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+# Listen The 443 Port
+
+When I was debugging, I closed the process that occupied port 443 according to the online tutorial which said the `wss` service have to use port 443. Then it cause error when accessing file on my server. I have to say I can easily access the file before.
+
+### Check the 443 port
+
+On another computer terminal
+
+`telnet xxx.xx.xx.xx 443`
+
+Found that port 443 is unreachable.
+
+### Check the server security group
+
+Find the security group under the list of cloud servers, open the 443 channel in the inbound direction.
+
+### Check the firewall
+
+Ubuntu comes with a much simpler firewall configuration tool than iptables in its distribution: `ufw`
+
+`apt-get install ufw`
+
+Use ufw to open port 443
+
+`ufw allow 443`
+
+Now port 443 can be talented, but there is nothing under `netstat -antp | grep 443`, According to common sense, information containing `0.0.0.0:443` should be displayed, which means this port is being monitored.
+
+### Check apache configuration
+
+Now the 443 port is opened but still not being listened. Check the apache configuration files under `/etc/apache2/sites-available`, I found `Listen 443` in file. And I configured apache by [Certbot](https://certbot.eff.org/), the configuration had no problem.
+
+### Violent resolution
+
+I had no choice
+
+`sudo /etc/init.d/apache2 restart`
+
+Then 
+
+`sudo Isof -iTCP -sTCP:LISTEN -P`
+
+I saw `apache2 9785 www-data 4u IPv4 448556 0t0 TCP *:443 (LISTEN)`
+
+Problem solved～
+