In order to forcefully let the namenode leave safemode, following command should be executed:
bin/hadoop dfsadmin -safemode leave
You are getting Unknown command error for your command as -safemode isn't a sub-command for hadoop fs, but it is of hadoop dfsadmin.
Also after the above command, I would suggest you to once run hadoop fsck so that any inconsistencies crept in the hdfs might be sorted out.
Use hdfs command instead of hadoop command for newer distributions. The hadoop command is being deprecated:
hdfs dfsadmin -safemode leave
hadoop dfsadmin has been deprecated and so is hadoop fs command, all hdfs related tasks are being moved to a separate command hdfs