The post guide you  how to install and configure oracle 11g  in CentOS (32 bit–64 bit)
Your hardware minimum requirements are

32- 64 Bit:

x86 / x86_64  compatible CPU
1 GB RAM
11 GB available space  (compatible space for both 32 and 64 bit)
2GB Swap

Before going to be installed Oracle Database need to check supporting packages has been installed in your system,

Few supporting packages should be installed,
 
# yum update
# yum install libaio*
# yum install bc

Create a oracle user name,
 
# useradd oracle

Install jdk7

Download the jdk7 packages from the bellow URL and install it using rpm command,
 
#  wget --no-cookies --no-check-certificate --header "Cookie: gpw_e24=http%3A%2F%2Fwww.oracle.com%2F; oraclelicense=accept-securebackup-cookie" "http://download.oracle.com/otn-pub/java/jdk/7u60-b19/jdk-7u60-linux-i586.rpm"

#  rpm -ivh jdk-7u21-linux-x64.rpm

Preparing...                ########################################### [100%]
   1:jdk                       ########################################### [100%]
Unpacking JAR files...
    rt.jar...
    jsse.jar...
    charsets.jar...
    tools.jar...
    localedata.jar...

Download the oracle-xe-11.2.0-1.0.x86_64
 
Note : I have decide to use HTTP port for Oracle : 8090 and database listener 1521

Extract that packages using unzip command
 
# unzip  oracle-xe-11.2.0-1.0.x86_64.rpm.zip

# cd Disk1

# rpm -ivh oracle-xe-11.2.0-1.0.x86_64.rpm

Preparing...                ########################################### [100%]
   1:oracle-xe              ########################################### [100%]
Executing post-install steps...
You must run '/etc/init.d/oracle-xe configure' as the root user to configure the database.

# /etc/init.d/oracle-xe configure

Oracle Database 11g Express Edition Configuration
-------------------------------------------------------------------------

This will configure on-boot properties of Oracle Database 11g Express
Edition.  The following questions will determine whether the database should
be starting upon system boot, the ports it will use, and the passwords that
will be used for database accounts.  Press to accept the defaults.
Ctrl-C will abort.
 
Specify the HTTP port that will be used for Oracle Application Express [8080]:8090
 
Specify a port that will be used for the database listener [1521]:1521
 
Specify a password to be used for database accounts.  Note that the same
password will be used for SYS and SYSTEM.  Oracle recommends the use of
different passwords for each database account.  This can be done after
initial configuration: (password)
Confirm the password:

Do you want Oracle Database 11g Express Edition to be started on boot (y/n) [y]:y
Starting Oracle Net Listener...Done
Configuring database...Done
Starting Oracle Database 11g Express Edition instance...Done
Installation completed successfully.
 

Set Oracle home path:
 
#  export LD_LIBRARY_PATH=/u01/app/oracle/product/11.2.0/xe/lib:$LD_LIBRARY_PATH

# export ORACLE_SID=XE

# export ORACLE_HOME=/u01/app/oracle/product/11.2.0/xe

#export PATH=$ORACLE_HOME/bin:$PATH

To conform that path whether has been set for ?
 
# echo  $ORACLE_HOME
/u01/app/oracle/product/11.2.0/xe

To check Oracle running status,
 
# /etc/init.d/oracle-xe status


LSNRCTL for Linux: Version 11.2.0.2.0 - Production on 13-JAN-2014 19:02:00

Copyright (c) 1991, 2011, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC_FOR_XE)))

STATUS of the LISTENER

------------------------

Alias                     LISTENER

Version                   TNSLSNR for Linux: Version 11.2.0.2.0 - Production

Start Date                13-JAN-2014 18:57:05

Uptime                    0 days 0 hr. 4 min. 59 sec

Trace Level               off

Security                  ON: Local OS Authentication

SNMP                      OFF

Default Service           XE

Listener Parameter File   /u01/app/oracle/product/11.2.0/xe/network/admin/listener.ora

Listener Log File         /u01/app/oracle/diag/tnslsnr/madhuporacle/listener/alert/log.xml

Listening Endpoints Summary...

  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC_FOR_XE)))

  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=thelinuxfaq.host.localdomain)(PORT=1521)))

  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=thelinuxfaq.host.localdomain)(PORT=8090))(Presentation=HTTP)(Session=RAW))

Services Summary...

Service "PLSExtProc" has 1 instance(s).

  Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...

Service "XE" has 1 instance(s).

  Instance "XE", status READY, has 1 handler(s) for this service...

Service "XEXDB" has 1 instance(s).

  Instance "XE", status READY, has 1 handler(s) for this service...

The command completed successfully


Open your browser using below  link :  
 
URL  : http://192.168.0.20:8090/apex/apex_admin
User Name: admin
password : password



The password for this account must be changed.



Set Environment Variable:

Need to set Oracle environment variables for users. Execute the follwing command,
 
# . /u01/app/oracle/product/11.2.0/xe/bin/oracle_env.sh

To set the environment permanently add above line in .bashrc or .bash_profile.
 
# sqlplus /nolog


SQL*Plus: Release 11.2.0.2.0 Production on Wed Mar 18 17:57:31 2015



Copyright (c) 1982, 2011, Oracle.  All rights reserved.



SQL>

or
 
# sqlplus sys/password  as sysdba


SQL> exit

Disconnected from Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

You have new mail in /var/spool/mail/root


I have faced three errors while installing oracle, That errors and solutions given below,

Error :1
 
This system does not meet the minimum requirements for swap space.  Based on
the amount of physical memory available on the system, Oracle Database 11g
Express Edition requires 2048 MB of swap space. This system has 2023 MB
of swap space.  Configure more swap space on the system and retry the
installation.

error: %pre(oracle-xe-11.2.0-1.0.x86_64) scriptlet failed, exit status 1
error:   install: %pre scriptlet failed (2), skipping oracle-xe-11.2.0-1.0

Solution:
 
You should set exact or more swap space for example ram space 2G swap must be 4G

Error : 2
 
# rpm -ivh oracle-xe-11.2.0-1.0.x86_64.rpm
error: Failed dependencies:
    libaio >= 0.3.104 is needed by oracle-xe-11.2.0-1.0.x86_64

Solution:
 
#  yum install libaio*

Error : 3
 
# rpm -ivh oracle-xe-11.2.0-1.0.x86_64.rpm
Preparing...                ########################################### [100%]
/var/tmp/rpm-tmp.WpsSX7: line 186: bc: command not found 

Solution:
 
# yum install bc

Do you want to uninstall the Oracle,
 
# rpm -qa | grep oracle
oracle-xe-11.2.0-1.0.x86_64

# rpm -e oracle-xe-11.2.0-1.0.x86_64

# rpm -qa | grep oracle