在测试spark计算时，将作业提交到yarn（模式–master yarn-cluster）上，想查看print到控制台这是imposible的，因为作业是提交到yarn的集群上，so 去yarn集群上看日志是很麻烦的，但有特别想看下print的信息，方便调试或者别的目的
在Spark的conf目录下，把log4j.properties.template修改为log4j.properties，原来的内容如下：
<code style="display: block; padding: 0px; color: inherit; font-family: ‘Source Code Pro‘, monospace; font-size: inherit; border-radius: 0px; background: transparent;" class="hljs avrasm has-numbering">#Set everything to be logged to the console log4j.rootCategory=INFO, console log4j.appender.console=org.apache.log4j.ConsoleAppender log4j.appender.console.target=System.err log4j.appender.console.layout=org.apache.log4j.PatternLayout log4j.appender.console.layout.ConversionPattern=%d{yy/MM/dd HH:mm:ss} %p %c{1}: %m%n #Settings to quiet third party logs that are too verbose log4j.logger.org.spark-project.jetty=WARN log4j.logger.org.spark-project.jetty.util.component.AbstractLifeCycle=ERROR log4j.logger.org.apache.spark.repl.SparkIMain$exprTyper=INFO log4j.logger.org.apache.spark.repl.SparkILoop$SparkILoopInterpreter=INFO</code>
把log4j.rootCategory=INFO, console改为log4j.rootCategory=WARN, console即可抑制Spark把INFO级别的日志打到控制台上。如果要显示全面的信息，则把INFO改为DEBUG。
如果希望一方面把代码中的println打印到控制台，另一方面又保留spark 本身输出的日志，可以将它输出到日志文件中
<code style="display: block; padding: 0px; color: inherit; font-family: ‘Source Code Pro‘, monospace; font-size: inherit; border-radius: 0px; background: transparent;" class="hljs avrasm has-numbering">log4j.rootCategory=INFO, console,FILE log4j.appender.console=org.apache.log4j.ConsoleAppender log4j.appender.console.target=System.err log4j.appender.console.layout=org.apache.log4j.PatternLayout log4j.appender.console.layout.ConversionPattern=%d{yy/MM/dd HH:mm:ss} %p %c{1}: %m%n # Settings to quiet third party logs that are too verbose log4j.logger.org.eclipse.jetty=WARN log4j.logger.org.eclipse.jetty.util.component.AbstractLifeCycle=ERROR log4j.logger.org.apache.spark.repl.SparkIMain$exprTyper=INFO log4j.logger.org.apache.spark.repl.SparkILoop$SparkILoopInterpreter=INFO log4j.appender.FILE=org.apache.log4j.DailyRollingFileAppender log4j.appender.FILE.Threshold=DEBUG log4j.appender.FILE.file=/home/hadoop/spark.log log4j.appender.FILE.DatePattern=‘.‘yyyy-MM-dd log4j.appender.FILE.layout=org.apache.log4j.PatternLayout log4j.appender.FILE.layout.ConversionPattern=[%-5p] [%d{yyyy-MM-dd HH:mm:ss}] [%C{1}:%M:%L] %m%n # spark log4j.logger.org.apache.spark=INFO</code>
上面的操作，spark的日志一方面打印到控制台，一方面写入到/home/hadoop/spark.log中了，这是日志的继承特性，后面再来改进，目前把log4j.rootCategory=INFO, console，FILE改为log4j.rootCategory=INFO, FILE即可
原文：http://www.cnblogs.com/abapscript/p/4734467.html