How to untrack a already tracked file in Git ?

git.sh

[arup@TeraDial (issue_40)]$ gvim
[arup@TeraDial (issue_40)]$ git status
# On branch issue_40
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#       modified:   .gitignore
#       modified:   Gemfile
#       modified:   config/database.yml
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#       .ruby-gemset
#       config/database.yml.example
no changes added to commit (use "git add" and/or "git commit -a")
[arup@TeraDial (issue_40)]$

Use the command

git rm --cached config/database.yml