Creating Device Files With mknod

Creating Device Files With mknod

You may need to create specific device files that are not created by MAKEDEV; for example, a device file for a partition that is not created by default. You can edit /dev/MAKEDEV or files in /dev/MAKEDEV.d as described in the section "Creating Device Files With MAKEDEV" in this chapter or use the mknod command to create a specific device special file in /dev.

The three forms of the mknod command are:

mknod  name b major minor 
mknod  name c major minor 
mknod  name p

The arguments of mknod are:

name: Specifies the name of the special file.
b: Specifies a block device.
c: Specifies a character device.
major: major specifies a device type that corresponds to an appropriate entry in the block or character device switch tables.
minor: The minor number indicates a unit of the device. It distinguishes peripheral devices from each other.
p: Specifies the special file as a first-in, first-out (FIFO) device. This is also known as a named pipe. Named pipes have nothing to do with disks; the use of this option is not described in this guide.

As an example, create a character (raw) device file for partition 3 of a SCSI disk that is on controller 0 at drive address 2 (partition 3 has been created by custom partitioning of the disk with fx). The value of name would be /dev/rdsk/dks0d2s3:

/dev/: All device files are in this directory.
rdsk/: The directory for character (raw) device files for disks.
dks: It is a SCSI disk.
0d2s3: Controller 0, drive address 2, partition 3.

To determine the values of major and minor, start by listing the contents of the device file directory for this disk:

# ls -l /dev/rdsk/dks0d2* 
crw-------    1 root     sys      128, 32 Nov 30 06:49 dks0d2s0
crw-------    1 root     sys      128, 33 Nov 30 06:49 dks0d2s1
crw-------    1 root     sys      128, 38 Nov 30 06:49 dks0d2s6
crw-------    1 root     sys      128, 39 Nov 30 06:49 dks0d2s7
crw-------    1 root     sys      128, 40 Nov 30 06:49 dks0d2vh
crw-------    1 root     sys      128, 42 Nov 30 06:49 dks0d2vol

The major device number for this disk is 128. Looking at the minor numbers, you can see that they are assigned based on the partition number. Partition 3 should be minor number 35.

The command to make a device file for the character device for this partition is:

# mknod /dev/rdsk/dks0d2s2 c 128 35