mount hides underlying files

[Jay O'Brien]

Chris Hill wrote:
> On Thu, 11 Nov 2004, Jay O'Brien wrote:
> 
> 
>>If I mkdir /test and then place files in /test, those files
>>are no longer visible when I use /test as a mount point. The
>>files become visible again when I unmount the device.
>>
>>I have read documentation explaining this phenomenon, and I
>>would like to review that documentation again. Is it in the
>>handbook?
> 
> 
> Yes. There is a discussion of this at
> 
> http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/disk-organization.html
> 
> Also see the following page.
> 

Chris,

Thank you, that answers the basic question, with the word "replaces". 
That is, when a filesystem is "mounted" to a directory, it "replaces" 
what was there, it doesn't add to it. This is different from my 
experience with other operating systems, and was confusing to me.

I do remember seeing a more verbose description, however, that 
discusses what happens to the underlying files when something is 
mounted over the top of their directory; I also vaguely remember 
something suggesting that this is a way to "hide" files from the 
casual observer, revealing the files by unmounting the file system 
that caused them to be hidden. I don't have a reason to hide files; 
I remember reading the discussions, and would like to read them
again.

Jay O'Brien