Setting Hostname on Ubuntu

For server my-server.dataone.org with IP 12.34.56.78:

/etc/hostname:

my-server

/etc/hosts:

127.0.0.1 localhost
12.34.56.78 my-server.dataone.org my-server

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

Then reboot or:

sudo hostname my-server