Unable to install pkg:s
We observed this issue at some schools running 10.11 where entire labs would get the "restricted" attribute mistakenly set on /private/tmp. If that's the issue, you can fix it by doing the following:


Reboot the computer and then hold down Command-R after the chime.
Choose "Terminal" from the Utilities menu.
Run csrutil disable
Restart the computer again.
Open Terminal and run the following commands: 

sudo chmod 1777 /tmp;
sudo chflags -R norestricted /private/tmp/;

Re-enable System Integrity Protection by rebooting the computer, holding down Command-R, choosing Utilities > Terminal, and running csrutil enable
Reboot the computer a final time.