Apt update

apt update
Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease
Hit:2 http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:3 http://archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit:4 http://archive.ubuntu.com/ubuntu bionic-security InRelease
Get:5 https://download.docker.com/linux/ubuntu bionic InRelease [64.4 kB]
Fetched 64.4 kB in 2s (34.2 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
98 packages can be upgraded. Run 'apt list --upgradable' to see them.

apt update
.../...
Reading package lists... Done
W: GPG error: http://downloads.linux.hpe.com/SDR/repo/mcp focal/current Release: The following signatures couldn't be verified because the public key is not available: 
NO_PUBKEY C208ADDE26C2B797
E: The repository 'http://downloads.linux.hpe.com/SDR/repo/mcp focal/current Release' 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.

Solution:

• A) sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys C208ADDE26C2B797
• B) deb [trusted=yes] http://www.your_not_trustedcert.org jessie main

apt update NO_PACKAGE_AS_ARGUMENT
E: The update command takes no arguments

Related terms

• apt update -y && apt upgrade -y
• apt-file
• /etc/apt/sources.list
• brew update

See also

• APT: wajig, apt-cache, add-apt-repository PPA, apt [ install | remove |purge | show | list | changelog | update | upgrade], do-release-upgrade, apt-mark, apt full-upgrade, sources.list, APT Automatic updates, unattended-upgrade, apt-transport-https, apt-get update, /etc/apt/, /etc/apt/apt.conf.d/50unattended-upgrades, /etc/apt/apt.conf.d/, /etc/apt/apt.conf.d/20auto-upgrades, apt-file, apt-utils