How to get back hosts file after accidental deletion

Question

I made a mistake and accidentally deleted hosts file from my system and cannot figure out how to get back my hosts (/etc/) file, when I do

sudo service apache2 restart

It's showing:

sudo: unable to resolve host SystemName.

I am using Ubuntu 14.04 LTS. I tried editing the hosts file sudo vi hosts and put:

127.0.0.1       localhost
::1             localhost ip6-localhost ip6-loopback
fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

But to no avail.

Answer 1

Seems like the issue is resolving the actual hostname of the machine you are on. Check your hostname by running the hostname command like this:

hostname

Or like this:

cat /etc/hostname

And let’s say your hostname is SystemName. Then you would have to add a line to your /etc/hosts file like this:

127.0.0.1       SystemName

So the whole /etc/hosts file would look like this:

127.0.0.1       localhost
127.0.0.1       SystemName
::1             localhost ip6-localhost ip6-loopback
fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

You could also consolidate those 127.0.0.1 entries like this:

127.0.0.1       localhost SystemName

Then the final /etc/hosts file would look like this:

127.0.0.1       localhost SystemName
::1             localhost ip6-localhost ip6-loopback
fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters