AWS error - sudo: unable to resolve host ip-10-0-xx-xx

I launched a new aws instance. My private ip is ip-10-0-xx-xx as per amazon console. Everytime when I do a sudo command, I get the following error

sudo: unable to resolve host ip-10-0-xx-xx

How can I rectify this error?

This issue is caused by not enabling enableDnsHostnames in your VPC configuration.

>enableDnsHostnames > >Indicates whether the instances launched in the VPC get DNS hostnames. If this attribute is true, instances in the VPC get DNS hostnames; otherwise, they do not. If you want your instances to get DNS hostnames, you must also set the enableDnsSupport attribute to true.

http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-dns.html#vpc-dns-updating

You should enable the DNS hostnames on your VPC: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-dns.html#vpc-dns-updating

If for some reason, you cannot enable it, you can still use the /etc/hosts to make it resolve, but this is definitely not the recommended solution

10.0.xx.xx ip-10-0-xx-xx

This worked for me:

Add the following line to /etc/hosts

127.0.0.1 ip-xxx-xx-x-xx

The ip thing is your private ip address

Can patch easily from command line as follows:

sudo sed -i /etc/hosts -e "s/^127.0.0.1 localhost$/127.0.0.1 localhost $(hostname)/"

And checked that a reboot, or stop, then start the aws instance would preserve it. In case it is lost, can easily re-apply on boot, and can be added to any provision for new vms.

Example

Before:

ubuntu@ip-177-11-22-333:~$ sudo id
sudo: unable to resolve host ip-177-11-22-333
uid=0(root) gid=0(root) groups=0(root)

Fix:

ubuntu@ip-177-11-22-333:~$ sudo sed -i /etc/hosts -e "s/^127.0.0.1 localhost$/127.0.0.1 localhost $(hostname)/"
sudo: unable to resolve host ip-177-11-22-333

After:

ubuntu@ip-177-11-22-333:~$ sudo id
uid=0(root) gid=0(root) groups=0(root)
ubuntu@ip-177-11-22-333:~$

Two Options:

1. Enabling the DNS hostnames for your VPC, so all the instances launched within the VPC will resolve the host

2. Edit /etc/hosts and add the below line

    127.0.0.1 localhost    
    123.0.0.1 ip-10-0-1-18 ## (Replace with the private ip)
   

This is something you will need to do for every instance that will be launch within your VPC.

enableDnsHostnames as described in Michael's comment is one prerequisite. The other is having your VPC's DHCP option set configured correctly. The problem you are coming up against is caused by search line missing from your /etc/resolv.conf ; it will be put in there at the time of DHCP assignment if you set domain-name of your DHCP option set appropriately. Read the linked AWS doc.

Add the following line to /etc/hosts

127.0.0.1 localhost
127.0.0.1 ip-xxx-xx-x-xx

The ip thing is your private ip address

Please also don't forget to reboot the instance after editing these

My issue was caused by an invalid DHCP Options set (in the VPC console). The default one that you typically want looks like this:

domain-name = ec2.internal
domain-name-servers = AmazonProvidedDNS

Somehow, my domain-name got changed to us-east-1.compute.internal, which resulted in the sudo: unable to resolve host ip-10-0-xx-xx warning every time I ran sudo. Changing back to the DHCP options above fixed it.

To enable DnsSupport attribute just use this command in your terminal

aws ec2 describe-vpc-attribute --vpc-id vpc-****** --attribute enableDnsSupport

Make sure replace * with your VPC Id for more info https://docs.aws.amazon.com/cli/latest/reference/ec2/describe-vpc-attribute.html

Run the following command;

sudo su -

and work as root. Then the start command will work.