Spark 1.4.1

sc.setLogLevel("WARN")

From comments in source code:

Valid log levels include: ALL, DEBUG, ERROR, FATAL, INFO, OFF, TRACE, WARN

Spark 2.x – 2.3.1

sparkSession.sparkContext().setLogLevel("WARN")

Spark 2.3.2

sparkSession.sparkContext.setLogLevel("WARN")