I would like to use the ImageMosaic plugin to set up a Geoserver layer which refers to a WorldImage, just like in the official tutorial.

As a simple test case, I put a custom folder into my Geoserver data directory with one World Image (image + WorldFile + projection). When I specify the folder location to a ImageMosaic Store in Geoserver, it simply displays the error message:

Could not list layers for this store, an error occurred retrieving them: Argument "value" should not be null.

On the other hand, when I put my image into a default folder that comes with the openGeo suite (like file:data/dem/ with the Medform Digital Elevation Data), the thing works as it should.

So I suspect there is something going wrong with user rights, can anybody enlighten me?

PS: My Geoserver error log

    INFO [geoserver.web] - Getting list of coverages for saved store file:mosaic
    java.lang.RuntimeException: Could not list layers for this store, an error occurred retrieving them: Argument "value" should not be null.
    at org.geoserver.web.data.layer.NewLayerPageProvider.getItemsInternal(NewLayerPageProvider.java:123)
    Caused by: java.lang.IllegalArgumentException: Argument "value" should not be null.
    at org.geotools.util.SoftValueHashMap.ensureNotNull(SoftValueHashMap.java:140)

1 Answer 1


The simple solution: contrary to other data sources for Geoserver, it seems that when you deal with an ImageMosaic you strictly need your data folder to be owned by user/usergroup tomcat6. So changing the user/usergroup from root to tomcat6 resolved the problem for me.

Useful commands for Linux:

  • display file ownership: $ ls -l (2nd column: owner, 3rd column: owner group)
  • change file owner: $ chown myownername myfile (add option -R for folders)
  • change file owner group: $ chgrp myownername myfile (add option -R for folders)
  • Heho! Which OS and Geoserver distribution do you use? I have the same issue and can't fix it. I use Geoserver 2.3.3 binary release on OpenSuse 12.3 and have only the Appache-user wwwrun, no user tomcat6. Did you change ownership of the whole geoserver's data-folder or only of the folder containing your images?
    – der Michi
    Commented Jul 3, 2013 at 17:05
  • I'm on Ubuntu 12.04 using GeoServer 2.2 (shipped with the OpenGeo Suite). I only changed the ownership of the folder containing the images. My GeoServer data folder is owned by tomcat6 by default. Maybe have a look at my original revision of the post including some more details on my failed attempts... Commented Jul 4, 2013 at 7:19
  • I played the whole day: The ImageMosaic in Geoserver 2.3.3 binary distribution works in Windows 7 and Ubuntu 10.4. Further the WAR-distribution works under Ubuntu 10.4 (Tomcat 6) under 12.4 (Tomcat 7) like a charm. Thanks!
    – der Michi
    Commented Jul 4, 2013 at 15:21
  • In case of standard ubuntu installation sudo chmod -R geoserver:geoserver mydatafolder worked. And it was not enough that all files/subfolders were under this user, also first level data subfolder had to be chown correctly.
    – JaakL
    Commented May 14, 2014 at 7:29

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