svn commit: r320803 - head/sbin/mount

[Rodney W. Grimes]

[ Charset ISO-8859-1 unsupported, converting... ]
> On Sat, 2017-07-08 at 09:50 -0700, Rodney W. Grimes wrote:
> > [ Charset UTF-8 unsupported, converting... ]
> > > 
> > > Author: trasz
> > > Date: Sat Jul??8 11:06:27 2017
> > > New Revision: 320803
> > > URL: https://svnweb.freebsd.org/changeset/base/320803
> > > 
> > > Log:
> > > ? Fix "mount -uw /" when the filesystem type doesn't match.
> > > ??
> > > ? This basically makes "mount -uw /" work when the filesystem
> > > ? mounted on / is NFS, but the one configured in fstab(5) is UFS,
> > > ? which can happen when you forget to modify fstab.
> > Please do not silence user errors because they are inconvinient,
> > this is a configuration error and the system should fail to?
> > mount the incorrectly configured root.
> > 
> > If we start changing things to silently ignore user configuration
> > errors we are going down a very slippery road.
> > 
> 
> IMO, this change fixes the right problem, but maybe does so the wrong
> way. ?Mount -u is by definition an update to an existing mount. ?There
> should be no need to consult /etc/fstab for an existing mount since the
> info is available from the kernel.
> 
> Note that I say the foregoing with my user hat on. ?I haven't looked at
> the code to see if there's some reason why my common-sensical way of
> thinking about it is actually impossible to implement for some reason.

This "check" saves one from the mistake of a wrong fstab that was
not properly written for nfs that is probably going to blow up when
it goes to get /usr or some other file system.  

Example of when this change can cause things to go very wrong for
an admin.

I rsync/however a system that is booting from disk onto my nice new
NAS box and setup exports of the file systems that I moved.  I further
set up dhcp/tftp/pxe to boot this NFS version of the system.

I forget to edit the etc/fstab in the copy on the NFS server.

I reboot the system via PXE, it gets its root file system via NFS
and now silently ignores my error and procededs to FFS mount all
the other file system.

Can you see the error in thinking this change is a good idea?


-- 
Rod Grimes                                                 rgrimes at freebsd.org