System Administration Guide, Volume 1

The newfs Command Syntax, Options, and Arguments

The newfs command is a friendlier version of the mkfs command that is used to create file systems. The newfs command is located in the /usr/sbin directory.

The syntax is:

newfs [-Nv] [mkfs_options] raw_device

The table below describes the options and arguments to the newfs command.

Table 40-4 The newfs Command Options and Arguments




Displays the file system parameters that would be used in creating the file system without actually creating it. This option does not display the parameters used to create an existing file system. 


Displays the parameters that are passed to the mkfs command.


Use the following options to set the parameters passed to the mkfs command. The options are listed below in the order they are passed to mkfs. Separate the options with spaces.

-s size

The size of the file system in sectors. The default is automatically determined from the disk label. 

-t ntrack

The number of tracks per cylinder on the disk. The default is determined from the disk label. 

-b bsize

The logical block size in bytes to use for data transfers. Specify the size of 4096 or 8192 (4 or 8 Kbytes). The default is 8192 bytes (8 Kbytes). 

-f fragsize

The smallest amount of disk space in bytes that is allocated to a file. Specify the fragment size in powers of two in the range from 512 to 8192 bytes. The default is 1024 bytes (1 Kbyte). 

-c cgsize

The number of disk cylinders per cylinder group. The default value is calculated by dividing the number of sectors in the file system by the number of sectors in a gigabyte, and then multiplying the result by 32. The default value ranges from 16 to 256.  

-m free

The minimum percentage of free disk space to allow. The default is ((64 Mbytes/partition size) * 100), rounded down to the nearest integer and limited between 1% and 10%, inclusively. 

-r rpm

The speed of the disk, in revolutions per minute. This setting is driver- or device-specific. If the drive can report how fast it spins, mkfs uses this value. If not, the default is 3600. This parameter is converted to revolutions per second before it is passed to mkfs.

-i nbpi

The number of bytes per inode to use in computing how many inodes to create. See the section above for the default values. 

-o opt

Optimization type to use for allocating disk blocks to files: space or time. The default is time.

-a apc

The number of alternate blocks per disk cylinder (SCSI devices only) to reserve for bad block placement. The default is 0. 

-d gap

(Rotational delay) The expected minimum number of milliseconds it takes the CPU to complete a data transfer and initiate a new data transfer on the same disk cylinder. The default is zero. 

-n nrpos

The number of different rotation positions in which to divide a cylinder group. The default is 8. 

-C maxcontig

The maximum number of blocks, belonging to one file, that will be allocated contiguously before inserting a rotational delay. The default varies from drive to drive. Drives without internal (track) buffers (or drives/controllers that don't advertise the existence of an internal buffer) default to 1. Drives with buffers default to 7. 

This parameter is limited in the following way: 

blocksize x maxcontig must be <= maxphys

maxphys is a read-only kernel variable that specifies the maximum block transfer size (in bytes) that the I/O subsystem is capable of satisfying. (This limit is enforced by mount, not by newfs or mkfs.)

This parameter also controls clustering. Regardless of the value of rotdelay, clustering is enabled only when maxcontig is greater than 1. Clustering allows higher I/O rates for sequential I/O and is described in tunefs(1M).


The special character (raw) device file name of the partition to contain the file system. This argument is required. 

Examples--newfs Command Options and Arguments

This newfs example uses the -N option to display file system information, including the backup superblocks.

# newfs -N /dev/rdsk/c0t0d0s0
/dev/rdsk/c0t0d0s0:  37260 sectors in 115 cylinders of 9 tracks, 36 sectors
        19.1MB in 8 cyl groups (16 c/g, 2.65MB/g, 1216 i/g)
superblock backups (for fsck -b #) at:
 32, 5264, 10496, 15728, 20960, 26192, 31424, 36656,