How to fix the "E: The repository 'xy jessie InRelease' is not signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details." error

How to fix the "E: The repository 'xy jessie InRelease' is not signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details." error:

nano /etc/apt/sources.list.d/raspi.list

nano /etc/apt/sources.list


To failing repositories add [trusted=yes], e.g. deb [trusted=yes] http://raspbian.raspberrypi.org/raspbian/ stretch main