RMAN does not run in linux console

am running Oracle10g on Red Hat Linux. Whenever I try
to run RMAN from the console, it does nothing. I am able to Ctrl-C out of
it back to the prompt so it does not hang the server.

I have tried RMAN target /
but it still does not work only show an error:
rman can't open target.

Any suggestions would be appreciated

make sure you are using the rman in ORACLE_HOME/bin linux has its own rman executable which is probably in the path before the proper one