void-packages/srcpkgs/openssh/files/sshdgenkeys.service

[Unit]
Description=OpenSSH server Key Generation
ConditionPathExists=|!/etc/ssh/ssh_host_dsa_key
ConditionPathExists=|!/etc/ssh/ssh_host_dsa_key.pub
ConditionPathExists=|!/etc/ssh/ssh_host_ecdsa_key
ConditionPathExists=|!/etc/ssh/ssh_host_ecdsa_key.pub
ConditionPathExists=|!/etc/ssh/ssh_host_ed25519_key
ConditionPathExists=|!/etc/ssh/ssh_host_ed25519_key.pub
ConditionPathExists=|!/etc/ssh/ssh_host_key
ConditionPathExists=|!/etc/ssh/ssh_host_key.pub
ConditionPathExists=|!/etc/ssh/ssh_host_rsa_key
ConditionPathExists=|!/etc/ssh/ssh_host_rsa_key.pub

[Service]
Type=oneshot
ExecStart=/usr/bin/ssh-keygen -A
RemainAfterExit=yes