Let me see if I get this right; you have Windows backup server and Linux client with Oracle running?  First make sure that Linux box doesn't have localhost listed next to its IP (localhost should go only again 127.0.0.1) - that's one possible cause of it.  Second, make sure you name resolution is set correctly.  SYSTEM user is found on Windows systems and since you backup Linux I see no reason other than some misconfiguration to yiled error like that.

Yes, all the running and the names are correct. I was doing backup /etc/hosts error was not.

On the client logs this error "nsrexecd 40 User %s cannot request command execution 1 0 6 SYSTEM"

Strange... but ok, go to Linux client properties and add in remote access SYSTEM@backup_server

Perhaps before that, go to Linux box, set oranev for database you wish to backup and do rman cmdfile to see if client initiated backup would correctly.

This error seems to indicate NMO is not installed on machine on which you are running this.  Well, it might be installed, but library supplied by NMO (libnwora) needs to be linked.  More correctly, switch to oracle user, go to $ORACLE_HOME/lib and do ln -s /usr/lib/libnwora.XX libobk.XX (where XX really depends on platform and architecture, but you will see that yourself).

I tried to do so:

# /u01/oracle/product/db/11.2.0/bin/rman target user/password@database cmdfile /opt/nsr/bin/full.sh

Recovery Manager: Release 11.2.0.2.0 - Production on Thu Mar 31 14:03:56 2011

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

connected to target database: DATABASE (DBID=1780902363)

RMAN> run {
2> allocate channel t1 type 'SBT_TAPE';
3> allocate channel t1 type 'SBT_TAPE';
4> send 'NSR_ENV=(NSR_SERVER=XXXXXX.XX, NSR_CLIENT=XXXXXX.XX)';
5> send channel t1 'NSR_ENV=(NSR_SERVER=XXXXXX.XX,NSR_CLIENT=XXXXXX.XX)';
6> backup full filesperset 4 format 'FULL_%d_$U' (database);
7> release channel t1;
8> }
9>
using target database control file instead of recovery catalog
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of allocate command on t1 channel at 03/31/2011 14:03:57
ORA-19554: error allocating device, device type: SBT_TAPE, device name:
ORA-27211: Failed to load Media Management Library
Additional information: 2

Recovery Manager complete.

this oracle problem? or am I doing something wrong?

well. it is /usr/lib/libnwora.XX under Linux... perhaps on other platforms is somewhere else... usually installation guide provides table with steps for each platform/Oracle version with correct names and paths... check it out.

work, but now terminates at backup:

1 retry attempted
XXXXXXX.XX:RMAN:\backupts_ful: No full backups of this save set were found in the media database; performing a full backup
EMC NetWorker Module for Oracle v5.0
Thu Mar 31 16:35:08 2011
NULL:     Connection timed out

firewall off, backup server and client are on the same network

# nsrnmoadmin -r list

NSR_NWPATH=/usr/sbin

NSR_ORACLECAT_MODE=undetermined

NSR_REMOVE_ON_FAILURE=FALSE

NSR_ORACLE_NLS_LANG=AMERICAN_AMERICA.AL32UTF8

NSR_ORACLECAT_LOG_FILE=

NSR_ORACLECAT_DEBUG_FILE=

NSR_TMPDIR=

NSR_BUNDLING=disabled

NSR_INCR_EXPIRATION=disabled

The fact that runs on nsrnmostart rman, written 500-600Mb and then terminates. Fulfills a very long time about 30 minutes, do not even know where to look to identify the problem ....

Ah wait, I was not aware that it runs and then break.  (if this is something you see when running from server which I guess it is since you mention nsrnmostart).  In such case, check group properties and make sure timeout is not set to 30 (by default) - changed it to 0.

One thing, which might not be obvious from docs, is to run on your client nsrnmoadmin -r list... this will create nwora.res resource (unless it exists already).

Back to your problem.  This looks as log from server... give it a try from client itself and make sure that part works.  "NULL:     Connection timed out" may suggest that routing might be wrong for some reason or any other blocking factor.  If it works from client, re-inspect nsrnmo file you used for backup from server.  Usually, I set only ORACLE_HOME, ORACLE_SID and ORACLE_USER inside.  Nevertheless, running this from client should give you more information on failure.

all works, thank you