reading what’s changed in the latest iPhone we tend to get comparisons to the immediate previous model. Not so helpful if you’re coming from a device that’s two or more years old. The “Compare iPhone Models” page helps. It includes devices all the way back to the iPhone 6 and the original SE. For example, I can see the weight and dimensions of my 12 Pro compared to a 15 Pro Max.

Security and Privacy

Support and HowTos

Scripting and Automation

Updates and Releases

To Listen

Support

If you are enjoying what you are reading here, please spread the word and recommend it to another Mac Admin!

If you want to support me and this website even further, then consider buying one (or all) of my books. It’s like a subscription fee, but you also get a useful book or two extra!

Weekly News Summary for Admins — 2023–09–08

The news summary is back! And right in time for the Apple event next week (Tuesday, Sep 12, 10am PDT)! This is a big heavy summary to catch up on the last eight weeks. If you believe I missed something, let me know and I will add it next week.


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We got macOS 13.5 and iOS 16.6 right at the beginning of the break and a few security updates since then. The macOS Sonoma beta is on the seventh incarnation, iOS 17 and watchOS on the eighth, and, oddly, tvOS is on the ninth.

But aside from the betas and looming system releases, there were many updates for popular MacAdmins tools and software. I myself used the break to write up a few tutorials that have been rattling around in my head for a while.

We have three more big MacAdmin conferences this year: Jamf Nation User Conference (JNUC) in Austin, Texas, USA, Sep 19–21, MacSysAdmin in Göteborg, Sweden, Oct 3–6 and Objective-by-the-Sea 6.0, in Spain, Oct 9–13.

This year, I will be presenting at MacSysAdmin in Göteborg! I have the closing session on Friday, and will be talking about “MacAdmin Tools” so do not leave early. If you are there, too, be sure to say ‘Hi!’ and you will be rewarded with with some Scripting OS X stickers.

Eight weeks of summer hiatus was a long time. There were several scheduling requirements that lead to the long break this year. I plan to organize this differently next year.

If you would rather get the weekly newsletter by email, you can subscribe to the Scripting OS X Weekly Newsletter here!! (Same content, delivered to your Inbox once a week.)

News and Opinion

macOS Sonoma and iOS 17

macOS and iOS Updates

Social Media

  • Aaron on X: “New in macOS Sonoma: You can now use one Mac to revive or restore another Mac that’s in DFU mode right from Finder. Previously you needed to install Apple Configurator to do this but now it’s built in! Accidentally stumbled upon this while playing around with some stuff.”

Security and Privacy

Support and HowTos

Scripting and Automation

Updates and Releases

To Watch

To Listen

Just for Fun

Support

If you are enjoying what you are reading here, please spread the word and recommend it to another Mac Admin!

If you want to support me and this website even further, then consider buying one (or all) of my books. It’s like a subscription fee, but you also get a useful book or two extra!

Build a notarized package with a Swift Package Manager executable

One of the most popular articles on this blog is “Notarize a Command Line Tool with notarytool.” In that post I introduced a workflow for Xcode to build and notarize a custom installer package for a command line tool. This workflow also works with apps and other projects that require a customized installer package building workflow. I use it in many of my own projects.

But Xcode is not the only way to build Swift binaries. Especially for command line tools, you can also use Swift Package Manager. This provides a mostly command line based interface to building and organizing your project, which you might prefer if you want to use an IDE that is not Xcode, or have Swift projects that need to run cross-platform.

I also have an older article on building a command line tool with Swift Package Manager. But then, I did not create an installer package or notarize the resulting binary.

Placing the binary in an installer package file is the best way to distribute a binary as you can control where in the file system the binary is installed. Notarizing the pkg file is necessary when you are distributing a command line tool, since it enables installations without scary dialogs or handling quarantine flags.

Also, some of the behavior of Swift Package Manager (SPM) and Xcode have changed since the previous posts. So, this article will introduce an updated workflow using Swift Package Manager tools and how to sign, package and notarize a command line tool for distribution.

Note on nomenclature: Swift Package Manager projects are called ‘packages.’ On macOS, installer files (with the pkg file extension) are also called ‘packages.’ We will be using SPM to build a notarized installation package (a pkg file) from a Swift package project. This is confusing. There is not much I can do about that other than using ‘installer package’ and ‘Swift package project’ to help distinguish.

Prerequisites

I wrote this article using Xcode 14.3.1 and Swift 5.8.1. It should also work with somewhat older or newer versions of Xcode and Swift, but I have not tested any explicitly.

Since I said earlier that using Swift Package Manager allows us to not use Xcode and maybe even build a cross-platform project, you may be wondering why we need Xcode. While we don’t need Xcode for our project, it is one way of installing all the tools we need, most importantly the swift and notarytool binaries. You get those from Developer Command Line tools, as well. We will also see that we can combine Xcode with the command line Swift Package Manager workflow, which I find a very useful setup.

To submit a binary to Apple’s notarization process you will need a Personal or Enterprise Apple Developer account, and access to the Developer ID Application and Developer ID Installer certificates from that account. A free Apple Developer account does not provide those certificates, but they are necessary for notarization

You can follow the instructions in the Xcode article on how to get the certificates and how to configure notarytool with an application specific password. If you had already done this previously you should be able to re-use all of that here. When you reach the ‘Preparing the Xcode Project’ section in that article, you can stop and continue here. Apple also has some documentation on how to configure notarytool.

The sample code we will be using will only work on macOS as it uses CoreFoundation functions. Installer packages and notarization are features of macOS, too, so this is not really a problem here. You can use this workflow to build macOS specific signed binaries and notarized installation pkg files from a cross-platform Swift package project. This will work as long as you keep in mind that the tools to sign, package and notarize only exist and/or work on macOS.

The sample code

We will build the same simple sample tool as in the last article. The prf command (short for ‘pref’ or ‘preference’) reads a default setting’s effective value using the CFPreferencesCopyAppValue function.

The macOS defaults command will read preferences, but only from the user level, or from a specified file path. This ignores one of the main features of macOS’ preferences system as it will not show if a value is being managed by a different preference level, such as the global domain, a file in /Library/Preferences, or (most importantly for MacAdmins) a configuration profile.

You can learn all about preferences and profiles in my book “Property Lists, Preferences and Profiles for Apple Administrators.”

We will build a really simple command line tool, named prf which shows the effective value of a setting, no matter where the value comes from. You could make this tool far more elaborate, but we will keep it simple, since the code is not the actual topic for this article.

We will also be using the Swift Argument Parser package to parse command line arguments and provide a help message. We could build this simple tool without using Argument Parser, but using an external package module is one of the strengths of using Swift Package Manager.

Create the Swift Package project

With all the preparations done, it is time to create our Swift package. We will do all the work in the shell, so open Terminal or your other favorite terminal app and navigate to the directory where you want to create the project.

> cd ~/Projects

Then create a new directory with the name swift-prf. This will contain all the files from the Swift package project. Change directory into that new directory. All following commands will assume this project directory is the current working directory.

> mkdir swift-prf
> cd swift-prf

Then run the swift tool to setup the template structure for our command line tool or ‘executable.’

> swift package init --type executable 
Creating executable package: swift-prf
Creating Package.swift
Creating .gitignore
Creating Sources/
Creating Sources/main.swift

You can inspect the hierarchy of files that the init tool created in the Finder (open .) or in your preferred editor or IDE.

.gitignore
Package.swift
Sources
    main.swift

`

You can open this package project in Xcode. In older versions of Xcode you had to run a special swift package command to generate the Xcode project, but now, Xcode can open Swift package projects directly. Use xed (the ‘Xcode text editor invocation tool’) to open the current directory in Xcode.

> xed .

There is a pre-filled .gitignore (which will be hidden in Finder and probably your IDE), a Package.swift, and a Sources directory with a single main.swift inside. If you want to use git (or another version control) system, now is the time to initialize with git init.

Build the project with swift build and/or run it with swift run. Not surprisingly, the template prints Hello, world!.

> swift build
Building for debugging...
[3/3] Linking swift-prf
Build complete! (0.92s)
> swift run  
Building for debugging...
Build complete! (0.11s)
Hello, world!

After building, there will also be a .build directory (also hidden in Finder, unless you toggle the visibility of invisible files using shift-command-.) which contains all the interim files. In the debug folder, you can find the swift-prf executable. You can run it directly:

> .build/debug/swift-prf
Hello, world!

You can clean all the generated pieces from the .build directory with swift package clean. This will leave some empty folders behind but remove all the interim and final products. This means the next build is going to take much longer, but this can be helpful after reconfiguring the Package.swift file or when the compiler gets confused.

Sidenote: when you use Xcode to edit your Swift package project, and choose Build or Run from the Xcode interface, then it will build and run in a different location (~/Library/Developer/Xcode/DerivedData/swift-prf-<random-letters>/Build). You need to be aware of this when you alternate between Xcode and the command line.

Configuring the Package

The Package.swift file contains the configuration for a Swift package project. You can see that the executable package template has a single target named swift-prf that builds from the files in Sources.

To change the name of the executable file, change the value of the name: of the .executableTarget to just prf. There is another name: earlier in the file, that sets the name of the entire project, you can leave that being swift-prf. They do not have to match.

Then build the project in the command line and run it directly:

> swift build
Building for debugging...
[3/3] Linking prf
Build complete! (0.51s)
> .build/debug/prf          
Hello, world!

We want to add the Swift Argument Parser package to our project as a dependency, so we can use its functionality in our code. For that, we will have to add a ‘dependency’ to the project and then to the target, as well. Modify the Package.swift file to match this:

// swift-tools-version: 5.8
// The swift-tools-version declares the minimum version of Swift required to build this package.
import PackageDescription
let package = Package(
  name: "swift-prf",
  products: [
    .executable(name: "prf", targets: ["prf"]),
  ],
  dependencies: [
    .package(url: "https://github.com/apple/swift-argument-parser", from: "1.2.0"),
  ],
  targets: [
    .executableTarget(
      name: "prf",
      dependencies: [.product(name: "ArgumentParser", package: "swift-argument-parser")],
      path: "Sources")
  ]
)

This means that our project uses the package available at the given URL, and our target is going to use the specific product (or module or framework) named ArgumentParser from that package. Some packages have several products combined out of several targets.

You can find more information on the format of the Package.swift file in this overview, and the full documentation.

The next time you build after this change, it will download the repository, build and link to toward your executable. That might take a while. The next build should be much faster again. Also, a Package.resolved file will appear in the project. This file caches the current versions of the included packages protecting you from unexpected changes when a package repo dependency updates. You can force Swift Package Manager to update the file with swift package update.

Sprinkle some code

Now that we have the Swift package project prepared, we can add the code to actually do something.

First, let’s keep the ‘Hello, world!’ for a moment, but put it in the right struct to use ArgumentParser. Change main.swift to:

import Foundation
import ArgumentParser
@main
struct PRF: ParsableCommand {
  func run() {
    print("Hello, world!")
  }
}

This should build and run fine from the command line with swift build and swift run. However, when you open this now in Xcode, you will see an error: 'main' attribute cannot be used in a module that contains top-level code

This comes from a long-running issue in Swift. In older versions of Swift it appears on the command line, as well. The work-around is easy though. It only seems to appear when the @main designator is the main.swift file. We can rename our main file to PRF.swift.

You may want to close the Xcode project window before you do this because this can confuse Xcode. If you manage to get Xcode into a confused state where the project in Xcode does not match what is on disk any more, quit Xcode and delete the .swiftpm/xcode directory, which is where Xcode keeps its generated files.

> mv Sources/main.swift Sources/PRF.swift

Now the project should build and run the same with the Swift Package Manager tools and in Xcode.

Now we can add the ‘full’ code for our tool. Keep in mind that the goal of this tutorial is not to learn how to write complex swift code for command line tools, but to learn the infrastructure requires to create and distribute them, so this code is intentionally simple and basic.

import Foundation
import ArgumentParser
@main
struct PRF: ParsableCommand {
  static var configuration = CommandConfiguration(
    commandName: "prf",
    abstract: "read effective preference value",
    version: "1.0"
  )
  @Argument(help: "the preference domain, e.g. 'com.apple.dock'")
  var domain: String
  @Argument(help: "the preference key, e.g. 'orientation'")
  var key: String
  func run() {
    let plist = CFPreferencesCopyAppValue(key as CFString, domain as CFString)
    print(plist?.description ?? "<no value>")
  }
}

When you compare that to the code from the last article, there are a few differences. We are using the @main attribute to designate the main entry point for the code (this was added in Swift 5.3) and I have added some help text to the tool and argument declarations.

When you use Swift Argument Parser, you should study the documentation on adding help to [commands](I have added some help text to the tool and argument declarations. ) and flags, arguments and options. (To be honest, you should read the entire documentation, a lot has changed since the last article.)

When you now run the tool:

> swift run  
Building for debugging...
[3/3] Linking prf
Build complete! (0.54s)
Error: Missing expected argument '<domain>'
OVERVIEW: read effective preference value
USAGE: prf <domain> <key>
ARGUMENTS:
  <domain>                the preference domain, e.g. 'com.apple.dock'
  <key>                   the preference key, e.g. 'orientation'
OPTIONS:
  --version               Show the version.
  -h, --help              Show help information.

We get the help text generated by Swift Argument Parser with the extra information we provided in the code.

If you want to provide the arguments to the swift run you have to add the executable name, as well:

> swift run prf com.apple.dock orientation       
Building for debugging...
Build complete! (0.11s)
left

Or you can run the executable directly from the .build/debug directory. (This will not automatically re-build the command like swift run does.

> .build/debug/prf com.apple.dock orientation
left

Since we provided a version in the CommandConfiguration, ArgumentParser automatically generates a --version option:

> .build/debug/prf --version       
1.0

Now that we have a simple but working tool, we can tackle the main part: we will package and notarize the tool for distribution.

Preparing the binary

When you run swift build or swift run it will compile the tool in a form that is optimized for debugging. This is not the form you want to distribute the binary in. Also, we want to compile the release binary as a ‘universal’ binary, which means it will contain the code for both Intel and Apple silicon, no matter which CPU architecture we are building this on.

The command to build a universal release binary is

> swift build --configuration release --arch arm64 --arch x86_64

When that command is finished, you will find the universal binary file in .build/apple/Products/Release/prf. we can check that it contains the Intel (x86_64) and Apple silicon (arm64) with the lipo tool:

> lipo -info .build/apple/Products/Release/prf
Architectures in the fat file: .build/apple/Products/Release/prf are: x86_64 arm64 

For comparison, the debug version of the binary only contains the platform you are currently on:

> lipo -info .build/debug/prf
Non-fat file: .build/debug/prf is architecture: arm64

Apple’s notarization process requires submitted binaries to fulfill a few restrictions. They need a timestamped signature with a valid Developer ID and have the ‘hardened runtime’ enabled.

Xcode will always sign code it generates, but the swift command line tool does not. We will have to sign it ourselves using the codesign tool. You will need the full name of your “Developer ID Application” certificate for this. (Don’t confuse it with the “Developer ID Installer” certificate, which we will need later.)

You can list the available certs with

> security find-identity -p basic -v

and copy the entire name (including the quotes) of your certificate. Then run codesign:

> codesign --sign "Developer ID Application: Your Name (ABCDEFGHJK)" --options runtime  --timestamp .build/apple/Products/Release/prf

You can verify the code signature with

> codesign --display --verbose .build/apple/Products/Release/prf

Build the installation package

Now that we have prepared the binary for distribution, we can wrap it in an package installer file.

To cover all deployment scenarios, we will create a signed ‘product archive.’ You can watch my MacDevOps presentation “The Encyclopedia of Packages” for all the gory details.

First, create a directory that will contain all the files we want put in the pkg. Then we copy the binary there.

> mkdir .build/pkgroot
> cp .build/apple/Products/Release/prf .build/pkgroot/

Then build a component pkg from the pkgroot:

> pkgbuild --root .build/pkgroot --identifier com.scriptingosx.prf --version 1.0 --install-location /usr/local/bin/ prf.pkg

The --identifier uses the common reverse domain notation. This is what the installer system on macOS uses to determine whether an installation is an upgrade, so you really need to pay attention to keep using the same identifier across different versions of the tool. The --version value should change on every update.

The --install-location determines where the contents of the payload (i.e. the contents of the pkgroot directory) get installed to. /usr/local/bin/ is a useful default for macOS, but you can choose other locations here.

Next, we need to wrap the component pkg inside a distribution package.

> productbuild --package prf.pkg --identifier com.scriptingosx.prf --version 1.0 --sign "Developer ID Installer: Your Name (ABCDEFGHJK)" prf-1.0.pkg

It is important that you use the “Developer ID Installer” certificate here. The --identifier and --version are optional with productbuild but this data required for some (admittedly rare) deployment scenarios, and we want to cover them all.

You can inspect the installer pkg file with a package inspection tool such as the amazing Suspicious Package. The package file should as a signed “Product Archive.”

We don’t need the component pkg anymore, and it’s presence might be confusing, so let’s remove it:

> rm prf.pkg

Note: If you want to learn more about building installation packages, check out my book “Packaging for Apple Administrators”

Notarization

We are nearly there, just two more steps.

It is important to notarize pkgs that will be installed by a user, because otherwise they will get a scary warning that Apple can’t verify the pkg for malicious software.

notarytool submits the installer package to Apple’s Notarization process and returns the results. Use the keychain profile name you set up, following the instructions in the previous article or the instructions from the Apple Developer page.

> xcrun notarytool submit prf-1.0.pkg --keychain-profile notary-example.com --wait

This will print a lot of logging, most of which is self-explanatory. The process might stall at the “waiting” step for a while, depending on how busy Apple’s servers are. You should eventually get status: Accepted.

If you got a different status, or if you are curious, you can get more detail about the process, including rejection reasons, with notarytool log. You will need the ‘Submission ID’ from the submission output:

xcrun notarytool log <submission-uuid> --keychain-profile notary-example.com

As the final step, you should ‘staple’ the notarization ticket to the pkg. This means that the (signed) notarization information is attached to the pkg-file, saving a round trip to Apple’s servers to verify the notarization status when a system evaluates the downloaded installer package file.

xcrun stapler staple prf-1.0.pkg
Processing: /Users/armin/Desktop/swift-prf/prf-1.0.pkg
Processing: /Users/armin/Desktop/swift-prf/prf-1.0.pkg
The staple and validate action worked!

And with that, we have a signed and notarized installation pkg file! You can verify this with spctl:

> spctl --assess --verbose -t install prf-1.0.pkg 
prf-1.0.pkg: accepted
source=Notarized Developer ID

Automation

While it is instructive to do this process manually, it is also quite complex and error-prone. If you have been following this blog for any time, you will know that I don’t stop at detailed step-by-step instructions with explanations.

You can find a script to automate all of these steps here. The enclosing repository includes the entire project (all three files) for your reference.

There is a section at the beginning with variables to modify with the information specific to your environment and project, such as your developer ID information and the name of the credential profile for notarytool. Then there are a few variables, such as the product name, and the installation package identifier.

Run the pkgAndNotarize.sh script from the root of the Swift package project directory.

./pkgAndNotarize.sh

The script creates the installer pkg file in the .build directory. The last line of output is the path to the final, signed, notarized and stapled pkg file.

The script mostly follows the process described above, with a few extras. For example, the script determines the version dynamically by running the tool with the --version option. It also uses the modern compression options I described in this post.

If any of the steps in the script fail, you can determine what exactly failed from the output, error message and error code.

(I belief that this could probably be a makefile, but I have no experience with that (yet). I guess I will need to ‘make’ time for this…)

Conclusion

Apple provides developers and MacAdmins with amazing platforms and tools to build all kinds of powerful apps, tools and automations. But then they don’t really document any of the processes or best practices at all. The amount of searching, guesswork, and frustrating trial and error necessary to piece all of this together for a workflow like this one is quite the shocking condemnation of Apple’s documentation.

There are glimmers of hope. The documentation for the notarization process and notarytool are exemplary.

But they only cover one piece of this puzzle. A developer building a tool has to still figure out how to

  • sign all the binaries properly
  • assemble the binaries and resources necessary into an installation package payload
  • how (and when, and when not) to use pre- and postinstall scripts
  • which kind of package installer to build and which tools to use
  • securely manage the Developer ID certificates (this is especially challenging for developer teams)
  • automate this workflow with Xcode or Swift Package Manager or a CI/CD system

MacAdmins often complain about poorly built installer pkgs, and often for good reasons. But to be fair, there are no best practices and little to no documentation for this from Apple. How are developers supposed to know all of this? Most MacAdmins can define what an installer package should do and not do, but wouldn’t be able to explain to a developer how to build such an installer package, let alone integrate that into their build automations. And most developers don’t even know a MacAdmin to ask about this.

Apple requires that developers create signed and notarized archives for software distribution. And I agree wholeheartedly with their motivations and goals here. But when impose requirements for distribution, you have to make the process of creating the installers the correct way easy, or at least well documented, whether you use Xcode or a different tool set, whether you want to distribute a simple self-contained app, a single command line tool, or a complex suite of tools and resources.

Apple has their work cut out to improve this. Official best practices and sample workflows for installer creation and distribution that consider and respect the requirements of MacAdmins for deployment, have been disgracefully lacking for a long time. The more requirements and security Apple piles on to application and tool distribution, the more desperately they need to provide documentation, best practices and guidance.

Until that happens, you have my paltry scripts.