macOS 10.15 Read Only root

[Chris Jones]

> On 30 Jun 2019, at 12:21 pm, Rainer Müller <raimue at macports.org> wrote:
> 
>> On 30/06/2019 04.15, Ryan Schmidt wrote:
>>> On Jun 29, 2019, at 19:53, Mark Anderson wrote:
>>> 
>>> Do we have any plans with how to deal with 10.15 not allowing us to create /opt if it doesn’t exist? Or does /opt just come with the file system? I can’t remember.
>> 
>> macOS does not come with an /opt directory.
>> 
>> I was not aware that macOS Catalina will prevent the creation of such directories, but I haven't read up on the new system yet. If that is true, then that sounds like a problem for us.
> 
> /opt will not reside on the read-only volume, but with the new concept of a
> "firmlink" it will be placed on another volume.
> 
> I was told the full list of these writable paths using firmlinks can be found in
> /usr/share/firmlinks

Thanks. It wasn't obvious to me how open things would be w.r.t. creating these firmlinks, whether it would be possible to create arbitrary ones, such as for /opt, or if Apple would only allow it for select locations. Either way, the installer will have to do something a little different to create them, as you first have to temporarily make / writable, create the MP volume in a read/write area and then firmlink it to /opt, and finally restore the read only attribute.

> Rainer