[Unit]
Description=Dropbear RSA Keygeneration.
After=syslog.target
Before=dropbear.service
ConditionPathExists=!/etc/dropbear/dropbear_rsa_host_key

[Service]
Type=oneshot
ExecStart=/usr/bin/dropbearkey -t rsa -f /etc/dropbear/dropbear_rsa_host_key
RemainAfterExit=yes