Error message 'sudo: unable to resolve host <USER>'

Question

I have this issue on AWS on some servers. Whenever I run sudo the terminal is stuck doing seemingly nothing, until it finally spits out this error message. My terminal looks like this:

ubuntu@(none):~$ sudo true
sudo: unable to resolve host (none)

What can I do to solve it?

Answer 1

Two things to check (assuming your machine is called my-machine, you can change this as appropriate):

1. That the /etc/hostname file contains just the name of the machine.

2. That /etc/hosts has an entry for localhost. It should have something like:

    127.0.0.1    localhost.localdomain localhost
    127.0.1.1    my-machine
   

If either of these files aren't correct (since you can't sudo), you may have to reboot the machine into recovery mode and make the modifications, then reboot to your usual environment.

Answer 2

Edit /etc/hosts and append your new hostname to the 127.0.0.1 line (or create a new line if you prefer that).

Mine looks like:

127.0.0.1       localhost localhost.localdomain penguin

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

Replace penguin in the above example by your new hostname as stated in the /etc/hostname file.

Answer 3

Note, this is an answer to this question which has been merged with this one.

Your hostname (dave00-G31M-ES2L) is not represented in /etc/hosts. Add an L to this line:

127.0.1.1   dave00-G31M-ES2

So it becomes:

127.0.1.1   dave00-G31M-ES2L

In order to accomplish this, open a console (press Ctrl+Alt+T) and type:

sudo gedit /etc/hosts

Add the letter L as mentioned, save and exit.

Answer 4

Add your hostname to /etc/hosts like so:

echo $(hostname -I | cut -d\  -f1) $(hostname) | sudo tee -a /etc/hosts

Answer 5

I had this issue when I was using ubuntu on a VPS. I solved it editing /etc/hosts file.

run this command:

sudo nano /etc/hosts

and then add:

127.0.0.1   localhost.localdomain localhost
127.0.1.1   ubuntu

I hope that will solve your issue :)

PS: Remember to reboot your computer!

Answer 6

I was having the same issue even though the hostname in my /etc/hostname file and /etc/hosts file matched.

My hostname was "staging_1". It turns out that you can't have an underscore in your hostname, which is why I was getting this error. Changing the underscore to a hyphen fixed my problem.

Answer 7

In AWS, go to your vpc and turn on "DNS Hostnames".

Answer 8

In my case it was the problem, I changed the hostname to man because I wanted to know if there are some parameters you can use on hostname. Instead it changed my hostname to man and I always got the same message like you

sudo: unable to resolve host (none)

after changing the hostname back to `localhost everything worked fine again

hostname localhost

Answer 9

I encountered this same error message. I think this discussion thread at AWS Developer Forums is a better solution:

"Go the the VPC management console, select the VPC, click on Actions, select Edit DNS Hostnames and select Yes."

https://forums.aws.amazon.com/thread.jspa?messageID=699718

Answer 10

Some terminal emulators will not update prompt with the correct hostname until you close and restart the emulator (lxterminal, I'm talking to you).

I spent 30min fighting with this error after editing my hostname and hosts files and running sudo service hostname restart until I ran sudo hostname and saw that the hostname was the new value, even though the prompt was showning the old value.

Answer 11

Sorry I can't help you much but, since it says "can't resolve host" try running:

hostname

And see if the output is the hostname of the machine. If not, the problem is the host configuration, not sudo.

Answer 12

OP wrote:

It was all in /etc/hostname. On two of our sick servers it looked like this:

ubuntu@(none):~$ cat /etc/hostname
linux-web-n ip-10-128-##-##

While on a server without this issue we had:

ubuntu@ip-10-128-##-###:~$ cat /etc/hostname
ip-10-128-##-###

Removed the linux-web-n portion, rebooted and everything was fine.

Answer 13

The symptom given in the question may correlate strongly with this more specific problem:

$ hostname --fqdn
hostname: Temporary failure in name resolution

There are different ways that this could be resolved, one of which is to add your hostname as localhost in /etc/hosts (as shown in several other answers). This may be the right thing to do in general, but it isn't the only possible resolution.

A "fully qualified domain name" may be supplied by an external DNS server or similar (if such is available on your network). In this case, sudo will not complain, despite the missing entry in /etc/hosts.

---

Note: sudo attempts to dereference the hostname, even though it isn't necessarily required, due to optional capabilities in the sudoers file. See sudo command trying to search for hostname.

As long as the delay isn't too long, this error message is typically harmless.

Answer 14

you might be getting an error if your hosts or hostname file contain illegal characters. Only these symbols are permitted: a-z, A-Z, 0-9

Answer 15

I had the same problem. I solved it by editing the /etc/hosts and /etc/hostname files... on the /etc/hosts file, just edit the top part as shown below.

#vi /etc/hosts
    127.0.0.1   localhost
    127.0.1.1   localhost  myhostname




#vi /etc/hostname
    myhostname

Answer 16

if you can't sudo you CAN log in as root via su. IE: su root (in an x-term). then give the root password when prompted, then you can edit the files with nano. The root password in 'buntu is the same as the password you would use for sudo.

Answer 17

I had this same problem! I changed my VPS's name through the online admin control panel which did not change the machine name in the hosts file All I did was run:

sudo nano /etc/hosts

Then I edited it from this:

127.0.1.1 Megabyte Megabyte
127.0.0.1 localhost

To this:

127.0.1.1 Debian Debian
127.0.0.1 localhost

and that fixed my error! Hope this helped!

Answer 18

If you are using Vagrant, then login into the guest and run apt-get --no-install-recommends install virtualbox-guest-utils