MacPorts and /opt/local on Catalina and Big Sur read only volumes

[Ryan Schmidt]

On Jun 25, 2021, at 21:03, Tabitha McNerney wrote:

> On a fresh Catalina or Big Sure system, if you cd to root / then sudo then try mkdir /opt or something else such as mkdir /hello the system won't allow it, I get this:
> 
> mkdir: /hello: Read-only file system
> 
> note: the MacBook I just tried this on also has FileVault enabled and its got one of those Apple T2 chips with a touch bar
> 
> How does the MacPorts Catalina or Big Sur pkg installer work around this restriction?

I don't know that we're doing anything. It just works.

There is some mechanism, that I don't understand, by which the system volume and the data volume are combined into a single presentation. Presumably the Installer app knows that you cannot install to the system volume, so it installs MacPorts to the data volume.