macOS 10.15 ("Catalina") became available from the Mac App Store on October 7th, 2019. It is assumed the only fully supported version of macOS, all previous versions are assumed to be insecure.
All macOS versions below 10.13.6 are definitely unsupported.
For an overview of new features in macOS 10.15 see https://www.apple.com/macos/catalina/features/
There are some important actions to take before you install it:
- Take note of the information on https://support.apple.com/en-us/HT201475
- Ensure that all the software you are using is compatible with it. See below for a list of known issues (be aware that the list is far from complete).
- Make sure to update all third party software you are using BEFORE upgrading to macOS 10.15. We expect that many updaters of older software will NOT WORK any more under macOS 10.15.
- Uninstall outdated software and software you don't use any more BEFORE upgrading to macOS 10.15. We expect that most uninstallers for outdated software will NOT WORK any more under macOS 10.15.
- Verify your hard-disk or SSD before doing the install.
- Make sure you have a recent backup, allowing you to recover your data in case of problems.
- Note that the upgrade will most likely convert the filesystem on your Mac, carefully read https://support.apple.com/en-us/HT208018 and re-check your backups!
- Make sure you have enough free disk space for the install image AND the installation process. The installer will start even if you don't have enough free space, it will fail and stubbornly try again after a restart. You will need to re-install your OS if this happens, data loss is quite likely...
- In case you migrate from a macOS version older than 10.14 you should also read the 'About macOS ...' articles concerning all intermediate versions of macOS.
32 Bit Applications
32 Bit Applications do not run on macOS 10.15, please read https://support.apple.com/en-us/HT208436. The feature 'How to find 32-bit apps on your Mac' mentioned on that page is only available on macOS 10.14 and newer. Update or remove your 32 bit apps BEFORE upgrading to macOS 10.15.
Brew users should check the news on ??? before upgrading to Catalina. Please note that we do not support brew or any tools installed through it.
Canon Printer Drivers
Fixed 17-Oct-19 16:00 for installaton via Self-Service: The Canon Printer Drivers package can not be installed under macOS 10.15. The printer drivers that have been installed before upgrading to macOS 10.15 appear to work after an upgrade to macOS 10.15.
Deny / Allow
macOS 10.15 has become very restrictive. You will get plenty of dialogs "Application X wants to access Y".
Version 6.8.1 of ESET is required for Catalina. If you have an older version installed via the Self-Service just delete the ESET Endpoint Antivirus.app from your Applications folder, then open the Self-Service and run the ‘Refresh Inventory’ policy. Within the next 20 minutes the new version of ESET will be installed. Another option is to the the remove and the re-install via the Self-Service, but this does take a bit longer.
Fink users should check the news on http://www.finkproject.org before upgrading to Catalina. Please note that we do not support fink or any tools installed through it.
The GPG Suite is not compatible with the MAil.app from macOS 10.15
HP Printer Drivers
Some HP printer drivers are not working under macOS 10.15
MacPorts users should check the news on ??? before upgrading to Catalina. Please note that we do not support MacPorts or any tools installed through it.
Mail.app appears to have problems creating IMAP accounts. Some users have reported that MAil.app is often very slow. Some users reported about mail messages being lost.
Version 12 of Mathematica is required for Catalina. Users have reported problems with copy & paste in celss with manual grouping. If you rely on that feature you better stay with Mathematica 11 and macOS Mojave.
Version 4.3 of Mattermost is required for macOS 10.15
Protected System Partition
All system files now resideon a dedicated and write protected partition. Tools that require write access to directories on the system partition will not work.
System Center Endpoint Protection
System Center Endpoint Protection (Microsoft SCEP) is not compatible with 10.15. You MUST uninstall SCEP before upgrading to macOS 10.15. You will not be able to install ESET Antivirus under macOS 10.15 if you leave SCEP on your Mac.
I have seen cases where the upgrade to Catalina broke XQuartz. Reinstalling the current version from https://www.xquartz.org/ solves the issue.