File disappear after 2nd level of mount using "bind" filesystem

intmail01 · 04-29-2015, 08:37 AM

Hello,

I mount several directory structure and use "bind" option.
The problem is that files disapears at certain level.
Follow the simplified example bellow.

The source file:

Code:

/home/john/file.txt

** First bind

Code:

command: mount --bind /home/john /share/john
command: ls /share/*
result: john
command: ls /share/john/*
result: file.txt

** The next bind

Code:

command: mount --bind /share /share2
command: ls /share2/*
result: john
command ls /share2/john/*
result: nothing !

Please tell me how to acces file.txt in /share2/john/
I do this example as root user.

Thank you

MensaWater · 04-29-2015, 09:28 AM

From "man mount"

Quote:

This call attaches only (part of) a single filesystem, not possible submounts.

Your first bind mount IS a submount so your second bind mount can't see that submount.
It may be possible to do another bind mount on top of your second bind mount to add the same subdirectory.

This is similar to the way NFS mounts work. If you export an NFS filesystem from one system to another only the filesystem itself is exported not any submounts that were mounted on top of the filesystem on the exporting server. You can export the subdirectories then NFS mount them on top of the first NFS mount on the client.

However, rather than doing bind mounts why not just make symbolic links?

rknichols · 04-29-2015, 10:24 AM

Quote:

Originally Posted by MensaWater

From "man mount"

This call attaches only (part of) a single filesystem, not possible submounts.

And goes on to say,

The entire file hierarchy including submounts is attached a second place using
mount --rbind olddir newdir
or shortoption
mount -R olddir newdir

So, you would need

Code:

mount --rbind /share /share2
        ^

to pick up the /share/john submount.

intmail01 · 04-30-2015, 02:00 AM

--rbind is the solution. Thanks for all.

intmail01 · 04-30-2015, 02:27 AM

Thread not really solved because the main goal is to export /share with NFS.
If I export /share through NFS the problem remains. I can't see the file.txt

** On the server /etc/exports contains line:

Code:

/share *(rw,fsid=0,sync,insecure,no_root_squash,no_subtree_check)

** On client:

Code:

command: mount -t nfs -o vers=4 server:/ /foo
command: tree /foo
result: john

There is no file.txt !

rknichols · 04-30-2015, 08:25 AM

Quote:

Originally Posted by intmail01

Thread not really solved because the main goal is to export /share with NFS.
If I export /share through NFS the problem remains. I can't see the file.txt

Indeed, that just isn't going to work well for an NFS export. Take a look at `man 5 exports` and note the warnings and limitations for the nohide option.

MensaWater · 04-30-2015, 08:50 AM

Quote:

Originally Posted by rknichols

And goes on to say,

The entire file hierarchy including submounts is attached a second place using
mount --rbind olddir newdir
or shortoption
mount -R olddir newdir

So, you would need

Code:

mount --rbind /share /share2
        ^

to pick up the /share/john submount.

D'oh! It certainly does say that and I don't know how I missed it. Thanks for the correction.

intmail01 · 05-04-2015, 02:12 AM

I tried "nohide" option in /etc/exports but no change.

rknichols · 05-04-2015, 08:48 AM

Quote:

Originally Posted by intmail01

I tried "nohide" option in /etc/exports but no change.

No great surprise there. The manpage does state the the option is only effective on exports to a single host, not to "*", and points out other potential problems with that option.