/dev/null questions

so I was messing around with /dev/null mooving files to it like ...

sudo mv test /dev/null

and reading it ...

:~$ cat /dev/null
this is a file
:~$ 

but then I made another file with the file saying this is another fileand then I went a head and read /dev/null again before moving the new file to /dev/null by doing cat and this is what happened

:~$ cat /dev/null
:~$ 

can someone please explain to Me what is happening I'm on ubuntu 18.04.

thanks.

1 Answer

From man null:

NAME null, zero - data sink
DESCRIPTION Data written to the /dev/null and /dev/zero special files is discarded. Reads from /dev/null always return end of file (i.e., read(2) returns 0), whereas reads from /dev/zero always return bytes containing zero ('\0' characters). These devices are typically created by: mknod -m 666 /dev/null c 1 3 mknod -m 666 /dev/zero c 1 5 chown root:root /dev/null /dev/zero
FILES /dev/null /dev/zero
NOTES If these devices are not writable and readable for all users, many programs will act strangely. Since Linux 2.6.31, reads from /dev/zero are interruptible by signals. (This change was made to help with bad latencies for large reads from /dev/zero.)
SEE ALSO chown(1), mknod(1), full(4)