mjhjmtu

I am running Debian 9.4. hostname works.

$ sudo strace -f hostnamectl
...snipped...
connect(3, sa_family=AF_UNIX, sun_path="/var/run/dbus/system_bus_socket", 33) = -1 ENOENT (No such file or directory)
...

Failed to create bus connection: No such file or directory

UPDATE: here are more information:

$ sudo systemctl status dbus.service dbus.socket
Unit dbus.service could not be found.
Unit dbus.socket could not be found.

$ ps -p 1 
PID TTY TIME CMD
1 ? 00:00:47 systemd

$ sudo systemctl list-unit-files --state=running
0 unit files listed.

$ sudo systemctl list-unit-files --state=enabled
...snipped...
26 unit files listed.

It looks like dbus package is missing.

Check if dbus package is installed or not using below command:

$ sudo dpkg -l | grep dbus
ii dbus 1.10.26-0+deb9u1 amd64 simple interprocess messaging system (daemon and utilities)
ii libdbus-1-3:amd64 1.10.26-0+deb9u1 amd64 simple interprocess messaging system (library)

If dbus package is installed you will get output as above.

If output is blank then dbus package is missing. You can install the package using below command:

$ sudo apt-get install dbus

After installing the package you can check the status:

$ sudo systemctl status dbus.service dbus.socket
● dbus.service - D-Bus System Message Bus
 Loaded: loaded (/lib/systemd/system/dbus.service; static; vendor preset: enabled)
 Active: active (running) since Fri 2018-09-07 23:39:14 EDT; 10s ago
 Docs: man:dbus-daemon(1)
 Main PID: 451 (dbus-daemon)
 Tasks: 1 (limit: 4915)
 CGroup: /system.slice/dbus.service
 └─451 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation

● dbus.socket - D-Bus System Message Bus Socket
 Loaded: loaded (/lib/systemd/system/dbus.socket; static; vendor preset: enabled)
 Active: active (running) since Fri 2018-09-07 23:39:14 EDT; 10s ago
 Listen: /var/run/dbus/system_bus_socket (Stream)