Sharing files with your Mac

A folder from 1985's point of view

Choose a folder in Settings → Shared folder and it appears inside the emulated machine at /n/macos. Your home folder is offered separately at/n/home. Both are ordinary directories to the Unix side — you canls them, cat from them, copy in and out, and compile from them.

$ ls /n/home
Desktop     Documents   Downloads   Pictures

$ cp /n/home/notes.txt .
$ wc -l notes.txt
      42 notes.txt

What is actually happening

This is not a bridge invented for the app. Peter Weinberger wrote a network file system for Research Unix in the mid-1980s, to bind the lab's machines into one logical system, and its client has been compiled into every Eighth Edition kernel since. It has had nothing to talk to since Datakit was switched off.

ipnx gives it a server again. The kernel's own netfs client does the mounting, speaking its original protocol, to a server running inside the app. The Unix side has no idea anything unusual is happening; as far as it is concerned another machine on the network is exporting a filesystem, which in 1985 it would have been.

Read-only unless you say otherwise

A share starts read-only. Turn on Allow the VAX to write for a folder and the emulated machine can create and modify files in it — which is genuinely useful and worth a moment's thought first, because the writer is a 1985 Unix with fourteen-character file names and no notion of your Mac's conventions.

Why your home folder is not the home directory

It would be the obvious design and it does not work. Eighth Edition file names are limited to fourteen characters, the filesystem is case-sensitive in a way macOS usually is not, and a great many names in a modern home folder simply cannot be represented. Making that the account's home directory would produce a machine that broke in a different place every day.

So the account's home is on the emulated disk, where 1985 rules apply consistently, and your Mac's files are reachable next door at /n/home.

Across a suspend

Shares are dropped before the app takes its snapshot and remounted after it resumes, and this is deliberate rather than incidental. The mount table lives in the emulated machine's memory and survives a snapshot perfectly; the network connection underneath it lives on your Mac and does not. Left alone, you would resume with a mount that could neither be used nor cleared.

You should not have to think about this — it is automatic. If you ever need to mount by hand, the command is:

$ /etc/nmount 10.0.2.2 9200 64 /n/macos

Speed

Fast enough to build software from. The protocol costs a round trip per path component rather than per byte, so its performance is measured in files per second, not megabytes — about 265 small files a second as it stands. Copying one large file will feel slower than you expect and reading a thousand small ones faster.

If the share is not there, check that the folder is still chosen in Settings and that networking is enabled — see networking.