If you have changed the hostname of your Linux PC, by using command from http://www.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,
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.