New posts are coming soon..

Hi Guys,

It's been a long time I didn't post any article or issue here. There were few transitions in my career and I was bit busy. Hence, I didn't get time to update or post. There are more technologies on which I'll discuss. Following are in pipeline :

Linux Kernel
A bit about Red Hat Company and Product
Linux troubleshooting step and basic concept
CISCO unified computing system( UCS )
CISCO Fabric Interconnect Switch, VLAN, port channeling etc
FCOE, FC protocol
Red Hat Cluster
Veritas Cluster
Veritas Volume Manager
DMP or Veritas Dynamic Multipathing
SAN/NAS
Vmware vSpehere Virtualization, ESX 5.0.0
vCenter and vCenter HeartBeat
vMotion, Update manager
Netapp Storage Filers, Volume, LUN,masking, mapping, exporting, system log analysis etc
SnapVault
Symantec Netbackup Tecnology
Scripting : Python and Perl

So, stay tune...Good Luck :)

A simple example of developing C program, patching and applying it to original source file

■ Purpose : Create a C program, compile it, apply patch to original file
■ OS Environemnt : Linus
■ Required Software : gcc
■ Implementation Steps : 

1. Create a test.c file and put below codes in it :

#include 
#include 
int main()
 {
 printf("\n I'm test\n");
return 0;
}

2. Compile above file and check its output :

$ gcc -o test test.c
$ ./test

I'm test

3. Applying patches or change codes and recompile it : 
Modify test.c and add new lines or codes in it. Lets say new file is test_modifed.c. This file contains following codes :

#include
#include
int main()
 {
 printf("\n I'm kamal \n");
 printf("\nI have added one more line. This comes from modifed code\n" );
return 0;
}

Compile & execute above program now :

$  gcc -o test_modified test_modified.c
$  ./test_modified

 I'm test

I have added one more line. This comes from modifed code

4. Create a patch file : 
Execute following command to create a patch in the same directory.  :

 $ diff -u test.c test_modified.c > test.patch.1

Here test.path.1 will contain following :

$ cat test.patch.1
--- test.c      2012-07-17 07:52:39.000000000 +0530
+++ test_modified.c     2012-07-17 07:54:41.000000000 +0530
@@ -3,5 +3,6 @@
 int main()
  {
  printf("\n I'm kamal \n");
+ printf("\nI have added one more line. This comes from modifed code\n" );
 return 0;
 }

5. Applying above patch to original file :

$ patch -u test.c < test.patch.1
patching file test.c

$ cat test.c
#include
#include
int main()
 {
 printf("\n I'm kamal \n");
 printf("\nI have added one more line. This comes from modifed code\n" );
return 0;
}

6. Reverting back to previous version :

$ patch -R test.c < test.patch.1
patching file test.c


$ cat test.c
#include
#include
int main()
 {
 printf("\n I'm kamal \n");
return 0;
}


7. Dry run : You can do dry-run (test prior to be originally changing codes in test.c)

$ patch -p0 --dry-run test.c < test.patch.1

How to redirect tomcat log to syslog server?

■ Purpose : Redirecting tomcat log messages to central syslog server
■ OS Environment : Linux[RHEL, Centos]
■  Required Application : tomcat, syslog
■  Assumption :  Assuming that we are going to use log4j tool to log the tomcat messages.
■  Implementation Steps :

1. Modify log4j.properties file :

In order to redirect these messages in syslog file, we should modify4j$CATALINA_BASE/lib/log4j.properties and make sure following entries are present :

log4j.rootLogger=INFO, CATALINA

# Define all the appenders
log4j.appender.CATALINA=org.apache.log4j.DailyRollingFileAppender
log4j.appender.CATALINA.File=${catalina.base}/logs/catalina.
log4j.appender.CATALINA.Append=true
log4j.appender.CATALINA.Encoding=UTF-8             
# Roll-over the log once per day
log4j.appender.CATALINA.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.CATALINA.layout = org.apache.log4j.PatternLayout
log4j.appender.CATALINA.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.LOCALHOST=org.apache.log4j.DailyRollingFileAppender
log4j.appender.LOCALHOST.File=${catalina.base}/logs/localhost.
log4j.appender.LOCALHOST.Append=true
log4j.appender.LOCALHOST.Encoding=UTF-8
log4j.appender.LOCALHOST.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.LOCALHOST.layout = org.apache.log4j.PatternLayout
log4j.appender.LOCALHOST.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.MANAGER=org.apache.log4j.DailyRollingFileAppender
log4j.appender.MANAGER.File=${catalina.base}/logs/manager.
log4j.appender.MANAGER.Append=true
log4j.appender.MANAGER.Encoding=UTF-8
log4j.appender.MANAGER.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.MANAGER.layout = org.apache.log4j.PatternLayout
log4j.appender.MANAGER.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.HOST-MANAGER=org.apache.log4j.DailyRollingFileAppender
log4j.appender.HOST-MANAGER.File=${catalina.base}/logs/host-manager.
log4j.appender.HOST-MANAGER.Append=true
log4j.appender.HOST-MANAGER.Encoding=UTF-8
log4j.appender.HOST-MANAGER.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.HOST-MANAGER.layout = org.apache.log4j.PatternLayout
log4j.appender.HOST-MANAGER.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Encoding=UTF-8
log4j.appender.CONSOLE.layout = org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

# Configure which loggers log to which appenders
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=INFO, LOCALHOST
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager]=\
  INFO, MANAGER
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/host-manager]=\
  INFO, HOST-MANAGER

 Note : It's added SYSLOG logger and appender along with other properties in above file. For more information about log4j, you can log on tomcat vendor site and check it from there.

2. Restart tomcat application or instance :
3. Redirect client log messages to syslog :

vi  syslog.conf and put below entry :

 *.* @IP_OF_syslog server

Note : Please replace IP address with appropriate IP. Make sure syslog ports (514) are open in sysog server.

How to configure apache-tomcat on linux box?

■  Purpose : Configure apache-tomcat 
■  OS Environment : Linux (RHEL, Centos)
■  Required Applications: JDk 1.7.0_03, Apache tomcat 6.0.35
■ Implementation Steps :

1.  JDK setup :

$ pwd
/jdk1.7.0_03
$ export JAVA_HOME=/jdk1.7.0_03
$ export PATH=$JAVA_HOME/bin:$PATH

$ which java
/jdk1.7.0_03/bin/java

$  java -version
java version "1.7.0_03"
Java(TM) SE Runtime Environment (build 1.7.0_03-b04)
Java HotSpot(TM) 64-Bit Server VM (build 22.1-b02, mixed mode)

2. Apache Tomcat setup :

$ groupadd tomcat
$ useradd -g tomcat -s /usr/sbin/nologin -m -d /home/tomcat tomcat
$ cd /var/lib
$ tar zxvf /usr/local/src/apache-tomcat-6.0.35.tar.gz
$ chown -R tomcat.tomcat /var/lib/apache-tomcat-6.0.35

3. Verify tomcat version  :

$ /var/lib/apache-tomcat-6.0.35/bin/version.sh

Output will look like below :
   
Using CATALINA_BASE: /var/lib/apache-tomcat-6.0.35
Using CATALINA_HOME: /var/lib/apache-tomcat-6.0.35
Using CATALINA_TMPDIR: /var/lib/apache-tomcat-6.0.35/temp
Using JRE_HOME: /jdk1.7.0_03
Using CLASSPATH: /var/lib/apache-tomcat-6.0.35/bin/bootstrap.jar
Server version: Apache Tomcat/6.0.35
Server built: Nov 28 2011 11:20:06
Server number: 6.0.35.0
OS Name: Linux
OS Version: 2.6.18-308.el5
Architecture: amd64
JVM Version: 1.7.0_03-b04
JVM Vendor: Oracle Corporation

4. Starting/Stopping Tomcat:

$ export CATALINA_HOME=/var/lib/apache-tomcat-6.0.35
$ export CATALINA_BASE=/var/lib/apache-tomcat-6.0.35
$ su -p -s /bin/sh tomcat $CATALINA_HOME/bin/startup.sh

You can make posix compliant script to run above script during booting. Export can be mentioned in root user's profile.

Output will look like  :

Using CATALINA_BASE: /var/lib/apache-tomcat-6.0.35
Using CATALINA_HOME: /var/lib/apache-tomcat-6.0.35
Using CATALINA_TMPDIR: /var/lib/apache-tomcat-6.0.35/temp
Using JRE_HOME: /jdk1.7.0_03
Using CLASSPATH: /var/lib/apache-tomcat-6.0.35/bin/bootstrap.jar

5. Check if tomcat process is running or not :

$ ps aux |grep java
tomcat 10711 9.4 10.1 463404 51696 pts/1 Sl 18:58 0:02 /jdk1.7.0_03/bin/java -Djava.util.logging.config.file=/var/lib/apache-tomcat-6.0.35/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djava.endorsed.dirs=/var/lib/apache-tomcat-6.0.35/endorsed -classpath /var/lib/apache-tomcat-6.0.35/bin/bootstrap.jar -Dcatalina.base=/var/lib/apache-tomcat-6.0.35 -Dcatalina.home=/var/lib/apache-tomcat-6.0.35 -Djava.io.tmpdir=/var/lib/apache-tomcat-6.0.35/temp org.apache.catalina.startup.Bootstrap start
root 10730 0.0 0.1 61232 724 pts/1 R+ 18:58 0:00 grep java


6. Shutdown tomcat application :

$ su -p -s /bin/sh tomcat $CATALINA_HOME/bin/shutdown.sh

Output will look like :

Using CATALINA_BASE: /var/lib/apache-tomcat-6.0.35
Using CATALINA_HOME: /var/lib/apache-tomcat-6.0.35
Using CATALINA_TMPDIR: /var/lib/apache-tomcat-6.0.35/temp
Using JRE_HOME: /jdk1.7.0_03
Using CLASSPATH: /var/lib/apache-tomcat-6.0.35/bin/bootstrap.jar

$ ps aux |grep java
root 10763 0.0 0.1 61232 724 pts/1 R+ 18:59 0:00 grep java

7. Switching to Tomcat User Account :

$ su - -s /bin/sh tomcat
$ id
uid=502(tomcat) gid=503(tomcat) groups=503(tomcat) context=root:system_r:unconfined_t:SystemLow-SystemHigh


Control+D to exit from tomcat shell

8. Setting Up First Tomcat JVM Instance :

$ mkdir -p /opt/tomcat-instance/sales.example.com
$ cd /opt/tomcat-instance/sales.example.com
$ cp -a /var/lib/apache-tomcat-6.0.35/conf .
$ mkdir common logs temp server shared webapps work
$ chown -R tomcat.tomcat /opt/tomcat-instance

9. Environment setup for instance :

$ su - -s /bin/sh tomcat
$ id
uid=1001(tomcat) gid=1001(tomcat) groups=1001(tomcat)
$ pwd
/home/tomcat
$ whoami
tomcat

$ cat /opt/tomcat-instance/sales.env 

export JAVA_HOME=/jdk1.7.0_03
export PATH=\$JAVA_HOME/bin:\$PATH
export CATALINA_HOME=/var/lib/apache-tomcat-6.0.35
export CATALINA_BASE=/opt/tomcat-instance/sales.example.com

10. Configuring Tomcat Network Ports : Since this is the first Tomcat instance that's being created here, the default port numbers can be left unchanged in $CATALINA_BASE/conf/server.xml (/opt/tomcat-instance/sales.example.com/conf/server.xml):

11. Starting First Tomcat Instance :

$ source /opt/tomcat-instance/sales.env
$ $CATALINA_HOME/bin/startup.sh

Output will look like :

Using CATALINA_BASE: /opt/tomcat-instance/sales.example.com
Using CATALINA_HOME: /var/lib/apache-tomcat-6.0.35
Using CATALINA_TMPDIR: /opt/tomcat-instance/sales.example.com/temp
Using JRE_HOME: /jdk1.7.0_03
Using CLASSPATH: /var/lib/apache-tomcat-6.0.35/bin/bootstrap.jar

12. Setting Up a Web Application for First Tomcat JVM Instance :

$ vi $CATALINA_BASE/conf/server.xml :


 docBase attribute is set to mysales which stands for the application name within the URL, i.e. "http://serverip/mysales" or "http://serverip:8080/mysales".

13. Setup home page for web Application :

$ cat $CATALINA_BASE/webapps/sales/index.html 

"http://www.w3.org/TR/html4/loose.dtd"

14. Restart First Tomcat Instance :

$ source /opt/tomcat-instance/sales.env
$ $CATALINA_HOME/bin/shutdown.sh
$ $CATALINA_HOME/bin/startup.sh

14. Test :
Access http://serverip/mysales/ , you'll see "Apache Tomcat Sales Home Page".

15. Deploying Java Servlet for Web Application in First Tomcat JVM Instance :

a. Setting up Java Servlet Layout :

$ mkdir -p $CATALINA_BASE/webapps/sales/WEB-INF/classes
$ mkdir $CATALINA_BASE/webapps/sales/WEB-INF/lib
b. Create a Java Servlet :

vi $CATALINA_BASE/webapps/sales/WEB-INF/classes/Sales.java  and put following entries in this file :

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class Sales extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("");
out.println("");
out.println("");
out.println("");
out.println("");
out.println("

Executing Sales ...

");
out.println("");
out.println("");
}
}

c. Compile above java program :

$ cd $CATALINA_BASE/webapps/sales/WEB-INF/classes
$ javac -classpath "$CATALINA_HOME/lib/*" Sales.java
$ ls
Sales.class Sales.java

d. Configuring the Java Servlet :

$ cat $CATALINA_BASE/webapps/sales/WEB-INF/web.xml
servlet_sales
Salesservlet_sales
/execute
e. Modify index.html &  put some entries :

$ vi $CATALINA_BASE/webapps/sales/index.html

16. Testing and Executing the Java Servlet :

 $ source /opt/tomcat-instance/sales.env
$ $CATALINA_HOME/bin/shutdown.sh
$ $CATALINA_HOME/bin/startup.sh

17. Out of  http://serverip/mysales/  will be 

Apache Tomcat Sales Home Page
Execute Sales

Now click on "Execute Sales", you'll see following :

Executing Sales ...

How to enable php with apache on linux?

Purpose : Enable php engine in apache
OS Environement : Linux [RHEL, Centos]
Application : php, apache httpd
Prerequisites : Make sure php is installed in the system first.
Implementation Steps : 

1. Locate libphp5.so

In most of cases, libphp5.so will be present inside /etc/httpd/modules

2. Add following in httpd.conf :

# Use for PHP 5.x:
LoadModule php5_module modules/libphp5.so
AddHandler php5-script .php

# Add index.php to your DirectoryIndex line:
DirectoryIndex index.html index.php

AddType text/html .php

# PHP Syntax Coloring
# (optional but useful for reading PHP source for debugging):

AddType application/x-httpd-php-source phps

3. Restart apache web server :

$ /etc/init.d/httpd restart

4. Verification :

$ httpd -t|grep -i php

5. Create a php file inside web directory. Put the following content in that file like :

vi info.php


phpinfo();
?>

6. Access the file through browser like http://localhost/info.php. If it shows all the enables php directives or modules then php works fine.

How to store sftp log messages in custom file on Linux ?

■  Purpose : store sftp log messages in custom file
■ OS Environment : RHEL 6
■  Applications: sftp, syslog
■  Prerequisites : Assuming chrooted environment is setup at /chroot, disable SELinux
■  Implementation Steps :

1. Modify sshd config file. 

Make sure "AUTHPRIV" facility is used in sshd_config file. Sample file looks like :

$ cat /etc/ssh/sshd_config :

Subsystem sftp internal-sftp -f AUTHPRIV -l VERBOSE

2. Use proper additional socket file in /etc/sysconfig/rsyslog like :

vi /etc/sysconfig/rsyslog

SYSLOGD_OPTIONS="-m 0 -a /chroots/dev/log"

3. Following lines should be present in /etc/rsyslog.conf :

Add following lines :

$InputUnixListenSocketHostname internal-sftp
$AddUnixListenSocket /chroots/dev/log

# Log internal-sftp activity in a separate file

:programname, isequal, "internal-sftp" -/var/log/sftp.log
:programname, isequal, "internal-sftp" ~
:programname, isequal, "sshd" -/var/log/sftp.log
:programname, isequal, "sshd" ~


4. Make sure that a hard link to socket file like :

$mkdir -p /chroots/dev
$ln /chroots/dev/log /chroots/dev/log

5. Restart rsyslog and sshd service :

$ service rsyslog restart
$ service sshd restart

6. Testing :

Open a terminal and execute following command on it like :

$tailf /var/log/sftp.log

Try to access SFTP account like :

$sftp username@IP
pw: 
Enter password You'll see that all sftp logs messages are available in /var/log/sftp.log. 

How to setup multiple gateways for multiple Ethernets?

■ Purpose : Setup multiple gateways in linux
■ OS Environment : Linux [RHEL 5, 6]
■  Application : iproute package
■  Implementation Steps :
■  Assumption : eth0 has gateway 10.1XX.69.1 and eth3's gateway is 10.1XX.66.1.

Concept : Defining the gateway in two tables in conjunction with each interface.

1. Put entries in routing table :

echo "1 ISP1" >> /etc/iproute2/rt_tables
echo "2 ISP2 " >> /etc/iproute2/rt_tables

2.  Setup routing rules for  ISP1 table:

$ ip route add default via 10.1XX.69.1 dev eth0 table ISP1
$ ip rule add from 10.1XX.69.0/24 table ISP1


For the ISP2 table:

$ ip route add default via 10.1XX.66.1 dev eth3 table ISP2
$ ip rule add from 10.1XX.66.0/24 table ISP2

3. Make above rules persistent:

Put below entries in rc.local file  :

ip route add default via 10.1XX.69.1 dev eth0 table ISP1
ip rule add from 10.1XX.69.0/24 table ISP1
ip route add default via 10.1XX.66.1 dev eth3 table ISP2
ip rule add from 10.1XX.66.0/24 table ISP2

Note : You should replace the IP addresses in above commands.