can a directory be none writeable when a disk mounted into it disappears?

[dieselnutjob]

The scenario:-
A small rootfs drive (like an SSD or something).
The rootfs has a directory like /data
There is a much larger many TB driver mounted as /data
So as far as applications are concerned /data is huge.
Now suppose that some application like syncthing is dumping a lot of data into /data
Let's say that something goes wrong with that big drive.
I want /data to be unusable, not for syncthing to fill up the entire rootfs.
Maybe permissions are the answer (so /data without anything mounted over it is only available to root)?

[reinob]

You can remove write permissions to the rootfs /data, so that if the overlaid /data is unmounted writes will fail.

[wizard10000]

I use "if mountpoint" to tell if something is actually mounted and if it's not mounted it bails out of the backup script. Looks like this -

Code: Select all

if /usr/bin/mountpoint -q /path/to/mountpoint
  then
    # backup script goes here
  else
    exit 1
fi
exit 0

Hope this helps -