The exact message is 's6-supervise mdevd: warning: unable to spawn ./run ( waiting 60 seconds): No such file or directory
Yes, it's a message from s6-supervise. As indicated by the first word. 🙂
The only new services added are mdevd and init-coldplug, copied from the examples in the s6-rc source.
Check the run script of your mdevd service. Chances are the shebang does not correspond to the path where you installed your execlineb binary. -- Laurent