Unable to install pkg:s I'm getting errors installing any pkg files. Seems to be valid for all pkgs, I uninstalled one app and run the pkg installer which fails for an app that was successfully installed 2 weeks ago. I'm guessing something related to permissions but I can't figure out what would have changed them... I'm on 10.11.6 and upgrading is currently not an option.  

The common issue seems to be:

Oct 20 20:08:16 Js-MBP installd[396]: PackageKit: Install Failed: Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted" UserInfo={NSFilePath=/private/tmp/PKInstallSandbox.XXXXXX} {
    NSFilePath = "/private/tmp/PKInstallSandbox.XXXXXX";
}


More complete logs: 

Oct 20 20:16:39 Js-MBP Installer[5195]: Configuring volume "Macintosh HD"
Oct 20 20:16:39 Js-MBP Installer[5195]: Free space on "Macintosh HD": 456,46 GB (456459907072 bytes).
Oct 20 20:16:39 Js-MBP Installer[5195]: Create temporary directory "/var/folders/c7/d1ppw5612z55mkslhqhqjyc00000gn/T//Install.51955utsOk"
Oct 20 20:16:39 Js-MBP Installer[5195]: IFPKInstallElement (1 packages)
Oct 20 20:16:39 Js-MBP Installer[5195]: PackageKit: Enqueuing install with framework-specified quality of service (utility)
Oct 20 20:16:39 Js-MBP installd[396]: PackageKit: ----- Begin install -----
Oct 20 20:16:52 Js-MBP installd[396]: PackageKit: Install Failed: Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted" UserInfo={NSFilePath=/private/tmp/PKInstallSandbox.XXXXXX} {
    NSFilePath = "/private/tmp/PKInstallSandbox.XXXXXX";
}
Oct 20 20:16:53 Js-MBP Installer[5195]: Install failed: The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
Oct 20 20:16:53 Js-MBP Installer[5195]: IFDInstallController 5A94F9E0 state = 8
Oct 20 20:16:53 Js-MBP Installer[5195]: Displaying 'Install Failed' UI.
Oct 20 20:16:53 Js-MBP Installer[5195]: 'Install Failed' UI displayed message:'The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.'.


Been struggling for a while to figure this out, any help is appreciated. Would really like not to have to do a clean install (setting up a new user does not help, tried that).
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.