Besides ora-00845:memory_target not supported on the This system

There are many articles about this error on the web, and some refer to the instructions in the Oracle documentation.

Setting Memory Target at Instance Startup on Linux
Starting with Oracle Database 11g Release 1 (11.1), Oracle provides the option of automatically managing SGA and PGA with A combined memory_targetparameter without has to set Sga_target and Pga_aggregate_target explicitly. This was supported on Linux, Windows, Solaris, HPUX, and AIX (reference Bug 7258378).
If you see the ORA-00845 error reported on Linux machines in Oracle instance startup when using the Memory_target paramete R, then check the size of/dev/shm. IF/DEV/SHM is isn't configured, then mount it sized to be at least the value of Memory_target. IF/DEV/SHM is configured but the amount of available space reported (through Df-k/dev/shm) are less than Memory_target, Then free the space or mount a larger/dev/shm to satisfy the memory_target size. Note that if you set thememory_max_target parameter greater than Memory_target and then ensure that/dev/shm are sized to bes a t least the value of Memory_max_target.
Memory Target for Oracle database instancesrunning database Configuration Assistant (DBCA) defaults to this Automatic Memo Ry Management option. In the case of upgrade or manual database Creation,memory_target can is specified in the initialization parameter file.

Most people understand that the requirement for/DEV/SHM must be at least less than the size of memory_max_target.

However, according to the actual situation of the test, it must be/DEV/SHM free space is not less than the size of memory_max_target.

For example

Sql> Show parameter target

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
Archive_lag_target integer 0
Db_flashback_retention_target integer 1440
Fast_start_io_target integer 0
Fast_start_mttr_target integer 0
memory_max_target Big Integer 6336M
Memory_target Big Integer 6336M
Parallel_servers_target Integer 16
Pga_aggregate_target Big Integer 0
Sga_target Big Integer 0

According to the parameters, thememory_max_target parameter is 6.18G

[Email protected] ~]# Mount-o REMOUNT,SIZE=10G/DEV/SHM
[Email protected] ~]# df-h
Filesystem Size used Avail use% mounted on
/dev/mapper/vg_centosdbo-lv_root 50G 42G 5.3G 89%/
tmpfs 10G 9.9G 144M 99%/DEV/SHM
/dev/sda2 485M 39M 421M 9%/boot
/DEV/SDA1 200M 260K 200M 1%/boot/efi
/dev/mapper/vg_centosdbo-lv_home 1.3T 504G 744G 41%/Home
[Email protected] ~]# su–oracle

Even here I set size to 10G. But the available space is only 144M.

At this point I started the database:

Sql*plus:release 11.2.0.1.0 Production on Wed Mar 30 14:29:21 2016

Copyright (c) 1982, Oracle. All rights reserved.

Sql> Conn/as SYSDBA
Connected to an idle instance.
Sql> Startup
Ora-00845:memory_target not supported on the This system

will still error.

As shown below, if the free space is guaranteed to be greater than memory_max_target, the database starts normally.

[Email protected] ~]# Mount-o REMOUNT,SIZE=16G/DEV/SHM
[Email protected] ~]# df-h
Filesystem Size used Avail use% mounted on
/dev/mapper/vg_centosdbo-lv_root 50G 42G 5.3G 89%/
tmpfs 16G 6.2G 9.9G 39%/DEV/SHM
/dev/sda2 485M 39M 421M 9%/boot
/DEV/SDA1 200M 260K 200M 1%/boot/efi
/dev/mapper/vg_centosdbo-lv_home 1.3T 504G 744G 41%/Home
[Email protected] ~]# Sqlplus/nolog
-bash:sqlplus:command not found
[Email protected] ~]# su-oracle
[Email protected] ~]$ Sqlplus/nolog

Sql*plus:release 11.2.0.1.0 Production on Wed Mar 30 14:30:41 2016

Copyright (c) 1982, Oracle. All rights reserved.

Sql> Conn/as SYSDBA
Connected to an idle instance.
Sql> Startup
ORACLE instance started.

Total System Global area 6614106112 bytes
Fixed Size 2213896 bytes
Variable Size 3556771832 bytes
Database buffers 3019898880 bytes
Redo buffers 35221504 bytes
Database mounted.
Database opened.
Sql>

As a result,/dev/shm defaults to half of system memory, although it may theoretically be larger than Memory_target, but database startup is likely to still cause an error.

Like the test library I used, Memory_target is 6.18G.

The default/DEV/SHM is half the memory, or about 7.7G. However, the database is still error-activated.

[[email protected] ~]# free-g
              total       used       free      shared    buffers     Cached
mem:             15         11           4          0           0        
-/+ buffers/cache:           0        
swap:            7           0          7
[[email protected] ~]# 

Besides ora-00845:memory_target not supported on the This system