@jhc
This is a permission issue you can resolve that by following the following step
As root switch to hdfs
# su - hdfs
As hdfs change the file permission
$ hdfs dfs -chmod 777 /user/root/tmp/data/x.csv
That will give execute to all including on x.csv thats not good security-wise a better option hive would be to copy the csv file to a location like /user/hive/[somewhere]/ where access has been locked down to hive user and readable by hive
$ hdfs dfs -cp /user/root/tmp/data/x.csv /user/hive
---------- or ------------
$ hdfs dfs -mv /user/spark/test.txt /user/hive
Now change permissions for hive user
$ hdfs dfs -chown hive:hdfs /user/hive/test.txt
Now re-running your CREATE external table command should work.