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NEWFS_MSDOS(8) System Manager's Manual NEWFS_MSDOS(8)

newfs_msdos
construct a new MS-DOS (FAT) file system

newfs_msdos [-N] [-a FAT-size] [-B boot] [-b block-size] [-c cluster-size] [-e dirents] [-F FAT-type] [-f format] [-h heads] [-I volid] [-i info] [-k backup] [-L label] [-m media] [-n FATs] [-O OEM] [-o hidden] [-r reserved] [-S sector-size] [-s total] [-u track-sizespecial [disktype]

The newfs_msdos utility creates a FAT12, FAT16, or FAT32 file system on device special, using disktab(5) entry disktype to determine geometry, if required.

The special file should be a raw device, for example /dev/rsd0i; if a relative path like sd0i is specified, the corresponding raw device is used.

The options are as follows:

FAT-size
Number of sectors per FAT.
boot
Get bootstrap from file.
block-size
File system block size (bytes per cluster). This should resolve to an acceptable number of sectors per cluster (see below).
cluster-size
Sectors per cluster. Acceptable values are powers of 2 in the range 1 through 128.
dirents
Number of root directory entries (FAT12 and FAT16 only).
FAT-type
FAT type (one of 12, 16, or 32).
format
Specify a standard (floppy disk) format. The eight standard formats are (capacities in kilobytes): 160, 180, 320, 360, 720, 1200, 1440, 2880.
heads
Number of drive heads.
volid
Volume ID.
info
Location of the file system info sector (FAT32 only). A value of 0xffff signifies no info sector.
backup
Location of the backup boot sector (FAT32 only). A value of 0xffff signifies no backup sector.
label
Volume label (up to 11 characters). The label should consist of only those characters permitted in regular DOS (8+3) filenames.
media
Media descriptor (acceptable range 0xf0 to 0xff).
Don't create a file system: just print out parameters.
FATs
Number of FATs. Acceptable values are 1 to 16 inclusive. The default is 2.
OEM
OEM string (up to 8 characters). The default is "BSD 4.4".
hidden
Number of hidden sectors.
reserved
Number of reserved sectors.
sector-size
Number of bytes per sector. Acceptable values are powers of 2 in the range 512 through 32768.
total
File system size.
track-size
Number of sectors per track.

FAT file system parameters occupy a "Boot Sector BPB (BIOS Parameter Block)" in the first of the "reserved" sectors which precede the actual file system. For reference purposes, this structure is presented below.
struct bsbpb {
	u_int16_t	bps;		/* [-S] bytes per sector */
	u_int8_t	spc;		/* [-c] sectors per cluster */
	u_int16_t	res;		/* [-r] reserved sectors */
	u_int8_t	nft;		/* [-n] number of FATs */
	u_int16_t	rde;		/* [-e] root directory entries */
	u_int16_t	sec;		/* [-s] total sectors */
	u_int8_t	mid;		/* [-m] media descriptor */
	u_int16_t	spf;		/* [-a] sectors per FAT */
	u_int16_t	spt;		/* [-u] sectors per track */
	u_int16_t	hds;		/* [-h] drive heads */
	u_int32_t	hid;		/* [-o] hidden sectors */
	u_int32_t	bsec;		/* [-s] big total sectors */
};

/* FAT32 extensions */
struct bsxbpb {
	u_int32_t	bspf;		/* [-a] big sectors per FAT */
	u_int16_t	xflg;		/* control flags */
	u_int16_t	vers;		/* file system version */
	u_int32_t	rdcl;		/* root directory start cluster */
	u_int16_t	infs;		/* [-i] file system info sector */
	u_int16_t	bkbs;		/* [-k] backup boot sector */
};

Create a file system, using default parameters, on /dev/rwd0i.
newfs_msdos /dev/rwd0i

Create a standard 1.44M file system, with volume label "foo", on /dev/rfd0c.

newfs_msdos -f 1440 -L foo fd0c

Exit status is 0 on success and 1 on error.

disktab(5), disklabel(8), fdisk(8), newfs(8)

The newfs_msdos command first appeared in OpenBSD 2.1.

Robert Nordier <rnordier@FreeBSD.org>.
July 10, 2014 OpenBSD-current