1， 11g设置归档重新登录启动报错
SQL> startup;
ORA-00845: MEMORY_TARGET not supported on this system
SQL>2，看Oracle的官方解释是：
Starting with Oracle Database 11g, the Automatic Memory Management feature requires more shared memory (/dev/shm)and file descriptors. The size of the shared memory should be at least the greater of MEMORY_MAX_TARGET and MEMORY_TARGET for each Oracle instance on the computer. If MEMORY_MAX_TARGET or MEMORY_TARGET is set to a non zero value, and an incorrect size is assigned to the shared memory, it will result in an ORA-00845 error at startup.
就是说MEMORY_MAX_TARGET的设置不能超过/dev/shm的大小，在oracle11g中新增的内存自动管理的参数MEMORY_TARGET,它能自动调整SGA和PGA，这个特性需要用到/dev/shm共享文件系统，而且要求/dev/shm必须大于MEMORY_TARGET，如果/dev/shm比MEMORY_TARGET小就会报错。
3，解决方案
2个修改地方：
在/etc/fstab里面，一是swap后面修改成defaults,size=11G，二是tmpfs后面修改成defaults,size=11G，修改完，如下所示
[root@testoracle1 oracle]# vim /etc/fstab
#
# /etc/fstab
# Created by anaconda on Tue Aug 18 16:46:25 2015
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/vg_testoracle1-lv_root / ext4 defaults 1 1
UUID=e10af7be-cb8b-4454-965d-0c2275fe75b9 /boot ext4 defaults 1 2
/dev/mapper/vg_testoracle1-lv_swap swap swap defaults,size=11G 0 0
tmpfs /dev/shm tmpfs defaults,size=11G 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0
~ 修改完后，需要重新挂载一下，才能生效：
[root@testoracle1 oracle]# mount -o remount,size=11G /dev/shm
[root@testoracle1 oracle]# 3，再次启动数据库，就不会报错了，正常启动：
SQL> startup;
ORACLE instance started.
Total System Global Area 1.1358E+10 bytes
Fixed Size 2216744 bytes
Variable Size 8925482200 bytes
Database Buffers 2415919104 bytes
Redo Buffers 13946880 bytes
Database mounted.
Database opened.
SQL> 4，标准的禁止归档模式：
SQL> alter system set log_archive_start=false scope=spfile; #禁用自归档
SQL> shutdown immediate;
SQL> startup mount; #重启数据库到mount模式
SQL> alter database noarchivelog; #修改为非归档模式
SQL> alter database open; #打数据文件
SQL> archive log list; #再次查看前归档模式
SQL> alter database noarchivelog;
alter database noarchivelog
*
ERROR at line 1:
ORA-38774: cannot disable media recovery - flashback database is enabled
SQL>
去查看闪回是否已经开启：
SQL> select flashback_on from v$database;
FLASHBACK_ON
------------------
YES
SQL> 去关闭闪回功能：
SQL> alter database flashback off;
Database altered.
SQL>
SQL> alter database flashback off;
Database altered.再关闭归档。
SQL> alter database noarchivelog;
Database altered.
SQL> archive log list;
Database log mode No Archive Mode
Automatic archival Disabled
Archive destination /oracle/app/oracle/flash_recovery_area/archivelog
Oldest online log sequence 337
Current log sequence 339
SQL>