fdisk -l output question

[kapilajayanath]

Hi,

I have the following question on the "fdisk -l" output.

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x8a588a58

Device Boot Start End Blocks Id System
/dev/sda1 * 1 3824 30716248+ 7 HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/sda2 3825 3836 96390 83 Linux
/dev/sda3 3837 18959 121475497+ 83 Linux
/dev/sda4 18960 19457 4000185 5 Extended
/dev/sda5 18960 19457 4000153+ 82 Linux swap / Solaris


What is the meaning of the plus(+) sign seen on Blocks field of some of the file systems?

Thanks,
Kapila

[efflandt]

It is possible that something changed your disk geoemetry so partitions no longer fall on cylinder boundaries or not whole blocks, hence the +. When I originally shrunk my XP Home partition sda2, ntfsresize kept cyl, head geometry like it was. But when I first installed WinXP 64-bit beta (on sda4), it changed my heads to 255 and cylinders to match that, and XP 64 would not even boot itself (much less anything else). I had to use fdisk from a Linux rescue CD to reconstruct my partition table without partition details written down (just some from memory in my head), so I had to experiment a bit before I got everything to boot (XP 64 on sda4 and XP home on sda2, sda1 is HP data).

When I later installed SuSE 9 on sda3 and was going to let it do its thing, I recognized that it was trying to do the same thing (change my disk geometry), so I said no, and to use sda3 as is.

When I recently installed Ubuntu on sda4, I manually just told it to format sda4 (overwriting expired XP 64 beta) and not change any partitions. As you can see from the following, my heads are not 255 (but it was 255 after XP 64 install, and may have been if I had let newer Linux versions do their thing). Not sure why OS's change the disk geometry, maybe so older operating systems (limited to 255 heads and 1024 cyl) can boot from more of the disk, but that can sometimes lose a little disk space or mess up existing OS's:

Disk /dev/sda: 200.0 GB, 200049647616 bytes
240 heads, 63 sectors/track, 25841 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes
Disk identifier: 0xf806f806

Device Boot Start End Blocks Id System
/dev/sda1 1 619 4679608+ b W95 FAT32
/dev/sda2 620 22600 166176360 7 HPFS/NTFS
/dev/sda3 22601 24226 12292560 83 Linux
/dev/sda4 * 24227 25841 12209400 83 Linux

[kapilajayanath]

Hi efflandt,

Thanks a lot for the explanation. But as you can see on the my output, only my "sda1" partition doesn't end up in cylinder boundary. sda3 and sda5 partitions also showing the plus(+) sign. When I checked with "parted" command, it doesn't have any comment about cylinder boundary. Please see the output below and advice.

(parted) print
Model: ATA SAMSUNG HM160HI (scsi)
Disk /dev/sda: 160GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number Start End Size Type File system Flags
1 32.3kB 31.5GB 31.5GB primary ntfs boot
2 31.5GB 31.6GB 98.7MB primary ext4
3 31.6GB 156GB 124GB primary ext4
4 156GB 160GB 4096MB extended
(parted)


Thanks,
Kapila

[mechro]

Here is the output on my system of both fdisk and sfdisk. sfdisk quotes cylinders with a minus sign. It may give you a clue as to what's occurring but you may have to whip out your binary/hex calculator to pin it down exactly.


anthony@anthony-desktop:~$ sudo fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
/dev/sda1 * 1 13054 104856223+ 83 Linux
/dev/sda2 13055 26108 104856255 83 Linux
/dev/sda3 26109 39162 104856255 83 Linux
/dev/sda4 39163 60801 173815267+ f W95 Ext'd (LBA)
/dev/sda5 39163 39293 1052226 82 Linux swap / Solaris
/dev/sda6 39294 52347 104856223+ 83 Linux
anthony@anthony-desktop:~$ sudo sfdisk -l

Disk /dev/sda: 60801 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start End #cyls #blocks Id System
/dev/sda1 * 0+ 13053 13054- 104856223+ 83 Linux
/dev/sda2 13054 26107 13054 104856255 83 Linux
/dev/sda3 26108 39161 13054 104856255 83 Linux
/dev/sda4 39162 60800 21639 173815267+ f W95 Ext'd (LBA)
/dev/sda5 39162+ 39292 131- 1052226 82 Linux swap / Solaris
/dev/sda6 39293+ 52346 13054- 104856223+ 83 Linux