问题
I just successfully set up Hadoop on my local machines. I am following one of the examples in a popular book I just bought. I am trying to get a list of all hadoop examples that comes with installation. I type the following command to do so:
bin/hadoop jar hadoop-*-examples.jar
Once I enter this I am supposed to get a list of Hadoop examples right? However all I see is this error message:
Not a valid JAR: /home/user/hadoop/hadoop-*-examples.jar
How do I solve this problem? Is it just a simple permission issue?
回答1:
This is most probably configuration issue or usage of invalid file paths.
Most probably the name of hadoop-*-examples.jar is not correct because in my version of Hadoop (1.0.0) file name is hadoop-examples-1.0.0.jar.
So I have run following command to list all examples and it works like charm:
bin/hadoop jar hadoop-examples-*.jar
An example program must be given as the first argument.
Valid program names are:
aggregatewordcount: An Aggregate based map/reduce program that counts the words in the input files.
aggregatewordhist: An Aggregate based map/reduce program that computes the histogram of the words in the input files.
dbcount: An example job that count the pageview counts from a database.
grep: A map/reduce program that counts the matches of a regex in the input.
join: A job that effects a join over sorted, equally partitioned datasets
multifilewc: A job that counts words from several files.
pentomino: A map/reduce tile laying program to find solutions to pentomino problems.
pi: A map/reduce program that estimates Pi using monte-carlo method.
randomtextwriter: A map/reduce program that writes 10GB of random textual data per node.
randomwriter: A map/reduce program that writes 10GB of random data per node.
secondarysort: An example defining a secondary sort to the reduce.
sleep: A job that sleeps at each map and reduce task.
sort: A map/reduce program that sorts the data written by the random writer.
sudoku: A sudoku solver.
teragen: Generate data for the terasort
terasort: Run the terasort
teravalidate: Checking results of terasort
wordcount: A map/reduce program that counts the words in the input files.
Also if I use same file name pattern as You I got error:
bin/hadoop jar hadoop-*examples.jar
Exception in thread "main" java.io.IOException: Error opening job jar: hadoop-*examples.jar
HTH
回答2:
You must specify the class name of the jar file which you want to use:
hadoop jar pathtojarfile classname arg1 arg2 ..
Example:
hadoop jar example.jar wordcount inputPath outputPath
回答3:
@Anup. The full / relative path to the jar file is required.
In your case it might be /home/user/hadoop/share/hadoop-*-examples.jar
The complete command from hadoop's directory might be
/home/user/hadoop/bin/hadoop /home/user/hadoop/share/hadoop-*-examples.jar
(I used absolute full paths there, but you can use relative paths).
回答4:
you will find the jar in $HADOOP_HOME/share/hadoop/mapreduce/hadoop-*-examples*.jar
来源：https://stackoverflow.com/questions/18808895/hadoop-preinstalled-example-jars