mount: what is the point of 'nouser' on the command line?

mount: what is the point of 'nouser' on the command line?

[Benno Schulenberg]

Hi all,

The man page of mount(8) currently contains the following example
to show how the -o option can be used:

    mount LABEL=mydisk -o noatime,nouser

As the command does not contain a mountpoint, it requires an entry
in fstab in order to work.  If that entry does not contain the keyword
'user' in the options field, then the mount will effectively already be
'nouser'.  If it does contain the keyword 'user', does specifying 'nouser'
then somehow exclude other users?  As far as I can tell it doesn't.

So, is it ever useful to specify '-o nouser' on the command line?


Something else.  On the man page of umount, shouldn't it say that
the -O and -t options are only effective in combination with -a?

Further, mount recognizes the options -L and -U besides the keywords
LABEL= and UUID=, but umount only recognizes the latter two.  For
symmetry it would be nice if umount also recognized -L and -U.

Benno

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Re: mount: what is the point of 'nouser' on the command line?

[Karel Zak]

On Mon, Jul 14, 2014 at 11:57:44AM +0200, Benno Schulenberg wrote:
> 
> The man page of mount(8) currently contains the following example
> to show how the -o option can be used:
> 
>     mount LABEL=mydisk -o noatime,nouser
> 
> As the command does not contain a mountpoint, it requires an entry
> in fstab in order to work.  If that entry does not contain the keyword
> 'user' in the options field, then the mount will effectively already be
> 'nouser'.  If it does contain the keyword 'user', does specifying 'nouser'
> then somehow exclude other users?  As far as I can tell it doesn't.

 It does not exclude others users. The idea of the "no*" options is 
 disable previously applied flags. The options from command line are
 evaluated after options from fstab, so for example "foo,bar" (fstab)
 and "nofoo" (command line)  means that "nofoo" negate the previous "foo".

 The "user" option is alias to "noexec,nosuid,nodev" mount flags. 
 
 I'm  not sure why, but "nouser" has never been implemented. So it does not
 have any effect and "user" from fstab is still applied -- maybe to
 avoid possible security bugs or so.

> So, is it ever useful to specify '-o nouser' on the command line?

 No, it would be better to remove it from the example and add to the
 man page note that "nouser" has no any effect and you have to 
 explicitly use "exec,suid,dev" to negate.

> Something else.  On the man page of umount, shouldn't it say that
> the -O and -t options are only effective in combination with -a?

 The -t is generic and it's usable in more case (for example to
 specify filesystem that should be tried for the device).

 The -O is really usable for -a only.

> Further, mount recognizes the options -L and -U besides the keywords
> LABEL= and UUID=, but umount only recognizes the latter two.  For
> symmetry it would be nice if umount also recognized -L and -U.

 I think -L and -U are mistakes maintained for backward compatibility,
 because TAG=value is more generic and extendable syntax. For example
 now we also supports PARTUUID= and PARTLABEL=.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: mount: what is the point of 'nouser' on the command line?

[Benno Schulenberg]

On Mon, Jul 14, 2014, at 16:57, Karel Zak wrote:
>  The "user" option is alias to "noexec,nosuid,nodev" mount flags. 

Ehm...  Not quite.  It *implies* those options, to lightly protect
the user from some dangers, but its main purpose is to allow
ordinary users to mount the filesystem so marked in fstab.  No?

> > So, is it ever useful to specify '-o nouser' on the command line?
> 
>  No, it would be better to remove it from the example

Will submit a patch later.


> > Something else.  On the man page of umount, shouldn't it say that
> > the -O and -t options are only effective in combination with -a?
> 
>  The -t is generic and it's usable in more case (for example to
>  specify filesystem that should be tried for the device).

Ehm...  I was talking about umount here, not mount.  :)

Benno

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Re: mount: what is the point of 'nouser' on the command line?

[Karel Zak]

On Mon, Jul 14, 2014 at 05:24:27PM +0200, Benno Schulenberg wrote:
> 
> On Mon, Jul 14, 2014, at 16:57, Karel Zak wrote:
> >  The "user" option is alias to "noexec,nosuid,nodev" mount flags. 
> 
> Ehm...  Not quite.  It *implies* those options, to lightly protect
> the user from some dangers, but its main purpose is to allow
> ordinary users to mount the filesystem so marked in fstab.  No?

 Sure, I have talked about the options and how the options are
 evaluated.

> > > So, is it ever useful to specify '-o nouser' on the command line?
> > 
> >  No, it would be better to remove it from the example
> 
> Will submit a patch later.

 Thanks.

> > > Something else.  On the man page of umount, shouldn't it say that
> > > the -O and -t options are only effective in combination with -a?
> > 
> >  The -t is generic and it's usable in more case (for example to
> >  specify filesystem that should be tried for the device).
> 
> Ehm...  I was talking about umount here, not mount.  :)

 Oh... sorry :-) Anyway, it's the same, the "-t" is usable without -a
 too. 

    umount -a -t <type, ...>

 the <type> is interpreted as pattern.

   umount -t <type>

 the <type> is filesystem type (so you can force umount to use for
 example /sbin/umount.<type>).

 The -O is usable with -a  only.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

umount: --types does not limit

[Benno Schulenberg]

On Tue, Jul 15, 2014, at 10:02, Karel Zak wrote:
>    umount -t <type>
> 
>  the <type> is filesystem type (so you can force umount to use for
>  example /sbin/umount.<type>).

Hmm.  But it's not working for me, the --types option does not limit
umount in any way.  In the man page it says: "Indicate  that the
actions should *only* be taken on filesystems of the specified type."

But, for example, here Suse is of type ext4 and gets mounted:

# ./mount -t ext4 /suse
# ./mount | grep suse
/dev/sda2 on /suse type ext4 (rw,noatime,noexec,nosuid,nodev,user)

Now I want to unmount all btrfs systems:

# ./umount -t btrfs /suse /zero /other
# ./mount | grep suse

It just unmounts everything that is mentioned, the -t has no
limiting effect.  So it is useful only with -a.

Benno

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Re: umount: --types does not limit

[Karel Zak]

On Tue, Jul 15, 2014 at 11:02:04AM +0200, Benno Schulenberg wrote:
> 
> On Tue, Jul 15, 2014, at 10:02, Karel Zak wrote:
> >    umount -t <type>
> > 
> >  the <type> is filesystem type (so you can force umount to use for
> >  example /sbin/umount.<type>).
> 
> Hmm.  But it's not working for me, the --types option does not limit
> umount in any way.  In the man page it says: "Indicate  that the
> actions should *only* be taken on filesystems of the specified type."
> 
> But, for example, here Suse is of type ext4 and gets mounted:
> 
> # ./mount -t ext4 /suse
> # ./mount | grep suse
> /dev/sda2 on /suse type ext4 (rw,noatime,noexec,nosuid,nodev,user)
> 
> Now I want to unmount all btrfs systems:
> 
> # ./umount -t btrfs /suse /zero /other
> # ./mount | grep suse
> 
> It just unmounts everything that is mentioned, the -t has no
> limiting effect.  So it is useful only with -a.

 grrr... you're right, I see.. libmount always overwrites the setting 
 by stuff from mtab.
 
 IMHO it would be nice to restrict the all the umount actions (like
 --recursive, --all-targets or when more mountpoints specified) by the
 pattern. I'll add this to the TODO file for v2.26.
 
 Thanks!
 
    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com