* Set /proc/sys/kernel/poweroff_cmd to Upstart's poweroff command

(rather than /sbin/poweroff).  Xen's "xm shutdown" needs this to
  enable the host to cleanly shutdown the guest.

svn path=/nixos/trunk/; revision=24094

modules/system/upstart-events/control-alt-delete.nix

@@ -15,4 +15,12 @@
           shutdown -r now 'Ctrl-Alt-Delete pressed'
         '';
     };
+
+  system.activationScripts.poweroff =
+    ''
+      # Allow the kernel to find the poweroff command.  This is used
+      # (for instance) by Xen's "xm shutdown" command to signal a
+      # guest to shut down cleanly.
+      echo ${config.system.build.upstart}/sbin/poweroff > /proc/sys/kernel/poweroff_cmd
+    '';
 }