如何解决centos防火墙无法启动？
centos防火墙无法启动，在线服务器都需要开启防火墙服务，这是linux系统安全防护最直接有效方式。
1、如果出现 
service iptables start service iptables restart
无法启动/重启防火墙时。
2、最佳的方法是修改配置文件
vi /etc/sysconfig/iptables[plain] view plaincopy# firewall configuration written by system-config-firewall # manual customization of this file is not recommended. *filter :input accept [0:0] :forward accept [0:0] :output accept [0:0] -a input -m state --state established,related -j accept -a input -p icmp -j accept -a input -i lo -j accept -a input -m state --state new -m tcp -p tcp --dport 22 -j accept -a input -j reject --reject-with icmp-host-prohibited -a forward -j reject --reject-with icmp-host-prohibited commit
然后再启动防火墙
service iptables start
查看防火墙服务
service iptables status
3、如果需要开启例外端口则，增加如下配置：
vi /etc/sysconfig/iptables [plain] view plaincopy# firewall configuration written by system-config-firewall # manual customization of this file is not recommended. *filter :input accept [0:0] :forward accept [0:0] :output accept [0:0] -a input -m state --state established,related -j accept -a input -p icmp -j accept -a input -i lo -j accept -a input -m state --state new -m tcp -p tcp --dport 22 -j accept -a input -m state --state new -m tcp -p tcp --dport 3306 -j accept -a input -j reject --reject-with icmp-host-prohibited -a forward -j reject --reject-with icmp-host-prohibited commit
如上，增加了3306服务端口
如果需要关闭防火墙自动启动则
查看状态
chkconfig --list iptables

关闭自动启动
chkconfig iptables off
查看状态
chkconfig --list iptables

相关参考：centos教程
以上就是如何解决centos防火墙无法启动的详细内容。