创建一个新的 instance 报错
[oracle@fiona2 ~]$ cd $ORACLE_HOME/dbs
[oracle@fiona2 dbs]$ ls
hc_ora11g.dat  hc_ORADB.dat  init.ora  initORADB.ora_1  lkORCL  orapwora11g  spfileora11g.ora
[oracle@fiona2 dbs]$ cp spfileora11g.ora spfiletest1.ora
[oracle@fiona2 dbs]$ export ORACLE_SID=test1
[oracle@fiona2 dbs]$ sqlplus "/ as sysdba"

SQL*Plus: Release 11.2.0.1.0 Production on Sat Nov 1 11:11:36 2014
Copyright (c) 1982, 2009, Oracle.  All rights reserved.
Connected to an idle instance.
SQL> startup nomount;
ORA-00845: MEMORY_TARGET not supported on this system
SQL> !
//查看ORA error
[oracle@fiona2 dbs]$ oerr ora 845
00845, 00000, "MEMORY_TARGET not supported on this system"
// *Cause: The MEMORY_TARGET parameter was not supported on this operating system or /dev/shm was not sized correctly on Linux.
// *Action: Refer to documentation for a list of supported operating systems. Or, size /dev/shm to be at least the SGA_MAX_SIZE on each Oracle instance running on the system.
[oracle@fiona2 dbs]$ df -lh
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2        20G   16G  3.4G  83% /
tmpfs           936M  444M  492M  48% /dev/shm
/dev/sda1       194M   34M  151M  19% /boot
/dev/sda3       5.9G  593M  5.1G  11% /home
//正常启动的instance
SQL> show parameter memory_target
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_target                        big integer 748M
///etc/fstab就是在开机引导的时候自动挂载到linux的文件系统
[oracle@fiona2 dbs]$ cat /etc/fstab
#
# /etc/fstab
# Created by anaconda on Mon Aug 25 00:29:27 2014
#
# 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
#
UUID=0b1c3b92-8f6c-49b8-b524-c6956449948a /                       ext4    defaults        1 1
UUID=4997e38d-f51f-4007-ba58-9ea63f1a97f7 /boot                   ext4    defaults        1 2
UUID=d0d5b515-bf43-435a-8650-3af8d5c38746 /home                   ext4    defaults        1 2
UUID=4ace5509-4053-43f7-9ed0-a5d8f3fc6bdb swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
//切换到root用户，扩大tmpfs的size
[oracle@fiona2 dbs]$ su root
Password: 
[root@fiona2 dbs]# umount /dev/shm
[root@fiona2 dbs]# mount tmpfs /dev/shm -t tmpfs -o size=2048m
[root@fiona2 dbs]# df -lh
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2        20G   16G  3.4G  83% /
tmpfs           2.0G     0  2.0G   0% /dev/shm
/dev/sda1       194M   34M  151M  19% /boot
/dev/sda3       5.9G  593M  5.1G  11% /home
tmpfs           2.0G     0  2.0G   0% /dev/shm
//重启验证
[root@fiona2 dbs]# su - oracle
[oracle@fiona2 ~]$ export ORACLE_SID=test1
[oracle@fiona2 ~]$ sqlplus "/ as sysdba"
SQL*Plus: Release 11.2.0.1.0 Production on Sat Nov 1 11:45:34 2014
Copyright (c) 1982, 2009, Oracle.  All rights reserved.
Connected to an idle instance.
SQL> startup nomount;
ORACLE instance started.
Total System Global Area  780824576 bytes
Fixed Size                  2217424 bytes
Variable Size             461376048 bytes
Database Buffers          314572800 bytes
Redo Buffers                2658304 bytes
SQL> show parameter memory_target
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_target                        big integer 748M


Reference:
tmpfs是一种基于内存的文件系统，它可以使用RAM，但它也可以使用swap分区来存储。
为防止tmpfs使用了全部VM，有时候要限制其大小。要创建一个最大为32 MB的tmpfs文件系统，键入：
# mount tmpfs /dev/shm -t tmpfs -o size=32m
添加到 /etc/fstab，应该是这样：
tmpfs /dev/shm tmpfs size=32m 0 0