Why kill -9 -1 doesn't work?

Question

From man kill:

kill -9 -1

      Kill all processes you can kill.

But when I do sudo /bin/kill -9 -1 nothing happens.

My uname -a for info:

Linux michal-Q530 3.16.0-45-generic #60~14.04.1-Ubuntu SMP Fri Jul 24 21:16:23 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

And I'm on Lubuntu.

UPDATE:

$ ps -e | wc -l
169
$ sudo /bin/kill -9 -1
$ ps -e | wc -l
169

Answer 1

Finally solved by using this:

sudo /bin/kill -9 -- -1

If the first PID is negative, it has to be preceded by -- so it's not interpreted as an option.

So the real behavior of /bin/kill is distinct from the behavior described in the man page.