Read-only bind mounts

As other commenters posted, the given method for producing a read-only bind mount will actually remount all the underlying filesystems (e.g., bind mounting /home/test1/asdf to /mnt, then making /mnt read-only will remount /home to be read-only).

To do this and *only* remount the bind mount as read-only:

mount -o bind /home/test/asdf /mnt
mount -o bind,remount,ro /mnt