Hmm, apparently there's more than one way this can fail:
2014-08-28 14:38:11,866.866 INFO:tasks.workunit.client.0.mira114.stderr:+ tar -xf /home/ubuntu/cephtest/hadoop_input/files.tar
2014-08-28 14:38:11,866.866 INFO:tasks.workunit.client.0.mira114.stderr:+ /home/ubuntu/cephtest/apache_hadoop/bin/hadoop fs -mkdir /wordcount_input
2014-08-28 14:38:12,094.094 INFO:tasks.workunit.client.0.mira114.stderr:Exception in thread "main" java.lang.NoClassDefFoundError: com/ceph/fs/CephFileAlreadyExistsException
2014-08-28 14:38:12,095.095 INFO:tasks.workunit.client.0.mira114.stderr: at java.lang.Class.forName0(Native Method)
2014-08-28 14:38:12,095.095 INFO:tasks.workunit.client.0.mira114.stderr: at java.lang.Class.forName(Class.java:270)
2014-08-28 14:38:12,095.095 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:820)
2014-08-28 14:38:12,095.095 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:865)
2014-08-28 14:38:12,095.095 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:1380)
2014-08-28 14:38:12,095.095 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:66)
2014-08-28 14:38:12,095.095 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1404)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:254)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:123)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FsShell.init(FsShell.java:82)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FsShell.run(FsShell.java:1745)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:79)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at org.apache.hadoop.fs.FsShell.main(FsShell.java:1895)
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr:Caused by: java.lang.ClassNotFoundException: com.ceph.fs.CephFileAlreadyExistsException
2014-08-28 14:38:12,096.096 INFO:tasks.workunit.client.0.mira114.stderr: at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
2014-08-28 14:38:12,097.097 INFO:tasks.workunit.client.0.mira114.stderr: at java.security.AccessController.doPrivileged(Native Method)
2014-08-28 14:38:12,097.097 INFO:tasks.workunit.client.0.mira114.stderr: at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
2014-08-28 14:38:12,097.097 INFO:tasks.workunit.client.0.mira114.stderr: at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
2014-08-28 14:38:12,097.097 INFO:tasks.workunit.client.0.mira114.stderr: at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
2014-08-28 14:38:12,097.097 INFO:tasks.workunit.client.0.mira114.stderr: at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
2014-08-28 14:38:12,097.097 INFO:tasks.workunit.client.0.mira114.stderr: ... 14 more
2014-08-28 14:38:12,107.107 INFO:tasks.workunit:Stopping ['hadoop/wordcount.sh'] on client.0...