true enlightenment: everything is a string over an IO socket

7. Everything is a FIFO

/dev/null sez nothing is also a file

Unfortunately, no one can be told what a file is. You have to see it for yourself.

This is your last chance. After this, there is no turning back. You take the blue pill - the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill - you stay in Wonderland and I show you how deep the file system goes.

Am I a file?

"How can files be real if the filesystem isn't real?" - Jaden Smith (probably)

You'll know you've reached stage 6 when you seriously start considering running Plan 9 as a daily driver

Missing stage 7: Not everything is a file.

Linux is closer than other *nixes (sysctl equivalents in some platforms are not files, but they are files in Linux).

However get very far into network and the file-like behaviors become more limited. From an application, at least you have a decent chance of having unseekable, but otherwise 'file-like' interaction with stream protocols. Then you need recvmsg/sendmsg. Then you want to deal with low level interaction with the network stack and dealing with NETLINK and such..

Files? In my Linux?

It's more likely than you think.

And the hidden 0th level that you only get after being nearly killed by a falling server rack:

"Files Aren't Things"

Which looks great on a tshirt, btw :p

Okay, but what are blocks then? A file is really just a bunch of blocked stacked together with the inode metadata also sitting on another block, so is everything just blocks or because you can emulate a block device on a filesystem, are blocks themselves files? If that last part is true then files are infinitely recursive and my head is starting to spin.

The troubles between stage 2 and 6 are probably realizing dirs are not files, and seeing that device and driver files are different things from data files. Then stage 6 would be realizing that filesystems themselves just sit on device files. The directories and data files are in the device files. In truth, everything is a device file.

But then, I propose a stage 7. Because when you trace it all back, with mounts pointing to device files sitting in mounted file systems, you see that /dev is a tempfs, mounted in a tempfs, in which device files are "mounted". The fondamental root, /, is underneath the root filesystem a tempfs too. At boot, the kernel makes a tempfs, and later overlays the rootfs mounted from the /dev mounted in the root tempfs.
Everything is a filesystem, ever,thing is mounted. The true files, device files, are mounted too. They are the mounting of a kernel module in the same way a directory - a filesystem - is a mounted kernel module.
The Linux world is a ying and yang between dir structures and mounted kernel modules. In all of this, data files, the "true files", don't even show up. At the end, it's just the kernel talking to itself.