Updating a Debian 9 I get this error with the “grafana” update:
$ apt update ... Ign:7 stretch InRelease Err:9 stretch Release 404 Not Found Reading package lists... Done E: The repository 'https://packagecloud.io/grafana/stable/debian stretch Release' does no longer have a Release file. 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. ...
To solve this problem you can follow the next steps.
First, install the “software-properties-common” library:
$ sudo apt-get install -y software-properties-common
Install the repository for stable releases:
$ sudo add-apt-repository "deb stable main"
Add the gpg key:
$ sudo wget -q -O - https://packages.grafana.com/gpg.key | apt-key add -
Remove the old repository file:
$ sudo rm /etc/apt/sources.list.d/grafana_stable.list
Now you can update the repo correctly:
$ sudo apt update