from.dfs() has Error in RStudio, but runs well in R console

[konstantin0921]

i have installed rmr2(3.3.1) rhdfs(1.0.8) into my Hadoop cluster successfully. then i used the simple demo from Internet to test my RHadoop environment. but it failed when the from.dfs() function was called.

from.dfs(out)
Error in hdfs.cmd() : Can't find an alternative for hdfs command

but when i typed the same program directly in R console, it works very well, the result of MapReduce can be correctly displayed. so i am confused, what is going wrong? can anyone help me? thanks