On Sun, 2021-01-31 at 22:49 +0300, Oleg Pykhalov wrote:
>   (operating-system
> 
>     (inherit base-system)
> 
>     (essential-services
> 
>      (modify-services (operating-system-default-essential-services base-system)
> 
>        (shepherd-root-service-type config => (shepherd-configuration
> 
>                                               (inherit config)
> 
>                                               (shepherd shepherd)))))))

I'm currently running "guix time-machine etcetera", which hasn't completed yet,
but here's some quick speculation on what could have went wrong:

You shouldn't write (operating-system-default-essential-services base-system),
but rather (operating-system-default-essential-services this-operating-system).

The essential-services field is thunked, basically that means that the expression
under essential-services can refer to the operating-system definition itself,
using the macro this-operating-system.

A  potentially fixed configuration is attached, I'll try to run it in a VM.