cent7 /usr/lib/systemd/system/
systemctl enable crond.service #讓某服務開機啟動
systemctl disable crond.service #不開機啟動
systemctl status crond.service #查看服務狀態
systemctl start crond.service #啟動某服務
systemctl stop crond.service #停止某服務
systemctl restart crond.service #重啟某服務
systemctl is-enabled crond #查看某服務是否開機啟
