Disk capacity unchanged after deleting 21 GB MacPorts

[Jim DeLaHunt]

Jerry:

On 2024-11-26 12:03, list_email--- via macports-users wrote:
> As a first step in re-installing MacPorts (long story), I ran
> 
> $ sudo port -fp uninstall installed
> 
> ...Before uninstalling, the Finder indicated that /opt/local contained 21 GB. After, /opt/local was nearly empty, as expected. I completed the steps indicated to complete the uninstallation.
> 
> I happened to check the “Used” quantity, as indicated by Finder on Get Info on my boot volume (which contained /opt/local) before uninstalling, and again after uninstalling. I expected to see this quantity reduced by 21 GB. But there was no change!
> 
> Why was the “Used” number unchanged after deleting 21 GB?

I am not an expert and don't have a definitive answer. But my first 
guess is: the APFS file system, and snapshots.  If something made a 
snapshot of the file system contents before you deleted everything in 
/opt/local, then maybe those file system contents are still present and 
occupying space in the snapshot.  Time Machine is one system which can 
create snapshots; there are probably others. And, you should ask 
yourself the question, what exactly is Finder's formula for its "Used" 
quantity?

Howard Oakley's excellent Eclectic Light Company blog has a steady 
stream of interesting details on the behaviour of Macs and macOS. The 
post, "Explainer: Disk free space" from 2021-12-04 
<https://eclecticlight.co/2021/12/04/explainer-disk-free-space/> may 
answer your question. There might be more insight in the blog posts 
tagged with "free space" <https://eclecticlight.co/tag/free-space/>.

TL;DR: File systems aren't as simple as they used to be.

I hope this is helpful,
      --Jim DeLaHunt