Installing RVM: getting error "There was an error(23)."
Your RVM is installed in /usr/local/rvm - it's often called system installation, this requires that your user ubuntu will be added to rvm group:
rvm group add rvm "$USER"
yes use $USER it will be replaced by your shell with your user name
then log out and log in, ensure with:
id
that your user is in rvm group,
finally just in case update permissions for RVM:
rvm fix-permissions