Question about "RMAN-06169:" and Oracle When i typed the command "backup database" it mentioned 

"RMAN-06169: could not read file header for datafile 5 error reason 4..."etc


and then i checked the STATUS of the datafile 5

(look at the picture)



so i tried to recover ,it didn't work. 

it told me that "ORA-00283: recovery session canceled due to errors
ORA-01110: data file 5: '/u01/app/oracle/oradata/abc/abc.dbf'
ORA-01157: cannot identify/lock data file 5 - see DBWR trace file
ORA-01110: data file 5: '/u01/app/oracle/oradata/abc/abc.dbf'
(datafile 7 is the same situation.)"

It reminded me that i once delected the document-abc under the graphic interface,which meant that i didn't use the command to delect the file.

so i tried to alter the datafile 5 and datafile 7..  it didn't work also.

how to alter the datafile 5 and 7? and backup database?
thanks very much~！
Try this command to SKIP the offline and corrupted datafiles:

BACKUP DATABASE
    SKIP INACCESSIBLE
    SKIP OFFLINE;



  SKIP INACCESSIBLE: Inaccessible datafiles. A datafile is only considered inaccessible if it cannot be read. Some offline datafiles can still be read because they exist on disk. Others have been deleted or moved and so cannot be
  read, making them inaccessible. 
  
  SKIP OFFLINE: skipping Offline datafiles;


Details: https://docs.oracle.com/cd/B12037_01/server.101/b10734/rcmbackp.htm