hadoop core provides serveral mechanisms for setting the classpath for your application:
you can set up a fixed base classpath by altering hadoop-env.sh, via the HADOOP_CLASSPATH environment variable or by setting that environment variable in the runtime
environment for the user that starts the hadoop servers.
you may run your jobs via the bin/hadoop jar command and supply a -libjars argument with a list of JARs
the distributedCache object provides a way to add files or archives to your runtime classpath.
一般优先使用DistributedCahce方式和-libjars方式
Using Shared Libraries
you can handle this in two ways:
Pass the shared library via the DistributedCache object.
Install the shared library on every TaskTracker machine, and have the JVM library loader path java.library.path include the installation directory.
bin/hadoop dfs -fs hdfs://master:8020 -ls
bin/hadoop job -jt master:8021 -list