If Macintosh HD IS your system folder, you should have made a mistake because '/Macintosh HD/tmp' = '/tmp' and Mac OS creates a link by default to /private/tmp from /tmp.
So if you did the three command lines I wrote, it should have done this :
1. copy the private/tmp folder into the link /tmp (which is a link to private/tmp folder); so it has copied all the private/tmp folder into itself.
2. you have removed the private/tmp folder
3. you have linked private/tmp to /tmp which is now a link to an unexisting file...
So that cannot work because Mac OS is unable to find any tmp folder...
Now you should add the initial /private/tmp folder and add a link to it from /tmp like this :
sudo mkdir /private/tmp
sudo ln -s /private/tmp /tmp
That should resolve your problem.