Tokyo - Can't serve web file

#bash #curl #ping #ss #iptables #chmod
Type: Fix
Description: There's a web server serving a file /var/www/html/index.html with content "hello sadserver" but when we try to check it locally with an HTTP client like curl 127.0.0.1:80, nothing is returned. This scenario is not about the particular web server configuration and you only need to have general knowledge about how web servers work.

Test: curl 127.0.0.1:80 should return: hello sadserver.

Notes and solution:

First, we try to make a HTTP request to the server.

curl 127.0.0.1:80

It doesn't give any response. To troubleshoot the connection, we can try to reach the host with the command ping.

ping -c 5 127.0.0.1

There is an established connection to the server.

Now, we have to make sure that the port is actually listening. We can test this with the command ss.

ss -l src :80

Where the -l lists all the listening sockets and src :80 filters only the port number 80.

if the port is listening and the connection with the server is established, maybe something is blocking the port connection.

To check this, we'll print the IP rules to see if something related to the HTTP request is blocked using iptables.

iptables -S

As we can see, the traffic entering from port 80 is being blocked by the IP rules.

To fix this, we'll have to override this rule so it accepts requests from that port.

iptables -R INPUT 1 -p tcp -m tcp --dport 80 -j ACCEPT

With this command we are Rewriting the rule so it ACCEPTS the requests coming from port 80.

We try again to make the request.

This time, we get a different error; but it seems that now it has to do with something related to permissions.

To troubleshoot this, we have to read the error log files from Apache, this log file it's located in the /var/log/apache2/error.log text file.

cat /var/log/apache2/error.log

The "file permissions deny server access: /var/www/html/index.html" tells us that Apache doesn't have the permissions necessary to read that file.

To check this, we'll look up the Apache's permissions regarding index.html.

ls -l /var/www/html/index.html

As we can see, only the owner root can read or write this file.

To fix this, we'll also give other users the capability of reading that file.

sudo chmod o+r /var/www/html/index.html

Now, we should get a response from the server.

Success!