Test website via local DNS resolver

The following help center article describes how you can easily test websites on a server on the Internet without having to make any adjustments to the DNS.

Requirements

Linux, macOS, Windows
Administrator authorization

General explanation

All common operating systems have a hosts file in which a simple mapping of IPv4 or IPv6 addresses to a FQDN (Fully Qualified Domain Name) can be stored for name resolution.

The syntax is the same for all operating systems, but the file is located at different positions in the file system depending on the operating system.

As soon as your system attempts to resolve a domain name to an IP address, it first checks the hosts file to see whether entries for the domain are stored there; if not, it sends the request to the configured DNS server as usual.

Remember to remove the changes after your tests to avoid unwanted side effects during DNS name resolution.

Please note that certificate error messages may occur if the web server with the IP address stored in /etc/hosts does not have a valid certificate for the domain you have specified.

Syntax

The file consists of pairs of IPv4 or IPv6 addresses and domain names as in the following example:

# Comment

# <ipv-4-address> <FQDN>
# <ipv-6-address> <FQDN>

1.2.3.4 staging-test.mydomain.com
2001:db8:1234:5678::1 staging-test.meinedomain.de

1.2.3.4 mydomain.com
2001:db8:1234:5678::1 meinedomain.de

In the above example, when staging-test.mydomain.com is called using IPv4, it resolves to 1.2.3.4 and with IPv6 to 2001:db8:1234:5678::1, although the DNS servers would resolve a different IP address. The same applies to the main domain meinedomain.de.

Linux and macOS

Under Linux and macOS, the file is located under /etc/hosts and can be edited in any standard editor such as nano.

Manipulating /etc/hosts requires root authorization, which is why the command usually has to be executed with sudo on clients.

sudo nano /etc/hosts

Windows

Windows manages the file under the path C:\Windows\System32\drivers\etc\hosts, which also requires administrator authorization to edit.

The following example opens the file for editing with the Windows Notepad editor.

\nCMD (administrator password must be entered manually):

runas /user:Administrator "notepad C:\path\to\file.txt"
Enter the password for Administrator:

PowerShell (UAC authorization, GUI-based yes/no):

Start-Process notepad.exe -ArgumentList "C:\Windows\System32\drivers\etc\hosts" -Verb RunAs

Frequent error messages

Expected web page is not loaded

If you believe that you are not accessing the correct website, it is possible that your local DNS cache still contains the original IP address (before customization), which means that the DNS query is not performed via /etc/hosts or via your configured DNS server.

Clearing the DNS cache on your client system is a possible solution here, which can be done as follows:

Windows

Open PowerShell or CMD:

ipconfig /flushdns

macOS

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

Linux

NetworkManager:

sudo nmcli general reload dns-full

Systemd resolver:

 sudo systemd-resolve --flush-caches

 sudo resolvectl flush-caches

Dnsmasq:

sudo systemctl restart dnsmasq