Could not get lock - ubuntu

I encountered some problems when I ran some apt-get in ubuntu then stopping it by pressing ctrl+z, and run some other apt-get command again, then suddenly the CLI throws - Could not get lock . . . . . . etc

I think there are many cases on how you get that "could not get lock..". What I did in mine is, run this in the CLI without the double quotes "killall -9 apt-get" and run apt-get again.