After my latest upgrade, which included 66-tools 0.0.5.1-1, I performed '66-update' as both root and local user. Following reboot, my system failed to start. It halted at the tty with a message:

login: trying to run a sulogin command
Give root password for maintenance
(or press Control-D to continue):

I was able to start most of the system by hand, but the dbus service failed to start. Looking at the logs, I found the following in /var/log/66/dbus/current:

2020-06-09 22:54:41.499805522  execl-toc : fatal: unable to get dirname of: system_bus_socket

The content of /usr/lib/66/service/dbus was:

[main]
@ type = longrun
@ version = 0.1.6
@ description = "dbus system daemon"
@ user = ( root )
@ maxdeath = 3
@ notify = 4
@ options = ( log env )
@ timeout-up = 3000

[start]
@ build = auto
@ execute = (
	execl-toc -S ${socket_name} -m 0777
	foreground { dbus-uuidgen --ensure }
	execl-cmdline -s { dbus-daemon ${cmd_args} }
)

[stop]
@ build = auto
@ execute = ( s6-rmrf ${socket_name} )

[environment]
cmd_args=!--system --print-pid=4 --nofork --nopidfile --address=unix:path=/run/dbus/system_bus_socket
socket_name=!/run/dbus/system_bus_socket

I was able to restore functionality to my system by modifying the '@ execute' line to:

@ execute= (
	execl-toc -S /run/dbus/system_bus_socket -m 0777
	foreground { dbus-uuidgen --ensure }
	execl-cmdline -s { dbus-daemon ${cmd_args} }
)

But I really don't understand why this would make a difference...