Experiences with union mounts in MacOS?

[Richard L. Hamilton]

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 <dluke at geeklair.net> wrote:
> 
> On Dec 16, 2018, at 11:03 AM, Ces VLC <cesarillovlc at 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
> 
>