systemctl status firewalld.service #查看firewall狀態
systemctl stop firewalld #關閉
systemctl start firewalld #開啟
systemctl disable firewalld #開機自動關閉
systemctl is-enabled firewalld.service #查看開機是否啟動
systemctl enabled firewalld #開機自動啟動
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了解下面命令：
systemctl #列出所有的系統服務
systemctl list-units #列出所有啟動unit
systemctl list-units --type service #列出類型為.service的已經啟動的unit
systemctl is-enabled sshd #查看ssh服務是否開機啟動
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