Next month (October), we’ll all be able to upgrade to macOS 10.15 Catalina. If you’ve decided that you’re going to move at least one of your Macs up to this new major release, you’ll need to start preparing now. Here are some pointers based on my experience with previous upgrades, and what’s changing in Catalina.

32-bit software

The most obvious issue you’ve got to tackle is the fact that Catalina won’t run any software – app, command tool, framework, extension, plugin, etc. – which is still 32-bit code. By this stage you should know which, if any, of your apps and other software will be affected by this, and have planned a way forward. If you haven’t, don’t try upgrading until you have.

One important fact to note here is not to trust anything reported in the Legacy Software section of System Information. Unfortunately this doesn’t get updated when you install 64-bit replacements, and continues to show ‘problems’ which you’ve already solved. If you’re in any doubt about an important app or tool, use my free ArchiChect to assess it thoroughly.

That said, you don’t have to prepare your fallback before upgrading, although it helps when you do. Catalina doesn’t delete 32-bit software, although if it encounters any in kernel extensions, System Preference panes, LaunchDaemons, or the like, it should move it out of the way. If you really have to, you can purchase, download and install Parallels Desktop 15 after you’ve upgraded to Catalina and discovered that an important app is still 32-bit, or otherwise non-functional. The only caution with this is that it might be hard to find the Mojave installer in the App Store, so now is the best time to ensure that you have that for 10.14.6.

If you do set up a Mojave VM hosted in Catalina, one issue you’ll face is ensuring that it’s fully up to date with security updates. Simply copy across my free SilentKnight, and although it won’t recognise its EFI firmware, it will download and install all the updates you need, as will LockRattler of course.

Notarization

If you know that a product you’re going to install has already been notarized, then you can install it before or after upgrading, as it should fly through Gatekeeper’s first run checks on either system. If you’re uncertain, or suspect that there could be problems, try to get it installed before upgrading, so that it clears its quarantine flag. You can also check an app’s notarization using my free app Taccy.

Although the requirements for kernel extensions haven’t changed from late releases of Mojave, approval of new third-party kernel extensions in Catalina requires a restart which can disrupt installation. Good products, such as Parallels Desktop 15, don’t have any problems with this interruption, and when your Mac has restarted to allow its extension to be loaded, the installer carries on where it left off. Other products may not cope as well with this, in which case it’s wise to install them before upgrading.

iCloud

The most frequent and severe problems reported by Catalina beta testers have been with iCloud. Apple appears to be addressing these by postponing the introduction of new features which may have been responsible. However, you shouldn’t take any chances with your iCloud during the upgrading process. Plan to make local copies and backups of all important documents you have stored in iCloud before upgrading.

If you run any Mac to be upgraded with its Desktop & Documents Folders stored in iCloud Drive, you may also find it less nerve-racking to disable that before starting the upgrade process. This normally empties your local Desktop and Documents folders, leaving their current contents stored in iCloud, so you’ll need a little time to copy those down to local storage and back them up. If you have more stored there than you can keep locally, you’ll have to plan this even more carefully.

I haven’t seen any reports of problems with iCloud database features such as Keychains, Contacts or Calendars, although immediately before an upgrade is an excellent time to ensure that you have good local backups.

Time Machine and backups

As far as anyone’s aware, Catalina doesn’t bring significant changes in Time Machine, although there will be the issue of whether to try including the read-only system volume in your backups, if you’re given a choice.

Ensure that you have not only a current Time Machine backup but also a second copy such as a clone made by Carbon Copy Cloner immediately before upgrading. macOS will make a snapshot before installation, but it’s always good to have full backups on other volumes. It’s also a good time to check that those Time Machine backups are in a good state of health, and run a functional test restoring a couple of documents and folders to confirm that.

The first Time Machine backup after upgrading is always a large one, and this time with the change in volumes could be even greater. This is because the non-system volume is renamed Macintosh HD – Data. Depending on how Time Machine treats this, it could result in what is effectively a full backup of your startup volume. I’m sure that early upgraders will tell us whether that happens, or Time Machine recognises that this is just an existing volume renamed.

Scripts and paths

I’ve already written about how the introduction of the read-only system volume can result in some changed paths, and mentioned above the renaming of the volume on which non-system data is stored. Apple has gone to lengths to try to ensure that these changes don’t break scripts, but until they’re actually tested you can’t be certain.

When tackling this, ensure that you use the appropriate way to see the path on your Catalina system: if you’re using a Unix-style path, for a shell script perhaps, then trace that path in Terminal. Finder’s illusions can be misleading, although if you drag from Finder into Terminal, macOS does the path conversion for you.

Secondary updates

When you’re planning for the upgrade, don’t forget that most non-bundled Apple apps are likely to be updated immediately afterwards. These could involve very large downloads, particularly if you use Pro apps or Xcode – and in my case, all of the above. In some cases, these will remove 32-bit support for conversion from old movie and other formats. If you’re unsure whether that will prevent access to some important documents, now is the time to perform final checks.

Reminder list

As you’re working through these and other checks, build yourself a list of the tasks which you need to complete before and shortly after upgrading. This is going to be a more complex upgrade than normal, but it shouldn’t prove overdemanding for the great majority of users.

Finally, in case you’ve lost the link, here are details of the compatibility of my free apps with Catalina. I’ve almost got there, I think. I hope the upgrade goes well for all of us.