How to Fix : sudo: unable to resolve host my_user: No such file or directory

If you have changed the hostname of your Linux PC, by using command from https://lynxbee.com/changing-hostname-in-ubuntu/ there are chances you may get an warnings like below everytime you type some commands with sudo permission in terminal and taking considerable time to return the command output,

$ time sudo cat /proc/version
sudo: unable to resolve host laptop: No such file or directory

real	0m30.039s
user	0m0.012s
sys	0m0.004s

So, it shows it took almost 30 sec for simple cat command to return and also returned an error/warning like “sudo: unable to resolve host laptop: No such file or directory” where “laptop” is my hostname.

To resolve this, we need to make sure following files has contents like below,

 $ cat /etc/hostname 

This should show your existing hostname you set using hostnamectl command.

 $ sudo vim /etc/hosts 

has follwing line,

127.0.0.0 your_hostname

Replace, “your_hostname” with proper hostname you have, in my case it should “laptop” as hostname.

Now try again same comamnd as above,

$ time sudo cat /proc/version

real	0m0.012s
user	0m0.000s
sys	0m0.008s 

and you see now warning, and very less time it took to execute that command.