Re: Umont ownership?

[Stephen Powell <zlinuxman@wowway.com>]

On Tue, 6 Apr 2010 10:23:16 -0400 (EDT), Camaleón wrote:
> 
> Uh? So it works fine for root user...
> 
> O.K., Let me check with my USB flash drive. After I plugg it:
> 
> ***
> sm01@stt008:~$ mount | grep fat
> /dev/sdc1 on /media/disk type vfat (rw,nosuid,nodev,uhelper=hal,shortname=lower,uid=1000)
> ***
> 
> I try to umount it:
> 
> ***
> sm01@stt008:~$ umount /media/disk
> ***
> 
> And now I verify it has been "really" umounted:
> 
> ***
> sm01@stt008:~$ mount | grep fat
> ***
> 
> Seems to be working here for my plain user.

I'll be the first to admit that I don't know much about this hotplug and
GUI stuff.  The closest I come to a hotplug event is to load an audio
CD into my CD drive.  I wait until the GNOME "Sound Juicer" application
auto-launches, wait for it to display the track titles, then I close the
window.  I then type "cdplay" at a shell prompt to use the analog
play method.  I never hot-plug a USB device, not because it's evil,
but because at this point I have no reason to do do.  Maybe someday I'll
hot-plug a USB device, just to see how it feels!  ;-)

But here's what I *do* know.  The root user can issue mount or umount
commands for any file system or mount point.  A non-root user *may* be able
to mount *some* file systems and *some* mount points depending on what is
specified in /etc/fstab.  Here is an excerpt from the man page for mount:

----------

   The non-superuser mounts.
          Normally, only the superuser can mount filesystems.  How-
          ever, when fstab contains the user option on a line, any-
          body can mount the corresponding system.

          Thus, given a line

                 /dev/cdrom  /cd  iso9660  ro,user,noauto,unhide

          any user can mount the iso9660 filesystem  found  on  his
          CDROM using the command

                 mount /dev/cdrom

          or

                 mount /cd

          For  more  details,  see  fstab(5).   Only  the user that
          mounted a filesystem can unmount it again.  If  any  user
          should be able to unmount, then use users instead of user
          in the fstab line.  The owner option is  similar  to  the
          user  option,  with the restriction that the user must be
          the owner of the special file. This may  be  useful  e.g.
          for  /dev/fd  if  a  login  script makes the console user
          owner of this device.  The group option is similar,  with
          the restriction that the user must be member of the group
          of the special file.

----------

HTH

-- 
  .''`.     Stephen Powell    <zlinuxman@wowway.com>
 : :'  :
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