diff --git a/modules/installer/grub/grub-menu-builder.sh b/modules/installer/grub/grub-menu-builder.sh
index ecb69ceb263..f23184b0a06 100644
--- a/modules/installer/grub/grub-menu-builder.sh
+++ b/modules/installer/grub/grub-menu-builder.sh
@@ -30,7 +30,7 @@ esac
 # the GRUB config file must be relative to the root of the /boot
 # filesystem.  `$bootRoot' is the path to be prepended to paths under
 # /boot.
-if [ "$(stat -f -c '%i' /)" = "$(stat -f -c '%i' /boot)" ]; then
+if [ "$(stat -c '%D' /.)" = "$(stat -c '%D' /boot/.)" ]; then
     bootRoot=/boot
     copyKernels="@copyKernels@" # user can override in the NixOS config
 else
diff --git a/modules/services/mail/postfix.nix b/modules/services/mail/postfix.nix
index 939260632c9..03c77885d06 100644
--- a/modules/services/mail/postfix.nix
+++ b/modules/services/mail/postfix.nix
@@ -287,7 +287,15 @@ in
 
         daemonType = "none";
 
-        respawn = false;
+        respawn = true;
+
+        script = ''
+          while ${pkgs.procps}/bin/ps `${pkgs.coreutils}/bin/cat /var/postfix/queue/pid/master.pid` |
+            grep -q postfix
+          do
+            ${pkgs.coreutils}/bin/sleep 1m
+          done
+        '';
 
         preStart =
           ''
diff --git a/modules/services/misc/nix-daemon.nix b/modules/services/misc/nix-daemon.nix
index a9a0bc70f1e..fcdcc8fb299 100644
--- a/modules/services/misc/nix-daemon.nix
+++ b/modules/services/misc/nix-daemon.nix
@@ -162,6 +162,10 @@ in
         internal = true;
         default = "";
         merge = mergeStringOption;
+        example = ''
+          export NIX_TARGET_LOAD=$(( 3 * $(${pkgs.coreutils}/bin/nproc) / 2 ))
+          export NIX_MAX_PARALLELIZATION=$NIX_TARGET_LOAD
+        '';
         description = "
           Environment variables used by Nix.
         ";
diff --git a/modules/services/printing/cupsd.nix b/modules/services/printing/cupsd.nix
index 40760ec8af5..0ac52fe1038 100644
--- a/modules/services/printing/cupsd.nix
+++ b/modules/services/printing/cupsd.nix
@@ -106,6 +106,11 @@ in
 
     services.dbus.packages = [cups];
 
+    # cups uses libusb to talk to printers, and does not use the
+    # linux kernel driver. If the driver is not in a black list, it
+    # gets loaded, and then cups cannot access the printers.
+    boot.blacklistedKernelModules = [ "usblp" ];
+
     environment.etc =
       [ # CUPS expects the following files in its ServerRoot.
         { source = "${cups}/etc/cups/mime.convs";
@@ -122,15 +127,17 @@ in
         startOn = "started network-interfaces";
         stopOn = "stopping network-interfaces";
 
+        environment = {
+          # Cups scripts for printing (psto...) require awk, sed, grep, ...
+          PATH = "${config.system.path}/bin";
+        };
+
         preStart =
           ''
             mkdir -m 0755 -p ${logDir}
             mkdir -m 0700 -p /var/cache/cups
             mkdir -m 0700 -p /var/spool/cups
             mkdir -m 0755 -p ${cfg.tempDir}
-
-            # Make USB printers show up.
-            ${modprobe}/sbin/modprobe usblp || true
           '';
 
         exec = "${cups}/sbin/cupsd -c ${pkgs.writeText "cupsd.conf" cfg.cupsdConf} -F";
diff --git a/modules/system/boot/stage-2-init.sh b/modules/system/boot/stage-2-init.sh
index 201c539bb6b..aaf135fe51a 100644
--- a/modules/system/boot/stage-2-init.sh
+++ b/modules/system/boot/stage-2-init.sh
@@ -131,9 +131,15 @@ echo "running activation script..."
 @activateConfiguration@ "$systemConfig"
 
 
-# Record the boot configuration.  !!! Should this be a GC root?
+# Record the boot configuration.
 if test -n "$systemConfig"; then
     ln -sfn "$systemConfig" /var/run/booted-system
+
+    # Prevent the booted system form being garbage-collected
+    # If it weren't a gcroot, if we were running a different kernel,
+    # switched system, and garbage collected all, we could not load
+    # kernel modules anymore.
+    ln -sfn /var/run/booted-system /nix/var/nix/gcroots/booted-system
 fi
 
 
diff --git a/modules/system/upstart/upstart.nix b/modules/system/upstart/upstart.nix
index 3110f376eec..cb3975e694c 100644
--- a/modules/system/upstart/upstart.nix
+++ b/modules/system/upstart/upstart.nix
@@ -21,6 +21,7 @@ let
   makeJob = job:
 
     let
+      hasMain = job.script != "" || job.exec != "";
 
       jobText =
         let log = "/var/log/upstart/${job.name}"; in
@@ -77,12 +78,14 @@ let
           ${optionalString job.task "task"}
           ${optionalString (!job.task && job.respawn) "respawn"}
 
-          ${optionalString (job.preStop != "") ''
+          ${ # preStop is run only if there is exec or script.
+             # (upstart 0.6.5, job.c:562)
+            optionalString (job.preStop != "") (assert hasMain; ''
             pre-stop script
               exec >> ${log} 2>&1
               ${job.preStop}
             end script
-          ''}
+          '')}
 
           ${optionalString (job.postStop != "") ''
             post-stop script
diff --git a/tests/subversion.nix b/tests/subversion.nix
index 5354a40452b..d43e369b437 100644
--- a/tests/subversion.nix
+++ b/tests/subversion.nix
@@ -19,7 +19,7 @@ let
 
         # To build the kernel with coverage instrumentation, we need a
         # special patch to make coverage data available under /proc.
-        kernel = pkgs.kernel.override (orig: {
+        linux = pkgs.linux.override (orig: {
           stdenv = cleanupBuildTree (keepBuildTree orig.stdenv);
           extraConfig =
             ''