systemctl status firewalld.service #查看firewall状态
systemctl stop firewalld #关闭
systemctl start firewalld #开启
systemctl disable firewalld #开机自动关闭
systemctl is-enabled firewalld.service #查看开机是否启动
systemctl enabled firewalld #开机自动启动
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了解下面命令：
systemctl #列出所有的系统服务
systemctl list-units #列出所有启动unit
systemctl list-units --type service #列出类型为.service的已经启动的unit
systemctl is-enabled sshd #查看ssh服务是否开机启动
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