fdisk fails with "Class not found"

[Aiza]

Bob Willcox wrote:
> I am trying to change the sysid of a slice (partition) on my disk from 5 to
> 165.  When it gets to the point of writing sector 0 it always fails with:
> 
> fdisk: Class not found
> fdisk: Failed to write sector zero
> 
> Can someone please tell me what this means, and how do I fix it?
> I have included the output from an fdisk attempt below.
> 
> Thanks,
> Bob
> 
> root at tavion:10 /usr/home/bob> fdisk -uv
> ******* Working on device /dev/ad4 *******
> parameters extracted from in-core disklabel are:
> cylinders=969021 heads=16 sectors/track=63 (1008 blks/cyl)
> 
> Figures below won't work with BIOS for partitions not in cyl 1
> parameters to be used for BIOS calculations are:
> cylinders=969021 heads=16 sectors/track=63 (1008 blks/cyl)
> 
> Do you want to change our idea of what BIOS thinks ? [n] 
> Media sector size is 512
> Warning: BIOS sector numbering starts with sector 1
> Information from DOS bootblock is:
> The data for partition 1 is:
> sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
>     start 63, size 524286945 (255999 Meg), flag 80 (active)
>         beg: cyl 0/ head 1/ sector 1;
>         end: cyl 1023/ head 15/ sector 63
> Do you want to change it? [n] 
> The data for partition 2 is:
> sysid 5 (0x05),(Extended DOS)
>     start 524297340, size 452470725 (220932 Meg), flag 0
>         beg: cyl 1023/ head 255/ sector 63;
>         end: cyl 1023/ head 14/ sector 63
> Do you want to change it? [n] y
> Supply a decimal value for "sysid (165=FreeBSD)" [5] 165
> Supply a decimal value for "start" [524297340] 
> Supply a decimal value for "size" [452470725] 
> Explicitly specify beg/end address ? [n] 
> sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
>     start 524297340, size 452470725 (220932 Meg), flag 0
>         beg: cyl 968/ head 4/ sector 1;
>         end: cyl 311/ head 14/ sector 63
> Are we happy with this entry? [n] y
> The data for partition 3 is:
> <UNUSED>
> Do you want to change it? [n] 
> The data for partition 4 is:
> <UNUSED>
> Do you want to change it? [n] 
> Partition 1 is marked active
> Do you want to change the active partition? [n]  
> 
> We haven't changed the partition table yet.  This is your last chance.
> parameters extracted from in-core disklabel are:
> cylinders=969021 heads=16 sectors/track=63 (1008 blks/cyl)
> 
> Figures below won't work with BIOS for partitions not in cyl 1
> parameters to be used for BIOS calculations are:
> cylinders=969021 heads=16 sectors/track=63 (1008 blks/cyl)
> 
> Information from DOS bootblock is:
> 1: sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
>     start 63, size 524286945 (255999 Meg), flag 80 (active)
>         beg: cyl 0/ head 1/ sector 1;
>         end: cyl 1023/ head 15/ sector 63
> 2: sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
>     start 524297340, size 452470725 (220932 Meg), flag 0
>         beg: cyl 968/ head 4/ sector 1;
>         end: cyl 311/ head 14/ sector 63
> 3: <UNUSED>
> 4: <UNUSED>
> Should we write new partition table? [n] y
> fdisk: Class not found
> fdisk: Failed to write sector zero
> 


The 'Class not found' you can ignore. Fdisk still worked.

Try dd if=/dev/zero of=/dev/xxx count=2
to remove the MBR them do fdisk -I /dev/xxx  command