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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-size
special [
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