[Unit]
Description=SSH RSA Keygeneration.
After=syslog.target
Before=sshd.service
ConditionPathExists=!/etc/ssh/ssh_host_rsa_key

[Service]
Type=oneshot
ExecStart=/usr/bin/ssh-keygen -q -t rsa -f /etc/ssh/ssh_host_rsa_key -C '' -N ''
RemainAfterExit=yes