System Administration Guide: Basic Administration

Creating a UFS File System

Before you can create a UFS file system on a disk, the disk must be formatted and divided into slices. A disk slice is a physical subset of a disk that is composed of a single range of contiguous blocks. A slice can be used either as a raw device that provides, for example, swap space, or to hold a disk-based file system. See Chapter 31, Managing Disks (Overview) for complete information on formatting disks and dividing disks into slices.

Volume management products, like Solaris Volume Manager, create more sophisticated volumes, that expand beyond single slice or single disk boundaries. For more information about using volumes, see Solaris Volume Manager Administration Guide.

Note –

Solaris device names use the term slice (and the letter s in the device name) to refer to the slice number. Slices are also called “partitions.”

You need to create UFS file systems only occasionally, because the Solaris operating environment automatically creates them as part of the installation process. You need to create (or re-create) a UFS file system when you want to do the following:

The newfs command is the standard way to create UFS file systems. The newfs command is a convenient front-end to the mkfs command, which actually creates the new file system. The newfs command reads parameter defaults, such as tracks per cylinder and sectors per track, from the disk label that will contain the new file system. The options you choose are passed to the mkfs command to build the file system.

Default Parameters for the newfs Command

To make a new file system on a disk slice, you almost always use the newfs command. The following table shows the default parameters that are used by the newfs command.


Default Value 

Block size 

8 Kbytes 

Fragment size 

1 Kbyte 

Minimum free space 

((64 Mbytes/partition size) * 100), rounded down to the nearest integer and limited to between 1% and 10%, inclusively 

Rotational delay 


Optimization type 


Number of inodes 

1 inode for each 2 Kbytes of data space 

How to Create a UFS File System

  1. Make sure you have met the following prerequisites:

    1. The disk must be formatted and divided into slices.

      For information on formatting disks and dividing disks into slices, see Chapter 31, Managing Disks (Overview).

    2. You need to know the device name of the slice that will contain the file system.

      For information on finding disks and disk slice numbers, see Chapter 32, Administering Disks (Tasks).

    3. If you are re-creating an existing UFS file system, unmount it.

    4. You must be superuser or assume an equivalent role.

  2. Create the UFS file system.

    # newfs [-N] [-b size] [-i bytes] /dev/rdsk/device-name


    Displays what parameters the newfs command would pass to the mkfs command without actually creating the file system. This option is a good way to test the newfs command.

    -b size

    Specifies the block size for the file system, either 4096 or 8192 bytes per block. The default is 8192. 

    -i bytes

    Specifies the number of bytes per inode. The default varies depending on the disk size. For more information, see newfs(1M).


    Specifies the disk device name on which to create the new file system. 

    The system asks for confirmation.

    Caution – Caution –

    Be sure you have specified the correct device name for the slice before performing this step. If you specify the wrong slice, you will erase its contents when the new file system is created. This error might cause the system to panic.

  3. To verify the creation of the UFS file system, check the new file system.

    # fsck /dev/rdsk/device-name

    The device-name argument specifies the name of the disk device that contains the new file system.

    The fsck command checks the consistency of the new file system, reports any problems, and prompts you before it repairs the problems. For more information on the fsck command, see Chapter 42, Checking UFS File System Consistency (Tasks) or fsck(1M).

Example—Creating a UFS File System

The following example shows how to create a UFS file system on /dev/rdsk/c0t1d0s7.

# newfs /dev/rdsk/c0t1d0s7
/dev/rdsk/c0t1d0s7:  725760 sectors in 720 cylinders of 14 tracks, 72 sectors
        354.4MB in 45 cyl groups (16 c/g, 7.88MB/g, 3776 i/g)
super-block backups (for fsck -F ufs -o b=#) at:
 32, 16240, 32448, 48656, 64864, 81072, 97280, 113488, 129696, 145904, 162112,
 178320, 194528, 210736, 226944, 243152, 258080, 274288, 290496, 306704,
 322912, 339120, 355328, 371536, 387744, 403952, 420160, 436368, 452576,
 468784, 484992, 501200, 516128, 532336, 548544, 564752, 580960, 597168,
 613376, 629584, 645792, 662000, 678208, 694416, 710624,

Where to Go From Here

To mount the UFS file system and make it available, go to Chapter 39, Mounting and Unmounting File Systems (Tasks).