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Old 08-22-2011, 05:01 PM
Trey Dockendorf
 
Default Mount --bind source / mountpoint out of sync

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 * /chroot/home/user1/example.com * none * *defaults,bind * 0 * 0
The mount is active, yet running a recursive diff between "/var/www/example.com" and "/chroot/home/user1/example.com" shows numerous differences.

Here's "mount" output------------------/dev/mapper/VolGroup00-LogVol00 on / type ext3 (rw)proc on /proc type proc (rw)sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)/dev/sda1 on /boot type ext3 (rw)tmpfs on /dev/shm type tmpfs (rw)none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)/dev/mapper/VolGroup00-lv_chroot on /chroot type ext3 (rw)
/var/www/example.com on /chroot/home/user1/example.com type none (rw,bind)/dev/mapper/VolGroup00-lv_var on /var type ext3 (rw)


I honestly have no idea how this is possible. *Is using "mount -o bind" not the best method to give a chrooted user access to a single directory outside the chroot? *Would it be better to leave the web root in the chroot and have Apache (outside chroot) reference that location?

Thanks- Trey
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Old 08-22-2011, 07:48 PM
Dennis Jacobfeuerborn
 
Default Mount --bind source / mountpoint out of sync

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.
>
> Here's "mount" output
> ------------------
> /dev/mapper/VolGroup00-LogVol00 on / type ext3 (rw)
> proc on /proc type proc (rw)
> sysfs on /sys type sysfs (rw)
> devpts on /dev/pts type devpts (rw,gid=5,mode=620)
> /dev/sda1 on /boot type ext3 (rw)
> tmpfs on /dev/shm type tmpfs (rw)
> none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
> /dev/mapper/VolGroup00-lv_chroot on /chroot type ext3 (rw)
> /var/www/example.com <http://example.com> on /chroot/home/user1/example.com
> <http://example.com> type none (rw,bind)
> /dev/mapper/VolGroup00-lv_var on /var type ext3 (rw)
>
>
> I honestly have no idea how this is possible. Is using "mount -o bind" not
> the best method to give a chrooted user access to a single directory
> outside the chroot? Would it be better to leave the web root in the chroot
> and have Apache (outside chroot) reference that location?

What kind of differences does the diff show? Missing files, corruption in
the files, do modifications that you make in one directory not show up in
the other?

Regards,
Dennis
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Old 08-22-2011, 08:15 PM
James Hogarth
 
Default Mount --bind source / mountpoint out of sync

On 22 August 2011 20:48, Dennis Jacobfeuerborn <dennisml@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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Old 08-22-2011, 10:27 PM
Trey Dockendorf
 
Default Mount --bind source / mountpoint out of sync

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

On 22 August 2011 20:48, Dennis Jacobfeuerborn <dennisml@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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http://lists.centos.org/mailman/listinfo/centos


@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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