Install instructions for Linux package managers
sudo curl -fsSo /usr/share/keyrings/modctl-archive-keyring.gpg https://pkg.modctl.org/pubkey.gpg
sudo curl -fsSo /etc/apt/sources.list.d/modctl.sources https://pkg.modctl.org/apt/modctl.sources
sudo apt update && sudo apt install modctl
sudo rpm --import https://pkg.modctl.org/pubkey.asc
sudo curl -fsSo /etc/yum.repos.d/modctl.repo https://pkg.modctl.org/rpm/modctl.repo
sudo dnf install modctl
curl -fsS https://pkg.modctl.org/pubkey.asc | sudo pacman-key -a -
sudo pacman-key --lsign-key 2AF87031171950F11C460B5AEF5F1F6026B2C9C5
/etc/pacman.conf before [core][modctl] Server = https://pkg.modctl.org/arch/$arch SigLevel = Required DatabaseRequired
sudo pacman -Sy modctl
The signing key must be locally signed with --lsign-key because it is not in the Arch Linux keyring.