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

Bjarne D Mathiesen macintosh at
Sat Jun 26 08:34:42 UTC 2021

Tabitha McNerney wrote:
> Hi all,
> I haven't installed a fresh MacPorts system in quite some time but will
> soon be doing so on a few Macs one running Catalina and the other Big
> Sur. Starting with Catalina, the root volume / is read-only so how do
> the MacPorts package installers set things up such that /opt/local can
> remain the default path to MacPorts for both read and write
> functionality on Catalina and Big Sur? 

/opt is one of the directories Apple defines at the / level as part of
the Data Volume

> Do the MacPorts package
> installers make use of Apple's new bi-directional firmlinks capability
> defined in /etc/synthetic.conf as also described on this page?

No. That's not necessary as /opt transparently exists and is writable.

> Thank you.
> -TM

In depth explanations are here :

So, If you go to /System/Volumes/Data in Terminal & do 'ls -l' you'll
see the opt directory.

Bjarne D Mathiesen
Korsør ; Danmark ; Europa
denne besked er skrevet i et totalt M$-frit miljø
MacPro 2010 ; OpenCore + macOS 10.15.7 Catalina
2 x 3,46 GHz 6-Core Intel Xeon ; 256 GB 1333 MHz DDR3 ECC RDIMM
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