On 2017-08-22 10:23, Hugo Mills wrote:

On Tue, Aug 22, 2017 at 10:12:25AM -0400, Austin S. Hemmelgarn wrote:

quoted

On 2017-08-22 09:53, Ulli Horlacher wrote:

quoted

On Tue 2017-08-22 (09:37), Austin S. Hemmelgarn wrote:

quoted

quoted

root@fex:~# df -T /local/.backup/home
Filesystem     Type  1K-blocks      Used Available Use% Mounted on
-              -    1073740800 104252160 967766336  10% /local/.backup/home

Hmm, now I'm really confused, I just checked on the Ubuntu 17.04 and
16.04.3 VM's I have (I only run current and the most recent LTS
version), and neither of them behave like this.

I have this kind of output on all of my Ubuntu hosts:

root@moep:~# grep PRETTY_NAME /etc/os-release
PRETTY_NAME="Ubuntu 16.04.3 LTS"

root@moep:~# df -T /usb/UF/tmp/blubb
Filesystem     Type 1K-blocks    Used Available Use% Mounted on
-              -     12581888 3690524   7253700  34% /usb/UF/tmp/blubb

root@moep:~# btrfs subvolume show /usb/UF/tmp/blubb
/usb/UF/tmp/blubb
         Name:                   blubb
         UUID:                   ecf8c804-d4a3-9948-89fe-b0c1971c25cb
         Parent UUID:            -
         Received UUID:          -
         Creation time:          2017-08-22 12:54:16 +0200
         Subvolume ID:           262
         Generation:             23
         Gen at creation:        22
         Parent ID:              5
         Top level ID:           5
         Flags:                  -
         Snapshot(s):

root@moep:~# dpkg -l | grep btrfs
ii  btrfs-tools                                 4.4-1ubuntu1                                 amd64        Checksumming Copy on Write Filesystem utilities

Hmm, interesting.  Are you using qgroups by chance?

    I get this behaviour (the "- -") only if it's a non-mounted
subvolume:

hrm@amelia:~ $ df -T .
Filesystem     Type  1K-blocks     Used Available Use% Mounted on
/dev/sdb1      btrfs 117220284 95271852  18611060  84% /home

hrm@amelia:~ $ sudo btrfs sub crea foo
Create subvolume './foo'

hrm@amelia:~ $ df -T ./foo
Filesystem     Type 1K-blocks     Used Available Use% Mounted on
-              -    117220284 95271880  18611032  84% /home/hrm/foo

hrm@amelia:~ $ sudo mkdir foo/bar
hrm@amelia:~ $ df -T foo/bar
Filesystem     Type 1K-blocks     Used Available Use% Mounted on
-              -    117220284 95271852  18611060  84% /home/hrm/foo

hrm@amelia:~ $ mkdir foo2

hrm@amelia:~ $ sudo mount /dev/sdb1 ./foo2 -o subvol=home/hrm/foo

hrm@amelia:~ $ df -T foo2
Filesystem     Type  1K-blocks     Used Available Use% Mounted on
/dev/sdb1      btrfs 117220284 95272384  18610528  84% /home/hrm/foo2

Wait, I think I see what's up here.  I was just calling `df -T` without 
pointing at the subvolume (which correctly ignores it because it's not 
actually mounted).  It looks like this is a side effect of the (rather 
irritating) fake mount-point behavior of subvolumes.