Re: Formatting FAT32 newfs_msdos returns read-only file system

["John D. Baker" <jdbaker%consolidated.net@localhost>]

On Mon, 21 Sep 2026, RVP wrote:

> You can't start a MBR partition on sector 1 (ie. track 0) on HDD-type
> media.  Start on track 1--or sector 2048 as per the alignment it wants
> to be in.

That depends.  I routinely start MBR partitions in sector 1.  Only in
a couple of cases has that been rejected, although I forget the context.
In those cases, I didn't have to offset much for it to work.  Admittedly
in the FreeDOS case below, I only partitioned the disk w/NetBSD, all the
formatting and setup (of the DOS partitions) were done with FreeDOS.

Eg:

$ fdisk wd4 
Disk: /dev/rwd4
NetBSD disklabel disk geometry:
cylinders: 29777, heads: 16, sectors/track: 63 (1008 sectors/cylinder)
total sectors: 30015216, bytes/sector: 512

BIOS disk geometry:
cylinders: 1023, heads: 92, sectors/track: 63 (5796 sectors/cylinder)
total sectors: 30015216

Partitions aligned to 5796 sector boundaries, offset 63

Partition table:
0: <UNUSED>
1: <UNUSED>
2: <UNUSED>
3: NetBSD (sysid 169)
    start 8, size 30015208 (14656 MB, Cyls 0/0/9-5178/55/63), Active
Bootselector disabled.
First active partition: 3
Drive serial number: 0 (0x00000000)


And on another machine:
$ fdisk wd0
Disk: /dev/rwd0
NetBSD disklabel disk geometry:
cylinders: 310101, heads: 16, sectors/track: 63 (1008 sectors/cylinder)
total sectors: 312581808, bytes/sector: 512

BIOS disk geometry:
cylinders: 1023, heads: 255, sectors/track: 63 (16065 sectors/cylinder)
total sectors: 312581808

Partitions aligned to 2048 sector boundaries, offset 2048

Partition table:
0: <UNUSED>
1: NetBSD (sysid 169)
    bootmenu: NetBSD
    start 4209030, size 304174710 (148523 MB, Cyls 262-19195), Active
2: Primary DOS with 32 bit FAT - LBA (sysid 12)
    bootmenu: FreeDOS
    start 1, size 4209029 (2055 MB, Cyls 0/0/2-261)
3: Primary DOS with 32 bit FAT - LBA (sysid 12)
    start 308383740, size 4198068 (2050 MB, Cyls 19196-19457/80/63)
Bootselector enabled, timeout 10 seconds.
First active partition: 1
Drive serial number: 0 (0x00000000)


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