I am running Centos 7 in a virtual machine. We use systemctl and hostnamectl, so dbus is included when we build our image as a dependency of systemd.

In the past, we have had no issue with dbus running correctly, and therefore hostnamectl, etc. Yesterday I generated a new image (without changing any settings) and we ran into this issue. Hostnamectl, systemd-logind.service and a couple of other services failed to run. Eventually, we found that it was due to the location of system_bus_socket. It was created in /run/dbus and should have been created in /var/run/dbus instead. Once a symlink was created to /var/run/dbus, all the failed systems ran correctly.

My question is why was the system_bus_socket created where it was? Is this a change of behavior? I checked the logs, and the version of dbus that yum installed was dbus-libs-1.10.24-7.el7.x86_64

Actually, the following packages were installed:
dbus x86_64 1:1.10.24-7.el7 centos-os 245 k
dbus-glib x86_64 0.100-7.el7 centos-os 102 k
dbus-libs x86_64 1:1.10.24-7.el7 centos-os 169 k
dbus-python x86_64 1.1.1-9.el7 centos-os 206 k

Run "rpm -ql dbus" and you'll see the files it installs.

I have a RHEL7.5 (CentOS is compiled from RHEL source) system that has dbus-1.10.24-7.el7.x86_64. When I ran the rpm -ql on that system it confirms it installed:
/run/dbus
The only thing it installed in /var is:
/var/lib/dbus

An older CentOS7.4.1708 has dbus-1.6.12-17.el7.x86_64. When I ran the rpm -ql on that system it instead shows it installed:
/var/lib/dbus
/var/run/dbus

On a RHEL6 system the /var/run/dbus file is created.

It appears sometime between dbus-1.6.12-17 and 1.10.24-7 they changed it.