[Unit]
Description=SSH RSA1 Keygeneration.
After=syslog.target
Before=sshd.service
ConditionPathExists=!/etc/ssh/ssh_host_key

[Service]
Type=oneshot
ExecStart=/usr/bin/ssh-keygen -q -t rsa1 -f /etc/ssh/ssh_host_key -C '' -N ''
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target