Usage: hadoop dfsadmin [GENERIC_OPTIONS] [-report] [-safemode enter | leave | get | wait] [-refreshNodes] [-finalizeUpgrade] [-upgradeProgress status | details | force] [-metasave filename] [-setQuota <quota> <dirname>...<dirname>] [-clrQuota <dirname>...<dirname>] [-help [cmd]]
ex:
hadoop dfsadmin -safemode leave