openSUSE-build-key from devel:microos:systemd-boot project
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Add repository and install manually
For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:microos:systemd-boot/openSUSE_Tumbleweed/devel:microos:systemd-boot.repo zypper refresh zypper install openSUSE-build-key