Huh, despite many years of using Linux on servers as well as for my main desktop OS, this bit of basic info has somehow passed me by! Thank you!
I have set the permissions on a test directory inside my share as follows:
drwxr-xr-x 1 nobody users 10 Oct 21 16:49 test/
I can read the directory via SMB, but still cannot write to it without the group write bit. I understand what you're saying about Samba ultimately being governed by the Linux filesystem permissions, but these look correct to me when authenticating as `nobody/user`. My understanding of the `nobody` user corresponds with itimpi's post - that `nobody` is just a regular user with no special semantics or magic - so I can only assume that there are SMB-level permissions, or I'm not actually authenticating as `nobody` somehow, but that's contrary to `smbstatus`.
I will read through your link and also run the permission fixer tool to see if it produces any different permissions that those I've set myself or are being set by docker containers.
The simple workaround is obviously to just set the group write bit, but I'd like to understand what's happening if possible.
Thanks for your help.