[Nix-dev] cleaning up old configurations

[Henning Thielemann]

Another beginners question ...

I am confused: The NixOS boot menu shows a list of 17 configurations. I 
want to remove some of them in order to free some space on the NixOS 
partition. I try

$ sudo nix-env --list-generations
   12   2015-08-30 11:20:39
   19   2015-12-22 11:50:11
   20   2016-07-15 15:52:44
   21   2016-11-20 13:09:56
   22   2016-11-20 13:10:06   (current)

in order to obtain the numbers for --delete-generations. However, it seems 
that the listed "generations" are something different from the 
"configurations" in the boot menu. How can I list and delete some of those 
configurations from the boot menu?


Btw. I think after upgrading NixOS it is a natural desire to get rid of 
some old versions. What about adding a pointer to
   http://nixos.org/nixos/manual/index.html#sec-upgrading
?