Hello Danny,

Danny Milosavljevic <dannym@scratchpost.org> writes:

[...]

> guix environment: error: some substitutes for the outputs of
> derivation
> `/gnu/store/zxxw95x9ivw1a10v6nk1ls6d9i1csh3y-gcc-toolchain-5.5.0.drv'
> failed (usually happens due to networking issues); try `--fallback' to
> build derivation from source

I was not able to reproduce this on a Guix System machine I have: are
you sure it's not a networking issue?

This is what I did:

--8<---------------cut here---------------start------------->8---
~$ guix pull --commit=e6049c84dab3031fb64defae2c45a20b512d4644

~$ guix describe
Generation 2    Jun 22 2019 08:54:10    (current)
  guix e6049c8
    repository URL: https://git.savannah.gnu.org/git/guix.git
    commit: e6049c84dab3031fb64defae2c45a20b512d4644

~$ guix environment -s i686-linux --ad-hoc gcc-toolchain@5.5.0
--8<---------------cut here---------------end--------------->8---

And I got a new env without errors.

HTH! Gio'.

-- 
Giovanni Biscuolo

Xelera IT Infrastructures