Re: finding root filesystem of a subvolume?

[Hugo Mills <hugo@carfax.org.uk>]

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On Tue, Aug 22, 2017 at 10:12:25AM -0400, Austin S. Hemmelgarn wrote:
> On 2017-08-22 09:53, Ulli Horlacher wrote:
> >On Tue 2017-08-22 (09:37), Austin S. Hemmelgarn wrote:
> >
> >>>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

   Hugo.

-- 
Hugo Mills             | "Your problem is that you have a negative
hugo@... carfax.org.uk | personality."
http://carfax.org.uk/  | "No, I don't!"
PGP: E2AB1DE4          |                              Londo and Vir, Babylon 5

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