hostname config only changes /etc/hostname, but misses /etc/hosts

[davidje13]

After running cloud-init with a user-data containing:

hostname: pi5

I find that every time I run sudo (for any command), it prints a warning:

$ sudo true
sudo: unable to resolve host pi5: Name or service not known

/etc/hostname is set correctly:

pi5

but /etc/hosts has the default value:

127.0.0.1	localhost
::1		localhost ip6-localhost ip6-loopback
ff02::1		ip6-allnodes
ff02::2		ip6-allrouters

127.0.1.1		raspberrypi

Manually running sudo raspi-config nonint do_hostname pi5 sets /etc/hosts correctly, fixing the issue.