Re: Filespace exhaustion on '/' partition

[Paul E Condon <pecondon@mesanetworks.net>]

On 20140513_0014+1000, David wrote:
> On 12 May 2014 23:45, Ron Leach <ronleach@tesco.net> wrote:
> > On 11/05/2014 22:07, Sven Joachim wrote:
> >>
> >> A simple "mount --bind / /mnt" makes all those files
> >> visible under /mnt, and you can delete them at your leisure.
> >>
> >
> > I mounted the root partition at /mnt/test and used du.
> >
> > server4:/home/ron# du /mnt/test/mnt -hx --max-depth=1
> > 2.7G    /mnt/test/mnt/backupserver
> > 0       /mnt/test/mnt/test
> > 2.7G    /mnt/test/mnt
> > server4:/home/ron#
> >
> > The 2.7GB is the remnant of a first backup attempt to a new backup server.
> > We backup over NFS, to a server mounted at /mnt/backupserver.
> >
> > During that backup trial, the new backup server was not configured
> > correctly, and this machine had not - actually - seen it, though it had
> > appeared to do so.  As a result, this machine tried to do a backup to that
> > destination, /mnt/backupserver, and had - evidently - filled the root
> > partition before complaining about space.
> >
> > I hadn't understood - then - what had happened, and I corrected (only) the
> > missing NFS export and connectivity.  That fix meant that the mountpoint no
> > longer 'pointed' to a set of directories on the root partition but - instead
> > - to the NFS export (correctly).  A 'proper' backup then succeeded; what I
> > hadn't realised, until now, was that the original set of failed-test
> > directories was still there, filling the partition and, moreover, now
> > invisible.
> 
> Whenever I create a directory that is going to be a mountpoint, I immediately
> set its immutable attribute to prevent exactly this. Nothing can be
> written in an
> immutable directory. chattr must be run by root user.
> 
> # mkdir mountpoint
> # chattr -V +i mountpoint

The fact that a mountpoint can be mis-interpreted by the system for
the root of a directory sub-tree on the parent disk has been around,
as a gotcha, pretty much from the beginning of Unix. 'mountpoint' is
also the name of a test program that allows a sysadmin to test for
this situation. Too much name space overloading here, IMHO, but I
can't make a good suggestion as to what to do about it ;-) 

-- 
Paul E Condon           
pecondon@mesanetworks.net