Data written on a null or zero special file is discarded.
Reads from the null special file always return end of
file, whereas reads from zero always return \0 characters.
null and zero are typically created by:
mknod -m 666 /dev/null c 1 3
mknod -m 666 /dev/zero c 1 5
chown root:mem /dev/null /dev/zero
If these devices are not writable and readable for all
users, many programs will act strange.
Linux 1992-11-21 NULL(4)