Expand the multi-user installer to support Linuxes with systemd

 - darwin installer: delete hardware report, not necessary
 - moves os-specific code from the darwin installer to to `poly_*`
   functions
 - adds profile.d support to the profile targets, which automatically
   handles many distros which don't have a /etc/bashrc but do have an
   /etc/profile.d
 - /bin/bash -> /usr/bin/env bash
 - document why each excluded shellcheck check is excluded
 - rename the multi-user to Daemon-based

4 files changed, 1034 insertions, 755 deletions

diff --git a/scripts/install-darwin-multi-user.sh b/scripts/install-darwin-multi-user.sh
index 716b6e9bc9..87c4c2b058 100644
--- a/scripts/install-darwin-multi-user.sh
+++ b/scripts/install-darwin-multi-user.sh
@@ -1,819 +1,144 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -eu
 set -o pipefail
 
-# Sourced from:
-# - https://github.com/LnL7/nix-darwin/blob/8c29d0985d74b4a990238497c47a2542a5616b3c/bootstrap.sh
-# - https://gist.github.com/expipiplus1/e571ce88c608a1e83547c918591b149f/ac504c6c1b96e65505fbda437a28ce563408ecb0
-# - https://github.com/NixOS/nixos-org-configurations/blob/a122f418797713d519aadf02e677fce0dc1cb446/delft/scripts/nix-mac-installer.sh
-# - https://github.com/matthewbauer/macNixOS/blob/f6045394f9153edea417be90c216788e754feaba/install-macNixOS.sh
-# - https://gist.github.com/LnL7/9717bd6cdcb30b086fd7f2093e5f8494/86b26f852ce563e973acd30f796a9a416248c34a
-#
-# however tracking which bits came from which would be impossible.
-
-readonly ESC='\033[0m'
-readonly BOLD='\033[38;1m'
-readonly BLUE='\033[38;34m'
-readonly BLUE_UL='\033[38;4;34m'
-readonly GREEN='\033[38;32m'
-readonly GREEN_UL='\033[38;4;32m'
-readonly RED='\033[38;31m'
-readonly RED_UL='\033[38;4;31m'
-readonly YELLOW='\033[38;33m'
-readonly YELLOW_UL='\033[38;4;33m'
-
-readonly CORES=$(sysctl -n hw.ncpu)
-readonly NIX_USER_COUNT="32"
-readonly NIX_BUILD_GROUP_ID="30000"
-readonly NIX_BUILD_GROUP_NAME="nixbld"
-readonly NIX_FIRST_BUILD_UID="30001"
-# Please don't change this. We don't support it, because the
-# default shell profile that comes with Nix doesn't support it.
-readonly NIX_ROOT="/nix"
 readonly PLIST_DEST=/Library/LaunchDaemons/org.nixos.nix-daemon.plist
 
-readonly PROFILE_TARGETS=("/etc/bashrc" "/etc/zshrc")
-readonly PROFILE_BACKUP_SUFFIX=".backup-before-nix"
-readonly PROFILE_NIX_FILE="$NIX_ROOT/var/nix/profiles/default/etc/profile.d/nix-daemon.sh"
-
-readonly NIX_INSTALLED_NIX="@nix@"
-readonly NIX_INSTALLED_CACERT="@cacert@"
-readonly EXTRACTED_NIX_PATH="$(dirname "$0")"
-
-readonly ROOT_HOME="/var/root"
-
-if [ -t 0 ]; then
-    readonly IS_HEADLESS='no'
-else
-    readonly IS_HEADLESS='yes'
-fi
+dsclattr() {
+    /usr/bin/dscl . -read "$1" \
+        | awk "/$2/ { print \$2 }"
+}
 
-headless() {
-    if [ "$IS_HEADLESS" = "yes" ]; then
-        return 0
-    else
-        return 1
+poly_validate_assumptions() {
+    if [ "$(uname -s)" != "Darwin" ]; then
+        failure "This script is for use with macOS!"
     fi
 }
 
-contactme() {
-    echo "We'd love to help if you need it."
-    echo ""
-    echo "If you can, open an issue at https://github.com/nixos/nix/issues"
-    echo ""
-    echo "Or feel free to contact the team,"
-    echo " - on IRC #nixos on irc.freenode.net"
-    echo " - on twitter @nixos_org"
+poly_service_installed_check() {
+    [ -e "$PLIST_DEST" ]
 }
 
-uninstall_directions() {
-    subheader "Uninstalling nix:"
-    local step=0
-
-    if [ -e "$PLIST_DEST" ]; then
-        step=$((step + 1))
+poly_service_uninstall_directions() {
         cat <<EOF
-$step. Delete $PLIST_DEST
+$1. Delete $PLIST_DEST
 
   sudo launchctl unload $PLIST_DEST
   sudo rm $PLIST_DEST
 
 EOF
-    fi
-
-    for profile_target in "${PROFILE_TARGETS[@]}"; do
-        if [ -e "$profile_target" ] && [ -e "$profile_target$PROFILE_BACKUP_SUFFIX" ]; then
-            step=$((step + 1))
-            cat <<EOF
-$step. Restore $profile_target$PROFILE_BACKUP_SUFFIX back to $profile_target
-
-  sudo mv $profile_target$PROFILE_BACKUP_SUFFIX $profile_target
-
-(after this one, you may need to re-open any terminals that were
-opened while it existed.)
-
-EOF
-        fi
-    done
+}
 
-    step=$((step + 1))
+poly_service_setup_note() {
     cat <<EOF
-$step. Delete the files Nix added to your system:
-
-  sudo rm -rf /etc/nix $NIX_ROOT $ROOT_HOME/.nix-profile $ROOT_HOME/.nix-defexpr $ROOT_HOME/.nix-channels $HOME/.nix-profile $HOME/.nix-defexpr $HOME/.nix-channels
-
-and that is it.
+ - load and start a LaunchDaemon (at $PLIST_DEST) for nix-daemon
 
 EOF
-
-}
-
-nix_user_for_core() {
-    printf "nixbld%d" "$1"
-}
-
-nix_uid_for_core() {
-    echo $((NIX_FIRST_BUILD_UID + $1 - 1))
 }
 
-dsclattr() {
-    /usr/bin/dscl . -read "$1" \
-        | awk "/$2/ { print \$2 }"
-}
-
-_textout() {
-    echo -en "$1"
-    shift
-    if [ "$*" = "" ]; then
-        cat
-    else
-        echo "$@"
-    fi
-    echo -en "$ESC"
-}
-
-header() {
-    follow="---------------------------------------------------------"
-    header=$(echo "---- $* $follow$follow$follow" | head -c 80)
-    echo ""
-    _textout "$BLUE" "$header"
-}
-
-warningheader() {
-    follow="---------------------------------------------------------"
-    header=$(echo "---- $* $follow$follow$follow" | head -c 80)
-    echo ""
-    _textout "$RED" "$header"
-}
-
-subheader() {
-    echo ""
-    _textout "$BLUE_UL" "$*"
-}
-
-row() {
-    printf "$BOLD%s$ESC:\\t%s\\n" "$1" "$2"
-}
-
-task() {
-    echo ""
-    ok "~~> $1"
-}
-
-bold() {
-    echo "$BOLD$*$ESC"
-}
-
-ok() {
-    _textout "$GREEN" "$@"
-}
-
-warning() {
-    warningheader "warning!"
-    cat
-    echo ""
-}
-
-failure() {
-    header "oh no!"
-    _textout "$RED" "$@"
-    echo ""
-    _textout "$RED" "$(contactme)"
-    trap finish_cleanup EXIT
-    exit 1
-}
-
-ui_confirm() {
-    _textout "$GREEN$GREEN_UL" "$1"
-
-    if headless; then
-        echo "No TTY, assuming you would say yes :)"
-        return 0
-    fi
-
-    local prompt="[y/n] "
-    echo -n "$prompt"
-    while read -r y; do
-        if [ "$y" = "y" ]; then
-            echo ""
-            return 0
-        elif [ "$y" = "n" ]; then
-            echo ""
-            return 1
-        else
-            _textout "$RED" "Sorry, I didn't understand. I can only understand answers of y or n"
-            echo -n "$prompt"
-        fi
-    done
-    echo ""
-    return 1
-}
-
-__sudo() {
-    local expl="$1"
-    local cmd="$2"
-    shift
-    header "sudo execution"
-
-    echo "I am executing:"
-    echo ""
-    printf "    $ sudo %s\\n" "$cmd"
-    echo ""
-    echo "$expl"
-    echo ""
-
-    return 0
-}
+poly_configure_nix_daemon_service() {
+    _sudo "to set up the nix-daemon as a LaunchDaemon" \
+          ln -sfn "/nix/var/nix/profiles/default$PLIST_DEST" "$PLIST_DEST"
 
-_sudo() {
-    local expl="$1"
-    shift
-    if ! headless; then
-        __sudo "$expl" "$*"
-    fi
-    sudo "$@"
-}
+    _sudo "to load the LaunchDaemon plist for nix-daemon" \
+          launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist
 
+    _sudo "to start the nix-daemon" \
+          launchctl start org.nixos.nix-daemon
 
-readonly SCRATCH=$(mktemp -d -t tmp.XXXXXXXXXX)
-function finish_cleanup {
-    rm -rf "$SCRATCH"
 }
 
-function finish_fail {
-    finish_cleanup
-
-    failure <<EOF
-Jeeze, something went wrong. If you can take all the output and open
-an issue, we'd love to fix the problem so nobody else has this issue.
-
-:(
-EOF
+poly_group_exists() {
+    /usr/bin/dscl . -read "/Groups/$1" > /dev/null 2>&1
 }
-trap finish_fail EXIT
-
-function finish_success {
-    finish_cleanup
 
-    ok "Alright! We're done!"
-    cat <<EOF
-
-Before Nix will work in your existing shells, you'll need to close
-them and open them again. Other than that, you should be ready to go.
-
-Try it! Open a new terminal, and type:
-
-  $ nix-shell -p nix-info --run "nix-info -m"
-
-Thank you for using this installer. If you have any feedback, don't
-hesitate:
-
-$(contactme)
-EOF
+poly_group_id_get() {
+    dsclattr "/Groups/$1" "PrimaryGroupID"
 }
 
-
-validate_starting_assumptions() {
-    if [ "$(uname -s)" != "Darwin" ]; then
-        failure "This script is for use with macOS!"
-    fi
-
-    if [ $EUID -eq 0 ]; then
-        failure <<EOF
-Please do not run this script with root privileges. We will call sudo
-when we need to.
-EOF
-    fi
-
-    if type nix-env 2> /dev/null >&2; then
-        failure <<EOF
-Nix already appears to be installed, and this tool assumes it is
-_not_ yet installed.
-
-$(uninstall_directions)
-EOF
-    fi
-
-    if [ "${NIX_REMOTE:-}" != "" ]; then
-        failure <<EOF
-For some reason, \$NIX_REMOTE is set. It really should not be set
-before this installer runs, and it hints that Nix is currently
-installed. Please delete the old Nix installation and start again.
-
-Note: You might need to close your shell window and open a new shell
-to clear the variable.
-EOF
-    fi
-
-    if echo "${SSL_CERT_FILE:-}" | grep -qE "(nix/var/nix|nix-profile)"; then
-        failure <<EOF
-It looks like \$SSL_CERT_FILE is set to a path that used to be part of
-the old Nix installation. Please unset that variable and try again:
-
-  $ unset SSL_CERT_FILE
-
-EOF
-    fi
-
-    for file in ~/.bash_profile ~/.bash_login ~/.profile ~/.zshenv ~/.zprofile ~/.zshrc ~/.zlogin; do
-        if [ -f "$file" ]; then
-            if grep -l "^[^#].*.nix-profile" "$file"; then
-                failure <<EOF
-I found a reference to a ".nix-profile" in $file.
-This has a high chance of breaking a new nix installation. It was most
-likely put there by a previous Nix installer.
-
-Please remove this reference and try running this again. You should
-also look for similar references in:
-
- - ~/.bash_profile
- - ~/.bash_login
- - ~/.profile
-
-or other shell init files that you may have.
-
-$(uninstall_directions)
-EOF
-            fi
-        fi
-    done
-
-    if [ -d /nix ]; then
-        failure <<EOF
-There are some relics of a previous installation of Nix at /nix, and
-this scripts assumes Nix is _not_ yet installed. Please delete the old
-Nix installation and start again.
-
-$(uninstall_directions)
-EOF
-    fi
-
-    if [ -d /etc/nix ]; then
-        failure <<EOF
-There are some relics of a previous installation of Nix at /etc/nix, and
-this scripts assumes Nix is _not_ yet installed. Please delete the old
-Nix installation and start again.
-
-$(uninstall_directions)
-EOF
-    fi
-
-    for profile_target in "${PROFILE_TARGETS[@]}"; do
-        if [ -e "$profile_target$PROFILE_BACKUP_SUFFIX" ]; then
-        failure <<EOF
-When this script runs, it backs up the current $profile_target to
-$profile_target$PROFILE_BACKUP_SUFFIX. This backup file already exists, though.
-
-Please follow these instructions to clean up the old backup file:
-
-1. Copy $profile_target and $profile_target$PROFILE_BACKUP_SUFFIX to another place, just
-in case.
-
-2. Take care to make sure that $profile_target$PROFILE_BACKUP_SUFFIX doesn't look like
-it has anything nix-related in it. If it does, something is probably
-quite wrong. Please open an issue or get in touch immediately.
-
-3. Take care to make sure that $profile_target doesn't look like it has
-anything nix-related in it. If it does, and $profile_target _did not_,
-run:
-
-  $ /usr/bin/sudo /bin/mv $profile_target$PROFILE_BACKUP_SUFFIX $profile_target
-
-and try again.
-EOF
-        fi
-
-        if grep -qi "nix" "$profile_target"; then
-            failure <<EOF
-It looks like $profile_target already has some Nix configuration in
-there. There should be no reason to run this again. If you're having
-trouble, please open an issue.
-EOF
-        fi
-    done
-
-    danger_paths=("$ROOT_HOME/.nix-defexpr" "$ROOT_HOME/.nix-channels" "$ROOT_HOME/.nix-profile")
-    for danger_path in "${danger_paths[@]}"; do
-        if _sudo "making sure that $danger_path doesn't exist" \
-           test -e "$danger_path"; then
-            failure <<EOF
-I found a file at $danger_path, which is a relic of a previous
-installation. You must first delete this file before continuing.
-
-$(uninstall_directions)
-EOF
-        fi
-    done
+poly_create_build_group() {
+    _sudo "Create the Nix build group, $NIX_BUILD_GROUP_NAME" \
+          /usr/sbin/dseditgroup -o create \
+          -r "Nix build group for nix-daemon" \
+          -i "$NIX_BUILD_GROUP_ID" \
+          "$NIX_BUILD_GROUP_NAME" >&2
 }
 
-setup_report() {
-    header "hardware report"
-    row "           Cores" "$CORES"
-
-    header "Nix config report"
-    row "        Temp Dir" "$SCRATCH"
-    row "        Nix Root" "$NIX_ROOT"
-    row "     Build Users" "$NIX_USER_COUNT"
-    row "  Build Group ID" "$NIX_BUILD_GROUP_ID"
-    row "Build Group Name" "$NIX_BUILD_GROUP_NAME"
-    if [ "${ALLOW_PREEXISTING_INSTALLATION:-}" != "" ]; then
-        row "Preexisting Install" "Allowed"
-    fi
-
-    subheader "build users:"
-
-    row "    Username" "UID"
-    for i in $(seq 1 "$NIX_USER_COUNT"); do
-        row "     $(nix_user_for_core "$i")" "$(nix_uid_for_core "$i")"
-    done
-    echo ""
+poly_user_exists() {
+    /usr/bin/dscl . -read "/Users/$1" > /dev/null 2>&1
 }
 
-create_build_group() {
-    local primary_group_id
-
-    task "Setting up the build group $NIX_BUILD_GROUP_NAME"
-    if ! /usr/bin/dscl . -read "/Groups/$NIX_BUILD_GROUP_NAME" > /dev/null 2>&1; then
-        _sudo "Create the Nix build group, $NIX_BUILD_GROUP_NAME" \
-              /usr/sbin/dseditgroup -o create \
-              -r "Nix build group for nix-daemon" \
-              -i "$NIX_BUILD_GROUP_ID" \
-              "$NIX_BUILD_GROUP_NAME" >&2
-        row "            Created" "Yes"
-    else
-        primary_group_id=$(dsclattr "/Groups/$NIX_BUILD_GROUP_NAME" "PrimaryGroupID")
-        if [ "$primary_group_id" -ne "$NIX_BUILD_GROUP_ID" ]; then
-            failure <<EOF
-It seems the build group $NIX_BUILD_GROUP_NAME already exists, but
-with the UID $primary_group_id. This script can't really handle
-that right now, so I'm going to give up.
-
-You can fix this by editing this script and changing the
-NIX_BUILD_GROUP_ID variable near the top to from $NIX_BUILD_GROUP_ID
-to $primary_group_id and re-run.
-EOF
-        else
-            row "            Exists" "Yes"
-        fi
-    fi
+poly_user_id_get() {
+    dsclattr "/Users/$1" "UniqueID"
 }
 
-create_build_user_for_core() {
-    local coreid
-    local username
-    local uid
-
-    coreid="$1"
-    username=$(nix_user_for_core "$coreid")
-    uid=$(nix_uid_for_core "$coreid")
-    dsclpath="/Users/$username"
-
-    task "Setting up the build user $username"
-
-    if ! /usr/bin/dscl . -read "$dsclpath" > /dev/null 2>&1; then
-        _sudo "Creating the Nix build user, $username" \
-              /usr/bin/dscl . create "$dsclpath" \
-              UniqueID "${uid}"
-        row "           Created" "Yes"
-    else
-        actual_uid=$(dsclattr "$dsclpath" "UniqueID")
-        if [ "$actual_uid" -ne "$uid" ]; then
-            failure <<EOF
-It seems the build user $username already exists, but with the UID
-with the UID $actual_uid. This script can't really handle that right
-now, so I'm going to give up.
-
-If you already created the users and you know they start from
-$actual_uid and go up from there, you can edit this script and change
-NIX_FIRST_BUILD_UID near the top of the file to $actual_uid and try
-again.
-EOF
-        else
-            row "            Exists" "Yes"
-        fi
-    fi
-
-    if [ "$(dsclattr "$dsclpath" "IsHidden")" = "1" ]; then
-        row "          IsHidden" "Yes"
-    else
-        _sudo "in order to make $username a hidden user" \
-              /usr/bin/dscl . -create "$dsclpath" "IsHidden" "1"
-        row "          IsHidden" "Yes"
-    fi
-
-    if [ "$(dsclattr "$dsclpath" "NFSHomeDirectory")" = "/var/empty" ]; then
-        row "          NFSHomeDirectory" "/var/empty"
-    else
-        _sudo "in order to give $username a safe home directory" \
-              /usr/bin/dscl . -create "$dsclpath" "NFSHomeDirectory" "/var/empty"
-        row "          NFSHomeDirectory" "/var/empty"
-    fi
-
-    if [ "$(dsclattr "$dsclpath" "RealName")" = "Nix build user $coreid" ]; then
-        row "          RealName" "Nix build user $coreid"
-    else
-        _sudo "in order to give $username a useful name" \
-              /usr/bin/dscl . -create "$dsclpath" "RealName" "Nix build user $coreid"
-        row "          RealName" "Nix build user $coreid"
-    fi
-
-    if [ "$(dsclattr "$dsclpath" "UserShell")" = "/sbin/nologin" ]; then
-        row "   Logins Disabled" "Yes"
-    else
-        _sudo "in order to prevent $username from logging in" \
-              /usr/bin/dscl . -create "$dsclpath" "UserShell" "/sbin/nologin"
-        row "   Logins Disabled" "Yes"
-    fi
-
-    if dseditgroup -o checkmember -m "$username" "$NIX_BUILD_GROUP_NAME" > /dev/null 2>&1 ; then
-        row "  Member of $NIX_BUILD_GROUP_NAME" "Yes"
-    else
-        _sudo "Add $username to the $NIX_BUILD_GROUP_NAME group"\
-            /usr/sbin/dseditgroup -o edit -t user \
-            -a "$username" "$NIX_BUILD_GROUP_NAME"
-        row "  Member of $NIX_BUILD_GROUP_NAME" "Yes"
-    fi
-
-    if [ "$(dsclattr "$dsclpath" "PrimaryGroupID")" = "$NIX_BUILD_GROUP_ID" ]; then
-        row "    PrimaryGroupID" "$NIX_BUILD_GROUP_ID"
-    else
-        _sudo "to let the nix daemon use this user for builds (this might seem redundant, but there are two concepts of group membership)" \
-              /usr/bin/dscl . -create "$dsclpath" "PrimaryGroupID" "$NIX_BUILD_GROUP_ID"
-        row "    PrimaryGroupID" "$NIX_BUILD_GROUP_ID"
-
-    fi
+poly_user_hidden_get() {
+    dsclattr "/Users/$1" "IsHidden"
 }
 
-create_build_users() {
-    for i in $(seq 1 "$NIX_USER_COUNT"); do
-        create_build_user_for_core "$i"
-    done
+poly_user_hidden_set() {
+    _sudo "in order to make $1 a hidden user" \
+          /usr/bin/dscl . -create "/Users/$1" "IsHidden" "1"
 }
 
-create_directories() {
-    _sudo "to make the basic directory structure of Nix (part 1)" \
-          mkdir -pv -m 0755 /nix /nix/var /nix/var/log /nix/var/log/nix /nix/var/log/nix/drvs /nix/var/nix{,/db,/gcroots,/profiles,/temproots,/userpool}
-
-    _sudo "to make the basic directory structure of Nix (part 2)" \
-          mkdir -pv -m 1777 /nix/var/nix/{gcroots,profiles}/per-user
-
-    _sudo "to make the basic directory structure of Nix (part 3)" \
-          mkdir -pv -m 1775 /nix/store
-
-    _sudo "to make the basic directory structure of Nix (part 4)" \
-          chgrp "$NIX_BUILD_GROUP_NAME" /nix/store
-
-    _sudo "to set up the root user's profile (part 1)" \
-          mkdir -pv -m 0755 /nix/var/nix/profiles/per-user/root
-
-    _sudo "to set up the root user's profile (part 2)" \
-          mkdir -pv -m 0700 "$ROOT_HOME/.nix-defexpr"
-
-    _sudo "to place the default nix daemon configuration (part 1)" \
-          mkdir -pv -m 0555 /etc/nix
+poly_user_home_get() {
+    dsclattr "/Users/$1" "NFSHomeDirectory"
 }
 
-place_channel_configuration() {
-    echo "https://nixos.org/channels/nixpkgs-unstable nixpkgs" > "$SCRATCH/.nix-channels"
-    _sudo "to set up the default system channel (part 1)" \
-          install -m 0664 "$SCRATCH/.nix-channels" "$ROOT_HOME/.nix-channels"
+poly_user_home_set() {
+    _sudo "in order to give $1 a safe home directory" \
+          /usr/bin/dscl . -create "/Users/$1" "NFSHomeDirectory" "$2"
 }
 
-welcome_to_nix() {
-    ok "Welcome to the Multi-User Nix Installation"
-
-    cat <<EOF
-
-This installation tool will set up your computer with the Nix package
-manager. This will happen in a few stages:
-
-1. Make sure your computer doesn't already have Nix. If it does, I
-   will show you instructions on how to clean up your old one.
-
-2. Show you what we are going to install and where. Then we will ask
-   if you are ready to continue.
-
-3. Create the system users and groups that the Nix daemon uses to run
-   builds.
-
-4. Perform the basic installation of the Nix files daemon.
-
-5. Configure your shell to import special Nix Profile files, so you
-   can use Nix.
-
-6. Start the Nix daemon.
-
-EOF
-
-    if ui_confirm "Would you like to see a more detailed list of what we will do?"; then
-        cat <<EOF
-
-We will:
-
- - make sure your computer doesn't already have Nix files
-   (if it does, I  will tell you how to clean them up.)
- - create local users (see the list above for the users we'll make)
- - create a local group ($NIX_BUILD_GROUP_NAME)
- - install Nix in to $NIX_ROOT
- - create a configuration file in /etc/nix
- - set up the "default profile" by creating some Nix-related files in
-   $ROOT_HOME
-EOF
-        for profile_target in "${PROFILE_TARGETS[@]}"; do
-            if [ -e "$profile_target" ]; then
-                cat <<EOF
- - back up $profile_target to $profile_target$PROFILE_BACKUP_SUFFIX
- - update $profile_target to include some Nix configuration
-EOF
-            fi
-        done
-        cat <<EOF
- - load and start a LaunchDaemon (at $PLIST_DEST) for nix-daemon
-
-EOF
-        if ! ui_confirm "Ready to continue?"; then
-            failure <<EOF
-Okay, maybe you would like to talk to the team.
-EOF
-        fi
-    fi
+poly_user_note_get() {
+    dsclattr "/Users/$1" "RealName"
 }
 
-chat_about_sudo() {
-    header "let's talk about sudo"
-
-    if headless; then
-        cat <<EOF
-This script is going to call sudo a lot. Normally, it would show you
-exactly what commands it is running and why. However, the script is
-run in a headless fashion, like this:
-
-  $ curl https://nixos.org/nix/install | sh
-
-or maybe in a CI pipeline. Because of that, we're going to skip the
-verbose output in the interest of brevity.
-
-If you would like to
-see the output, try like this:
-
-  $ curl -o install-nix https://nixos.org/nix/install
-  $ sh ./install-nix
-
-EOF
-        return 0
-    fi
-
-    cat <<EOF
-This script is going to call sudo a lot. Every time we do, it'll
-output exactly what it'll do, and why.
-
-Just like this:
-EOF
-
-    __sudo "to demonstrate how our sudo prompts look" \
-           echo "this is a sudo prompt"
-
-    cat <<EOF
-
-This might look scary, but everything can be undone by running just a
-few commands. We used to ask you to confirm each time sudo ran, but it
-was too many times. Instead, I'll just ask you this one time:
-
-EOF
-    if ui_confirm "Can we use sudo?"; then
-        ok "Yay! Thanks! Let's get going!"
-    else
-        failure <<EOF
-That is okay, but we can't install.
-EOF
-    fi
+poly_user_note_set() {
+    _sudo "in order to give $username a useful note" \
+          /usr/bin/dscl . -create "/Users/$1" "RealName" "$2"
 }
 
-install_from_extracted_nix() {
-    (
-        cd "$EXTRACTED_NIX_PATH"
-
-        _sudo "to copy the basic Nix files to the new store at $NIX_ROOT/store" \
-              rsync -rlpt ./store/* "$NIX_ROOT/store/"
-
-        if [ -d "$NIX_INSTALLED_NIX" ]; then
-            echo "      Alright! We have our first nix at $NIX_INSTALLED_NIX"
-        else
-            failure <<EOF
-Something went wrong, and I didn't find Nix installed at
-$NIX_INSTALLED_NIX.
-EOF
-        fi
-
-        _sudo "to initialize the Nix Database" \
-              $NIX_INSTALLED_NIX/bin/nix-store --init
-
-        cat ./.reginfo \
-            | _sudo "to load data for the first time in to the Nix Database" \
-                   "$NIX_INSTALLED_NIX/bin/nix-store" --load-db
-
-        echo "      Just finished getting the nix database ready."
-    )
+poly_user_shell_get() {
+    dsclattr "/Users/$1" "UserShell"
 }
 
-shell_source_lines() {
-    cat <<EOF
-
-# Nix
-if [ -e '$PROFILE_NIX_FILE' ]; then
-  . '$PROFILE_NIX_FILE'
-fi
-# End Nix
-
-EOF
+poly_user_shell_set() {
+    _sudo "in order to give $1 a safe home directory" \
+          /usr/bin/dscl . -create "/Users/$1" "UserShell" "$2"
 }
-configure_shell_profile() {
-    for profile_target in "${PROFILE_TARGETS[@]}"; do
-        if [ -e "$profile_target" ]; then
-            _sudo "to back up your current $profile_target to $profile_target$PROFILE_BACKUP_SUFFIX" \
-                  cp "$profile_target" "$profile_target$PROFILE_BACKUP_SUFFIX"
-
-            shell_source_lines \
-                | _sudo "extend your $profile_target with nix-daemon settings" \
-                        tee -a "$profile_target"
-        fi
-    done
 
+poly_user_in_group_check() {
+    username=$1
+    group=$2
+    dseditgroup -o checkmember -m "$username" "$group" > /dev/null 2>&1
 }
 
-setup_default_profile() {
-    _sudo "to installing a bootstrapping Nix in to the default Profile" \
-          HOME=$ROOT_HOME "$NIX_INSTALLED_NIX/bin/nix-env" -i "$NIX_INSTALLED_NIX"
-
-    _sudo "to installing a bootstrapping SSL certificate just for Nix in to the default Profile" \
-          HOME=$ROOT_HOME "$NIX_INSTALLED_NIX/bin/nix-env" -i "$NIX_INSTALLED_CACERT"
+poly_user_in_group_set() {
+    username=$1
+    group=$2
 
-    _sudo "to update the default channel in the default profile" \
-          HOME=$ROOT_HOME NIX_SSL_CERT_FILE=/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt "$NIX_INSTALLED_NIX/bin/nix-channel" --update nixpkgs
+    _sudo "Add $username to the $group group"\
+          /usr/sbin/dseditgroup -o edit -t user \
+          -a "$username" "$group"
 }
 
-
-place_nix_configuration() {
-    cat <<EOF > "$SCRATCH/nix.conf"
-build-users-group = $NIX_BUILD_GROUP_NAME
-
-max-jobs = $NIX_USER_COUNT
-cores = 1
-sandbox = false
-EOF
-    _sudo "to place the default nix daemon configuration (part 2)" \
-          install -m 0664 "$SCRATCH/nix.conf" /etc/nix/nix.conf
+poly_user_primary_group_get() {
+    dsclattr "/Users/$1" "PrimaryGroupID"
 }
 
-configure_nix_daemon_plist() {
-    _sudo "to set up the nix-daemon as a LaunchDaemon" \
-          ln -sfn "/nix/var/nix/profiles/default$PLIST_DEST" "$PLIST_DEST"
-
-    _sudo "to load the LaunchDaemon plist for nix-daemon" \
-          launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist
-
-    _sudo "to start the nix-daemon" \
-          launchctl start org.nixos.nix-daemon
-
+poly_user_primary_group_set() {
+    _sudo "to let the nix daemon use this user for builds (this might seem redundant, but there are two concepts of group membership)" \
+          /usr/bin/dscl . -create "/Users/$1" "PrimaryGroupID" "$2"
 }
 
+poly_create_build_user() {
+    username=$1
+    uid=$2
+    builder_num=$3
 
-main() {
-    welcome_to_nix
-    chat_about_sudo
-
-    if [ "${ALLOW_PREEXISTING_INSTALLATION:-}" = "" ]; then
-        validate_starting_assumptions
-    fi
-
-    setup_report
-
-    if ! ui_confirm "Ready to continue?"; then
-        ok "Alright, no changes have been made :)"
-        contactme
-        trap finish_cleanup EXIT
-        exit 1
-    fi
-
-    create_build_group
-    create_build_users
-    create_directories
-    place_channel_configuration
-    install_from_extracted_nix
-
-    configure_shell_profile
-
-    set +eu
-    . /etc/profile
-    set -eu
-
-    setup_default_profile
-    place_nix_configuration
-    configure_nix_daemon_plist
-
-    trap finish_success EXIT
+    _sudo "Creating the Nix build user (#$builder_num), $username" \
+          /usr/bin/dscl . create "/Users/$username" \
+          UniqueID "${uid}"
 }
-
-
-main
diff --git a/scripts/install-multi-user.sh b/scripts/install-multi-user.sh
new file mode 100644
index 0000000000..0e9500a98e
--- /dev/null
+++ b/scripts/install-multi-user.sh
@@ -0,0 +1,793 @@
+#!/usr/bin/env bash
+
+set -eu
+set -o pipefail
+
+# Sourced from:
+# - https://github.com/LnL7/nix-darwin/blob/8c29d0985d74b4a990238497c47a2542a5616b3c/bootstrap.sh
+# - https://gist.github.com/expipiplus1/e571ce88c608a1e83547c918591b149f/ac504c6c1b96e65505fbda437a28ce563408ecb0
+# - https://github.com/NixOS/nixos-org-configurations/blob/a122f418797713d519aadf02e677fce0dc1cb446/delft/scripts/nix-mac-installer.sh
+# - https://github.com/matthewbauer/macNixOS/blob/f6045394f9153edea417be90c216788e754feaba/install-macNixOS.sh
+# - https://gist.github.com/LnL7/9717bd6cdcb30b086fd7f2093e5f8494/86b26f852ce563e973acd30f796a9a416248c34a
+#
+# however tracking which bits came from which would be impossible.
+
+readonly ESC='\033[0m'
+readonly BOLD='\033[38;1m'
+readonly BLUE='\033[38;34m'
+readonly BLUE_UL='\033[38;4;34m'
+readonly GREEN='\033[38;32m'
+readonly GREEN_UL='\033[38;4;32m'
+readonly RED='\033[38;31m'
+readonly RED_UL='\033[38;4;31m'
+readonly YELLOW='\033[38;33m'
+readonly YELLOW_UL='\033[38;4;33m'
+
+readonly NIX_USER_COUNT="32"
+readonly NIX_BUILD_GROUP_ID="30000"
+readonly NIX_BUILD_GROUP_NAME="nixbld"
+readonly NIX_FIRST_BUILD_UID="30001"
+# Please don't change this. We don't support it, because the
+# default shell profile that comes with Nix doesn't support it.
+readonly NIX_ROOT="/nix"
+
+readonly PROFILE_TARGETS=("/etc/bashrc" "/etc/profile.d/nix.sh" "/etc/zshrc")
+readonly PROFILE_BACKUP_SUFFIX=".backup-before-nix"
+readonly PROFILE_NIX_FILE="$NIX_ROOT/var/nix/profiles/default/etc/profile.d/nix-daemon.sh"
+
+readonly NIX_INSTALLED_NIX="@nix@"
+readonly NIX_INSTALLED_CACERT="@cacert@"
+readonly EXTRACTED_NIX_PATH="$(dirname "$0")"
+
+readonly ROOT_HOME=$(echo ~root)
+
+if [ -t 0 ]; then
+    readonly IS_HEADLESS='no'
+else
+    readonly IS_HEADLESS='yes'
+fi
+
+headless() {
+    if [ "$IS_HEADLESS" = "yes" ]; then
+        return 0
+    else
+        return 1
+    fi
+}
+
+contactme() {
+    echo "We'd love to help if you need it."
+    echo ""
+    echo "If you can, open an issue at https://github.com/nixos/nix/issues"
+    echo ""
+    echo "Or feel free to contact the team,"
+    echo " - on IRC #nixos on irc.freenode.net"
+    echo " - on twitter @nixos_org"
+}
+
+uninstall_directions() {
+    subheader "Uninstalling nix:"
+    local step=0
+
+    if poly_service_installed_check; then
+        step=$((step + 1))
+        poly_service_uninstall_directions "$step"
+    fi
+
+    for profile_target in "${PROFILE_TARGETS[@]}"; do
+        if [ -e "$profile_target" ] && [ -e "$profile_target$PROFILE_BACKUP_SUFFIX" ]; then
+            step=$((step + 1))
+            cat <<EOF
+$step. Restore $profile_target$PROFILE_BACKUP_SUFFIX back to $profile_target
+
+  sudo mv $profile_target$PROFILE_BACKUP_SUFFIX $profile_target
+
+(after this one, you may need to re-open any terminals that were
+opened while it existed.)
+
+EOF
+        fi
+    done
+
+    step=$((step + 1))
+    cat <<EOF
+$step. Delete the files Nix added to your system:
+
+  sudo rm -rf /etc/nix $NIX_ROOT $ROOT_HOME/.nix-profile $ROOT_HOME/.nix-defexpr $ROOT_HOME/.nix-channels $HOME/.nix-profile $HOME/.nix-defexpr $HOME/.nix-channels
+
+and that is it.
+
+EOF
+
+}
+
+nix_user_for_core() {
+    printf "nixbld%d" "$1"
+}
+
+nix_uid_for_core() {
+    echo $((NIX_FIRST_BUILD_UID + $1 - 1))
+}
+
+_textout() {
+    echo -en "$1"
+    shift
+    if [ "$*" = "" ]; then
+        cat
+    else
+        echo "$@"
+    fi
+    echo -en "$ESC"
+}
+
+header() {
+    follow="---------------------------------------------------------"
+    header=$(echo "---- $* $follow$follow$follow" | head -c 80)
+    echo ""
+    _textout "$BLUE" "$header"
+}
+
+warningheader() {
+    follow="---------------------------------------------------------"
+    header=$(echo "---- $* $follow$follow$follow" | head -c 80)
+    echo ""
+    _textout "$RED" "$header"
+}
+
+subheader() {
+    echo ""
+    _textout "$BLUE_UL" "$*"
+}
+
+row() {
+    printf "$BOLD%s$ESC:\\t%s\\n" "$1" "$2"
+}
+
+task() {
+    echo ""
+    ok "~~> $1"
+}
+
+bold() {
+    echo "$BOLD$*$ESC"
+}
+
+ok() {
+    _textout "$GREEN" "$@"
+}
+
+warning() {
+    warningheader "warning!"
+    cat
+    echo ""
+}
+
+failure() {
+    header "oh no!"
+    _textout "$RED" "$@"
+    echo ""
+    _textout "$RED" "$(contactme)"
+    trap finish_cleanup EXIT
+    exit 1
+}
+
+ui_confirm() {
+    _textout "$GREEN$GREEN_UL" "$1"
+
+    if headless; then
+        echo "No TTY, assuming you would say yes :)"
+        return 0
+    fi
+
+    local prompt="[y/n] "
+    echo -n "$prompt"
+    while read -r y; do
+        if [ "$y" = "y" ]; then
+            echo ""
+            return 0
+        elif [ "$y" = "n" ]; then
+            echo ""
+            return 1
+        else
+            _textout "$RED" "Sorry, I didn't understand. I can only understand answers of y or n"
+            echo -n "$prompt"
+        fi
+    done
+    echo ""
+    return 1
+}
+
+__sudo() {
+    local expl="$1"
+    local cmd="$2"
+    shift
+    header "sudo execution"
+
+    echo "I am executing:"
+    echo ""
+    printf "    $ sudo %s\\n" "$cmd"
+    echo ""
+    echo "$expl"
+    echo ""
+
+    return 0
+}
+
+_sudo() {
+    local expl="$1"
+    shift
+    if ! headless; then
+        __sudo "$expl" "$*"
+    fi
+    sudo "$@"
+}
+
+
+readonly SCRATCH=$(mktemp -d -t tmp.XXXXXXXXXX)
+function finish_cleanup {
+    rm -rf "$SCRATCH"
+}
+
+function finish_fail {
+    finish_cleanup
+
+    failure <<EOF
+Jeeze, something went wrong. If you can take all the output and open
+an issue, we'd love to fix the problem so nobody else has this issue.
+
+:(
+EOF
+}
+trap finish_fail EXIT
+
+function finish_success {
+    finish_cleanup
+
+    ok "Alright! We're done!"
+    cat <<EOF
+
+Before Nix will work in your existing shells, you'll need to close
+them and open them again. Other than that, you should be ready to go.
+
+Try it! Open a new terminal, and type:
+
+  $ nix-shell -p nix-info --run "nix-info -m"
+
+Thank you for using this installer. If you have any feedback, don't
+hesitate:
+
+$(contactme)
+EOF
+}
+
+
+validate_starting_assumptions() {
+    poly_validate_assumptions
+
+    if [ $EUID -eq 0 ]; then
+        failure <<EOF
+Please do not run this script with root privileges. We will call sudo
+when we need to.
+EOF
+    fi
+
+    if type nix-env 2> /dev/null >&2; then
+        failure <<EOF
+Nix already appears to be installed, and this tool assumes it is
+_not_ yet installed.
+
+$(uninstall_directions)
+EOF
+    fi
+
+    if [ "${NIX_REMOTE:-}" != "" ]; then
+        failure <<EOF
+For some reason, \$NIX_REMOTE is set. It really should not be set
+before this installer runs, and it hints that Nix is currently
+installed. Please delete the old Nix installation and start again.
+
+Note: You might need to close your shell window and open a new shell
+to clear the variable.
+EOF
+    fi
+
+    if echo "${SSL_CERT_FILE:-}" | grep -qE "(nix/var/nix|nix-profile)"; then
+        failure <<EOF
+It looks like \$SSL_CERT_FILE is set to a path that used to be part of
+the old Nix installation. Please unset that variable and try again:
+
+  $ unset SSL_CERT_FILE
+
+EOF
+    fi
+
+    for file in ~/.bash_profile ~/.bash_login ~/.profile ~/.zshenv ~/.zprofile ~/.zshrc ~/.zlogin; do
+        if [ -f "$file" ]; then
+            if grep -l "^[^#].*.nix-profile" "$file"; then
+                failure <<EOF
+I found a reference to a ".nix-profile" in $file.
+This has a high chance of breaking a new nix installation. It was most
+likely put there by a previous Nix installer.
+
+Please remove this reference and try running this again. You should
+also look for similar references in:
+
+ - ~/.bash_profile
+ - ~/.bash_login
+ - ~/.profile
+
+or other shell init files that you may have.
+
+$(uninstall_directions)
+EOF
+            fi
+        fi
+    done
+
+    if [ -d /nix ]; then
+        failure <<EOF
+There are some relics of a previous installation of Nix at /nix, and
+this scripts assumes Nix is _not_ yet installed. Please delete the old
+Nix installation and start again.
+
+$(uninstall_directions)
+EOF
+    fi
+
+    if [ -d /etc/nix ]; then
+        failure <<EOF
+There are some relics of a previous installation of Nix at /etc/nix, and
+this scripts assumes Nix is _not_ yet installed. Please delete the old
+Nix installation and start again.
+
+$(uninstall_directions)
+EOF
+    fi
+
+    for profile_target in "${PROFILE_TARGETS[@]}"; do
+        if [ -e "$profile_target$PROFILE_BACKUP_SUFFIX" ]; then
+        failure <<EOF
+When this script runs, it backs up the current $profile_target to
+$profile_target$PROFILE_BACKUP_SUFFIX. This backup file already exists, though.
+
+Please follow these instructions to clean up the old backup file:
+
+1. Copy $profile_target and $profile_target$PROFILE_BACKUP_SUFFIX to another place, just
+in case.
+
+2. Take care to make sure that $profile_target$PROFILE_BACKUP_SUFFIX doesn't look like
+it has anything nix-related in it. If it does, something is probably
+quite wrong. Please open an issue or get in touch immediately.
+
+3. Take care to make sure that $profile_target doesn't look like it has
+anything nix-related in it. If it does, and $profile_target _did not_,
+run:
+
+  $ /usr/bin/sudo /bin/mv $profile_target$PROFILE_BACKUP_SUFFIX $profile_target
+
+and try again.
+EOF
+        fi
+
+        if grep -qi "nix" "$profile_target"; then
+            failure <<EOF
+It looks like $profile_target already has some Nix configuration in
+there. There should be no reason to run this again. If you're having
+trouble, please open an issue.
+EOF
+        fi
+    done
+
+    danger_paths=("$ROOT_HOME/.nix-defexpr" "$ROOT_HOME/.nix-channels" "$ROOT_HOME/.nix-profile")
+    for danger_path in "${danger_paths[@]}"; do
+        if _sudo "making sure that $danger_path doesn't exist" \
+           test -e "$danger_path"; then
+            failure <<EOF
+I found a file at $danger_path, which is a relic of a previous
+installation. You must first delete this file before continuing.
+
+$(uninstall_directions)
+EOF
+        fi
+    done
+}
+
+setup_report() {
+    header "Nix config report"
+    row "        Temp Dir" "$SCRATCH"
+    row "        Nix Root" "$NIX_ROOT"
+    row "     Build Users" "$NIX_USER_COUNT"
+    row "  Build Group ID" "$NIX_BUILD_GROUP_ID"
+    row "Build Group Name" "$NIX_BUILD_GROUP_NAME"
+    if [ "${ALLOW_PREEXISTING_INSTALLATION:-}" != "" ]; then
+        row "Preexisting Install" "Allowed"
+    fi
+
+    subheader "build users:"
+
+    row "    Username" "UID"
+    for i in $(seq 1 "$NIX_USER_COUNT"); do
+        row "     $(nix_user_for_core "$i")" "$(nix_uid_for_core "$i")"
+    done
+    echo ""
+}
+
+create_build_group() {
+    local primary_group_id
+
+    task "Setting up the build group $NIX_BUILD_GROUP_NAME"
+    if ! poly_group_exists "$NIX_BUILD_GROUP_NAME"; then
+        poly_create_build_group
+        row "            Created" "Yes"
+    else
+        primary_group_id=$(poly_group_id_get "$NIX_BUILD_GROUP_NAME")
+        if [ "$primary_group_id" -ne "$NIX_BUILD_GROUP_ID" ]; then
+            failure <<EOF
+It seems the build group $NIX_BUILD_GROUP_NAME already exists, but
+with the UID $primary_group_id. This script can't really handle
+that right now, so I'm going to give up.
+
+You can fix this by editing this script and changing the
+NIX_BUILD_GROUP_ID variable near the top to from $NIX_BUILD_GROUP_ID
+to $primary_group_id and re-run.
+EOF
+        else
+            row "            Exists" "Yes"
+        fi
+    fi
+}
+
+create_build_user_for_core() {
+    local coreid
+    local username
+    local uid
+
+    coreid="$1"
+    username=$(nix_user_for_core "$coreid")
+    uid=$(nix_uid_for_core "$coreid")
+
+    task "Setting up the build user $username"
+
+    if ! poly_user_exists "$username"; then
+        poly_create_build_user "$username" "$uid" "$coreid"
+        row "           Created" "Yes"
+    else
+        actual_uid=$(poly_user_id_get "$username")
+        if [ "$actual_uid" -ne "$uid" ]; then
+            failure <<EOF
+It seems the build user $username already exists, but with the UID
+with the UID $actual_uid. This script can't really handle that right
+now, so I'm going to give up.
+
+If you already created the users and you know they start from
+$actual_uid and go up from there, you can edit this script and change
+NIX_FIRST_BUILD_UID near the top of the file to $actual_uid and try
+again.
+EOF
+        else
+            row "            Exists" "Yes"
+        fi
+    fi
+
+    if [ "$(poly_user_hidden_get "$username")" = "1" ]; then
+        row "            Hidden" "Yes"
+    else
+        poly_user_hidden_set "$username"
+        row "            Hidden" "Yes"
+    fi
+
+    if [ "$(poly_user_home_get "$username")" = "/var/empty" ]; then
+        row "    Home Directory" "/var/empty"
+    else
+        poly_user_home_set "$username" "/var/empty"
+        row "    Home Directory" "/var/empty"
+    fi
+
+    if [ "$(poly_user_note_get "$username")" = "Nix build user $coreid" ]; then
+        row "              Note" "Nix build user $coreid"
+    else
+        poly_user_note_set "$username" "Nix build user $coreid"
+        row "              Note" "Nix build user $coreid"
+    fi
+
+    if [ "$(poly_user_shell_get "$username")" = "/sbin/nologin" ]; then
+        row "   Logins Disabled" "Yes"
+    else
+        poly_user_shell_set "$username" "/sbin/nologin"
+        row "   Logins Disabled" "Yes"
+    fi
+
+    if poly_user_in_group_check "$username" "$NIX_BUILD_GROUP_NAME"; then
+        row "  Member of $NIX_BUILD_GROUP_NAME" "Yes"
+    else
+        poly_user_in_group_set "$username" "$NIX_BUILD_GROUP_NAME"
+        row "  Member of $NIX_BUILD_GROUP_NAME" "Yes"
+    fi
+
+    if [ "$(poly_user_primary_group_get "$username")" = "$NIX_BUILD_GROUP_ID" ]; then
+        row "    PrimaryGroupID" "$NIX_BUILD_GROUP_ID"
+    else
+        poly_user_primary_group_set "$username" "$NIX_BUILD_GROUP_ID"
+        row "    PrimaryGroupID" "$NIX_BUILD_GROUP_ID"
+    fi
+}
+
+create_build_users() {
+    for i in $(seq 1 "$NIX_USER_COUNT"); do
+        create_build_user_for_core "$i"
+    done
+}
+
+create_directories() {
+    _sudo "to make the basic directory structure of Nix (part 1)" \
+          mkdir -pv -m 0755 /nix /nix/var /nix/var/log /nix/var/log/nix /nix/var/log/nix/drvs /nix/var/nix{,/db,/gcroots,/profiles,/temproots,/userpool}
+
+    _sudo "to make the basic directory structure of Nix (part 2)" \
+          mkdir -pv -m 1777 /nix/var/nix/{gcroots,profiles}/per-user
+
+    _sudo "to make the basic directory structure of Nix (part 3)" \
+          mkdir -pv -m 1775 /nix/store
+
+    _sudo "to make the basic directory structure of Nix (part 4)" \
+          chgrp "$NIX_BUILD_GROUP_NAME" /nix/store
+
+    _sudo "to set up the root user's profile (part 1)" \
+          mkdir -pv -m 0755 /nix/var/nix/profiles/per-user/root
+
+    _sudo "to set up the root user's profile (part 2)" \
+          mkdir -pv -m 0700 "$ROOT_HOME/.nix-defexpr"
+
+    _sudo "to place the default nix daemon configuration (part 1)" \
+          mkdir -pv -m 0555 /etc/nix
+}
+
+place_channel_configuration() {
+    echo "https://nixos.org/channels/nixpkgs-unstable nixpkgs" > "$SCRATCH/.nix-channels"
+    _sudo "to set up the default system channel (part 1)" \
+          install -m 0664 "$SCRATCH/.nix-channels" "$ROOT_HOME/.nix-channels"
+}
+
+welcome_to_nix() {
+    ok "Welcome to the Multi-User Nix Installation"
+
+    cat <<EOF
+
+This installation tool will set up your computer with the Nix package
+manager. This will happen in a few stages:
+
+1. Make sure your computer doesn't already have Nix. If it does, I
+   will show you instructions on how to clean up your old one.
+
+2. Show you what we are going to install and where. Then we will ask
+   if you are ready to continue.
+
+3. Create the system users and groups that the Nix daemon uses to run
+   builds.
+
+4. Perform the basic installation of the Nix files daemon.
+
+5. Configure your shell to import special Nix Profile files, so you
+   can use Nix.
+
+6. Start the Nix daemon.
+
+EOF
+
+    if ui_confirm "Would you like to see a more detailed list of what we will do?"; then
+        cat <<EOF
+
+We will:
+
+ - make sure your computer doesn't already have Nix files
+   (if it does, I  will tell you how to clean them up.)
+ - create local users (see the list above for the users we'll make)
+ - create a local group ($NIX_BUILD_GROUP_NAME)
+ - install Nix in to $NIX_ROOT
+ - create a configuration file in /etc/nix
+ - set up the "default profile" by creating some Nix-related files in
+   $ROOT_HOME
+EOF
+        for profile_target in "${PROFILE_TARGETS[@]}"; do
+            if [ -e "$profile_target" ]; then
+                cat <<EOF
+ - back up $profile_target to $profile_target$PROFILE_BACKUP_SUFFIX
+ - update $profile_target to include some Nix configuration
+EOF
+            fi
+        done
+        poly_service_setup_note
+        if ! ui_confirm "Ready to continue?"; then
+            failure <<EOF
+Okay, maybe you would like to talk to the team.
+EOF
+        fi
+    fi
+}
+
+chat_about_sudo() {
+    header "let's talk about sudo"
+
+    if headless; then
+        cat <<EOF
+This script is going to call sudo a lot. Normally, it would show you
+exactly what commands it is running and why. However, the script is
+run in a headless fashion, like this:
+
+  $ curl https://nixos.org/nix/install | sh
+
+or maybe in a CI pipeline. Because of that, we're going to skip the
+verbose output in the interest of brevity.
+
+If you would like to
+see the output, try like this:
+
+  $ curl -o install-nix https://nixos.org/nix/install
+  $ sh ./install-nix
+
+EOF
+        return 0
+    fi
+
+    cat <<EOF
+This script is going to call sudo a lot. Every time we do, it'll
+output exactly what it'll do, and why.
+
+Just like this:
+EOF
+
+    __sudo "to demonstrate how our sudo prompts look" \
+           echo "this is a sudo prompt"
+
+    cat <<EOF
+
+This might look scary, but everything can be undone by running just a
+few commands. We used to ask you to confirm each time sudo ran, but it
+was too many times. Instead, I'll just ask you this one time:
+
+EOF
+    if ui_confirm "Can we use sudo?"; then
+        ok "Yay! Thanks! Let's get going!"
+    else
+        failure <<EOF
+That is okay, but we can't install.
+EOF
+    fi
+}
+
+install_from_extracted_nix() {
+    (
+        cd "$EXTRACTED_NIX_PATH"
+
+        _sudo "to copy the basic Nix files to the new store at $NIX_ROOT/store" \
+              rsync -rlpt ./store/* "$NIX_ROOT/store/"
+
+        if [ -d "$NIX_INSTALLED_NIX" ]; then
+            echo "      Alright! We have our first nix at $NIX_INSTALLED_NIX"
+        else
+            failure <<EOF
+Something went wrong, and I didn't find Nix installed at
+$NIX_INSTALLED_NIX.
+EOF
+        fi
+
+        _sudo "to initialize the Nix Database" \
+              $NIX_INSTALLED_NIX/bin/nix-store --init
+
+        cat ./.reginfo \
+            | _sudo "to load data for the first time in to the Nix Database" \
+                   "$NIX_INSTALLED_NIX/bin/nix-store" --load-db
+
+        echo "      Just finished getting the nix database ready."
+    )
+}
+
+shell_source_lines() {
+    cat <<EOF
+
+# Nix
+if [ -e '$PROFILE_NIX_FILE' ]; then
+  . '$PROFILE_NIX_FILE'
+fi
+# End Nix
+
+EOF
+}
+
+configure_shell_profile() {
+    # If there is an /etc/profile.d directory, we want to ensure there
+    # is a nix.sh within it, so we can use the following loop to add
+    # the source lines to it. Note that I'm _not_ adding the source
+    # lines here, because we want to be using the regular machinery.
+    #
+    # If we go around that machinery, it becomes more complicated and
+    # adds complications to the uninstall instruction generator and
+    # old instruction sniffer as well.
+    if [ -d /etc/profile.d ]; then
+        _sudo "create a stub /etc/profile.d/nix.sh which will be updated" \
+              touch /etc/profile.d/nix.sh
+    fi
+
+    for profile_target in "${PROFILE_TARGETS[@]}"; do
+        if [ -e "$profile_target" ]; then
+            _sudo "to back up your current $profile_target to $profile_target$PROFILE_BACKUP_SUFFIX" \
+                  cp "$profile_target" "$profile_target$PROFILE_BACKUP_SUFFIX"
+
+            shell_source_lines \
+                | _sudo "extend your $profile_target with nix-daemon settings" \
+                        tee -a "$profile_target"
+        fi
+    done
+}
+
+setup_default_profile() {
+    _sudo "to installing a bootstrapping Nix in to the default Profile" \
+          HOME="$ROOT_HOME" "$NIX_INSTALLED_NIX/bin/nix-env" -i "$NIX_INSTALLED_NIX"
+
+    _sudo "to installing a bootstrapping SSL certificate just for Nix in to the default Profile" \
+          HOME="$ROOT_HOME" "$NIX_INSTALLED_NIX/bin/nix-env" -i "$NIX_INSTALLED_CACERT"
+
+    _sudo "to update the default channel in the default profile" \
+          HOME="$ROOT_HOME" NIX_SSL_CERT_FILE=/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt "$NIX_INSTALLED_NIX/bin/nix-channel" --update nixpkgs
+}
+
+
+place_nix_configuration() {
+    cat <<EOF > "$SCRATCH/nix.conf"
+build-users-group = $NIX_BUILD_GROUP_NAME
+
+max-jobs = $NIX_USER_COUNT
+cores = 1
+sandbox = false
+EOF
+    _sudo "to place the default nix daemon configuration (part 2)" \
+          install -m 0664 "$SCRATCH/nix.conf" /etc/nix/nix.conf
+}
+
+main() {
+    if [ "$(uname -s)" = "Darwin" ]; then
+        # shellcheck source=./install-darwin-multi-user.sh
+        . "$EXTRACTED_NIX_PATH/install-darwin-multi-user.sh"
+    elif [ "$(uname -s)" = "Linux" ] && [ -e /run/systemd/system ]; then
+        # shellcheck source=./install-systemd-multi-user.sh
+        . "$EXTRACTED_NIX_PATH/install-systemd-multi-user.sh"
+    else
+        failure "Sorry, I don't know what to do on $(uname)"
+    fi
+
+    welcome_to_nix
+    chat_about_sudo
+
+    if [ "${ALLOW_PREEXISTING_INSTALLATION:-}" = "" ]; then
+        validate_starting_assumptions
+    fi
+
+    setup_report
+
+    if ! ui_confirm "Ready to continue?"; then
+        ok "Alright, no changes have been made :)"
+        contactme
+        trap finish_cleanup EXIT
+        exit 1
+    fi
+
+    create_build_group
+    create_build_users
+    create_directories
+    place_channel_configuration
+    install_from_extracted_nix
+
+    configure_shell_profile
+
+    set +eu
+    . /etc/profile
+    set -eu
+
+    setup_default_profile
+    place_nix_configuration
+    poly_configure_nix_daemon_service
+
+    trap finish_success EXIT
+}
+
+
+main
diff --git a/scripts/install-nix-from-closure.sh b/scripts/install-nix-from-closure.sh
index 3e5676f419..8416fb9673 100644
--- a/scripts/install-nix-from-closure.sh
+++ b/scripts/install-nix-from-closure.sh
@@ -29,8 +29,15 @@ if [ "$(uname -s)" = "Darwin" ]; then
         exit 1
     fi
 
-    printf '\e[1;31mSwitching to the Multi-User Darwin Installer\e[0m\n'
-    exec "$self/install-darwin-multi-user"
+    printf '\e[1;31mSwitching to the Daemon-based Installer\e[0m\n'
+    exec "$self/install-multi-user"
+    exit 0
+fi
+
+# Linux & Systemd support
+if [ "$(uname -s)" = "Linux" ] && [ -e /run/systemd/system ]; then
+    printf '\e[1;31mSwitching to the Daemon-based Installer\e[0m\n'
+    exec "$self/install-multi-user"
     exit 0
 fi
 
diff --git a/scripts/install-systemd-multi-user.sh b/scripts/install-systemd-multi-user.sh
new file mode 100644
index 0000000000..04bc539a10
--- /dev/null
+++ b/scripts/install-systemd-multi-user.sh
@@ -0,0 +1,154 @@
+#!/usr/bin/env bash
+
+set -eu
+set -o pipefail
+
+readonly SERVICE_SRC=/lib/systemd/system/nix-daemon.service
+readonly SERVICE_DEST=/etc/systemd/system/nix-daemon.service
+
+readonly SOCKET_SRC=/lib/systemd/system/nix-daemon.socket
+readonly SOCKET_DEST=/etc/systemd/system/nix-daemon.socket
+
+poly_validate_assumptions() {
+    if [ "$(uname -s)" != "Linux" ]; then
+        failure "This script is for use with Linux!"
+    fi
+}
+
+poly_service_installed_check() {
+    [ "$(systemctl is-enabled nix-daemon.service)" = "linked" ] \
+        || [ "$(systemctl is-enabled nix-daemon.socket)" = "enabled" ]
+}
+
+poly_service_uninstall_directions() {
+        cat <<EOF
+$1. Delete the systemd service and socket units
+
+  sudo systemctl stop nix-daemon.socket
+  sudo systemctl stop nix-daemon.service
+  sudo systemctl disable nix-daemon.socket
+  sudo systemctl disable nix-daemon.service
+  sudo systemctl daemon-reload
+EOF
+}
+
+poly_service_setup_note() {
+    cat <<EOF
+ - load and start a service (at $SERVICE_DEST
+   and $SOCKET_DEST) for nix-daemon
+
+EOF
+}
+
+poly_configure_nix_daemon_service() {
+    _sudo "to set up the nix-daemon service" \
+          systemctl link "/nix/var/nix/profiles/default$SERVICE_SRC"
+
+    _sudo "to set up the nix-daemon socket service" \
+          systemctl enable "/nix/var/nix/profiles/default$SOCKET_SRC"
+
+    _sudo "to load the systemd unit for nix-daemon" \
+          systemctl daemon-reload
+
+    _sudo "to start the nix-daemon.socket" \
+          systemctl start nix-daemon.socket
+
+    _sudo "to start the nix-daemon.service" \
+          systemctl start nix-daemon.service
+
+}
+
+poly_group_exists() {
+    getent group "$1" > /dev/null 2>&1
+}
+
+poly_group_id_get() {
+    getent group "$1" | cut -d: -f3
+}
+
+poly_create_build_group() {
+    _sudo "Create the Nix build group, $NIX_BUILD_GROUP_NAME" \
+          groupadd -g "$NIX_BUILD_GROUP_ID" --system \
+          "$NIX_BUILD_GROUP_NAME" >&2
+}
+
+poly_user_exists() {
+    getent passwd "$1" > /dev/null 2>&1
+}
+
+poly_user_id_get() {
+    getent passwd "$1" | cut -d: -f3
+}
+
+poly_user_hidden_get() {
+    echo "1"
+}
+
+poly_user_hidden_set() {
+    true
+}
+
+poly_user_home_get() {
+    getent passwd "$1" | cut -d: -f6
+}
+
+poly_user_home_set() {
+    _sudo "in order to give $1 a safe home directory" \
+          usermod --home "$2" "$1"
+}
+
+poly_user_note_get() {
+    getent passwd "$1" | cut -d: -f5
+}
+
+poly_user_note_set() {
+    _sudo "in order to give $1 a useful comment" \
+          usermod --comment "$2" "$1"
+}
+
+poly_user_shell_get() {
+    getent passwd "$1" | cut -d: -f7
+}
+
+poly_user_shell_set() {
+    _sudo "in order to prevent $1 from logging in" \
+          usermod --shell "$2" "$1"
+}
+
+poly_user_in_group_check() {
+    groups "$1" | grep -q "$2" > /dev/null 2>&1
+}
+
+poly_user_in_group_set() {
+    _sudo "Add $1 to the $2 group"\
+          usermod --append --groups "$2" "$1"
+}
+
+poly_user_primary_group_get() {
+    getent passwd "$1" | cut -d: -f4
+}
+
+poly_user_primary_group_set() {
+    _sudo "to let the nix daemon use this user for builds (this might seem redundant, but there are two concepts of group membership)" \
+          usermod --gid "$2" "$1"
+
+}
+
+poly_create_build_user() {
+    username=$1
+    uid=$2
+    builder_num=$3
+
+    _sudo "Creating the Nix build user, $username" \
+          useradd \
+          --home-dir /var/empty \
+          --comment "Nix build user $builder_num" \
+          --gid "$NIX_BUILD_GROUP_ID" \
+          --groups "$NIX_BUILD_GROUP_NAME" \
+          --no-user-group \
+          --system \
+          --shell /sbin/nologin \
+          --uid "$uid" \
+          --password "!" \
+          "$username"
+}