I try to install mongo using mongo documentation: Install MongoDB on Ubuntu no errors were mentioned during the installation. But when I run the mongo command following error was displayed in the terminal.
Failed global initialization: BadValue Invalid or no user locale set. Please ensure LANG and/or LC_* environment variables are set correctly
Looks like your locale settings are broken or non-existent on that VM, or at least that session on that VM. One of MongoDB's dependencies (boost) will fail when a locale is not correctly set (see SERVER-9032). For reference, before the change in SERVER-9032 this problem still happened but looked like this.
Sometimes logging out and back in can fix it (only broken for current session), or you can try running sudo locale-gen to make sure generation is successful.
In the meantime, as a workaround to get mongo (or mongod etc.) running, just set your LC_ALL variable manually before starting the program:
export LC_ALL=C
mongo
