How come hosts file redirection fails?

Question

I am trying to redirect google.com to my local machine for fun and learning with this /etc/hosts file on my Mac.

127.0.0.1 www.google.com

However, www.google.com still maps to the Google home page when I visit it in Chrome on my Mac. Why?

Basically, this is all I did:

1. Type sudo vim /etc/hosts in terminal.
2. Inputted 127.0.0.1 www.google.com into the hosts file.
3. Saved and quit vim.

Solution 1

The hosts file doesn't work this way. You can only use it to map an hostnames to IP addresses, not to localhost.

For your case you'd use 127.0.0.1 www.google.com, i.e. map www.google.com to 127.0.0.1.

If you want to map more hostnames to a singe IP, you just add those hostnames in the same line, e.g. 127.0.0.1 www.a.com www.b.com.

Solution 2

A web browser isn't the best way to check if your hosts syntax is correct. Try executing

ping www.google.com

and verify that it pings 127.0.0.1.

The reason why Chrome appears to ignore your hosts file is caching:

If Chrome has already queried the IP lately (the definition of lately most likely depends on the time to live (TTL) returned by the DNS server), it will bypass the hosts file, since it already knows the correct IP. This is done to speed up web browsing.

To make Chrome respect the new entry, do the follwing:

1. Edit /etc/hosts as @Renan described.

2. Go to chrome://chrome/settings/clearBrowserData.

3. Choose since the beginning of time.

4. Check Empty the cache, but uncheck everything else.

5. Click Clear browsing data and wait for it to finish.

6. Restart Chrome.

Chrome should respect your hosts file now.

Solution 3

My answer is a combination of the above because I am connecting to my office via Fortinet SSL VPN for Ubuntu 16.04.

The first thing I had to do is bring up my terminal console and run the following command:

sudo nano /etc/resolvconf/resolv.conf.d/base

I added the following example:

searchdomain domain.local
nameserver xxx.xxx.xxx.xxx
nameserver xxx.xxx.xxx.xxx

Then I saved the file by pressing CTRL-O and closed nano by pressing CTRL-X.

I then did the following and it worked perfectly:

To make Chrome respect the new entry, do the follwing:

Edit /etc/hosts as @Renan described.

1. Go to chrome://chrome/settings/clearBrowserData.
2. Choose since the beginning of time.
3. Check Empty the cache, but uncheck everything else.
4. Click Clear browsing data and wait for it to finish.
5. Restart Chrome.

Chrome should respect your hosts file now.

Comments

[David Faux]

Thank you. I just changed the /etc/hosts file on my Mac to 127.0.0.1 www.google.com. However, google.com still leads to the Google home page. Do I need to refresh anything? Should I restart my computer?

[Renan]

You shouldn't need to. Try adding 127.0.0.1 google.com (without the www) after this line and check whether it works.

[David Faux]

127.0.0.1 google.com isn't working either. I'm not sure what's going on ... I know that /etc/hosts is a soft link to /private/etc/hosts on a Mac, but I don't think that helps at all.

[Renan]

Does 127.0.0.1 www.example.com, then acessing www.example.com, works?

[David Faux]

No, example.com still oddly leads to iana.org/domains/example on my Mac with 127.0.0.1 www.example.com as my /etc/hosts file.

[Dennis]

A technicality: hosts maps hostnames to IP addresses, not vice versa.

[Synetech]

@Dennis, that’s what I was going to say, but then again, it really does work both ways when you think about it, because it creates an association between two items.

[Synetech]

I learned this a long time ago with IE6. If I made a change to the HOSTS file while IE was still open, I would have to specifically close it and run it again for it to pick up the changes. This goes for most programs. Some programs however (like versions of Chrome from the past year or two) will actually re-read the HOSTS file periodically, so if you make a change, just wait a minute or two, then refresh (no need to clear the cache). (This re-reading policy is handy sometimes like this, but usually pretty bad in reality since it is wasteful, and particularly bad if the HOSTS file is large.)

[Dennis]

@Synetech: Chrome picks up changes in hosts instantly, as long as the entry isn't a hostname that's already cached. I assume that it checks hosts only if the TTL has past. With big web sites, that can take a while.

[Synetech]

I don’t know the specifics about how different versions go about re-reading the HOSTS file, but you can use Filemon/ProcMon to see it in action; chrome.exe will occasionally read the entire file.

[hakunin]

There is a less brutal way of flushing chrome's DNS cache superuser.com/questions/203674/…

[Dennis]

@hakunin: Neat. On Chromium 25.0.1364.160 Ubuntu 12.04, this isn't even necessary anymore. I checked in net-internals/#dns, and the host cache gets cleared automatically when /etc/hosts is altered.