Clear Space to Fix Catalina Update Restart Loop
I haven’t been using my old 2012 MacBook Air recently, so I wasn’t surprised when System Preferences displayed a badge alerting me to updates. It wanted to install Security Update 2021-002 for macOS 10.15 Catalina and Safari 14.1, so I clicked the Update Now button and received a dialog telling me that I needed to restart to complete the update. No problem, so I clicked Restart.
The MacBook Air promptly restarted, and I logged in again, only to discover that nothing had been installed. I tried again, and once again, the Mac just restarted without installing the updates. I switched to a different admin account, but the problem recurred, all without any error dialogs that might have shed some light on the problem.
On a hunch, I checked the free space available on the MacBook Air’s internal 256 GB SSD. It was about 7 GB, which didn’t seem ridiculously low for just a security update, but after some hunting around on the Internet, I found some suggestions that too little free space could cause the installer to fail silently. I downloaded GrandPerspective, my favorite utility for identifying large files, cleared 40 GB, and tried again. This time the update installed as it was supposed to.
The moral of the story is to make sure you have sufficient free space before installing even a security update. What’s sufficient? That’s unclear, though 47 GB was enough, and some of the comments suggest that 20–30 GB would work.
Of course, the larger lesson is that it’s not a good idea to let a Mac’s internal drive get too full. If you search, you’ll find recommendations ranging from 5% to 20%, comments suggesting that percentages don’t make much sense for larger drives, and responses pointing out that it all depends on what you’re doing. Clearly, 7 GB free on a 256 GB SSD (2.7%) wasn’t enough for an installation to proceed, whereas 47 GB (18%) was. We also know that if you want to upgrade to macOS 11 Big Sur, it needs at least 35.5 GB to upgrade from 10.12 Sierra or later and 44.5 GB to upgrade from earlier versions of macOS.
So I’d suggest that 50 GB may be a safe minimum for most Macs. More is always better due to virtual memory swap files, the need for large caches, and APFS snapshots.
Have you had trouble after running low on free space? Share your experiences in the comments.
Thanks for the reminder! I had not launched GrandPerspective (or similar app) in a while on my laptop. When I did, I found tens of GBs worth of Apple events in my Podcasts folder, which I did not need to save.
GrandPerspective is a nice app, but I prefer its cousin, Disk Inventory X. It is based on the Linux KDirStat app.
I prefer it because it presents a list-view of all your files. You can select any file or folder and immediately see it in the graphical view. It also presents an index panel to show what file types correspond to each color.
The only downside is that the author has not signed the app, so Gatekeeper makes you jump through a few hoops (right-click it and select Open) the first time you run it. If this bothers you, then I recommend scanning it for malware before you run it the first time.
OmniDiskSweeper is free. I like it because instead of graphics, I simply get column view (which I usually use in Finder already) lists sorted by size so I can focus right away on what presents the biggest potential payoff.
It’s old, but they maintain it (albeit as a bit of a side project I guess).
The suggestion that is quite old but in my opinion still valid: free space on your disk should be double the amount of installed RAM. If you have 16GB RAM, free space on your disk after reboot should be 32 GB.
As the OS uses the disk for virtual memory aka swap.
I run Onyx once a Month, plus Parallels Toolbox has clean up features. Coming from early Windows iterations, combined with computers of the time where 80GB was a nice chunky drive, I am somewhat obsessive about free space.
Many, many thanks for this Adam. For the last month, I’ve been getting warnings that my 2 year old 500GB SSD was getting full with less than 20GB available. I was wondering would I have to get a new bigger disk to keep my 2011 MacBook Pro going; as it is a fine machine and I don’t need “bigger, faster, better” yet, I’m happy to use it for another few years. Anyway, I downloaded GrandPerspective and it showed up a 68GB file in the Library. It was linked to the WavePad application which I have used just once, and more than a year ago; I can’t recall why I needed it back then. I deleted the app and its preference files, etc., and suddenly I’ve got 90GB of free space. What a relief!
While the reminder to “know thou drive space” and the comments about various apps to ‘clean’ wasted space are nice, how ‘ out this: Apple, if there’s not enough free space, just tell us. DUH.
Apple could do better with this. You’ll certainly get warnings when you’re too low on drive space for normal activities to take place, but things like upgrades require a lot more free space. It would be nice if Apple would acknowledge that and build in some additional gentle warnigns.
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