强制重启了下，结果就发现 iptables 用不了了，提示
[root ~]# systemctl restart iptables.service
Job for iptables.service failed because the control process exited with error code. See "systemctl status iptables.service" and "journalctl -xe" for details.
[root ~]# systemctl status iptables.service
● iptables.service - IPv4 firewall with iptables
Loaded: loaded (/usr/lib/systemd/system/iptables.service; disabled; vendor preset: disabled)
Active: failed (Result: exit-code) since Fri 2016-05-20 06:32:09 UTC; 14s ago
Process: 23631 ExecStart=/usr/libexec/iptables/iptables.init start (code=exited, status=1/FAILURE)
Main PID: 23631 (code=exited, status=1/FAILURE)

May 20 06:32:09 vultr.guest systemd[1]: Starting IPv4 firewall with iptables...
May 20 06:32:09 vultr.guest iptables.init[23631]: iptables: Applying firewall rules: iptables-restore v1.4.21: iptables-restore: unable to initialize table 'filter'
May 20 06:32:09 vultr.guest iptables.init[23631]: Error occurred at line: 4
May 20 06:32:09 vultr.guest iptables.init[23631]: Try `iptables-restore -h' or 'iptables-restore --help' for more information.
May 20 06:32:09 vultr.guest iptables.init[23631]: [FAILED]
May 20 06:32:09 vultr.guest systemd[1]: iptables.service: main process exited, code=exited, status=1/FAILURE
May 20 06:32:09 vultr.guest systemd[1]: Failed to start IPv4 firewall with iptables.
May 20 06:32:09 vultr.guest systemd[1]: Unit iptables.service entered failed state.
May 20 06:32:09 vultr.guest systemd[1]: iptables.service failed.

重装了 iptables 还是不行。
试试这个 http://www.kwx.gd/CentOSApp/iptables-unable-filter.html

都 centos7 了，直接用 firewall 呗，干嘛还用 iptables