Why do Ethernet devices not show up in "/dev"?

Question

Generally I have noticed that plugging in a new device in a Linux system causes a new entry to be listed in /dev (assuming you have the correct drivers).

For example:

1. When you plug in a new hard drive you get /dev/sdb.
2. When you plug in a serial device you get /dev/ttyS0.

When I plug in an Ethernet device, why don't I get something like /dev/eth0?

Is there a device listing for Ethernet ports?

I know you can see port names using ifconfig, I am just wondering if something shows up in /dev too.

Answer 1

It's a good question. The reason is essentially historical; different groups with different goals and priorities added pieces of Unix over time, and the differences among various APIs are a reflection of this history. I think the original device file concept goes back to Bell Labs, whereas network sockets were added later at UC Berkeley. Bell was trying to create a nice clean maintainable paradigm for AT&T's operations, whereas Berkeley needed to add internet features that didn't fit easily into that paradigm. Technically it would be possible to go back and create a /dev/eth0 file today (see below), but it would involve rewriting a prohibitive amount of legacy code.

Slight OT: If the subject interests you, consider taking a look at Plan 9, which took "everything is a file" to greater extremes (just don't expect it to have very many modern, usable applications):

http://www.faqs.org/docs/artu/plan9.html

many facilities that under Unix are accessed through various ad-hoc interfaces like BSD sockets, fcntl(2), and ioctl(2) are in Plan 9 accessed through ordinary read and write operations on special files analogous to device files

Answer 2

Hello nowadays the /dev directory is populated by udev, a daemon that reads the /sys directory, and create those files. If you want to use fdisk and gdisk, you are forced to use devices found in /dev. And to see the the tty and pty used. I think BSD allocates an ethernet interface in /dev, where you can write and read to.

Answer 3

Not so long ago Ethernet devices did appear as /dev/eth0, /dev/eth1 and so on. There are still applications that expect to find them there, but are now disappointed and sometimes unusable. Fortunately not too many.