I just tried (Mojave) a couple of times. Once, a dmg attached but manually mounted over a non-empty directory; didn't see the contents below, although I suppose I might have messed up somehow. Another time, an NFS mount over the same non-empty directory, where I _did_ see both. The dmg had to be read-only, the NFS mount didn't; I wonder if that mattered (esp. since the lower layer was read-write).
> On Dec 17, 2018, at 11:32, Daniel J. Luke <dl...@geeklair.net> wrote: > > On Dec 16, 2018, at 11:03 AM, Ces VLC <cesarillo...@gmail.com> wrote: >> But I'm a bit afraid because it seems to be a little used feature in the >> Mac, so, if I'll be the only one in the planet using it, I guess it can be >> like sort of a minefield walk, likely to use little-tested stuff. > > it would be interesting to see how well it worked (or didn't work), but I > wouldn't want to rely on it for anything important. > >> I searched for it, and the only problems I saw reported is that Finder >> doesn't seem to honor union mounts, but that wouldn't be a problem for me, >> as I won't be using Finder for browsing the mount directory. If it works >> fine at the Terminal, then it's fine for me. >> >> Do you have any experience using union mounts on MacOS? Did it work fine for >> you? Did you find any problem/issues? > > I have a vague recollection of having problems with it back when I tried to > use it for something that sounds similar (I wanted to use it to isolate > changes made by a build or packaging system from the underlying OS). I don't > recall why I ended up stopping that experiment, though. Since you're already > using disk images, though - maybe you can use a shadowfile to get one layer > of image combining? > > -- > Daniel J. Luke > >
