Before you start coding a web application. You must read this.

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How Browsers Work: Behind the scenes of modern web browsers

An excellent resource for you to know before you code. 

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Nagios - How it works, the workflow!

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While working on a Nagios setup, its often difficult to explain how it works. I beleive in principle of "A picture says thousand word". Hence, started searching the internet, but didn't found any which is simple and easy to understand.

So created my own. For all those Nagios lovers, here's my version of it.

Hope this helps many people, like me!

- Ani
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AWS for newbie

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If you are new to amazon's web services aka. Amazon cloud you must go and visit slideshare,search for aws. There are end number of documents and presentations to help you to start with. But before heading to slideshare, please read all the official whitepapers.
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EnStratus: A Service to Manage Your Cloud Infrastructure by @alexwilliams

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via Twitter

September 15, 2013 at 08:29PM
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Distributing Your Blog Content: The Best Auto-Posting Services

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via Twitter

September 15, 2013 at 07:32PM
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Checking and detecting host Virtualization

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How to check if the host is running as Virtual Machine (VM) or Physical Machine? and more importantly which Virtualization technology?

So here it is how to acheive that. Run the following command as superuser (root) :
dmidecode -s system-manufacturer
the output should be something


then run

dmidecode | grep -i "vm" 

it should show result like

Product Name: KVM 
(which means running KVM Virtualization)

Product Name: HVM domU 
(which means running XEN Virtualization)

then run

dmesg | grep -i virtual

Different virtual host will throw different output, similar to :


VMware vmxnet virtual NIC driver
   Vendor: VMware    Model: Virtual disk      Rev: 1.0
 hda: VMware Virtual IDE CDROM Drive, ATAPI CD/DVD-ROM drive

 Qemu or KVM

 CPU: AMD QEMU Virtual CPU version 0.9.1 stepping 03
  skipping (on a virtual guest)

or sometime

[    0.000000] Booting paravirtualized kernel on KVM

Microsoft VirtualPC:

 # dmesg | grep -i virtual
 hda: Virtual HD, ATA DISK drive
 hdc: Virtual CD, ATAPI CD/DVD-ROM drive

Xen :

# dmesg | grep -i xen
Xen virtual console successfully installed as tty1

Virtuozzo :

# dmesg
(returns no output)

# cat /var/log/dmesg
(returns no output)

# ls -al /proc/vz
veinfo  veinfo_redir  veredir  vestat  vzaquota  vzdata

On longer-running systems, you may need to grep /var/log/dmesg instead.

If that doesn't produce anything useful, try using dmidecode to look at the BIOS information. Frequently, there will be at least one component identifying itself as virtualized:


     # dmidecode | egrep -i 'manufacturer|product'
     Manufacturer: VMware, Inc.
     Product Name: VMware Virtual Platform

Microsoft VirtualPC:

     # dmidecode | egrep -i 'manufacturer|product'
     Manufacturer: Microsoft Corporation
     Product Name: Virtual Machine


     # dmidecode | egrep -i 'vendor'
     Vendor: QEMU


     # dmidecode
     /dev/mem: Permission denied


     # dmidecode | grep -i domU
           Product Name: HVM domU

You should just examine the output of dmidecode directly rather than trying to grep as above, in case the output changes. QEMU, for example, doesn't report the vendor in all versions.

Next, check disk devices for identification as virtualized:


    # cat /proc/ide/hd*/model
    VMware Virtual IDE CDROM Drive
    # cat /proc/scsi/scsi
    Attached devices:
    Host: scsi0 Channel: 00 Id: 00 Lun: 00
      Vendor: VMware   Model: Virtual disk     Rev: 1.0
      Type:   Direct-Access                    ANSI SCSI revision: 02

Microsoft VirtualPC:

    # cat /proc/ide/hd*/model
    Virtual HD
    Virtual CD

QEMU, KVM, or Xen:

    # cat /proc/ide/hd*/model


    # ls -al /dev/vzfs
    b-----x--- 1 root root 0, 19 2009-04-06 15:04 /dev/vzfs

The following bash script can also be used.

#!/bin/bash -
# @configure_input@
# Copyright (C) 2008-2011 Red Hat Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

# 'virt-what' tries to detect the type of virtualization being
# used (or none at all if we're running on bare-metal).  It prints
# out one of more lines each being a 'fact' about the virtualization.
# Please see also the manual page virt-what(1).
# This script should be run as root.
# The following resources were useful in writing this script:
# .


function fail {
    echo "virt-what: $1"
    exit 1

function usage {
    echo "virt-what [options]"
    echo "Options:"
    echo "  --help          Display this help"
    echo "  --version       Display version and exit"
    exit 0

# Handle the command line arguments, if any.

TEMP=`getopt -o v --long help --long version --long test-root: -n 'virt-what' -- "$@"`
if [ $? != 0 ]; then exit 1; fi
eval set -- "$TEMP"

while true; do
    case "$1" in
    --help) usage ;;
            # Deliberately undocumented: used for 'make check'.
            shift 2
    -v|--version) echo $VERSION; exit 0 ;;
    --) shift; break ;;
    *) fail "internal error ($1)" ;;

# Add /sbin and /usr/sbin to the path so we can find system
# binaries like dmicode.
# Add /usr/libexec to the path so we can find the helper binary.

# Check we're running as root.

uid=`id -u`
if [ "$uid" != 0 ]; then
    fail "this script must be run as root"

# Many fullvirt hypervisors give an indication through CPUID.  Use the
# helper program to get this information.


# Check for various products in the BIOS information.
# Note that dmidecode doesn't exist on non-PC architectures.  On these,
# this will return an error which is ignored (error message redirected
# into $dmi variable).

dmi=`LANG=C dmidecode 2>&1`

# Architecture.
# Note for the purpose of testing, we only call uname with -p option.

arch=`uname -p`

# Check for VMware.
# cpuid check added by Chetan Loke.

if [ "$cpuid" = "VMwareVMware" ]; then
    echo vmware
elif echo "$dmi" | grep -q 'Manufacturer: VMware'; then
    echo vmware

# Check for Hyper-V.
if [ "$cpuid" = "Microsoft Hv" ]; then
    echo hyperv

# Check for VirtualPC.
# The negative check for cpuid is to distinguish this from Hyper-V
# which also has the same manufacturer string in the SM-BIOS data.
if [ "$cpuid" != "Microsoft Hv" ] &&
    echo "$dmi" | grep -q 'Manufacturer: Microsoft Corporation'; then
    echo virtualpc

# Check for VirtualBox.
# Added by Laurent Léonard.
if echo "$dmi" | grep -q 'Manufacturer: innotek GmbH'; then
    echo virtualbox

# Check for OpenVZ / Virtuozzo.
# Added by Evgeniy Sokolov.
# /proc/vz - always exists if OpenVZ kernel is running (inside and outside
# container)
# /proc/bc - exists on node, but not inside container.

if [ -d $root/proc/vz -a ! -d $root/proc/bc ]; then
    echo openvz

# Check for Linux-VServer
if cat $root/proc/self/status | grep -q "VxID: [0-9]*"; then
    echo linux_vserver

# Check for UML.
# Added by Laurent Léonard.
if grep -q 'UML' $root/proc/cpuinfo; then
    echo uml

# Check for IBM PowerVM Lx86 Linux/x86 emulator.
if grep -q '^vendor_id.*PowerVM Lx86' $root/proc/cpuinfo; then
    echo powervm_lx86

# Check for Hitachi Virtualization Manager (HVM) Virtage logical partitioning.
if echo "$dmi" | grep -q 'Manufacturer.*HITACHI' &&
   echo "$dmi" | grep -q 'Product.*HVM LPAR'; then
    echo virtage

# Check for IBM SystemZ.
if grep -q '^vendor_id.*IBM/S390' $root/proc/cpuinfo; then
    echo ibm_systemz
    if [ -f $root/proc/sysinfo ]; then
        if grep -q 'VM.*Control Program.*z/VM' $root/proc/sysinfo; then
            echo ibm_systemz-zvm
        elif grep -q '^LPAR' $root/proc/sysinfo; then
            echo ibm_systemz-lpar
            # This is unlikely to be correct.
            echo ibm_systemz-direct

# Check for Parallels.
if echo "$dmi" | grep -q 'Vendor: Parallels'; then
    echo parallels

# Check for Xen.

if [ "$cpuid" = "XenVMMXenVMM" ]; then
    echo xen; echo xen-hvm
elif [ -f $root/proc/xen/capabilities ]; then
    echo xen
    if grep -q "control_d" $root/proc/xen/capabilities; then
        echo xen-dom0
        echo xen-domU
elif [ -f $root/sys/hypervisor/type ] &&
    grep -q "xen" $root/sys/hypervisor/type; then
    # Ordinary kernel with pv_ops.  There does not seem to be
    # enough information at present to tell whether this is dom0
    # or domU.  XXX
    echo xen
elif [ "$arch" = "ia64" ]; then
    if [ -d $root/sys/bus/xen -a ! -d $root/sys/bus/xen-backend ]; then
        # PV-on-HVM drivers installed in a Xen guest.
        echo xen
        echo xen-hvm
        # There is no virt leaf on IA64 HVM.  This is a last-ditch
        # attempt to detect something is virtualized by using a
        # timing attack.
        virt-what-ia64-xen-rdtsc-test > /dev/null 2>&1
        case "$?" in
            0) ;; # not virtual
            1) # Could be some sort of virt, or could just be a bit slow.
                echo virt

# Check for QEMU/KVM.
# Parallels exports KVMKVMKVM leaf, so skip this test if we've already
# seen that it's Parallels.  Xen uses QEMU as the device model, so
# skip this test if we know it is Xen.

if [ ! "$skip_qemu_kvm" ]; then
    if [ "$cpuid" = "KVMKVMKVM" ]; then
    echo kvm
        # XXX This is known to fail for qemu with the explicit -cpu
        # option, since /proc/cpuinfo will not contain the QEMU
        # string.  The long term fix for this would be to export
        # another CPUID leaf for non-accelerated qemu.
        if grep -q 'QEMU' $root/proc/cpuinfo; then
        echo qemu

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