New mac user here (Linux background). I'm running macOS Catalina (Beta5). I've noticed there are 5 volumes in my main disk container. One is mounted at /, that I understand, it's the system, another is /System/Volumes/Data, which I tough it would be the Linux /home, but it's not, so what it it?

Also what are the other two unmounted volumes? One might be the recovery one, but the other? Thanks!

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Catalina introduces a new file system where there is a blend of read-only system files and a read-write user space interleaved on a folder by folder basis.

The easy way to move forward is just save to /usr/local and other traditional places where Apple expects user modifications to be saved.

Some of the implementation is quite normal for Unix/Linux like sparse files not being allocated and copy on write and cloning of an entire file system / snapshots. Other items like Firmlinks that act as “wormholes” between two containers / filesystems to present an unified file tree, System Integrity Protection and APFS specific features are quite new still to everyone.

You can see this better with df or diskutil apfs list command line tools than the Disk Utility view.

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  • Why are there copies of my applications in there? They don't seem to be simlinked, as best as I can tell. If I was to delete one, should it be the ones in /Applications? – jktravis Oct 11 '19 at 22:36
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    @jktravis Applications is even weird than any other folder. See the paragraph on Applications here eclecticlight.co/2019/10/11/… – bmike Oct 12 '19 at 3:26
  • I wouldn't say that Firmlinks is a new and unknown concept for Linux users actually.. it's used very much the same way as you use overlayfs (or other similar features such as unionfs and aufs) on Linux. For example you can do the "blending" that you see in the Applications folder, where some files are from the read-only volume, and others are from the read-write volume. – jksoegaard Oct 13 '19 at 17:08

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