Unfortunately I changed my Ubuntu 18.04 sources.list. How can I restore sources.list file in my Ubuntu software?
I got these errors while editing sources.list:
$ sudo gedit /etc/apt/sources.list
** (gedit:3491): WARNING **: 10:51:37.148: Set document metadata failed: Setting attribute metadata::gedit-spell-language not supported
** (gedit:3491): WARNING **: 10:51:37.148: Set document metadata failed: Setting attribute metadata::gedit-encoding not supported
** (gedit:3491): WARNING **: 10:51:52.500: Set document metadata failed: Setting attribute metadata::gedit-position not supported
$ sudo apt-get upadate
E: Invalid operation upadate
