[CentOS] Mount --bind source / mountpoint out of sync

Trey Dockendorf treydock at gmail.com
Mon Aug 22 22:27:08 UTC 2011


On Mon, Aug 22, 2011 at 3:15 PM, James Hogarth <james.hogarth at gmail.com>wrote:

> On 22 August 2011 20:48, Dennis Jacobfeuerborn <dennisml at conversis.de>
> wrote:
> > On 08/22/2011 07:01 PM, Trey Dockendorf wrote:
> >> I have a shared web server that users can SSH / SFTP into to access
> their
> >> web content.  Each users home directory is in a change root, and I use
> >> "mount -o bind" to put their respective webpage's document root into
> their
> >> home directory.  Recently I was made aware that the contents of the
> mount's
> >> source are not the same as the mount point's, which I don't see how that
> is
> >> possible.
> >>
> >> The file system is 3 virtual disks...each part of the same volume group.
>  I
> >> have three LVMs, "/" , "/chroot" , and "/var".
> >>
> >> Here's the entry in /etc/fstab...
> >>
> >> /var/www/example.com <http://example.com>   /chroot/home/user1/
> example.com
> >> <http://example.com>   none    defaults,bind   0   0
> >>
> >> The mount is active, yet running a recursive diff between
> >> "/var/www/example.com <http://example.com>" and
> >> "/chroot/home/user1/example.com <http://example.com>" shows numerous
> >> differences.
> >>
>
>
> This is a bit of a shot in the dark perhaps but in which order was the
> bind mount and httpd restarted last happen? Is it possible that httpd
> has a file handle to the inode where the underlying directory for the
> place being mounted too rather than the directory that is being bound?
> If you unmount the binding do you see any files there? Which location
> has the most recent files? These are the questions that first time to
> my mind for troubleshooting purposes.
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@Dennis,

The differences were basically any changes made by the user , but for how
long I'm unsure.  It was reported today but that could be that he wasn't
using the files until today.  The differences between the the mount point
and source were a wide range of things from small file changes or entire
directories...nothing corrupt, but it seemed like there was a point in which
changes made to the mount point (within the chroot) no longer appeared at
the mount source.

@James

When I unmounted the directory there were indeed files in the mount point's
folder.  It seemed that the mount point (in chroot) was the only thing
effected by changes, not the source (out of chroot).  I don't understand the
question about httpd and the file handle inode.  Could you explain?

What was strange (and maybe this is expected while still mounted), rsync did
not have an effect when run in an attempt to update the source with the
mount point.  I ended up having to restore from last night's backup to
resolve this, but am extremely puzzled as to why this happened, and a bit
worried as this was going to be my new method for allowing access to hosted
web services via SSH / SFTP.

Thanks
- Trey
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