R 字数示例代码：
library(rmr2)
map <- function(k,lines) {
words.list <- strsplit(lines, '\s')
words <- unlist(words.list)
return( keyval(words, 1) )
}
reduce <- function(word, counts) {
keyval(word, sum(counts))
}
wordcount <- function (input, output=NULL) {
mapreduce(input=input, output=output, input.format = "text", map=map, reduce=reduce)
}
system("/opt/hadoop/hadoop-2.5.1/bin/hadoop fs -rm -r /wordcount/out")
hdfs.root <- 'wordcount'
hdfs.data <- file.path(hdfs.root, 'data')
hdfs.out <- file.path(hdfs.root, 'out')
当我执行 R 代码的最后一条语句时，它给出了以下错误消息。
Error: java.lang.RuntimeException: PipeMapRed.waitOutputThreads(): subprocess failed with code 1
at org.apache.hadoop.streaming.PipeMapRed.waitOutputThreads(PipeMapRed.java:320)
at org.apache.hadoop.streaming.PipeMapRed.mapRedFinished(PipeMapRed.java:533)
at org.apache.hadoop.streaming.PipeMapper.close(PipeMapper.java:130)
at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:61)
at org.apache.hadoop.streaming.PipeMapRunner.run(PipeMapRunner.java:34)
at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:430)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:342)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:168)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1614)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:163)
错误后，它会显示：
INFO mapreduce.Job: map 100% reduce 100%
和
ERROR streaming.StreamJob: Job not Successful! Streaming Command Failed!
输出文件夹是在 HDFS 中创建的，但不生成任何结果。知道可能导致问题的原因吗？
更新 1：
我发现了Hadoop为localhost：8042的特定作业提供的错误日志
Dec 11, 2014 3:26:38 PM com.google.inject.servlet.InternalServletModule$BackwardsCompatibleServletContextProvider get
WARNING: You are attempting to use a deprecated API (specifically, attempting to @Inject ServletContext inside an eagerly created singleton. While we allow this for backwards compatibility, be warned that this MAY have unexpected behavior if you have more than one injector (with ServletModule) running in the same JVM. Please consult the Guice documentation at http://code.google.com/p/google-guice/wiki/Servlets for more information.
Dec 11, 2014 3:26:40 PM com.sun.jersey.guice.spi.container.GuiceComponentProviderFactory register
INFO: Registering org.apache.hadoop.mapreduce.v2.app.webapp.JAXBContextResolver as a provider class
Dec 11, 2014 3:26:40 PM com.sun.jersey.guice.spi.container.GuiceComponentProviderFactory register
INFO: Registering org.apache.hadoop.yarn.webapp.GenericExceptionHandler as a provider class
Dec 11, 2014 3:26:40 PM com.sun.jersey.guice.spi.container.GuiceComponentProviderFactory register
INFO: Registering org.apache.hadoop.mapreduce.v2.app.webapp.AMWebServices as a root resource class
Dec 11, 2014 3:26:40 PM com.sun.jersey.server.impl.application.WebApplicationImpl _initiate
INFO: Initiating Jersey application, version 'Jersey: 1.9 09/02/2011 11:17 AM'
Dec 11, 2014 3:26:40 PM com.sun.jersey.guice.spi.container.GuiceComponentProviderFactory getComponentProvider
INFO: Binding org.apache.hadoop.mapreduce.v2.app.webapp.JAXBContextResolver to GuiceManagedComponentProvider with the scope "Singleton"
Dec 11, 2014 3:26:43 PM com.sun.jersey.guice.spi.container.GuiceComponentProviderFactory getComponentProvider
INFO: Binding org.apache.hadoop.yarn.webapp.GenericExceptionHandler to GuiceManagedComponentProvider with the scope "Singleton"
Dec 11, 2014 3:26:45 PM com.sun.jersey.guice.spi.container.GuiceComponentProviderFactory getComponentProvider
INFO: Binding org.apache.hadoop.mapreduce.v2.app.webapp.AMWebServices to GuiceManagedComponentProvider with the scope "PerRequest"
log4j:WARN No appenders could be found for logger (org.apache.hadoop.ipc.Server).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
有人知道问题是什么吗？
更新 2：
我在 $HADOOP_HOME/logs/userlogs/[application_id]/[container_id]/stderr 中找到了额外的日志记录信息：
...
Error : .onLoad failed in loadNamespace() for 'rhdfs', details:
call: fun(libname, pkgname)
error: Environment variable HADOOP_CMD must be set before loading package rhdfs
Warning in FUN(c("base", "methods", "datasets", "utils", "grDevices", "graphics", :
can't load rhdfs
Loading required package: rmr2
Error in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]) :
there is no package called ‘stringr’
...
在深入研究错误日志后，似乎我已经在用户级别安装了 R 库，我应该在系统级别安装该库。有关如何将 R 库安装到系统级别的详细信息，请参阅此线程。（"dev_tools"包可能会派上用场，记得在 sudo 下运行 R，或者你可以更喜欢sudo R CMD INSTALL [package_name] ）
您可以通过 system.file(package="[package_name]") 仔细检查 R 中的软件包安装路径，尽管这始终显示软件包的第一个首选库路径。所以我强烈建议以前安装的用户库。
再运行几次以仔细检查错误日志，并确保包在 R system lib 中正确安装。stderr日志很有帮助，但之前没有人指出实际位置：-（