How to use the command mknod (with examples)

The mknod command is used to create block or character special files in Unix-like operating systems. These special files can represent devices such as hardware devices or virtual devices.

Use case 1: Creating a block device

Code:

sudo mknod path/to/device_file b major_device_number minor_device_number

Motivation: Creating a block device is useful when you want to simulate a storage device, such as a hard drive or a USB drive. This can be helpful for testing or virtualization purposes.

Explanation:

• sudo: This command is used to run the mknod command with root privileges.
• mknod: The mknod command to create a device file.
• path/to/device_file: The full path and name of the device file you want to create.
• b: Indicates that we want to create a block device.
• major_device_number: The major device number for the device file.
• minor_device_number: The minor device number for the device file.

Example output:

sudo mknod /dev/sdb b 8 16

This will create a block device file named /dev/sdb with the major device number 8 and minor device number 16.

Use case 2: Creating a character device

Code:

sudo mknod path/to/device_file c major_device_number minor_device_number

Motivation: Creating a character device is useful when you want to represent a device that transfers data character by character, such as a keyboard or a printer.

Explanation:

• sudo: This command is used to run the mknod command with root privileges.
• mknod: The mknod command to create a device file.
• path/to/device_file: The full path and name of the device file you want to create.
• c: Indicates that we want to create a character device.
• major_device_number: The major device number for the device file.
• minor_device_number: The minor device number for the device file.

Example output:

sudo mknod /dev/hello c 7 3

This will create a character device file named /dev/hello with the major device number 7 and minor device number 3.

Use case 3: Creating a FIFO (queue) device

Code:

sudo mknod path/to/device_file p

Motivation: Creating a FIFO device is useful for inter-process communication, where one process can write data to the FIFO and another process can read the data from the FIFO.

Explanation:

• sudo: This command is used to run the mknod command with root privileges.
• mknod: The mknod command to create a device file.
• path/to/device_file: The full path and name of the FIFO device file you want to create.
• p: Indicates that we want to create a FIFO device.

Example output:

sudo mknod /dev/myfifo p

This will create a FIFO device file named /dev/myfifo.

Use case 4: Creating a device file with default SELinux security context

Code:

sudo mknod -Z path/to/device_file type major_device_number minor_device_number

Motivation: Creating a device file with a specific SELinux security context can be necessary when working with SELinux-enabled systems, ensuring that the device file has the correct security context.

Explanation:

• sudo: This command is used to run the mknod command with root privileges.
• mknod: The mknod command to create a device file.
• -Z: Specifies that we want to set the SELinux security context for the created device file.
• path/to/device_file: The full path and name of the device file you want to create.
• type: Specifies the type of device file.
• major_device_number: The major device number for the device file.
• minor_device_number: The minor device number for the device file.

Example output:

sudo mknod -Z /dev/sdcard b 1 0

This will create a block device file named /dev/sdcard with the major device number 1, minor device number 0, and with the default SELinux security context.