diff --git a/scripts/install-nix-from-closure.sh b/scripts/install-nix-from-closure.sh
index ab20774bbf0..f6a4d4f9fcc 100644
--- a/scripts/install-nix-from-closure.sh
+++ b/scripts/install-nix-from-closure.sh
@@ -1,184 +1,896 @@
 #!/bin/sh
+## NOTE: If you would decide to change shebang to `/usr/bin/env sh`
+## - investigate the question more to be really sure,
+## as `/usr/bin/env sh` usage is less portable then `/bin/sh`,
+## at least - using env is much less secure.
+
+
+###############################
+###  Main information
+###############################
+{
+
+#
+# Nix installation script
+# Shell script for POSIX-comapible environments
+#
+###############################
+#
+# Upstream URL:
+# https://github.com/NixOS/nix/blob/master/scripts/install-nix-from-closure.sh
+#
+# Currently script follows POSIX.1-2017 (POSIX is simultaneously the
+# IEEE Std 1003.1™-2017 and the
+# The Open Group Technical Standard Base Specifications, Issue 7)
+# POSIX standard is accessible at:
+# http://pubs.opengroup.org/onlinepubs/9699919799
+#
+# Script strives to be fully transactional, as much as shell script can be.
+# That means that only after all required checks script starts to do changes.
+# And if script not succeeds in some action - it catches the error and
+# rolls back, if that is possible with a shell script.
+#
+# If you foud a way to improve the script - let us know.
+#
+#
+# Additional notes:
+# `/bin/sh -u` is not possible to do, because many Docker environments
+# have unset USER variable.
+#
+true # so {...} body has some code, shell will not permit otherwise
+
+}
+
+
+###############################
+###  Documentation
+###############################
+{
+
+#
+#      Installer consist of:
+#      1. Setup environment
+#      2. Main constants
+#      3. CLI control constants
+#      4. CLI output functions
+#      5. Program stage functions
+#      6. Main function
+#      7. Invocation of the main function (aka "Start of the script")
+#
+#
+
+# Special things about this script
+#
+# 1) Script tries to be fully POSIX compatible,
+# code heavy follows that requirement.
+#
+# 2) Notice, Warning, Error, ErrorRevert level massages have a special
+# functions. That is done to be:
+#   * uniformal in output
+#   * proper color highlihtgting
+#   * proper message classification
+#   * informative for the user
+#   * convinient for use in the code
+#   * code readability
+#   * less function invocations
+#   * to have an extendable and editable output system in a shell script
+# all at the same time.
+#
+# Message body starts from a new line.
+# And has 4 spaces from the left. Always.
+#
+# Code example:
+###############################
+#
+#        notice "
+#
+#    Install executed for ROOT.
+#
+#    Doing classic Linux package manager mode.
+#    In Nix this mode is called: single-user mode for root.
+#
+#    Nix can do multi-user mode, and manage package trees for users
+#    independently.
+#    "
+#
+###############################
+#
+# This is the best balance of code simplicity and code readability found so far.
+#
+# Output of the example (in a green color):
+###############################
+#
+#./install: Notice:
+#
+#    Install executed for ROOT.
+#
+#    Doing classic Linux package manager mode.
+#    In Nix this mode is called: single-user mode for root.
+#
+#    Nix can do multi-user mode, and manage package trees for users
+#    independently.
+#
+###############################
+#
+true # so {...} body has some code, shell will not permit otherwise
+
+}
+
+
+###############################
+###  Setup environment
+###############################
+{
+
+# Set the character collating sequence to be numeric ASCII/C standard.
+readonly LC_COLLATE=C
+# Set the character set to be the standard one-byte ASCII.
+readonly LANG=C
+# Set default umask; to be non-restrictive and friendly to others.
+# umask obviously can heavy influence Nix work, and functioning of packages.
+umask 022
+
+}
+
+
+###############################
+###  Main constants
+###############################
+{
+
+# NOTE: If you are changing the destanation from `/nix` to something other -
+# please read the link:
+# https://nixos.org/nixos/nix-pills/install-on-your-running-system.html#idm140737316619344
+# TL;DR: Destination path change - changes the package hashes.
+# Nix relies on hashes to determine packages.
+# Local hashes & the central binary cache repository hashes not going to match.
+# That mean that Nix going to compile packages from sources.
+readonly dest='/nix'
+readonly self="$(dirname "$(realpath "$0")")"
+readonly nix="@nix@"
+readonly cacert="@cacert@"
+readonly appname="$0"
+
+}
+
+
+###############################
+###  CLI control constants
+###############################
+{
+
+# This chain is created to output color for normal circumstances.
+# If CI desides to report to the processes that they run in a terminal,
+# while at the same time CI not took effort to parse the terminal color
+# commands, and also not took effort to have according to it's possibilities
+# $TERM configuration record in a termcap DB - well it is really on a CI.
+
+# If the file descriptor reports a terminal - then try to use correct DB colors
+if test -t ; then
+    # If terminal reports a terminfo/termcap DB of colors available - use DB.
+    # Else - use literal color codes.
+    if tput colors > /dev/null 2>&1 ; then
+        # use tput and terminfo DB
+        readonly red=$(tput setaf 1)
+        readonly green=$(tput setaf 2)
+        readonly yellow=$(tput setaf 3)
+        readonly blue=$(tput setaf 4)
+        readonly bold=$(tput smso)
+        readonly reset=$(tput sgr0) # Reset to default output
+    else
+        # tput is not present on some systems (Alpine Linux),
+        # this trick allows to store, not 'codes' - literal term command symbol.
+        readonly red=$(printf '\033[1;31m')
+        readonly green=$(printf '\033[1;32m')
+        readonly yellow=$(printf '\033[1;33m')
+        readonly blue=$(printf '\033[1;34m')
+        readonly bold=$(printf '\033[1m')
+        readonly reset=$(printf '\033[0;m') # Reset to default output
+    fi
+fi
 
-set -e
+}
 
-dest="/nix"
-self="$(dirname "$0")"
-nix="@nix@"
-cacert="@cacert@"
 
+###############################
+###  CLI output functions
+###############################
+{
 
-if ! [ -e "$self/.reginfo" ]; then
-    echo "$0: incomplete installer (.reginfo is missing)" >&2
-fi
+# NOTE: Script output corresponds to the classification of massages
+# [RFC 5424](https://tools.ietf.org/html/rfc5424) - "The Syslog Protocol"
+# Standard holds an industy-wide agreed criterias for messages.
+# For example, systemd/journald messages fully correspond to RFC 5424.
 
-if [ -z "$USER" ]; then
-    echo "$0: \$USER is not set" >&2
-    exit 1
-fi
+# NOTE: Unified output function
+# Every message in the script gets eventually printed by this function
+print() {
+    # Using `printf`, because it is more portable than `echo`.
 
-if [ -z "$HOME" ]; then
-    echo "$0: \$HOME is not set" >&2
-    exit 1
-fi
+    # Would take message from "$message", or from the first argument.
+    # So using it for both flaxibly chaining for any functions and both
+    # a as simple:
+    # print 'Output message to user'
+    # - are both possible at the same time.
+    if [ -z "$message" ]; then
+        message="$1"
+    fi
+    if [ -z "$color" ]; then
+        color="$reset"
+    fi
+    if [ -z "$prefix" ]; then
+        prefix='Info'
+    fi
 
-# macOS support for 10.10 or higher
-if [ "$(uname -s)" = "Darwin" ]; then
-    if [ $(($(sw_vers -productVersion | cut -d '.' -f 2))) -lt 10 ]; then
-        echo "$0: macOS $(sw_vers -productVersion) is not supported, upgrade to 10.10 or higher"
+    # This line makes all prints in script
+    # Form of message:
+    # Application: Prefix: Body of message
+    printf '%s%s: %s: %s%s\n' "$color" "$appname" "$prefix" "$message" "$reset"
+
+    # At this lines, output of message is done. So unset print variables.
+    unset color
+    unset prefix
+    unset message
+}
+
+# Since 'info' name is already taken by the well known Unix textinfo reader -
+# just use 'print' for Info level messages
+
+notice() {
+    message="$1"
+    color="$green"
+    prefix='Notice'
+    print
+}
+
+warning() {
+    message="$1"
+    color="$yellow"
+    prefix='Warning'
+    >&2 print
+}
+
+# NOTE: 'error' throws the exit signal
+error() {
+    message="$1"
+    exitSig="$2"
+    color="$red"
+    prefix='Error'
+    >&2 print
+    if [ -z "$exitSig" ]; then
         exit 1
     fi
-fi
+}
 
-# Determine if we could use the multi-user installer or not
-if [ "$(uname -s)" = "Darwin" ]; then
-    echo "Note: a multi-user installation is possible. See https://nixos.org/nix/manual/#sect-multi-user-installation" >&2
-elif [ "$(uname -s)" = "Linux" ] && [ -e /run/systemd/system ]; then
-    echo "Note: a multi-user installation is possible. See https://nixos.org/nix/manual/#sect-multi-user-installation" >&2
-fi
+# NOTE: 'errorRevert' is a function to print messages in 'error' form
+# when script catches an error and during a revert.
+# It does not throw exit signal, so we can keep add to the error message
+# before we decide in the end to launch the 'error' that throws exit signal.
+errorRevert() {
+    message="$1"
+    color="$red"
+    prefix='Error'
+    >&2 print
+}
 
-INSTALL_MODE=no-daemon
-# Trivially handle the --daemon / --no-daemon options
-if [ "x${1:-}" = "x--no-daemon" ]; then
-    INSTALL_MODE=no-daemon
-elif [ "x${1:-}" = "x--daemon" ]; then
-    INSTALL_MODE=daemon
-elif [ "x${1:-}" != "x" ]; then
-    (
-        echo "Nix Installer [--daemon|--no-daemon]"
-
-        echo "Choose installation method."
-        echo ""
-        echo " --daemon:    Installs and configures a background daemon that manages the store,"
-        echo "              providing multi-user support and better isolation for local builds."
-        echo "              Both for security and reproducibility, this method is recommended if"
-        echo "              supported on your platform."
-        echo "              See https://nixos.org/nix/manual/#sect-multi-user-installation"
-        echo ""
-        echo " --no-daemon: Simple, single-user installation that does not require root and is"
-        echo "              trivial to uninstall."
-        echo "              (default)"
-        echo ""
-    ) >&2
-    exit
-fi
+contactUs() {
+    print '
 
-if [ "$INSTALL_MODE" = "daemon" ]; then
-    printf '\e[1;31mSwitching to the Daemon-based Installer\e[0m\n'
-    exec "$self/install-multi-user"
-    exit 0
-fi
+    To search/open bugreports: https://github.com/nixos/nix/issues
 
-if [ "$(id -u)" -eq 0 ]; then
-    printf '\e[1;31mwarning: installing Nix as root is not supported by this script!\e[0m\n'
-fi
+    To contact the team and community:
+     - IRC: #nixos on irc.freenode.net
+     - Twitter: @nixos_org
 
-echo "performing a single-user installation of Nix..." >&2
+    Matrix community rooms: https://matrix.to/#/@nix:matrix.org
+                            https://matrix.to/#/@nixos:matrix.org
+    '
+}
 
-if ! [ -e $dest ]; then
-    cmd="mkdir -m 0755 $dest && chown $USER $dest"
-    echo "directory $dest does not exist; creating it by running '$cmd' using sudo" >&2
-    if ! sudo sh -c "$cmd"; then
-        echo "$0: please manually run '$cmd' as root to create $dest" >&2
-        exit 1
-    fi
-fi
+}
 
-if ! [ -w $dest ]; then
-    echo "$0: directory $dest exists, but is not writable by you. This could indicate that another user has already performed a single-user installation of Nix on this system. If you wish to enable multi-user support see http://nixos.org/nix/manual/#ssec-multi-user. If you wish to continue with a single-user install for $USER please run 'chown -R $USER $dest' as root." >&2
-    exit 1
-fi
 
-mkdir -p $dest/store
+###############################
+###  Checking requirements
+###############################
+{
+
+checkingRequirements() {
+# NOTE: This function - checks only, - do not make any changes to the system.
+# And becouse of that and POSIx - it can be universally reused.
 
-printf "copying Nix to %s..." "${dest}/store" >&2
+    checkBundle() {
+        if ! [ -e "$self/.reginfo" ]; then
+            error "
+
+    Installer is incomplete ('$self/.reginfo' is missing)
+    "
+        fi
+    }
+
+    checkEnv() {
+
+        if [ "$(id -u)" -eq 0 ]; then
+            # TODO: At least merge single/multiuser,
+            # when https://github.com/NixOS/nix/issues/1559 solved.
+            # TODO: Reword after scripts integration and option switching
+            # becomes clear.
+            notice "
+
+    Install executed for ROOT.
+
+    Doing systemwide root install - this is classic Linux package manager mode.
+    In Nix this mode is called: single-user mode for root.
+
+    Nix has a multi-user mode.
+    That is the main Nix mode,
+    it allows users manage their own independent trees of packages.
+    "
+        fi
+
+        # In case USER is not set
+        # Example: running inside container
+        if [ -z "$USER" ]; then
+            notice "
+
+    Environment variable USER is not set.
+    "
+            readonly USER="$(id -u -n)"    # id is POSIX
+            print "Detected username: $USER"
+        fi
+
+        if [ -z "$HOME" ]; then
+            error "
+
+    Environment variable HOME is not set.
+    "
+        fi
+
+    }
+
+    checkHome() {
+
+        if [ ! -e "$HOME" ]; then
+            error "
+
+    Home directory '$HOME' does not exist.
+    "
+        fi
+
+    # -d also resolves symbolic soft links if they point to directory
+        if [ ! -d "$HOME" ]; then
+            error "
+
+    Home directory '$HOME' is not a directory, nor a link to one.
+    "
+        fi
+
+        if [ ! -w "$HOME" ]; then
+            error "
+
+    Home directory '$HOME' is not writable for user '$USER'. No deal.
+    "
+        fi
+
+        # POSIX: `ls` is only able. No `test -O`, `find` can do this in POSIX
+        # AWK is more portable then `cut -d'c' -fN`
+        if [ "$(ls -ld "$HOME" | awk '{print $3}')" != "$USER" ]; then
+            contactUs    # Let's get particular reports and solutions
+            error "
+
+    Home directory '$HOME' is not owned by user '$USER'.
+    If you have legitimate case, please file a bug with description.
+    We gather information on particular cases.
+    "
+        fi
+
+        if [ ! -x "$HOME" ]; then
+            error "
+
+    Home directory '$HOME' is not marked as executable for user '$USER',
+    how then we are going to go into it?
+    "
+        fi
+
+    }
+
+    checkDest() {
+
+     if [ -e "$dest" ]; then
+        # Destination directory exist. Nix is/was installed before, be cautious.
+
+        # Once more -d also resolves soft links to their targets
+        if [ ! -d "$dest" ]; then
+            error "
+
+    Destination '$dest' exists, but is not a directory, nor a link to one.
+    "
+        fi
+
+        if [ ! -w $dest ]; then
+            # Do not mindlessly help a user to chroot the directory
+            # - that is a disservice.
+            # Let user who does not know - at least a chanse to search and read
+            # on the topic.
+            # Person needs to know/find command themselves, and know about
+            # consequences.
+            error "
+
+    Destination directory '$dest' exists, but is not writable for user '$USER'.
+
+    To enable multi-user support see:
+    http://nixos.org/nix/manual/#ssec-multi-user
+
+    To nevertheless do a single-user install for '$USER':
+    recursively set user '$USER' as owner for '$dest' directory.
+    "
+        fi
+
+        # If checks are OK
+        warning "
+
+    Destination directory '$dest' already exists. Skipping creation of '$dest'.
+    "
 
-for i in $(cd "$self/store" >/dev/null && echo ./*); do
-    printf "." >&2
-    i_tmp="$dest/store/$i.$$"
-    if [ -e "$i_tmp" ]; then
-        rm -rf "$i_tmp"
     fi
-    if ! [ -e "$dest/store/$i" ]; then
-        cp -Rp "$self/store/$i" "$i_tmp"
-        chmod -R a-w "$i_tmp"
-        chmod +w "$i_tmp"
-        mv "$i_tmp" "$dest/store/$i"
-        chmod -w "$dest/store/$i"
+
+    if [ -e "$dest"/store ]; then
+
+        if [ ! -d "$dest"/store ]; then
+            error "
+
+    Store directory '$dest/store' exists and it's not a directory nor a link
+    to one.
+    "
+        fi
+
+        if [ ! -w "$dest"/store ]; then
+            error "
+
+    Store directory '$dest/store' exists, but is not writable for user '$USER'.
+
+    This could indicate that another user has already performed
+    a single-user installation of Nix on this system.
+
+    If you wish to enable multi-user support see:
+    https://nixos.org/nix/manual/#ssec-multi-user
+
+    To nevertheless do a single-user install for '$USER':
+    recursively set user '$USER' as owner for '$dest/store' directory.
+    "
+        fi
+
     fi
-done
-echo "" >&2
 
-echo "initialising Nix database..." >&2
-if ! $nix/bin/nix-store --init; then
-    echo "$0: failed to initialize the Nix database" >&2
-    exit 1
-fi
+    }
 
-if ! "$nix/bin/nix-store" --load-db < "$self/.reginfo"; then
-    echo "$0: unable to register valid paths" >&2
-    exit 1
-fi
+    # Invocation of functions
+    mainCheckingRequirements() {
 
-. "$nix/etc/profile.d/nix.sh"
+        checkBundle
 
-if ! "$nix/bin/nix-env" -i "$nix"; then
-    echo "$0: unable to install Nix into your default profile" >&2
-    exit 1
-fi
+        checkEnv
 
-# Install an SSL certificate bundle.
-if [ -z "$NIX_SSL_CERT_FILE" ] || ! [ -f "$NIX_SSL_CERT_FILE" ]; then
-    $nix/bin/nix-env -i "$cacert"
-    export NIX_SSL_CERT_FILE="$HOME/.nix-profile/etc/ssl/certs/ca-bundle.crt"
-fi
+        checkHome
 
-# Subscribe the user to the Nixpkgs channel and fetch it.
-if ! $nix/bin/nix-channel --list | grep -q "^nixpkgs "; then
-    $nix/bin/nix-channel --add https://nixos.org/channels/nixpkgs-unstable
-fi
-if [ -z "$_NIX_INSTALLER_TEST" ]; then
-    $nix/bin/nix-channel --update nixpkgs
-fi
+        checkDest
+
+    }
+
+    # Execute the whole checkingRequirements()
+    mainCheckingRequirements
+
+}
+
+}
+
+
+###############################
+###  Check installer mode
+###############################
+{
+
+checkInstallerMode() {
+    # Determine what mode of installer should be used
+    if [ "$(uname -s)" = "Darwin" ]; then
+        echo "Note: a multi-user installation is possible. See https://nixos.org/nix/manual/#sect-multi-user-installation" >&2
+    elif [ "$(uname -s)" = "Linux" ] && [ -e /run/systemd/system ]; then
+        echo "Note: a multi-user installation is possible. See https://nixos.org/nix/manual/#sect-multi-user-installation" >&2
+    fi
+
+    INSTALL_MODE=no-daemon
+    # Trivially handle the --daemon / --no-daemon options
+    if [ "x${1:-}" = "x--no-daemon" ]; then
+        readonly INSTALL_MODE=no-daemon
+    elif [ "x${1:-}" = "x--daemon" ]; then
+        readonly INSTALL_MODE=daemon
+    elif [ "x${1:-}" != "x" ]; then
+        error '
+
+    Nix Installer [--daemon|--no-daemon]
+      --daemon:    Force the installer to use the Daemon
+                   based installer, even though it may not
+                   work.
+
+      --no-daemon: Simple, single-user installation that does not require root
+                   and that is trivial to uninstall
+                   (default)
+    '
+    fi
+}
 
-added=
-if [ -z "$NIX_INSTALLER_NO_MODIFY_PROFILE" ]; then
+}
 
-    # Make the shell source nix.sh during login.
-    p=$HOME/.nix-profile/etc/profile.d/nix.sh
 
-    for i in .bash_profile .bash_login .profile; do
-        fn="$HOME/$i"
-        if [ -w "$fn" ]; then
-            if ! grep -q "$p" "$fn"; then
-                echo "modifying $fn..." >&2
-                echo "if [ -e $p ]; then . $p; fi # added by Nix installer" >> "$fn"
+###############################
+###  Exec installer mode
+###############################
+{
+
+execInstallerMode() {
+    if [ "$INSTALL_MODE" = "daemon" ]; then
+        notice '
+
+    Entering daemon-based installer
+    '
+        exec "$self/install-multi-user"
+    fi
+}
+
+}
+
+
+###############################
+###  Install Nix
+###############################
+{
+
+installNix() {
+
+    # In this function, if some action makes any change to the system,
+    # or error is possible - that needs to be wrapped in a function.
+    # For example, having func(){...}.
+    # Inside func() you start with setup of traps, before errors/actions happen.
+    # So when catch happen - according revert functions be launched:
+    # 'trap funcRevertOnCondition condition'.
+    # And funcRevertOnCondition is described right after the trap.
+    #
+    # Once more, now in code. How all actions operate inside this function:
+    #**************************************************
+    #
+    #    installNix() {
+    #
+    #        func() {
+    #
+    #            trap 'funcRevertOnCondition $LINENO $?' condition
+    #            funcRevertOnCondition() {
+    #                errorRevert "Received Error signal from line $1"
+    #                # revert action
+    #                >&2 contactUs # This function gives contact information
+    #                exit "$?"
+    #            }
+    #
+    #            # action of functions
+    #            # 'exit SIG # to the trap that catches exit SIG'
+    #        }
+    #
+    #        func
+    #
+    #    }
+    #
+    #**************************************************
+
+    # Nix is pure, and claims to be transactional.
+    # So show people clean transactional installation.
+
+    createDest() {
+
+        trap destCreateRevert 1
+
+        destCreateRevert() {
+            # all means failed, Exit!
+            error "
+
+    Can't get root access to create  directory '$dest'. All variants failed.
+    Exiting...
+    "
+        }
+
+        # Shell parses variable with current user, so value under sudo/su not changes.
+        # It is const, but don't move it above USER set/checks.
+        readonly cmd="mkdir -m 0755 $dest && chown $USER $dest"
+
+        # Trying to create $dest by all means
+
+        # If user has rights to successfully execute $cmd. Else -> try to elevate rights section
+        if sh -c "$cmd" > /dev/null 2>&1 ; then
+            print "Creating $dest directory by running $cmd using $USER rights"
+        else
+            if command -v sudo > /dev/null 2>&1 ; then
+                print "Creating $dest directory by running $cmd using sudo:"
+                # Using sudo to create directory
+                if ! sudo sh -c "$cmd" && print "Exiting privileged mode." ; then
+                    # It is not Warning by rules, by logging rules goes to stderr
+                    >&2 notice "
+
+    Could not succefully execute command with 'sudo'.
+    "
+                fi
+            else
+                print "'sudo' seems not installed"
             fi
-            added=1
-            break
+
         fi
-    done
 
-fi
+        # If dest still not created (with user or sudo) - use su to access root
+        if [ ! -d "$dest" ] ; then
+            print 'Trying to get privileges using su and root password'
+            if ! su root sh -c "$cmd" && print 'Exiting priviliged mode.'; then
+                exit 1 # Look into the trap
+            fi
+        fi
+    }
+
+    createStore() {
+        trap createStoreRevert 1
+        createStoreRevert() {
+            error "
+
+    Script tried to create '$dest/store', but it already exists.
+    We do checks '$dest/store' existence before installation.
+    Probaly something went wrong with the installation script.
+
+    Please:
+      * gather information of your setup conditions
+      * search does BUG exists
+      * make further actions
+    "
+        }
+        mkdir -p "$dest"/store
+    }
+
+    copyNix() {
+        print "Copying Nix to '$dest/store': "
+
+        for object in $(cd "$self/store" >/dev/null && echo ./*); do
+            printf '.'
+            get="$self/store/$object"
+            tmp="$dest/store/$object.$$" ## $$ - is process PID
+            put="$dest/store/$object"
+
+            # If $dest/store/$object.$$ exists - remove. Very certain - it is a directory from previous cycle.
+            if [ -e "$tmp" ]; then
+                rm -rf "$tmp"
+            fi
+            # If $put does not exist - populate it.
+            if ! [ -e "$put" ]; then
+                # Copy $get to $tmp
+                cp -Rp "$get" "$tmp"
+                # Remove write permissions from $tmp recursively
+                chmod -R a-w "$tmp"
+                # Place $tmp as $put
+                mv "$tmp" "$put"
+            else
+                print "Already exists, skipping: '$put'"
+            fi
 
-if [ -z "$added" ]; then
-    cat >&2 <<EOF
+        done
+        printf '\n'
+    }
 
-Installation finished!  To ensure that the necessary environment
-variables are set, please add the line
+    initializeDB() {
+        notice "
 
-  . $p
+    Initializing Nix database...
+    "
+        if ! "$nix/bin/nix-store" --init; then
+            error "
 
-to your shell profile (e.g. ~/.profile).
-EOF
-else
-    cat >&2 <<EOF
+    Failed to initialize the Nix database
+    "
+        fi
 
-Installation finished!  To ensure that the necessary environment
-variables are set, either log in again, or type
+        if ! "$nix/bin/nix-store" --load-db < "$self/.reginfo"; then
+            error "
 
-  . $p
+    Unable to register valid paths
+    "
+        fi
+    }
+
+    setupProfile() {
+        # Modifying current runtime environment variables to use Nix.
+        # Persistent changes are configured later.
+        print "Launching $nix/etc/profile.d/nix.sh"
+        # shellcheck source=/dev/null
+        . "$nix/etc/profile.d/nix.sh"
+        print "Left $nix/etc/profile.d/nix.sh"
+        if ! "$nix/bin/nix-env" -i "$nix"; then
+            error "
+
+    Unable to install Nix into your default profile
+    "
+        fi
+    }
+
+    installCerts() {
+        # Install an SSL certificate bundle.
+        trap 'installCertsRevert $LINENO $?' INT TERM ABRT QUIT
+        subscribeChannelsRevert() {
+            errorRevert "Received Error signal from line $1"
+            errorRevert "Reverting installation of certificate bundle"
+            "$nix/bin/nix-env" --uninstall "$cacert"
+            error "
+
+    Changes reverted.
+    " "$2"
+        }
+        print 'Installing SSL certificate bundle.'
+        "$nix/bin/nix-env" --install "$cacert"
+        readonly NIX_SSL_CERT_FILE="$HOME/.nix-profile/etc/ssl/certs/ca-bundle.crt"
+        export NIX_SSL_CERT_FILE
+    }
+
+    subscribeChannels() {
+        # Subscribe the user to the Nixpkgs channel and fetch it.
+        trap 'subscribeChannelsRevert $LINENO $?' INT TERM ABRT QUIT
+        subscribeChannelsRevert() {
+            errorRevert "Received Error signal from line $1"
+            errorRevert "Reverting channels subscriptions: nixpkgs"
+            "$nix"/bin/nix-channel --remove nixpkgs
+            error "
+
+    Changes reverted.
+    " "$2"
+        }
+        readonly channelUrl='https://nixos.org/channels/nixpkgs-unstable'
+        print "Subscribing to channel: nixpkgs=$channelUrl"
+        "$nix"/bin/nix-channel --add "$channelUrl"
+    }
+
+    updateRepos() {
+        # Subscribe the user to the Nixpkgs channel and fetch it.
+        trap 'updateReposRevert $LINENO $?' INT TERM ABRT QUIT
+        updateReposRevert() {
+            error "
+
+    Received Error signal from line $1
+    " "$2"
+        }
+        print 'Pulling information from channel: nixpkgs'
+        # nix-channel should be fully transactional, so no 'nix-channel --rollback'
+        "$nix"/bin/nix-channel --update nixpkgs
+    }
+
+    # Wrap function invocations process into function
+    mainInstallNix() {
+
+        # TODO: Determine to write single/multi user after bug #1559 is resolved
+        notice '
+
+    Performing a single-user installation of Nix:
+    '
+
+        if [ ! -d "$dest" ] ; then
+            createDest
+        fi
 
-in your shell.
-EOF
-fi
+        createStore
+
+        copyNix
+
+        initializeDB
+
+        setupProfile
+
+
+        if [ -z "$NIX_SSL_CERT_FILE" ] || [ ! -f "$NIX_SSL_CERT_FILE" ]; then
+            installCerts
+        fi
+
+        if ! "$nix"/bin/nix-channel --list | grep -q '^nixpkgs '; then
+            subscribeChannels
+        fi
+
+        if [ -z "$_NIX_INSTALLER_TEST" ]; then
+            updateRepos
+        fi
+
+        notice '
+
+    Installation finished. 8)
+    '
+
+    }
+
+    # Invoke main function for installNix
+    mainInstallNix
+}
+
+}
+
+
+###############################
+###  Postinstall
+###############################
+{
+
+postinstall() {
+
+    notice '
+
+    Launching postinstall tasks:
+    '
+    added=0
+    if [ -z "$NIX_INSTALLER_NO_MODIFY_PROFILE" ]; then
+        # Make shell to source nix.sh during login.
+        readonly nix_profile="$HOME/.nix-profile/etc/profile.d/nix.sh"
+        for file in .bash_profile .bash_login .profile; do
+            user_profile="$HOME/$file"
+            if [ -w "$user_profile" ]; then
+                if ! grep -q "$nix_profile" "$user_profile"; then
+                    notice "
+
+    Modifying $user_profile...
+    "
+                    printf 'if [ -e %s ]; then . %s; fi # added by Nix installer\n'\
+                           "$nix_profile" "$nix_profile" >> "$user_profile"
+                fi
+                added=1
+                break
+            fi
+        done
+    fi
+
+    # TODO: Investigate use of:
+    # "Attempting to execute login from any shell but the login shell will produce an error message"
+
+    if [ "$added" -eq 0 ]; then
+        notice "
+
+    Installation finished!
+    To ensure that environment variables are set for Nix,
+    please add the line
+
+    . $nix-profile
+
+    to your shell profile (e.g. ~/.profile).
+    "
+
+    else
+        notice "
+
+    Installation finished!
+    To use Nix - re-login to shell environment.
+    Or to use it directly now, in the current runtime environment -
+    run this script to set Nix-specific environment variables:
+
+    . $nix-profile
+
+    in current runtime environment.
+    "
+    fi
+}
+
+}
+
+
+###############################
+###  Main function
+###############################
+main() {
+
+    checkingRequirements
+    checkInstallerMode "$@"
+    execInstallerMode
+    installNix
+    postinstall
+    contactUs
+
+}
+
+
+###############################
+### Start of the script
+###############################
+main "$@"