ora-00845解决方法
[oracle@up ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Tue Nov 10 19:26:05 2015
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup;
ORA-00845: MEMORY_TARGET not supported on this system
SQL>
错误原因：tmpfs空间不能小于MEMORY_TARGET的值，tmpfs空间太小数据库无法启动
[root@up ~]# vi /u01/app/oracle/product/11.2.0/dbs/init.ora
db_name='ORCL'
memory_target=1G
processes = 150
audit_file_dest='<ORACLE_BASE>/admin/orcl/adump'
audit_trail ='db'
db_block_size=8192
db_domain=''
数据库参数文件里memory_target参数的大小为1G
[root@up ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 26G 17G 7.4G 70% /
tmpfs 242M 0 242M 0% /dev/shm
/dev/sda1 190M 28M 153M 16% /boot
tmpfs空间大小242M，所以无法启动数据库
解决方法，在/etc/fstab里修改tmpfs的挂载选项，增大tmpfs的空间
[root@up ~]# vi /etc/fstab
UUID=a6948461-a0e3-4e64-bf75-e9a45864d48a / ext4 defaults 1 1
UUID=0d5a41b3-3988-467f-be75-93e0e4fad1e9 /boot ext4 defaults 1 2
UUID=bba460fd-bdbe-4a7e-ba49-4016f4633067 swap swap defaults 0 0
tmpfs /dev/shm tmpfs defaults,size=2G 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tmpfs挂载，将tmpfs空间大小设置为2G
重启系统
[root@up ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 26G 17G 7.4G 70% /
tmpfs 2.0G 0 2.0G 0% /dev/shm
/dev/sda1 190M 28M 153M 16% /boot
更改后tmpfs为2G
[root@up ~]# su - oracle
[oracle@up ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Tue Nov 10 19:40:28 2015
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup;
ORACLE instance started.
Total System Global Area 409194496 bytes
Fixed Size 2213856 bytes
Variable Size 301991968 bytes
Database Buffers 96468992 bytes
Redo Buffers 8519680 bytes
Database mounted.
Database opened.
问题解决，数据库启动完毕