[9fans] union mount

[9fans] union mount

[Matthias Teege]

Moin,

looks like, I don't understand the union mount not completly.  I have
a directory called "foo" with some documents.  Now I need some files
from another dir called "bar".  New files should go to foo.

% mkdir /usr/mtg/foo
% touch /usr/mtg/foo/hello
% bind -ac /usr/mtg/bar /usr/mtg/foo

but if I now create a new file in /usr/mtg/foo it goes to bar.

So I try

% bind -bc /usr/mtg/foo /usr/mtg/foo
% bind -ac /usr/mtg/bar /usr/mtg/foo

and the it works.  New files goes to foo but a ls show me the files in
foo two times (which I understand).

What is wrong in the first case?

Matthias

Re: [9fans] union mount

[Richard Miller]

Lots of people (like me) miss this detail at first.

mount(1) says:

  ... When a
  new file is created in a union directory, it is
  placed in the first element of the union that has
  been bound or mounted with the -c flag.

But foo was not a union directory before you bound
bar onto it, so it didn't have a -c flag.  The trick is
to start by making a union with just foo in it:

  mkdir /usr/mtg/foo
  bind -c /usr/mtg/foo /usr/mtg/foo
  bind -a /usr/mtg/bar /usr/mtg/foo

will have the desired effect.

-- Richard