Simon Krenger

There is always something that gets in the way. One problem I regularly stumble upon when installing a new Oracle 11g R2 installation is the following error when I try to start the database:

SQL> startup nomount;
ORA-00845: MEMORY_TARGET not supported on this system

So I keep this post mainly for my own reference when installing a new database on a Linux system.

This error comes up because you tried to use the Automatic Memory Management (AMM) feature of Oracle 11g R2. Well done, but it seems that your shared memory filesystem (shmfs) is not big enough. So let’s look at the steps necessary to enlarge your shared memory filesystem to avoid the error above.

First of all, login as root and have a look at the filesystem:

[root@oracle-em oracle]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_oracleem-lv_root
                       93G   19G   69G  22% /
tmpfs                 5.9G  112K  5.9G   1% /dev/shm
/dev/sda1             485M   99M  362M  22% /boot

So we can see that tmpfs has a size of 6GB. We can change the size of that filesystem by issuing the following command (where “12g” is the size I want for my MEMORY_TARGET):

[root@oracle-em oracle]# mount -t tmpfs shmfs -o size=12g /dev/shm

This command (re)mounts the shmfs filesystem (check this post for more information about shmfs) with the option “size=12g“.

The shared memory file system should be big enough to accommodate the MEMORY_TARGET and MEMORY_MAX_TARGET values, or Oracle will throw the ORA-00845 error. Note that when changing something with the mount command, the changes are not permanent.

To make the change persistent, edit your /etc/fstab file to include the option you specified above:

[root@oracle-em ~]# cat /etc/fstab
[..]
tmpfs                   /dev/shm                tmpfs   size=12g        0 0
[..]

In my case, I replaced the “defaults” option with the size=12g option. After saving the file, the changes should be permanent. Now back to Oracle. Let’s see if we can start the database now…

SQL> startup nomount
ORACLE instance started.

Total System Global Area 1.1758E+10 bytes
Fixed Size                  2239056 bytes
Variable Size            5939135920 bytes
Database Buffers         5804916736 bytes
Redo Buffers               12128256 bytes

Bingo! Now go and enjoy your automatically managed memory configuration!