It allows applications to run in different priviledge contexts and allows you inherit privilidges on a network, off the top of my head.

Unless you _want_ your solitare game have the ability to enumerate your contacts and send mail.

macOS and iOS use a completely different mechanism to ensure a game doesn’t read my contacts or make network requests. It has nothing to do with Unix-style users.

They could have built that on top of BeOS just as well as on NextStep.

Unix permissions will allow you do to that perfectly fine.

I agree that iOS isn’t multi-user in any real, like, multiple user accounts intended to be used by real people sense.

I wonder, though, it is based on MacOS somehow, right? Which is based on BSD. Could there be some left over multi-user plumbing sticking around in a technical sense?

Yes, iOS still uses users in the technical "Unix" sense, they're just not mapped to actual physical users, but instead to various services.

Android is in a similar boat. They're still an important way to manage filesystem access of programs.

Android isn't in a similar boat, AOSP has full isolated Multi-User support that is realized through Unix users. You can create new users through Settings and they have their own home screen, apps and files.

Most vendors have this enabled now and things like work accounts/MDM use the same system.

https://source.android.com/docs/devices/admin/multi-user

iOS barely uses that. Processes commonly run as “mobile” or “root”, but it does not matter very much. POSIX users and access permissions are archaic, and, in my opinion, don’t match with how almost any device is being used nowadays. iOS implements its own concepts through entitlements, containers, vaults, sandboxes etc. (Look up the “Apple Platform Security Guide” for details.)

> Shared iPad security in iPadOS

> [...] User data is partitioned into separate directories, each in their own data protection domains and protected by both UNIX permissions and sandboxing.

POSIX users are quite important.

Yeah, it basically doesn't use UNIX permissions at all.

In the very early public slides announcing the iPhone, I believe Jobs referred to iOS as "Mac OS X".

Multi-user would have likely been bolted on one way or another at some point, as had happened when other OSes gained fundamental new features.

Was any operating system actually able to go from single-user to multi-user so easily? Windows NT and OS X were totally rewritten from the ground up relative to their single-user predecessors Windows 9x and classic Mac OS.

NT is closer to a mainframe OS than 9x and it came out in the win3 era

Yeah, I actually used NT 3.51 for some time. However it was the NT line that replaced the 9x line, at least from the consumer perspective.

NT had no predecessor (at least from Microsoft; architecturally it's predecessor would be VMS). It was ground-up multi-user. Mac OS [Classic] was not OS X's predecessor, either -- it was NeXTStep.

You are right on the technical lineage, but I was referring to how these products were (ultimately) presented commercially. The facts that they are both older than one might think and they were developed with specific goals from the start I think more clearly illustrate that you can't just "bolt on" such fundamental differences.

yea, a big one. Once there was an intentionally multi-user-from-ground-up OS called "Multics". Dude named ken thompson or dennis ritchie or something worked on it but was like "bro, so bloated". So dude writes a DISK BENCHMARKING system, single user, called it "Unix" as if to castrate multics. The original unix was disk benchmarking, barebones. So we know how that moved into multi-user

source: kernighans readingbook, "unix a memoir" or something like that, great read

I'm not sure how much that really counts. According to [1], the time that Unix spent as a single-user operating system was intentionally very short-lived. Even the earliest version of the operating system that can be reconstructed today had multiple logins and processes, though only one could be active at a time. It seems that, by the time Unix was written in C, ported to multiple architectures, and spreading outside of Bell Labs, it was already multi-user.

[1] https://retrocomputing.stackexchange.com/a/10908

> Why was multiuser so important?

Because computing devices, and access to them, was not so ubiquitous back then. Families all had to share a single computer. Business users had to share access to large servers. There were no smartphones. Some had to travel to an educational setting just to see or use a computer.

Heh, funny you mention that, considering Be's pivot to BeIA. Some Be engineers also worked on the (unreleased) Palm OS Cobalt, and eventually, Android. (And then Fuschia, but I don't think that OS will ever hit smartphones.)