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Re: BTRFS and debian

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Le 13/07/2018 à 03:13, David Christensen a écrit :
> file(1) -- no:
> 
> 2018-07-12 17:55:01 root@po ~
> # file /dev/sda1
> /dev/sda1: block special (8/1)

You must add the option -s so that file looks into the special device 
file contents.

> wipefs(8) -- not today (!).

Don't worry, despite its dreadful name, wipefs does not wipe anything 
without the -a or -o option, it just displays found metadata.

>> Note that this setup is flawed when using a partition on an SCSI-like 
>> disk : the installer writes the device name /dev/sdX which is known to 
>> be not persistent (that's why UUIDs are used instead when possible). 
>> But a plain dm-crypt device has no header and UUID. It would be more 
>> reliable to use the PARTUUID= (synthetic on a DOS-partitioned disk) 
>> instead.
> 
> I have been using /dev/disk/by-id/* successfully for a while, but 

Did the installer automatically wrote this in /etc/crypttab or did you 
replace the original device name ?

> /dev/disk/by-partuuid sounds even better -- this will prevent confusion 
> if and when I move partitions or images to other devices.

Beware that unlike a UUID or LABEL, a PARTUUID or PARTLABEL is stored in 
the partition table, not in the partition data.
Also note that a DOS partition table entry does not contain a UUID nor 
LABEL, and the PARTUUID is artificially built by combining the 32-bit 
"disk identifier" field in the MBR and the partition number. So if the 
partition number or the disk identifier changes, the PARTUUID changes.

In short :
- if you move the disk contents (including the partition table) to 
another disk, the PARTUUID is preserved ;
- if you move the partition contents to another partition, the PARTUUID 
is not preserved.

There is a hackish way to add a UUID to a plain dm-crypt partition : 
write metadata of any kind at the beginning of the partition (ext2, 
swap, LUKS...) and specify an offset for dm-crypt data beyond the metadata.

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BTRFS and debian Ge <gpdsbe@mailbox.org> - 2018-07-09 20:20 +0200
  Re: BTRFS and debian Matthew Crews <mailinglists@mattcrews.com> - 2018-07-09 21:40 +0200
    Re: BTRFS and debian Ulf Volmer <u.volmer@u-v.de> - 2018-07-09 22:00 +0200
      Re: BTRFS and debian Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-07-09 23:00 +0200
        Re: BTRFS and debian Ulf Volmer <u.volmer@u-v.de> - 2018-07-09 23:10 +0200
      Re: BTRFS and debian Matthew Crews <mailinglists@mattcrews.com> - 2018-07-09 23:40 +0200
  Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-10 05:40 +0200
    Re: BTRFS and debian Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-07-11 20:40 +0200
      Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-12 05:10 +0200
        Re: BTRFS and debian Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-07-12 07:50 +0200
          Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-13 03:20 +0200
            Re: BTRFS and debian Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-07-14 00:40 +0200
              Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-14 03:00 +0200
                Re: BTRFS and debian Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-07-14 11:10 +0200
                Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-14 21:40 +0200
                Re: BTRFS and debian Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-07-14 23:10 +0200
            Re: BTRFS and debian Zenaan Harkness <zenaan@freedbms.net> - 2018-07-14 01:40 +0200
    Re: BTRFS and debian David Wright <deblis@lionunicorn.co.uk> - 2018-07-12 20:00 +0200
      Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-13 05:00 +0200
        Re: BTRFS and debian Dan Ritter <dsr@randomstring.org> - 2018-07-13 12:00 +0200
          Re: BTRFS and debian <tomas@tuxteam.de> - 2018-07-13 12:30 +0200
          Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-14 03:10 +0200
        Re: BTRFS and debian Zenaan Harkness <zenaan@freedbms.net> - 2018-07-14 01:40 +0200
          Re: BTRFS and debian David Christensen <dpchrist@holgerdanske.com> - 2018-07-14 03:10 +0200
            Re: BTRFS and debian Zenaan Harkness <zenaan@freedbms.net> - 2018-07-14 12:00 +0200
              Re: BTRFS and debian Reco <recoverym4n@gmail.com> - 2018-07-14 12:30 +0200
                Re: BTRFS and debian Zenaan Harkness <zenaan@freedbms.net> - 2018-07-14 12:40 +0200
              Wrapping lines, was Re: BTRFS and debian David Wright <deblis@lionunicorn.co.uk> - 2018-07-15 05:20 +0200
                Re: Wrapping lines, was Re: BTRFS and debian Zenaan Harkness <zenaan@freedbms.net> - 2018-07-15 05:30 +0200
                Re: Wrapping lines, was Re: BTRFS and debian Zenaan Harkness <zenaan@freedbms.net> - 2018-07-15 12:30 +0200
        Re: BTRFS and debian Zenaan Harkness <zenaan@freedbms.net> - 2018-07-14 11:40 +0200

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