Linux: Understanding /dev (And Why It’s Not Just a Folder)

If you’ve ever peeked inside your Linux filesystem and found the /dev/ directory, you might have thought, “Hey, just another folder.” But oh no, dear reader, /dev/ is not just a folder. It’s the beating heart of Linux device management!

What Is /dev?

In Linux, /dev/ is a special directory that contains device files, which are interfaces to various hardware and pseudo-devices. Unlike normal files, these represent actual hardware components like hard drives, keyboards, and even your mouse.

Think of it this way: Instead of your system handling devices through some abstract magic, Linux treats everything as a file. Want to read data from a USB drive? Read from /dev/sdb. Want to send something to your printer? Write to /dev/lp0. It’s that simple!

Types of Device Files

Device files in /dev/ come in two main flavors:

1. Character Devices - These handle data in streams, one byte at a time (e.g., /dev/tty, /dev/random).
2. Block Devices - These deal with data in blocks (e.g., /dev/sda, /dev/loop0).

To check which type a device file is, use:

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ls -l /dev/

You’ll see a c for character devices and a b for block devices in the output.

Major and Minor Numbers

Each device file has major and minor numbers that identify its driver and specific device.

Use this command to check:

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ls -l /dev/sda

You might see something like:

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brw-rw---- 1 root disk 8, 0 Feb 27 12:34 /dev/sda

Here, 8 is the major number (indicating the disk driver) and 0 is the minor number (the first disk).

Common Devices in /dev/

How to Create a Device File

If, for some reason, a device file goes missing, you can create it manually using mknod. Example:

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sudo mknod /dev/mydevice c 180 0

This creates a character device with major number 180 and minor number 0.

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