Re: mount weirdness

From	Michael Stone <mstone@debian.org>
Newsgroups	linux.debian.user
Subject	Re: mount weirdness
Date	2019-08-08 20:20 +0200
Message-ID	<ysVb3-cT-5@gated-at.bofh.it> (permalink)
References	<yrRVU-17f-13@gated-at.bofh.it> <ysLOp-2NH-1@gated-at.bofh.it> <ysRh7-6dT-9@gated-at.bofh.it> <ysS3w-6w2-27@gated-at.bofh.it> <ysU5k-80i-13@gated-at.bofh.it>
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On Thu, Aug 08, 2019 at 12:09:11PM -0500, David Wright wrote:
>On Thu 08 Aug 2019 at 10:56:46 (-0400), Michael Stone wrote:
>> On Thu, Aug 08, 2019 at 09:04:00AM -0500, David Wright wrote:
>> > wren 08:50:11 ~# lsblk -f | grep sda7
>> > ├─sda7       ext4        swan07      4a4e352f-2180-4083-92b4-f46e4e0104b4 /wrenbk
>> > wren 08:50:26 ~# mkdir /wa1 /somethingelse
>> > wren 08:50:49 ~# mount /dev/sda7 /somethingelse
>> > mount: /dev/sda7 is already mounted or /somethingelse busy
>> >       /dev/sda7 is already mounted on /wrenbk
>> > 32 wren 08:51:16 ~# mount /dev/sda7 /wa1
>> > mount: /dev/sda7 is already mounted or /wa1 busy
>> >       /dev/sda7 is already mounted on /wrenbk
>> > 32 wren 08:51:31 ~# rmdir /wa1 /somethingelse
>> > wren 08:51:53 ~#
>>
>> It's already been said repeatedly that you should post the bottom of
>> dmesg output because kernel mount errors show up there but not in the
>> output of the mount command.
>
>I've plenty of mount errors, which you've quoted, so I think you might
>be addressing somebody else. Or have I missed something? But anyway,
>dmesg's tail is attached, with a timecheck from earlier in the file so
>that you can exercise forensic skills in tying the times above to
>those in dmesg.

No, I'm addressing you. It's very common for mount to say something like 
"can't do that" but you need a kernel error message to explain why 
because the kernel mount API isn't verbose. (As I said in a previous 
message.) Example:

# mount -o norecovery,loop test.img /mnt
mount: /mnt: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
# dmesg | tail -n 1
[268039.035599] XFS (loop0): no-recovery mounts must be read-only.

In this case the dmesg output doesn't add anything, but it's generally 
good for completeness. 

>But the 2-1 vote wasn't whether error messages were emitted, but
>whether the system should mount an already-mounted partition onto
>another mount point. I get error messages and the mount fails.
>Others get no error messages (though they haven't demonstrated
>the lack) and a successful mount, so currently I'm in a minority
>of one.

That's not a matter for voting, it's something that was implemented 
years ago, in the 2.4 kernel:

potato:~# uname -a
Linux potato 2.2.19-idepci #1 Wed Mar 20 20:33:20 EST 2002 i686 unknown
potato:~# mount
/dev/hda1 on / type ext2 (rw,errors=remount-ro,errors=remount-ro)
proc on /proc type proc (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
potato:~# mount /dev/hda1 /mnt
mount: /dev/hda1 already mounted or /mnt busy
mount: according to mtab, /dev/hda1 is mounted on /

woody:~# uname -a
Linux woody 2.4.18-686-smp #1 SMP Sun Apr 14 12:07:19 EST 2002 i686 unknown
woody:~# mount
/dev/hda1 on / type ext2 (rw,errors=remount-ro)
proc on /proc type proc (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
woody:~# mount /dev/hda1 /mnt
woody:~# ls /mnt
bin  boot  cdrom  dev  etc  floppy  home  initrd  initrd.img  lib  lost+found  mnt  opt  proc  root  sbin  tmp	usr  var  vmlinuz  vmlinuz.old

So you're confusing a completely different issue with something fairly 
unique to your system. I'm not sure if you've somehow managed to turn 
that off via a switch that I'm just not familiar with, or if there's 
something else going on. There's a reference to dm in your dmesg, so 
possibly a dm driver is grabbing your block device and preventing 
multiple access. There are a few other possibilities, but suffice it to 
say that they aren't typical.

Thread

mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-05 22:40 +0200
  Re: mount weirdness Andrei POPESCU <andreimpopescu@gmail.com> - 2019-08-06 08:10 +0200
    Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-06 17:10 +0200
      Re: mount weirdness rhkramer@gmail.com - 2019-08-06 17:40 +0200
        Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-06 19:40 +0200
          Re: mount weirdness Richard Hector <richard@walnut.gen.nz> - 2019-08-06 19:50 +0200
            Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-06 20:00 +0200
              Re: mount weirdness Richard Hector <richard@walnut.gen.nz> - 2019-08-06 20:20 +0200
      Re: mount weirdness Felix Miata <mrmazda@earthlink.net> - 2019-08-06 17:40 +0200
        Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-06 19:30 +0200
  Re: mount weirdness "Thomas Schmitt" <scdbackup@gmx.net> - 2019-08-06 17:40 +0200
    Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-06 19:20 +0200
      Re: mount weirdness David Wright <deblis@lionunicorn.co.uk> - 2019-08-06 20:50 +0200
        Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-07 19:50 +0200
          Re: mount weirdness Greg Wooledge <wooledg@eeg.ccf.org> - 2019-08-07 20:00 +0200
          Re: mount weirdness David Wright <deblis@lionunicorn.co.uk> - 2019-08-07 22:50 +0200
      Re: mount weirdness "Thomas Schmitt" <scdbackup@gmx.net> - 2019-08-06 21:00 +0200
        Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-07 20:00 +0200
          Re: mount weirdness "Thomas Schmitt" <scdbackup@gmx.net> - 2019-08-07 23:30 +0200
  Re: mount weirdness Curt <curty@free.fr> - 2019-08-08 10:20 +0200
    Re: mount weirdness Curt <curty@free.fr> - 2019-08-08 10:50 +0200
      Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-09 21:20 +0200
    Re: mount weirdness "Thomas Schmitt" <scdbackup@gmx.net> - 2019-08-08 12:00 +0200
      Re: mount weirdness Curt <curty@free.fr> - 2019-08-08 14:40 +0200
      Re: mount weirdness Michael Stone <mstone@debian.org> - 2019-08-08 14:40 +0200
        Re: mount weirdness Curt <curty@free.fr> - 2019-08-08 15:00 +0200
    Re: mount weirdness David Wright <deblis@lionunicorn.co.uk> - 2019-08-08 16:10 +0200
      Re: mount weirdness Michael Stone <mstone@debian.org> - 2019-08-08 17:00 +0200
        Re: mount weirdness David Wright <deblis@lionunicorn.co.uk> - 2019-08-08 19:10 +0200
          Re: mount weirdness Greg Wooledge <wooledg@eeg.ccf.org> - 2019-08-08 19:20 +0200
          Re: mount weirdness Michael Stone <mstone@debian.org> - 2019-08-08 20:20 +0200
            Re: mount weirdness David Wright <deblis@lionunicorn.co.uk> - 2019-08-09 18:30 +0200
              Re: mount weirdness Greg Wooledge <wooledg@eeg.ccf.org> - 2019-08-09 19:00 +0200
                Re: mount weirdness "Thomas Schmitt" <scdbackup@gmx.net> - 2019-08-09 20:00 +0200
      Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-09 22:00 +0200
    Re: mount weirdness Dennis Wicks <wix@mgssub.com> - 2019-08-09 21:20 +0200

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