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How to determine if the nix sandbox is in effect on a system

Do the same as the nix-info script, which nix-builds this file and inspects the exit code.

Short version:

nix-build --no-out-link -E 'import <nixpkgs/pkgs/tools/nix/info/multiuser.nix>' 2> /dev/null

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Initial state

We want to squash the v commits in

v1
v2
v3
k1
k2

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% NIX_PATH=nixpkgs=. /usr/bin/time nix-build --no-link -A duplicity
these derivations will be built:
  /nix/store/73in6wzsqzpsi6k4y4x2qqi3az9rnkff-duplicity-0.7.19.drv
building '/nix/store/73in6wzsqzpsi6k4y4x2qqi3az9rnkff-duplicity-0.7.19.drv' on 'ssh://static-haskell-nix-ci'...
copying path '/nix/store/75c1irykc5r095djhxhnxrj9r0s0gph7-1359.2.3' from 'https://cache.nixos.org'...
copying path '/nix/store/lcckqzhp6khmzb9833frnh47g7fsjgik-1359.2.2' from 'https://cache.nixos.org'...
copying path '/nix/store/srgh1frvgvz141rish0pyjn520rgff38-1359.2.1' from 'https://cache.nixos.org'...
copying path '/nix/store/q8mapr5b3z26h7hackmnsk3sirjxqcq8-duplicity-0.7.19.tar.gz' from 'https://cache.nixos.org'...
copying path '/nix/store/g2za9nam04lpb5h8s7dd0y51r3lg75x6-gnutar-in-test.patch' from 'https://cache.nixos.org'...
copying path '/nix/store/ijvka0qiq3c7sk19sgs1mvm49qwpzgpl-python2.7-pyOpenSSL-19.0.0' from 'https://cache.nixos.org'...

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% ./hadrian/build.stack.sh -j --flavour=quickest --verbose
| Building Stage1 libraries: binary, Cabal, ghc, ghc-boot, ghc-boot-th, ghc-heap, ghci, hpc, mtl, parsec, template-haskell, text, transformers, terminfo, array, base, bytestring, containers, deepseq, directory, filepath, ghc-compact, ghc-prim, haskeline, integer-gmp, pretty, process, rts, stm, time, xhtml, libiserv, unix
| Building Stage1 programs: ghc, ghc-pkg, hp2ps, hsc2hs, unlit, haddock, hpc, ghc-iserv, runghc

| Building Stage2 libraries: binary, Cabal, ghc, ghc-boot, ghc-boot-th, ghc-heap, ghci, hpc, mtl, parsec, template-haskell, text, transformers, terminfo, array, base, bytestring, containers, deepseq, directory, filepath, ghc-compact, ghc-prim, haskeline, integer-gmp, pretty, process, rts, stm, time, xhtml, libiserv, unix
| Building Stage2 programs: ghc, ghc-pkg, hp2ps, hsc2hs, unlit, haddock, hpc, ghc-iserv, runghc

| Building Stage3 libraries: 
| Building Stage3 programs: 

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unpacking source archive /nix/store/cqq2m229cpgms09gcf3a3z07774d36d0-odp-dpdk-1.22.0.0_DPDK_18.11.tar.gz
source root is odp-dpdk-1.22.0.0_DPDK_18.11
setting SOURCE_DATE_EPOCH to timestamp 1566561796 of file odp-dpdk-1.22.0.0_DPDK_18.11/test/validation/api/traffic_mngr/traffic_mngr.c
patching sources
autoreconfPhase
autoreconf: Entering directory `.'
autoreconf: configure.ac: not using Gettext
autoreconf: running: aclocal --force -I m4
autoreconf: configure.ac: tracing
autoreconf: running: libtoolize --copy --force

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"The [TH] Recompilation Problem"

Usually, when you use ghci's :reload or ghc --make (with -O0 to disable unfoldings which are used for cross-module inlining), after changing implementation code of functions, GHC will incrementally recompile only the modules you changed, making for a fast development experience when iterating on implementation details.

(When you change API like functions types, export lists, etc.,

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module SocketUtils
  ( isPortOpen
  , simpleSockAddr
  ) where

import           Data.Word (Word8)
import           Foreign.C.Error (Errno(..), eCONNREFUSED)
import           GHC.IO.Exception (IOException(..))
import           Network.Socket (PortNumber, socket, connect, close', Family(AF_INET), SocketType(Stream), SockAddr(SockAddrInet), tupleToHostAddress)
import           UnliftIO.Exception (try, bracket, throwIO)

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{
  systemd.services.static-haskell-nix-cachix-push-daemon = {
    requiredBy = [ "multi-user.target" ];
    after = [
      "network-online.target"
    ];
    environment.HOME = "/root";
    path = [ pkgs.nix ]; # cachix shells out to nix binaries
    serviceConfig = {
      ExecStart = "${pkgs.cachix}/bin/cachix push static-haskell-nix --watch-store";

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#!/usr/bin/env bash

# Installs NixOS on a Hetzner server, wiping the server.
#
# This is for a specific server configuration; adjust where needed.
#
# Prerequisites:
#   * Update the script to adjust SSH pubkeys, hostname, NixOS version etc.
#
# Usage:

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#!/usr/bin/env bash

# Installs NixOS on an OVH server, wiping the server.
#
# This is for a specific server configuration; adjust where needed.
# Originally written for an OVH STOR-1 server.
#
# Prerequisites:
#   * Create a LUKS key file at /root/benacofs-luks-key
#     e.g. by copying it up.