Index: magnolia-core/src/main/java/info/magnolia/setup/CoreModuleVersionHandler.java
===================================================================
--- magnolia-core/src/main/java/info/magnolia/setup/CoreModuleVersionHandler.java	(revision 49980)
+++ magnolia-core/src/main/java/info/magnolia/setup/CoreModuleVersionHandler.java	(working copy)
@@ -233,6 +233,10 @@
                 .addTask(new BootstrapConditionally("Security", "Bootstraps security-base role.", "/mgnl-bootstrap/core/userroles.security-base.xml"))
         );
 
+        register(DeltaBuilder.update("4.5", "")
+                .addCondition(new SystemTmpDirCondition())
+        );
+
     }
 
     private PropertyValueDelegateTask fixMimetype(String mimeType, final String previouslyWrongValue, final String fixedValue) {
@@ -288,6 +292,8 @@
         u2.workspaceHasOldIndexer();
 
         conditions.add(new CheckNodeTypesDefinition());
+        conditions.add(new SystemTmpDirCondition());
+
         return conditions;
     }
 }
Index: magnolia-core/src/main/java/info/magnolia/setup/SystemTmpDirCondition.java
===================================================================
--- magnolia-core/src/main/java/info/magnolia/setup/SystemTmpDirCondition.java	(revision 0)
+++ magnolia-core/src/main/java/info/magnolia/setup/SystemTmpDirCondition.java	(revision 0)
@@ -0,0 +1,70 @@
+/**
+ * This file Copyright (c) 2011 Magnolia International
+ * Ltd.  (http://www.magnolia-cms.com). All rights reserved.
+ *
+ *
+ * This file is dual-licensed under both the Magnolia
+ * Network Agreement and the GNU General Public License.
+ * You may elect to use one or the other of these licenses.
+ *
+ * This file is distributed in the hope that it will be
+ * useful, but AS-IS and WITHOUT ANY WARRANTY; without even the
+ * implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE, TITLE, or NONINFRINGEMENT.
+ * Redistribution, except as permitted by whichever of the GPL
+ * or MNA you select, is prohibited.
+ *
+ * 1. For the GPL license (GPL), you can redistribute and/or
+ * modify this file under the terms of the GNU General
+ * Public License, Version 3, as published by the Free Software
+ * Foundation.  You should have received a copy of the GNU
+ * General Public License, Version 3 along with this program;
+ * if not, write to the Free Software Foundation, Inc., 51
+ * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * 2. For the Magnolia Network Agreement (MNA), this file
+ * and the accompanying materials are made available under the
+ * terms of the MNA which accompanies this distribution, and
+ * is available at http://www.magnolia-cms.com/mna.html
+ *
+ * Any modifications to this file must keep this entire header
+ * intact.
+ *
+ */
+package info.magnolia.setup;
+
+import info.magnolia.module.InstallContext;
+import info.magnolia.module.delta.AbstractCondition;
+
+import java.io.File;
+import java.io.IOException;
+
+/**
+ * A {@link info.magnolia.module.delta.Condition} which checks the system temporary folder (as per the java.io.tmpdir property) exists and is writable.
+ * It can happen that users accidentally delete the temp folder, which can cause all sorts of trouble. (JackRabbit uses it while importing files, for example)
+ *
+ * @version $Revision: $ ($Author: $)
+ */
+public class SystemTmpDirCondition extends AbstractCondition {
+    private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(SystemTmpDirCondition.class);
+
+    public SystemTmpDirCondition() {
+        super("System temporary folder check", "Ensures the system temporary folder exists and is usable by the current process.");
+    }
+
+    @Override
+    public boolean check(InstallContext installContext) {
+        try {
+            final File f = File.createTempFile("magnolia.core.check", "tmp");
+            log.debug("Temp file was successfully created as {}, we can delete it and proceed.", f.getAbsolutePath());
+            f.delete();
+            return true;
+        } catch (IOException e) {
+            final String tmpDirProperty = System.getProperty("java.io.tmpdir");
+            log.error("The system could not create a temporary file: {}. Please check if {} exists and is writable by the current process. {}", new Object[]{e.getMessage(), tmpDirProperty, e});
+            installContext.error("The system could not create a temporary file: " + e.getMessage() + ". Please check if " + tmpDirProperty + " exists and is writable by the current process.", e);
+            return false;
+        }
+
+    }
+}