Just when you think it’s safe to upgrade to macOS Catalina, we start hearing of strange and serious problems, like its security checks getting completely out of hand and slowing app launch drastically. Over the last few weeks, as more Mac users take the plunge and upgrade, I’ve been hearing of more and more such cases. Are these bugs and should we still hold off upgrading?

In making the decision to upgrade to Catalina, you must bear in mind that in terms of structural change this is possibly the most major upgrade since you first installed Mac OS X. Because of that, the risk of the upgrade not working perfectly the first time is significant. This all comes back to the introduction of the read-only System volume.

For the Catalina installer to complete successfuly, it has to do the following:

1. rename your existing startup volume with ” – Data” appended;
2. remove all existing system folders and files from that new Data volume;
3. change the folder layout on the Data volume;
4. create a new System volume, and install the new system there;
5. set the volume types of the System and Data volumes, and convert them into an APFS Volume Group;
6. create new firmlinks to connect the two volumes.

The installer also has to update the firmware in your Mac, and replace the contents of the Recovery volume.

There’s a great deal of potential for minor errors to occur in this complex process. Although major errors appear very rare, minor problems are more common.

Before upgrading

If you suspect that you might have anything installed which significantly deviates from the standard pre-Catalina boot volume layout, it’s worth bringing that volume back to the standard before trying to upgrade. This applies particularly to additional top-level folders. Catalina does make provision for /opt, which is firmlinked to the Data volume, but other non-standard top-level folders could cause unpredictable results.

In case you’re not sure what a standard pre-Catalina boot volume layout looks like, that’s it above, and you can download a PDF version from here: Mojave2

Contrast the standard layout on Catalina’s System volume:

available here as a PDF: CatalinaSysR

For the sake of completeness, here’s the standard layout on Catalina’s Data volume:

available here as a PDF: CatalinaDataR

After upgrading

If you have upgraded and your Mac is suffering from strange problems, there are several fixes available. First, ensure that any third-party extensions and customisations are fully up to date, or remove them. When you’re confident that it’s not the result of an adverse interaction like that, try starting up in Safe mode, letting your Mac run for a minute or two, then restarting normally. Although this is unlikely to fix anything major, it can be curative for some problems perhaps with LaunchServices.

Then, using SilentKnight or LockRattler, check that your firmware has been properly updated for Catalina. If it hasn’t, you’ll need to reinstall the current version of macOS, which is the only way to update your firmware now.

After that, your choice is which type of reinstall should you use. Reinstalling Catalina brings a higher chance of fixing problems, as the installer doesn’t have the task of reconfiguring your startup volume into two: that has already been accomplished, so the chances of failure in the installer should be significantly less.

Normally the smallest and quickest to try is the latest Combo update, which won’t be available until the 10.15.2 update is released. Then comes the regular installer, obtained through the App Store and Software Update. Beyond that is reinstalling from Recovery mode, and – most drastic of all – a clean reinstall from there.

Catalina does still have plenty of bugs, but if you seem to be the only person affected by something quite prominent, it’s more likely to be a clash with third-party software, or an error in its installation. If addressing those doesn’t help, try contacting Apple Support, who by now should be well aware of how to deal with your problems.