Why can I move things to /dev/null despite it being a pseudo-device represented by a file?
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
.
When you do this:
# mv oi /dev/null
You are actually doing the equivalent of the following
# rm /dev/null
# mv oi /dev/null
You can't
# uname -sr
Linux 2.6.32-ARCH
# touch a
# mv a /dev/null
mv: inter-device move failed: `a' to `/dev/null'; unable to remove target: Permission denied