修改全局环境变量（）：

vim /etc/vim/vimrc

添加如下配置（推荐）

set tabstop=4

set shiftwidth=4

set softtabstop=4

set expandtab

释义：

set tabstop=4 " The width of a TAB is set to 4.

                    " Still it is a \t. It is just that

                    " Vim will interpret it to be having

                    " a width of 4.

set shiftwidth=4    " Indents will have a width of 4

set softtabstop=4  " Sets the number of columns for a TAB

set expandtab      " Expand TABs to spaces

cited from https://stackoverflow.com/questions/1878974/redefine-tab-as-4-spaces