Reconfiguring Network Interfaces in CentOS/RHEL Systems Cloned with vCenter

While cloning CentOS VMs in our environment, I ran into a problem where eth0 wouldn’t start up. When trying to start the networking service, the following error popped up:

Bringing up interface eth0: Device eth0 does not seem to be preset, delaying initialization.      [FAILED]


The reason this error occurs is because networking adapters in cloned VMs are assigned unique MAC addresses, so they don’t conflict with the parent VM. During OS installation, the installer detects the network adapter and udev configures the mapping between the device eth0 and the MAC address. When the MAC address changes udev thinks the device is missing.

To fix this, we need to update udev’s mapping rules to point the eth0 definition to the device with the correct MAC address. Open the file /etc/udev/rules.d/70-persistent-net.rules. You should see something similar to what is below:

# PCI device 0x8086:0x100f (e1000) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:50:56:9c:00:16", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

# PCI device 0x8086:0x100f (e1000) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:50:56:9c:00:18", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

As you can see there are two PCI ethernet adapters present. The original one from the parent VM (MAC: 9c:00:16) and the new one from the current VM (MAC: 9c:00:18). To fix the issue you need to change the eth0 device definition to have the correct MAC address (9c:00:18) and remove the eth1 device. Your resulting file will look like so:

You have to update the /etc/sysconfig/network-scripts/ifcfg-eth0 file to reflect the correct MAC address. Then, after a quick system restart your eth0 adapter will be back up.

Date and Time in Linux

Set Date

Use the following syntax to set new data and time:
date --set="STRING"

set new data to 23 Jan 2012 2:12:15

date --set="Tue Jan 23 2:12:15 EDT 2012"

You can format as belwo:

date +%Y%m%d -s "20120910"


Set Time

Use the following syntax to set time:

# date +%T -s "11:10:05"

11Hour (hh)

10: Minute (mm)

05: Second (ss)

Use %p locale’s equivalent of either AM or PM, enter:

# date +%T%p -s "2:12:30AM"

# date +%T%p -s "11:12:30PM"

Resizing (Shrinking) Guest Hard Drive Sizes With VMware Standalone Converter (vSphere 5) ESXi Server 5.1

If you want to shrink your guest hard drive size then you can use VMware Converter standalone converter

1. Installing VMware converter is pretty straightforward, run the install file and accept all the defaults. Install the converter on same machine (Virtual) that you want to resize.

2. Run the application

3. Choose Open> convert machine> choose this local machine

4. Choose the destination type (in this case choose VMware Infrastructure virtual machine) and enter the credentials for ESXi Server

5. Customize the size of disk, CPU, RAM what you want, (We are working on decreasing the size of disk)

6. Confirm the size and go for convert, it will take some time according to the machine size and configuration

7. Delete the source machine as you have now less disk size virtual machine on ESXi Server.

Configuring Network Time Protocol (NTP) on ESX/ESXi 4.1 and ESXi 5.0 hosts using the vSphere Client

To configure NTP on ESX/ESXi 4.1 and ESXi 5.0 hosts:

1. Connect to the ESX/ESXi host using the vSphere Client.
2. Select a host in the inventory.
3. Click the Configuration tab.
4. Click Time Configuration.
5. Click Properties.
6. Click Options.
7. Click NTP Settings.
8. Click Add.
9. Enter the NTP Server name. For example, 0.pool.ntp.org and 1.pool.ntp.org.
10. Click OK.
11. Click the General tab.
12. Click Start automatically under Startup Policy.
13. Click Start and click OK.
14. Click OK to exit.

Installation of VMware Tools in a Linux guest (CentOS 6.3)

To install VMware Tools in a Linux guest operating system using Compiler:
Ensure that your Linux virtual machine is powered on.
If you are running a GUI interface, open a command shell.

Note: Log in as a root user, or use the sudo command to complete each of these steps.

Click VM in the virtual machine menu, then click Guest > Install/Upgrade VMware Tools and click OK.
To create a mount point, run:

mkdir /mnt/cdrom

To mount the CDROM, run:

mount /dev/cdrom /mnt/cdrom

To copy the Compiler gzip tar file to a temporary local directory, run:

cp /mnt/cdrom/VMwareTools-<version>.tar.gz /tmp/

Where <version> is the VMware Tools package version.

To determine the version of VMware tools, run:

ls /mnt/cdrom

You see an output similar to:

# VMwareTools-5.0.0-12124.tar.gz

To change to the tmp directory and extract the contents of the tar file into a new directory called vmware-tools-distrib, run:
cd /tmp
tar -zxvf VMwareTools-<version>.tar.gz

To change directory to vmware-tools-distrib and run the vmware-install.pl PERL script to install VMware Tools, run:
cd vmware-tools-distrib
./vmware-install.pl

Notes:
Follow the screen prompts to install the VMware Tools. Options in square brackets are default choices and can be selected by pressing Enter.
To compile VMware Tools successfully, you need gcc Compiler and Linux Kernel sources provided by your Linux distribution. Consult your Linux distribution documentation for details on how to install these packages.
It is normal for the console screen to go blank for a short time during the installation when the display size changes.
Some warnings or errors are normal, like when a files does not exist.
Depending on the Linux distribution, your network service might restart after installation. VMware recommends that you invoke this command from the console and not remotely.

If you are running a GUI interface, restart your X Window session for any mouse or graphics changes to take effect.
To start VMware Tools running in the background during an X Window session, run:

/usr/bin/vmware-toolbox &

Depending on your environment you may need to unmount the CDROM. To unmount the CDROM, run:

umount /mnt/cdrom

Depending on your environment, you may need to manually end the VMware Tools installation. To end the VMware Tools install, click VM in the virtual machine menu, then click Guest > End VMware Tools Install.
To remove VMware Tools installation packages, run:
cd
rm /tmp/VMwareTools-<version>.tar.gz
rm -rf /tmp/vmware-tools-distrib

Installing tomcat7 on CentOS 6.3

Java should be installed before installing tomcat, please read my previous blog to install java

Download apache tomcat from here

#wget http://apache.techartifact.com/mirror/tomcat/tomcat-7/v7.0.39/bin/apache-tomcat-#7.0.39.tar.gz
#tar -xvf apache-tomcat-7.0.39.tar.gz
#mv apache-tomcat-7.0.39 tomcat-7.0.39
#mv tomcat-7.0.39/ /usr/share/
cd /usr/share/tomcat-7.0.39/

Now create tomcat service and set it to start on boot

#vim /etc/init.d/tomcat and paste the below on to that

#!/bin/bash
# description: Tomcat Start Stop Restart
# processname: tomcat
# chkconfig: 234 20 80
export JAVA_HOME
PATH=$JAVA_HOME/bin:$PATH
export PATH
CATALINA_HOME=/usr/share/tomcat7

case $1 in
start)
sh $CATALINA_HOME/bin/startup.sh
;;
stop)
sh $CATALINA_HOME/bin/shutdown.sh
;;
restart)
sh $CATALINA_HOME/bin/shutdown.sh
sh $CATALINA_HOME/bin/startup.sh
;;
esac
exit 0 

#chkconfig --add tomcat
#chkconfig --level 234 tomcat on
#chkconfig --list tomcat

Now you can start stop tomcat by executing the below command
#service tomcat stop
#service tomcat start

This should work fine now.

Installing Redis on Linux (CentOS 6.3)

Download redis from redis.io

#wget https://redis.googlecode.com/files/redis-2.4.17.tar.gz
#tar -xvf redis-2.4.17.tar.gz
#cd /opt/redis-2.4.17/src
#make install

now this copy redis-server, redis-cli and conf file to /usr/local/bin
open the port in firewall for redis
now make this service run on start up add the below line in rc.local

#vim /etc/rc.local

nohup /usr/local/bin/redis-server &

Close the editor and now the server will start at boot, check by redis-cli

#cd /usr/local/bin

#./redis-cli

redis 127.0.0.1:6379>

It is installed and working now.

Installation of Java Runtime Edition (JRE) 1.7 in Centos 6.2 and Uninstallation of JDK

Uninstallation of JDK (Open Java)
# yum remove java

Installing from rpm package

Go to the Oracel Download page and download the package.

# wget http://download.oracle.com/otn-pub/java/jdk/7u17-b02/jdk-7u17-linux-x64.rpm

Go to the downloaded location

change the package mode to executeable

# chmod 755 jdk-7u17-linux-x64.rpm

Install it

# yum install jdk-7u17-linux-x64.rpm

Now check the version

# java -version

You should get the result like below:

java version "1.7.0_17"
Java(TM) SE Runtime Environment (build 1.7.0_17-b02)
Java HotSpot(TM) 64-Bit Server VM (build 23.7-b01, mixed mode)

Setting JAVA_HOME for a single user and all users:

check java by

#which java
/usr/bin/java

we can check whether this java file is located

# ls -al /usr/bin/java
lrwxrwxrwx. 1 root root 26 Mar 24 20:15 /usr/bin/java -> /usr/java/default/bin/java

#cd /usr/java
#ls -al
drwxr-xr-x.  3 root root 4096 Mar 24 20:15 .
drwxr-xr-x. 14 root root 4096 Mar 24 20:15 ..
lrwxrwxrwx.  1 root root   16 Mar 24 20:15 default -> /usr/java/latest
drwxr-xr-x.  8 root root 4096 Mar 24 20:15 jdk1.7.0_17
lrwxrwxrwx.  1 root root   21 Mar 24 20:15 latest -> /usr/java/jdk1.7.0_17

The above shoes that default softlink to /usr/java/latest and latset softlink to /usr/java/jdk1.7.0_17
The genuine directory for java is /usr/java/jdk1.7.0_17

For a single user:

# vi ~/.bash_profile
# export JAVA_HOME=/usr/java/jdk1.7.0_17
# export PATH=$PATH:/usr/java/jdk1.7.0_17/bin

For all users:

# vi /etc/profile
# export JAVA_HOME=/usr/java/jdk1.7.0_17
# export PATH=$PATH:/usr/java/jdk1.7.0_17/bin