• Using `nano` command

sudo nano <filename>

After that click `Ctrl + X`, then press `Y` or `N` to accept change and `Enter` to finish.

• Using `vim` command

sudo vim <filename>

Press `i` to switch insert mode and modify. Once you have done, click `Esc` and write `:wq` to save and exist.

• Using Emacs

sudo emacs <filename>

Press `Ctrl + Space` to switch insert mode and conduct to modify content. Then, press `Ctrl + X`, `Ctrl + S` to save and exist.