Install 12c Enterprise Manager

Prerequisites 

Download and Install Oracle Database 11g R2 on linux platform

Download Enterprise Manager Cloud control from following link

http://www.oracle.com/technetwork/oem/grid-control/downloads/index.html

If you have performed a default database installation you will need to de-configure Enterprise Manager Database Control. Run the following command as the "oracle" user.

$ emca -deconfig dbcontrol db -repos drop -SYS_PWD <sys pasword> -SYSMAN_PWD <sysman password>

Make following initialization parameter changes and restart the instance

$sqlplus / AS SYSDBA
SQL>ALTER SYSTEM SET processes=300 SCOPE=SPFILE;
SQL>ALTER SYSTEM SET session_cached_cursors=200 SCOPE=SPFILE
SQL>ALTER SYSTEM SET sga_target=2G SCOPE=SPFILE;
SQL>ALTER SYSTEM SET shared_pool_size=600M SCOPE=SPFILE;
SQL>ALTER SYSTEM SET pga_aggregate_target=1G SCOPE=SPFILE;
SQL>ALTER SYSTEM SET job_queue_processes=20 SCOPE=SPFILE;

SQL>SHUTDOWN IMMEDIATE
SQL>STARTUP

If you have done a default installation as described here, the UNDO tablespace will be autoextensible. If you have done a custom installation make sure the UNDO tablespace is at least 200M in size. Also, make sure you have 3 redo logs of at least 300M to prevent a warning during the installation.

Cloud Control Installation

Create Following installation directories for management server and agent

$ mkdir -p /u01/app/oracle/oms12cr3
$ mkdir -p /u01/app/oracle/agent12cr3

Unzip the cloud control media and begin the installation by running runinstaller

$ mkdir em
$ unzip -d em em12103p1_linux64_disk1.zip
$ unzip -d em em12103p1_linux64_disk2.zip
$ unzip -d em em12103p1_linux64_disk3.zip
$ cd em

$ ./runInstaller

If you wish to receive support information enter the e-mail address else skip

If you wish to check for updates enter the details else skip

If you have completed all the prerequisites then installation pass all the checks

Select 'Create a new Enterprise Manager System' and 'simple' option

Enter Middleware and Agent installation locations

Enter Administrator password and Database Details

If you have any additional warnings, check they don't look like show-stoppers, then click the 'OK' button to continue and click 'Install' button to begin the installation

When prompted, run the root scripts, then click the 'OK' button
Make note of the URL below and close. Copy of following information are stored in /u01/app/oracle/oms12cr3/oms/install/setupinfo.txt file.

Login to the EM using above URL.

Startup and Shutdown Enterprise Manager

Oracle Management Server

export OMS_HOME=/u01/app/oracle/oms12cr3/oms
$OMS_HOME/bin/emctl start oms
$OMS_HOME/bin/emctl stop oms
$OMS_HOME/bin/emctl status oms

Agent

export AGENT_HOME=/u01/app/oracle/agent12cr3/core/12.1.0.3.0
$AGENT_HOME/bin/emctl start agent
$AGENT_HOME/bin/emctl stop agent
$AGENT_HOME/bin/emctl status agent