前两天重启服务器之后发现 fail2ban 启动失败，出现如下错误：
/etc/init.d/fail2ban restart
[....] Restarting fail2ban (via systemctl): fail2ban.service
Job for fail2ban.service failed because the control process exited with error code. See "systemctl status fail2ban.service" and "journalctl -xe" for details.
failed!
检查日志
journalctl -xe
查看具体错误
/usr/bin/fail2ban-client -v -v start
看到结果：
fail2ban.service: Failed with result 'start-limit-hit'.
具体错误一目了然。其实重要的就是 Debug 的内容。