btrfsctl -s returns 1

I wrote a script generating snapshots of several subvolumes. But the script failed after taking the first snapshot.

I then did it by hand:

operation complete
Btrfs v0.19-4-gab8fb4c

1

Usually commands return 0 if everything went ok (and it seems that the snapshot was taken correctly).

Has the returned "1" some special meaning?

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Another, minor issue:

Mayby my manual is out of date. It tells me

...
-s snapshot-name directory
Creates a new snapshot of the directory specified.
...

but as I learned one can only take a snapshot of a subvolume.

Greetings, Michael