This is just half of what Time Machine does. What people are constantly missing is that Apple Time Machine is fast, as it does not need to walk through the whole filesystem to find changed files. Thanks to FSEvents, introduced in Mac OS X Leopard, it knows which directories actually contain changed files and hence usually only needs to check a small fraction of the filesystem. (Not sure if it still works that way after the switch to APFS).

This would of course also be possible on Linux (using *notify), and there are some projects who try to do this, but it's really hard to do it reliably. You might argue that this feature is less important nowadays because NVME SSDs are so fast, but still, I remember very well how astonished I was that creating a new time machine snapshot on OS X Leopard took mere seconds.

Ha. That's a throwback.

I did the same thing, but with a more detailed writeup, in 2009: https://nuxx.net/blog/2009/12/06/time-machine-for-freebsd/

It was really handy, but I now use borg as it just works better.

Used this technique (albeit counter-based, not time-based) successfully for backing up the 2006 World Cup site newsfeed[0] configurations/data. Had 6 rotating backups on two hosts. Never had to use them (as best I remember) but it was definitely comforting to know they were there in case of urgent rollback.

[0] Not strictly the right name but I've forgotten. Y!uk people of that era know what I mean.

"borg" has basically solved backups permanently. It's deduplicated, even across snapshots, compressed, and end-to-end encrypted. I'm surprised it's not more well known.

The original post that introduced this idea into general public: http://www.mikerubel.org/computers/rsync_snapshots/

I’m sure others will chime in that they used hard links like this before then, however as noted in that page, it’s the one that made it popular enough that rsync was updated to support the idea natively.

Seems similar to https://rsnapshot.org/

Isn't it also how timeshift [1] backups are working?

[1] https://github.com/linuxmint/timeshift

I use bontmia since forever, based on the same rsync feature (link-dest for creating hard links to the unmodified files since the last backup). It also supports backup rotation and I think it's quite solid/reliable after all these years: https://github.com/hcartiaux/bontmia

Reminds me of a tool I used to use that did a similar thing: https://github.com/jeremywohl/glastree

If we spoke about a Linux box, one that prudently ran ZFS, or XFS on top of LVM, it would be possible to make a snapshot before the diffing and sending, so that the snapshot would be indeed point-in-time. IDK if whatever macOS uses for the filesystem supports snapshots.

Otherwise, I think, restic or kopia are better for proper backups, and Syncthing for keeping a mirror copy. But the simplicity of this script in charming.

Need to combine this with LVM or BTRFS or similar to be a true snapshot. Rsnapshot supports LVM snapshot pretty good.

sounds similar to rdiff-backup ( https://rdiff-backup.net ).

I know some folks that have been using that for a very long time as well.

I've been using a bash encapsulation of this for a long time, works great.

https://github.com/laurent22/rsync-time-backup

Isn’t restic better for backups overall?

Anyone have a good script for macOS triggered by launchd, ideally something that uses FSEvents to check for directory changes?

restic to s3 has been very reliable - haven't tried borg.

One big drawback of these solutions is that they cannot archive the system apps properly. Nor can they be used during the OS setup.

TM integration is just so convenient...

Why make hard links when you can use rsync or syncthing to just make an actual copy on an external hard drive eg via wifi or just remotely?