In Ubuntu 18.04, gksu
package is removed.
But some packages are need gksu package that was created before 18.04. In this case, this package can be alternative 'gksu' package.
This package just make symbolic link to forward arguments to polkit.
sudo add-apt-repository ppa:woowahan-jaehoon/gksu-alternative
sudo apt-get update
PPA: https://launchpad.net/~woowahan-jaehoon/+archive/ubuntu/gksu-alternative