[emporas]

The issue is bigger than that.

Why not two people share a device, and when passed from one person to another, delete applications and install all apps and profiles from scratch using verified checksums saved on a blockchain. An OS which could do that is something like Nix. When passed to the previous person same thing, delete and install everything from scratch.

Using smartphones in a smart way, not a dumb way, like timesharing mainframes of the past. Same procedure could be applied to cars and other devices.

[rerdavies]

Android's Multiple Users feature does exactly this. Multiple users accounts with all user data completely sandboxed and restricted to each user. All user data is cryptographically protected on storage devices.

The actual SE filesystem available to a logged in user is pretty complicated. But the short story is that user-data is completely isolated. Presumably application binaries (which require digital signatures by default) are shared; although the "installed" state is not. Successive releases of Android have restricted access to any legacy "shared" data on the device (media folders particularly; pictures and video taken by the camera device have been strongly protected since Forever).

Verified checksums on a blockchain are only useful if they are verified by some provider who associates a blockchain ID with a real-world identity. Not sure what "blockchain" really adds. If anyone can create a blockchain ID, then "verification" doesn't really provide useful information.

[emporas]

> Multiple users accounts with all user data completely sandboxed and restricted to each user.

User data and user programs. Clean installation kind of user programs.

> Verified checksums on a blockchain are only useful if they are verified by some provider who associates a blockchain ID with a real-world identity.

Nix associates a unique id to each program version or package or config file. The verification happens on the Nix package manager.

The user uploads his exact config of OS somewhere, in his own home server, at a goverment server, at AWS, on a blockchain, somewhere. A blockchain seems like the best solution to me.

[nine_k]

This assumes that these two persons will never need to use a smartphone at the same moment, which is a bit of a logistical puzzle.

Installing apps is the trivial part; isolating, or removing / reinstalling user data is much harder. Especially a few gigabytes of it. An SD card could work maybe.

This all goes against the grain of the smarthpone UX, the idea of a highly personal device that you can use for anything, and might need (or benefit from) at an arbitrary moment.

If the point is reducing e-waste, the solution would rather be opening up the hardware enough to provide long-term software support, LineageOS-style.

[emporas]

> This assumes that these two persons will never need to use a smartphone at the same moment, which is a bit of a logistical puzzle.

In general no one wants to share anything with anyone, but when two people cannot afford a device individually, but it is within reach when they buy it together, time-sharing becomes a totally acceptable solution.

> Installing apps is the trivial part; isolating, or removing / reinstalling user data is much harder. An SD card could work maybe.

Checksums might overlap by quite a bit. No need to remove programs installed by both users. If the total installation of each user is 10 GB, but the installation diverges 300MB only, not a big deal in most cases.