1、Use the CONFIGURE CONTROLFILE AUTOBACKUP command to eanable

设置RMAN配置文件，将CONFIGE CONTROLFILE AUTOBACKUP 为ON状态，可以是实现控制文件的备份。如果CONFIGURE CONTROLFILE AUTOBACKUP 为OFF,那么在备份system表空间的时候，也会备份congrol file。

2、when enabled,RMAN automatically performs a back up of the control file and current server parameter file after BACKUP or COPY commands.

3、Back ups also occur after structural changes to the database .

4、Backup is given a default name.

备份Controlfile与system parameter file的方法

（一）、设置如下配置参数，实现controlfile与system parameter file的备份 

RMAN> show all;

RMAN configuration parameters for database with db_unique_name POLI are:
CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # default
CONFIGURE BACKUP OPTIMIZATION OFF; # default
CONFIGURE DEFAULT DEVICE TYPE TO DISK; # default
CONFIGURE CONTROLFILE AUTOBACKUP ON;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '%F'; # default
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE MAXSETSIZE TO UNLIMITED; # default
CONFIGURE ENCRYPTION FOR DATABASE OFF; # default
CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default
CONFIGURE COMPRESSION ALGORITHM 'BASIC' AS OF RELEASE 'DEFAULT' OPTIMIZE FOR LOAD TRUE ; # default
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/oracle/dbs/snapcf_poli.f'; # default

 （二）、执行命令backup current controlfile，实现controlfile与spfile的备份;(单独执行controlfile与spfile的命令)

RMAN> backup current controlfile;

Starting backup at 23-MAR-13
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current control file in backup set
channel ORA_DISK_1: starting piece 1 at 23-MAR-13
channel ORA_DISK_1: finished piece 1 at 23-MAR-13
piece handle=/u01/flash_recovery_area/POLI/backupset/2013_03_23/o1_mf_ncnnf_TAG20130323T234359_8nvmg18j_.bkp tag=TAG20130323T234359 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:03
Finished backup at 23-MAR-13

Starting Control File Autobackup at 23-MAR-13
piece handle=/u01/flash_recovery_area/POLI/autobackup/2013_03_23/o1_mf_n_810863044_8nvmg4dv_.bkp comment=NONE
Finished Control File Autobackup at 23-MAR-13

（三）、使用include子句，实现control file的备份

RMAN> backup datafile 4 include current controlfile;

Starting backup at 23-MAR-13
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00004 name=/u01/oradata/poli/users01.dbf
channel ORA_DISK_1: starting piece 1 at 23-MAR-13
channel ORA_DISK_1: finished piece 1 at 23-MAR-13
piece handle=/u01/flash_recovery_area/POLI/backupset/2013_03_23/o1_mf_nnndf_TAG20130323T234751_8nvmo843_.bkp tag=TAG20130323T234751 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:03
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current control file in backup set
channel ORA_DISK_1: starting piece 1 at 23-MAR-13
channel ORA_DISK_1: finished piece 1 at 23-MAR-13
piece handle=/u01/flash_recovery_area/POLI/backupset/2013_03_23/o1_mf_ncnnf_TAG20130323T234751_8nvmod9y_.bkp tag=TAG20130323T234751 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 23-MAR-13

Starting Control File Autobackup at 23-MAR-13
piece handle=/u01/flash_recovery_area/POLI/autobackup/2013_03_23/o1_mf_n_810863277_8nvmofjy_.bkp comment=NONE
Finished Control File Autobackup at 23-MAR-13

（四）、使用SQL命令备份controlfile

RMAN> sql "alter database backup controlfile  to ''/tmp/poli_df.bak''";

sql statement: alter database backup controlfile  to ''/tmp/poli_df.bak''