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I am trying to extend a partition using sfdisk on debian 8. I am running the following command:

    sfdisk -H 255 -S 63 --quiet --Linux --leave-last -uM --force --no-reread /dev/md1 -N4 < /tmp/abc

I am getting the following error when I ran the command:

    Successfully wrote the new partition table
    Re-reading the partition table ...
    sfdisk: BLKRRPART: Device or resource busy
    sfdisk: The command to re-read the partition table failed.
    Run partprobe(8), kpartx(8) or reboot your system now,before using mkfs
    sfdisk: If you created or changed a DOS partition, /dev/foo7, say, then use dd(1) to zero the first 512 bytes:  dd if=/dev/zero of=/dev/foo7 bs=512 count=1 (See fdisk(8).)

Why does the re-read happen when I have mentioned --no-reread? I am running this on sfdisk from util-linux 2.25.2. When I run the same command on sfdisk from sfdisk (util-linux-ng 2.17.2), I do not experience this error. Is there any difference between the two which is causing this error to occur?

vvnikhil
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1 Answers1

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The --no-reread option tells sfdisk to not check for if the device is in use (e.g. mounted or swap).

The error you are getting is from the sfdisk telling the kernel that the partition information has changed; the kernel is responding "hey, this device is already in use; I'm not going to read the new partition data".

So now the kernel copy of the partition data is different to the actual data on the disk.

Without the --no-reread then sfdisk wouldn't let you do the partitioning at all.

Stephen Harris
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  • How do I get the kernel to update the partition table then? – vvnikhil Jul 17 '16 at 23:29
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    `sfdisk` tells you; `partprobe`, `kpartx` or a reboot. If the disk is in use (eg it's your root disk sharing with other partitions) it may be a reboot is the only way. It's what I'd do, to be safe :-) – Stephen Harris Jul 18 '16 at 01:43
  • Is there a reason why I see this error when I am running sfdisk from util-linux 2.25.2 and not when I am running sfdisk (util-linux-ng 2.17.2). Thanks in advance. – vvnikhil Jul 18 '16 at 14:38