[Bug 1481158] Re: sfdisk gets cylinder calculation wrong when using sectors

[Peter D.]

I suspect that this causes a problem that later versions do not clean
up.  In this case the sequences was (probably) partition with Trusty,
install Trusty, delete Trusty, .... , install Wily (without re-
partitioning).  The current partition table as displayed by fdisk on
Trusty is clearly wrong for partition three (the one with Wily installed
on it).

It is not obvious how to fix this without repartitioning, and re-
installing.  Neither is it obvious how much (if any) real trouble it has
caused.

There has been persistent non-sense CHS and Disk-ID values on my phone's
micro SD card, as well as some reliability trouble.  It was partitioned
and formatted under Trusty.

$ sudo fdisk /dev/sda

Welcome to fdisk (util-linux 2.26.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): x

Expert command (m for help): v
Remaining 54093 unallocated 512-byte sectors.

Expert command (m for help): p

Disk /dev/sda: 298.1 GiB, 320068705792 bytes, 625134191 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x25f55d02

Device     Boot     Start       End   Sectors Id Type                 Start-C/H/S   End-C/H/S Attrs
/dev/sda1  *         2048  21655619  21653572 83 Linux                    0/33/32 1023/63/254    80
/dev/sda2        21659646 600000511 578340866  5 Extended             1023/63/254 1023/63/254      
/dev/sda3       600000512 625088511  25088000 83 Linux                  484/42/77 1021/55/244      
/dev/sda4       625121280 625133567     12288 83 Linux                1023/63/254 1023/63/254      
/dev/sda5        21659648  42125311  20465664 83 Linux                1023/63/254 1023/63/254      
/dev/sda6        42127360  62590975  20463616 83 Linux                1023/63/254 1023/63/254      
/dev/sda7        62593024  83071538  20478515 82 Linux swap / Solaris 1023/63/254 1023/63/254      
/dev/sda8        83073024 102602751  19529728 83 Linux                1023/63/254 1023/63/254      
/dev/sda9       102604800 122134096  19529297 83 Linux                1023/63/254 1023/63/254      
/dev/sda10      122136576 141666303  19529728 83 Linux                1023/63/254 1023/63/254      
/dev/sda11      141668352 161197648  19529297 83 Linux                1023/63/254 1023/63/254      
/dev/sda12      161200128 599994367 438794240 83 Linux                1023/63/254 1023/63/254      
/dev/sda13      599996416 600000511      4096 83 Linux                1023/63/254 1023/63/254      

Partition table entries are not in disk order.

Expert command (m for help): q

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https://bugs.launchpad.net/bugs/1481158

Title:
  sfdisk gets cylinder calculation wrong when using sectors

Status in util-linux package in Ubuntu:
  Fix Released
Status in util-linux source package in Trusty:
  Triaged

Bug description:
  If you try and specify the starting offset for the partition in
  sectors and ask sfdisk to use the rest of the disk (with "+"), sfdisk
  will incorrectly calculate the end cylinders and not create the
  partition.  For example

  ---

  # dd if=/dev/zero of=/tmp/disk.img bs=1M count=10
  # losetup -f /tmp/disk.img
  # sfdisk -uS /dev/loop1 <<EOF
  2048 + L *
  0 0;
  0 0;
  0 0;
  EOF
  Checking that no-one is using this disk right now ...
  BLKRRPART: Invalid argument
  OK
  Disk /dev/loop1: cannot get geometry

  Disk /dev/loop1: 1 cylinders, 255 heads, 63 sectors/track

  sfdisk: ERROR: sector 0 does not have an msdos signature
   /dev/loop1: unrecognized partition table type
  Old situation:
  No partitions found
  New situation:
  Warning: The partition table looks like it was made
    for C/H/S=*/71/5 (instead of 1/255/63).
  For this listing I'll assume that geometry.
  Units = sectors of 512 bytes, counting from 0

     Device Boot    Start       End   #sectors  Id  System
  /dev/loop1p1   *      2048     20479      18432  83  Linux
  		start: (c,h,s) expected (5,54,4) found (0,32,33)
  		end: (c,h,s) expected (57,48,5) found (1,70,5)
  /dev/loop1p2             0         -          0   0  Empty
  /dev/loop1p3             0         -          0   0  Empty
  /dev/loop1p4             0         -          0   0  Empty
  Warning: partition 1 does not end at a cylinder boundary
  end of partition 1 has impossible value for cylinders: 1 (should be in 0-0)

  sfdisk: I don't like these partitions - nothing changed.
  (If you really want this, use the --force option.)

  ---

  Using the --force flag writes out the correct partitions.  I also note
  this is fixed in 2.26, which has a large rewrite of sfdisk and uses
  sectors by default

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