[Unit]
Description=OpenSSH Server Key Generation
ConditionPathExists=|!/etc/ssh/ssh_host_rsa_key
ConditionPathExists=|!/etc/ssh/ssh_host_ecdsa_key
ConditionPathExists=|!/etc/ssh/ssh_host_ed25519_key
PartOf=sshd.service sshd.socket

[Service]
ExecStart=/usr/sbin/sshd-keygen
Type=oneshot
RemainAfterExit=yes