problem description
to use impression notes in Ubuntu18.04, install client everpad under linux
via ppa:
sudo add-apt-repository ppa:nvbn-rm/ppa
sudo apt-get update
the platform version of the problem and what methods you have tried
prompt that there is no published file when executing sudo add-apt-repository ppa:nvbn-rm/ppa
related codes
Hit:1 http://archive.ubuntukylin.com:10006/ubuntukylin xenial InRelease
Ign:2 http://dl.google.com/linux/ch. stable InRelease
Hit:3 http://dl.google.com/linux/ch. stable Release
Get:5 http://security.ubuntu.com/ub. bionic-security InRelease [83.2 kB]
Hit:6 http://cn.archive .ubuntu.com /. bionic InRelease
Ign:7 http://cn.archive.ubuntu.com/. Bionic-updates InRelease
Err:9 http://cn.archive.ubuntu.com/. . bionic-backports InRelease
Reading package lists. Done
E: The repository "http://ppa.launchpad.net/nvbn-rm/ppa/ubuntu bionic Release" does not 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.