Re: How to convert a directory to a subvolume

[Hugo Mills <hugo@carfax.org.uk>]

On Sat, Apr 30, 2022 at 04:08:59PM -0400, John Center wrote:
> Hi,
> 
> I just installed Ubuntu 22.04 with a btrfs raid1 root filesystem.  I want to convert a directory, like /opt, into a subvolume. I haven’t been having much luck.  /opt is empty right now, so it’s a good candidate for conversion.  Could someone please explain how to do it?  I’ve been at a dozen different websites, & tried different variations of the “btrfs subvolume create” command, but nothing works when I go to mount it.  I think I’m missing something simple, but not sure what it is.

   You can't convert a directory into a subvolume.

   Since the directory in question is empty, just delete it and create
a subvol there instead:

# rmdir /opt
# btrfs sub create /opt

   If there's stuff in there, you need to create the subvolume with a
different name, copy the contents of the directory into it (optionally
with --reflink=always) and then delete the original directory and move
the subvolume into its place.

   Hugo.

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