Summary of Oracle 11g Database startup errors

1. The ORA-00845: MEMORY_TARGET not supported on this system is prompted when the database is started
(MEMORY_TARGET, the new memory automatic management parameter in Oracle 11g, can automatically adjust SGA and PGA. This feature requires the/dev/shm shared file system, and/dev/shm must be greater than MEMORY_TARGET. If/dev/shm is smaller than MEMORY_TARGET, an error is returned)
Figure:

Solution:
[Root @ CentOS ~] # Df-h
Filesystem Size Used Avail Use % Mounted on
/Dev/mapper/VolGroup-lv_root 25 GB 11G 14G 45%/
Tmpfs 1.0G 751 M 274 M 74%/dev/shm -- the value is small.
/Dev/sda1 485 M 30 M 430 M 7%/boot
/Dev/sr0 3.6G 3.6G 0 100%/media/CentOS_6.4_Final
[Root @ centos ~] # Mount-o remount, size = 2G/dev/shm -- modify the size and no error will be reported.
[Root @ centos ~] # Df-h
Filesystem Size Used Avail Use % Mounted on
/Dev/mapper/VolGroup-lv_root
25G 11G 14G 45%/
Tmpfs 2.0G 751 M 1.3G 37%/dev/shm
/Dev/sda1 485 M 30 M 430 M 7%/boot
/Dev/sr0 3.6G 3.6G 0 100%/media/CentOS_6.4_Final
[Root @ centos ~] #

Test:

2. An error occurred while starting the oem control interface.
[Oracle @ centos ~] $ Emctl stop dbconsole
Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0
Copyright (c) 1996,200 9 Oracle Corporation. All rights reserved.
Https: // centos: 1158/em/console/aboutApplication
Stopping Oracle Enterprise Manager 11g Database Control...
... Stopped.
[Oracle @ centos ~] $ Emctl start dbconsole
Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0
Copyright (c) 1996,200 9 Oracle Corporation. All rights reserved.
Https: // centos: 1158/em/console/aboutApplication
Starting Oracle Enterprise Manager 11g Database Control
........................................ ........................................ ....
... Failed.
------------------------------------------------------------------
Logs are generated in directory/home/oracle/app/oracle/product/11.2.0/dbhome_1/centos_orcl/sysman/log
[Oracle @ centos ~] $ Tailf-n 3/home/oracle/app/oracle/product/11.2.0/dbhome_1/centos_orcl/sysman/log/emdctl. trc -- view the last three lines of logs and prompt for route and host errors
14:54:47, 568 Thread-3032057536 WARN http: nmehl_connect_internal: connect failed to (centos: 1158): No route to host (error = 113)
15:02:50, 071 Thread-3032803008 WARN http: nmehl_connect_internal: connect failed to (centos: 3938): No route to host (error = 113)
15:02:50, 073 Thread-3032803008 ERROR main: nmectla_agentctl: Error connecting to https: // centos: 3938/emd/main. Returning status code 1

Solution:
[Root @ centos ~] # Ifconfig eth1 -- check the server's route and Host IP address. It is best to set it to static
Eth1 Link encap: Ethernet HWaddr 08: 00: 27: 5C: 4A: F6
Inet addr: 2.2.2.114 Bcast: 2.2.2.255 Mask: 255.255.255.0
Inet6 addr: fe80: a00: 27ff: fe5c: 4af6/64 Scope: Link
Up broadcast running multicast mtu: 1500 Metric: 1
RX packets: 88220 errors: 0 dropped: 0 overruns: 0 frame: 0
TX packets: 43011 errors: 0 dropped: 0 overruns: 0 carrier: 0
Collisions: 0 FIG: 1000
RX bytes: 6611001 (6.3 MiB) TX bytes: 29439365 (28.0 MiB)
[Root @ centos ~] # Route-n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
2.2.2.0 0.0.0.0 255.255.255.0 U 1 0 0 eth1
0.0.0.0 2.2.2.1 0.0.0.0 UG 0 0 0 eth1
[Root @ centos ~] #

Test:
[Oracle @ centos ~] $ Emctl start dbconsole -- started successfully
Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0
Copyright (c) 1996,200 9 Oracle Corporation. All rights reserved.
Https: // centos: 1158/em/console/aboutApplication
Starting Oracle Enterprise Manager 11g Database Control ...... started.
------------------------------------------------------------------
Logs are generated in directory/home/oracle/app/oracle/product/11.2.0/dbhome_1/centos_orcl/sysman/log
[Oracle @ centos ~] $

3. Control File loss (the database cannot be started due to control file loss)
1234567891011121314 [oracle @ centos ~] $ Sqlplus
SQL * Plus: Release 11.2.0.1.0 Production on Sat Jan 25 09:31:04 2014
Copyright (c) 1982,200 9, Oracle. All rights reserved.
Enter user-name:/as sysdba
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 661209088 bytes
Fixed Size 1338560 bytes
Variable Size 494928704 bytes
Database Buffers 159383552 bytes
Redo Buffers 5558272 bytes
ORA-00205: error in identifying control file, check alert log for more info
SQL>

Solution:
[Oracle @ centos ~] $ Ll app/oracle/oradata/orcl/control011.ctl -- view two control file names
-Rw-r ----- 1 oracle oinstall 9748480 Jan 25 app/oracle/oradata/orcl/control011.ctl
[Oracle @ centos ~] $
[Oracle @ centos ~] $ Ll app/oracle/flash_recovery_area/orcl/control02.ctl
-Rw-r -----. 1 oracle oinstall 9748480 Jan 25 app/oracle/flash_recovery_area/orcl/control02.ctl
[Oracle @ centos ~] $ Vim app/oracle/product/11.2.0/dbhome_1/dbs/initorcl. ora -- open the configuration file to see if the file name is correct.
*. Control_files = '/home/oracle/app/oracle/oradata/orcl/control01.ctl ', '/home/oracle/app/oracle/flash_recovery_area/orcl/control02.ctl' -- the first control file name is incorrect. You can change it to the correct one.

Test:
[Oracle @ centos ~] $ Sqlplus
SQL * Plus: Release 11.2.0.1.0 Production on Sat Jan 25 09:42:31 2014
Copyright (c) 1982,200 9, Oracle. All rights reserved.
Enter user-name:/as sysdba
Connected:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0-Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL>