Why can I move things to /dev/null despite it being a pseudo-device represented by a file?

I always thought of /dev/null as a black hole, in the way that all data I send there will not be echoed back. However there's a problem with that definition. According to Wikipedia:

/dev/null is a special file, not a directory, so one cannot move files into it with the Unix mv command.

So following this definition, why can I mv stuff there? For example, I can easily do:

# touch oi
# mv oi /dev/null

What's going on there?

Solution 1:

If you'll try to move anything to /dev/null under a plain user (not root), you will get a Permission denied error because mv something /dev/null is actually trying to delete /dev/null and then move something to what /dev/null was.

If you will try to do it under root, it will delete /dev/null (and then move the file provided by you in it's place)! You can restore it by rebooting or typing the following in a root shell (on Linux): mknod /dev/null c 1 3; chmod a+w /dev/null or in BSD: mknod /dev/null c 3 2; chmod a+w /dev/null.

Solution 2:

When you do this:

# mv oi /dev/null

You are actually doing the equivalent of the following

# rm /dev/null
# mv oi /dev/null