例如
journalctl -u prometheus-webhook-dingtalk -n 20 --no-pager
journalctl -u prometheus-webhook-dingtalk -n 20 --no-pager --since today
journalctl -u prometheus-webhook-dingtalk -n 20 --no-pager --since "2020-08-26 05:25" --until "2020-08-26 05:30"
journalctl -u prometheus-webhook-dingtalk -n 20 --no-pager --since "5 minutes ago"
journalctl -u prometheus-webhook-dingtalk -n 20 --no-pager --since "2 hours ago"
-u是--unit的缩写
-n是行数，默认是10行
--no-pager 改为正常的标准输出