Log4J2: How to log the exact same output to both file and console?

The following lines are from the start of my log4j2 properties file:

rootLogger.level = INFO
rootLogger.appenderRef.stdout.ref = LOG_ROOT
rootLogger.appenderRef.startup.ref = START_UP_LOG
rootLogger.appenderRef.handler.ref = HANDLER_LOG
appender.LOG_ROOT.type = RollingFile
appender.LOG_ROOT.name = LOG_ROOT
appender.LOG_ROOT.fileName = logs/${hostName}_app.log
appender.LOG_ROOT.filePattern = logs/${hostName}_am.log.%d{yyyy-MM-dd}_%i.gz
appender.LOG_ROOT.layout.type = PatternLayout
appender.LOG_ROOT.layout.charset = UTF-8
appender.LOG_ROOT.layout.pattern = %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5p - (%F:%L) %m%n
appender.LOG_ROOT.policies.type = Policies
appender.LOG_ROOT.policies.time.type = TimeBasedTriggeringPolicy
appender.LOG_ROOT.policies.time.interval = 1
appender.LOG_ROOT.policies.time.modulate = true
appender.LOG_ROOT.policies.size.type = SizeBasedTriggeringPolicy
appender.LOG_ROOT.policies.size.size=5120MB
appender.LOG_ROOT.strategy.type = DefaultRolloverStrategy
appender.LOG_ROOT.strategy.fileIndex = nomax
appender.LOG_ROOT.strategy.delete.type = Delete
appender.LOG_ROOT.strategy.delete.basePath = logs
appender.LOG_ROOT.strategy.delete.ifFileName.type = IfFileName
appender.LOG_ROOT.strategy.delete.ifFileName.glob = *am.log.*
appender.LOG_ROOT.strategy.delete.ifAccumulatedFileCount.type = IfAccumulatedFileCount
appender.LOG_ROOT.strategy.delete.ifAccumulatedFileCount.exceeds = 180

In the properties file, I also have other loggers that uses the LOG_ROOT appender. For instance,

logger.ORG_HIBERNATE_SQL.name = org.hibernate.SQL
logger.ORG_HIBERNATE_SQL.level = INFO
logger.ORG_HIBERNATE_SQL.additivity = false
logger.ORG_HIBERNATE_SQL.appenderRef.rolling.ref = LOG_ROOT

In addition to the existing log file, I want to display the exact same LOG_ROOT contents to the console as well. Is there any way I can "clone" the log output to the console?

I you use the same layout, you'll get the same output:

rootLogger.appenderRef.console.ref = CONSOLE
appender.CONSOLE.type = Console
appender.CONSOLE.name = CONSOLE
appender.CONSOLE.layout.type = PatternLayout
appender.CONSOLE.layout.charset = UTF-8
appender.CONSOLE.layout.pattern = %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5p - (%F:%L) %m%n

If you wish to ensure that the patterns are the same in all appenders, define a user property:

property.PATTERN = %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5p - (%F:%L) %m%n

and use ${PATTERN} wherever it is required.

Edit: Loggers by default also log to their parent's appenders (additivity="true"). If you disable additivity you'll have to add a reference to the CONSOLE appender to each logger that directly uses LOG_ROOT.

In your case it is probably easier to leave additivity at its default true value, keep just the LOG_ROOT and CONSOLE appenders on the root logger and move the START_UP_LOG and HANDLER_LOG appender to more specific logger.