How to change the hostname in ubuntu without restart server

sudo vi /etc/hostname

change the existing old_hostname with new_hostname

sudo vi /etc/hosts

change the existing old_hostname with new_hostname

127.0.1.1 old_hostname -> 127.0.1.1 new_hostname

Issues following command without reset the system

sudo hostname new_hostname

Using curl to download file

curl http://some.url --output some.file

which --output flag denotes the filename (some.file) of the downloaded URL (http://some.url)