On Sun, Aug 13, 2017 at 04:19:54PM +0300, Oleg Pykhalov wrote:
> I'm trying to understand what is “garbage collector root” aka “gc root”.

Garbage-collector roots (GC roots) are items in /gnu/store that are
registered to protect them from the garbage collector:

https://www.gnu.org/software/guix/manual/html_node/Invoking-guix-gc.html

You can see the GC root symlinks in /var/guix/gcroots. You can make a
new GC root manually by adding a symlink to the store item you want to
preserve. For example:

$ ln --symbolic $(guix build hello) /var/guix/gcroots/my-hello

> 1. Is “$HOME/.guix-profile” a “gc root”?

Yes, this is mentioned in the manual, section Invoking guix package:

https://www.gnu.org/software/guix/manual/html_node/Invoking-guix-package.html

> 2. I need to build a package, but don't install it.  Just preserve it
> for offloading.  Is “guix build --root=$HOME/.guix-profile PACKAGE” (run
> as non root user) what I want?  Or if not, what FILE in “--root=FILE” do
> I need to pass?

I've never used this feature, so I'm not sure if the value of FILE can
be anywhere on the filesystem, or if it has to be in /var/guix/gcroots.
Hopefully someone else can clarify this. Or you can read the code or
experiment :)