News for hackers. Stuff that matters.

A comment on What Is Nix?. Parent comment

Re:What Is Nix? by aeontech on Wednesday May 20, 2020 @07:52PM (#23253409)
It's not a bug in macOS, it's a security feature.

However, you can use synthetic firmlinks to define arbitrary root-level paths that _are_ writable.

See `man synthetic.conf` and check out https://derflounder.wordpress.com/2020/01/18/creating-root-l... for an example usage.

PS: It looks like nix has a PR open to test that solution here: https://github.com/NixOS/nix/pull/3212

[ Parent | on HN ]
Re:What Is Nix? by danieldk on Thursday May 21, 2020 @02:11AM (#23255350)
However, you can use synthetic firmlinks to define arbitrary root-level paths that _are_ writable.

See `man synthetic.conf`

No, synthetic.conf only creates directories or symlinks. If it actually created firmlinks, the problem would probably be much smaller.

The problem with symlinks is that some builds use realpath. If /nix was a symlink to e.g. /usr/local/nix, this would result in /usr/local/nix being used in this builds. This leads to various build problems [1] and can result in the wrong paths ending up in binaries. If this happens on a builder, the resulting binaries are not portable between macOS + Nix machines.

So, instead the only way to get it currently working is to use synthetic.conf to create a new top-level directory and mount a APFS volume with the Nix store there.

If Apple actually allowed creating firmlinks with synthetic.conf, the Nix installation would be drastically simplified. /nix could just be a firmlink to e.g. /usr/local/nix, since realpath does not report the actual path on firmlinks.

[1] https://github.com/NixOS/nix/issues/2926#issuecomment-559989...

[ Parent | on HN ]
Re:What Is Nix? by aeontech on Thursday May 21, 2020 @07:32PM (#23266898)
I stand corrected, I must have misunderstood the doc.
[ Parent | on HN ]