Testing HTTP/1.1 responses

Before changing DNS A records for a website, it’s prudent to check that the webserver with the IP address to which you’re going to change the records will actually serve a website with the relevant hostname; that is, if it’s an Apache HTTPD webserver, that it has a valid VirtualHost definition for the site.

If you don’t actually have administrative access to the webserver to check this, there are many basic ways to test it; from the command line, three of the most useful include using curl, wget, or plain old telnet. For each, the method comprises manipulating the HTTP/1.1 request of the target webserver such that the website you want to test is used as the hostname in the Host header.

Using curl

Perhaps the quickest and tidiest way to check this from a Unix command line is using curl, the binary frontend to the libcurl library. You do this by making an HTTP/1.1 request of the target server’s IP address, while including an explicitly specified value for the Host. This is done using the -H option:

$ curl -H "Host: sanctum.geek.nz"

This spits out quite a lot of information, including some on stderr, so you may choose to filter it and just check for the <title> tag, with a little bit of context, to make sure the site you expected really is being returned as the appropriate response:

$ !! 2>/dev/null | grep -C3 '<title>'
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width" />
<title>Arabesque | Systems, Tools, and Terminal Science</title>
<link rel="profile" href="http://gmpg.org/xfn/11" />
<link rel="stylesheet" type="text/css" media="all" href="https://sanctum...
<link rel="pingback" href="https://blog.sanctum.geek.nz/xmlrpc.php" />

Using wget

An equivalent to the curl method can be achieved using the --header option for the commonly available wget:

$ wget --header="Host: sanctum.geek.nz/arabesque" -q -O -

Using telnet

If you don’t have curl available, Telnet works just as well on both Windows and Unix-like systems, though it’s a little more awkward to work with, as you have to type the request and its headers straight into the TCP session:

$ telnet 80
Connected to
Escape character is '^]'.
GET / HTTP/1.1
Host: sanctum.geek.nz/arabesque

Note that you need to press Enter twice after writing in the hostname to check to complete the HTTP request. If this spits the HTML of your expected page back at you and closes the connection, then you’ve got some indication that things are configured correctly.

Yet another option to test this, particularly if you want to actually view the site in a browser, is to change your system’s hosts file to force DNS resolution to be different for the appropriate hostname on your local system.

Thanks to commenter Jaime Herazo for suggesting the wget method in the comments, and commenter sam for suggesting the -C option for grep.