Re: Snapshots of individual files

[Roman Mamedov <rm@romanrm.net>]

On Tue, 23 Dec 2025 12:08:04 +0000
BP25 <bp25@posteo.net> wrote:

> Is there a standard way to 'follow' the same file along its snapshotted
> versions? Say, ask btrfs to return the list of snapshotted versions by
> giving input this or that file in the current version of the filesystem?
> Note that if such file was deleted and another with the same name created I
> don't want that new file also to show up. And related question, is there any
> command that would list the snapshotted files which have no corresponding in
> the current version of the file system (for example because I deleted such
> file after having snapshotted it)?

There is none of that :)

I put "snapshotted" files in quotes for a reason, it is not a snapshot and
there is no snapshot tree or inheritance.

It is a lightweight instant copy, which lets you to very quickly and
efficiently hold on to states of that file as it was at various points in the
past, if you want to. Where you put it, or which scenarios you envision, is up
to you.

I use this to backup running file-backed VMs, first reflink the image to a
file, then can safely start to gzip that file or copy it to a remote host. The
running VM otherwise would ruin the consistency, with ongoing writes to
its image halfway in that process.

Cool part is that like the snapshots, this is done instantly and consumes no
extra disk space, only the changed bits in the "current" file will. Or you can
go ahead and start changing both files at the same time, that too, will only
increase overall space usage by the amount of changed portions.

-- 
With respect,
Roman