diff --git a/install_yunohost b/install_yunohost
index 569cf1f..33bfa5d 100755
--- a/install_yunohost
+++ b/install_yunohost
@@ -15,8 +15,112 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-YUNOHOST_LOG="/var/log/yunohost-installation.log"
-THIS_MACHINE_RELEASE="$(lsb_release -c | awk '{print $2}')"
+set -u
+
+# Globals
+
+readonly YUNOHOST_LOG="/var/log/yunohost-installation.log"
+readonly THIS_MACHINE_RELEASE="$(lsb_release -c | awk '{print $2}')"
+
+###############################################################################
+# Main functions                                                              #
+###############################################################################
+
+function usage() {
+  print "
+Usage :
+  `basename $0` [-a] [-d <DISTRIB>] [-h]
+
+Options :
+  -a      Enable automatic mode. No questions are asked.
+          This does not perform the post-install step.
+  -d      Choose the distribution to install ('stable', 'testing', 'unstable').
+          Defaults to 'stable'
+  -h      Prints this help and exit
+"
+}
+
+function parse_options()
+{
+    AUTOMODE=0
+    DISTRIB=stable
+    BUILD_IMAGE=0
+
+    while getopts ":aid:h" option; do
+        case $option in
+            a)
+                AUTOMODE=1
+                export DEBIAN_FRONTEND=noninteractive
+                ;;
+            d)
+                DISTRIB=$OPTARG
+                ;;
+            i)
+                # This hidden option will allow to build generic image for Rpi/Olimex
+                BUILD_IMAGE=1
+                ;;
+            h)
+                usage
+                exit 0
+                ;;
+            :)
+                usage
+                exit 1
+                ;;
+            \?)
+                usage
+                exit 1
+                ;;
+        esac
+    done
+}
+
+function main()
+{
+    parse_options
+
+    step ensure_root || die "This script must be run as root"
+
+    if is_raspbian ; then
+        step ensure_pi_logout || die "The user pi should be logged out"
+    fi
+
+    step upgrade_system                || die "Unable to update the system"
+    step installscript_dependencies    || die "Unable to install dependencies to install script"
+    step create_custom_config          || die "Creating custom configuration file /etc/yunohost/yunohost.conf failed"
+    step confirm_installation          || die "Installation cancelled at your request"
+    step setup_package_source          || die "Setting up deb package sources failed"
+    step apt_update                    || die "Error caught during 'apt-get update'"
+    step register_debconf              || die "Unable to insert new values into debconf database"
+    step workaround_avahi_installation || die "Unable to install workaround for avahi installation"
+    step install_yunohost_packages     || die "Installation of Yunohost packages failed"
+    step restart_services              || die "Error caught during services restart"
+
+    if is_raspbian ; then
+        step del_user_pi     || die "Unable to delete user pi"
+        step change_hostname || die "Unable to change hostname"
+        step setup_firstboot || die "Unable to setup firstboot"
+    fi
+
+    if [[ "$BUILD_IMAGE" == "1" ]] ; then
+        step clean_image || die "Unable to clean image"
+    fi
+
+    if is_raspbian ; then
+        # Reboot should be done before postinstall to be able to run iptables rules
+        reboot
+    fi
+
+    step post_install || die "Post-installation failed"
+
+    # Success !
+    success
+    exit 0
+}
+
+###############################################################################
+# Helpers                                                                     #
+###############################################################################
 
 function print() {
     printf "%s\n" "$*";
@@ -89,6 +193,10 @@ function is_raspbian() {
     return 0
 }
 
+###############################################################################
+# Installation steps                                                          #
+###############################################################################
+
 function apt_get_wrapper() {
     if [[ "$AUTOMODE" == "0" ]] ;
     then
@@ -406,101 +514,4 @@ Do you want to try again now?
     return 0
 }
 
-function usage() {
-  print "
-Usage :
-  `basename $0` [-a] [-d <DISTRIB>] [-h]
-
-Options :
-  -a      Enable automatic mode. No questions are asked.
-          This does not perform the post-install step.
-  -d      Choose the distribution to install ('stable', 'testing', 'unstable').
-          Defaults to 'stable'
-  -h      Prints this help and exit
-"
-}
-
-# Treat unset variables as an error when performing
-# parameter expansion. An error message will be written
-# to the standard error, and a non-interactive shell will exit.
-set -u
-
-function parse_options()
-{
-    AUTOMODE=0
-    DISTRIB=stable
-    BUILD_IMAGE=0
-
-    while getopts ":aid:h" option; do
-        case $option in
-            a)
-                AUTOMODE=1
-                export DEBIAN_FRONTEND=noninteractive
-                ;;
-            d)
-                DISTRIB=$OPTARG
-                ;;
-            i)
-                # This hidden option will allow to build generic image for Rpi/Olimex
-                BUILD_IMAGE=1
-                ;;
-            h)
-                usage
-                exit 0
-                ;;
-            :)
-                usage
-                exit 1
-                ;;
-            \?)
-                usage
-                exit 1
-                ;;
-        esac
-    done
-}
-
-function main()
-{
-    parse_options
-
-    step ensure_root || die "This script must be run as root"
-
-    if is_raspbian ; then
-        step ensure_pi_logout || die "The user pi should be logged out"
-    fi
-
-    step upgrade_system                || die "Unable to update the system"
-    step installscript_dependencies    || die "Unable to install dependencies to install script"
-    step create_custom_config          || die "Creating custom configuration file /etc/yunohost/yunohost.conf failed"
-    step confirm_installation          || die "Installation cancelled at your request"
-    step setup_package_source          || die "Setting up deb package sources failed"
-    step apt_update                    || die "Error caught during 'apt-get update'"
-    step register_debconf              || die "Unable to insert new values into debconf database"
-    step workaround_avahi_installation || die "Unable to install workaround for avahi installation"
-    step install_yunohost_packages     || die "Installation of Yunohost packages failed"
-    step restart_services              || die "Error caught during services restart"
-
-    if is_raspbian ; then
-        step del_user_pi     || die "Unable to delete user pi"
-        step change_hostname || die "Unable to change hostname"
-        step setup_firstboot || die "Unable to setup firstboot"
-    fi
-
-    if [[ "$BUILD_IMAGE" == "1" ]] ; then
-        step clean_image || die "Unable to clean image"
-    fi
-
-    if is_raspbian ; then
-        # Reboot should be done before postinstall to be able to run iptables rules
-        reboot
-    fi
-
-    step post_install || die "Post-installation failed"
-
-    # Success !
-    success
-    exit 0
-}
-
 main