Mac - when your disk is really, really full

My wife's 2012 (OSX Catalina, 10.15) MacBook Air has been struggling recently with a hard disk that seems to have no hesitation in filling itself to the absolute brim (like `78kb space remaining`). The problem is that APFS, being a journaling file system, wants to write a record of your attempt to call `rm ~/Downloads/stupid-big-file.mp4`, but doesn't have the space to do so - preventing the `rm` from running, and so escaping this situation is far harder than it should be. This has happened a number of times now, and after various attempts to use ["Target Disk Mode"](https://support.apple.com/en-au/guide/mac-help/mchlp1443/mac) via a daisy-chain of Thunderbolt-to-FireWire adapters, Apple Disk Utility in Recovery Mode, and a [GParted LiveCD](https://gparted.org/livecd.php) to mount the drive, this typically-unassuming but excellent [Stack Exchange answer](https://apple.stackexchange.com/a/371323/117415) has ended up being my saviour. It always takes me ages to re-stumble upon it because my Googling is typically for phrases like "resize APFS partition" which leads you to [articles like this one](https://www.macobserver.com/tips/resize-your-apfs-container/) which is totally overkill for the situation. The **TL;DR** is - you can safely use the `diskutil` utility to `remove` the volume that is named `VM`, and APFS will then automatically resize the overfull "Macintosh HD" volume to get that space back. Just be aware that the Mac will always prefer to have *some* VM, so the long-term solution is probably to keep several tens of Gb free so that the two volumes can coexist in harmony. While I'm linking to useful Apple-disaster-recovery-related Stack answers, while you're in Recovery Mode and trying to figure out what files to nuke, Apple helpfully removes the link to `du`. [This answer gives the full path](https://superuser.com/a/1279144/386135) (which on the aforementioned 2012 Mac is actually `/Volumes/Macintosh\ HD/usr/bin/du` as per one of the comments).