mknod

Additional Notes

mknod creates a block or character device file in the filesystem. Device files are the interface between user space and kernel device drivers. Each device file has a major number (identifying the driver) and a minor number (identifying the specific device instance).

On modern Linux systems, device files are created automatically by udev (or devtmpfs) at boot time, so mknod is rarely needed. It is primarily used in minimal environments, initramfs, containers, or when manually setting up a device node that udev does not handle.

Syntax

mknod [options] name type major minor

Parameters

• name: Path to the device file to create.
• type: Device type: b for block device, c or u for character device, p for a FIFO (named pipe).
• major: The major device number (integer). Ignored for FIFOs.
• minor: The minor device number (integer). Ignored for FIFOs.

Common Options

• -m mode, --mode mode: Set the file permissions (e.g., -m 644).
• -Z, --context: Set the SELinux security context.
• --help: Show help and exit.
• --version: Show version information.

Examples

mknod /dev/null c 1 3

Create the /dev/null character device (major 1, minor 3).

mknod -m 660 /dev/sda b 8 0

Create a block device with permissions 660.

mknod /tmp/myfifo p

Create a named pipe (FIFO) at /tmp/myfifo.

mknod /dev/loop0 b 7 0

Create the first loop device.

Common Device Numbers

• 1, 3: /dev/null (character)
• 1, 8: /dev/random (character)
• 1, 9: /dev/urandom (character)
• 8, 0: /dev/sda (block, first SCSI/SATA disk)
• 8, 1: /dev/sda1 (first partition)
• 7, 0: /dev/loop0 (block, first loop device)
• 4, 0: /dev/tty0 (character, first virtual console)

Practical Notes

• Use ls -l /dev/sda to see the major/minor numbers of existing devices.
• Device major numbers are assigned by the Linux kernel and listed in Documentation/admin-guide/devices.txt.
• In most cases, let udev manage device files. Only use mknod in recovery or embedded scenarios.
• To remove a device file, use rm just like a regular file.