Frequently Asked Questions

What is the difference between VDS and VPS?

Virtual private server (VPS) is a term used by Internet hosting services to refer to a virtual machine. The term is used for emphasizing that the virtual machine, although running in software on the same physical computer as other customers’ virtual machines, is functionally equivalent to a separate physical computer, is dedicated to the individual customer’s needs, has the privacy of a separate physical computer, and can be configured to run as a server computer (i.e. to run server software). The term Virtual Dedicated Server or VDS is used less often for the same concept.

Should I choose KVM or OpenVZ for my VPS?

KVM does not provide anywhere near the performance of OpenVZ (or Virtuozzo, its commercial equivalent). It’s extremely important to note that KVM requires a running kernel inside the VPS, whereas OpenVZ runs containers using a shared kernel. This means that a 256MB KVM VPS does not actually have the same amount of memory available to userspace that OpenVZ does. OpenVZ is an extremely lightweight virtualization technology that easily outperforms full virtualization.
KVM does provide better isolation, although this isn’t usually apparent to userspace in a container.

KVM is true virtualization where the VPS operates as its own server, independently of the host node. OpenVZ is a container style of virtualization which relies on the host node’s kernel. KVM has no restrictions in terms of functionality, but it has more overhead than OpenVZ. OpenVZ is constrained by the host node kernel, but it has less overhead in the containers themselves. KVM is generally more stable than OpenVZ.
So it’s up to you to decide.

How to enable SNMP on CentOS?

To enable SNMP on CentOS

yum install net-snmp-utils -y
yum install net-snmp -y
mv /etc/snmp/snmpd.conf /etc/snmp/
vi /etc/snmp/snmpd.conf
rocommunity public

Save and Exit

/etc/init.d/snmpd start
chkconfig snmpd on

Make sure you configured your Firewall

Install LAMP Server CentOS 6

sudo yum install httpd
sudo /usr/bin/mysql_secure_installation
By default, a MySQL installation has an anonymous user, allowing anyone
to log into MySQL without having to have a user account created for
them.  This is intended only for testing, and to make the installation
go a bit smoother.  You should remove them before moving into a
Remove anonymous users? [Y/n] y                                            
 ... Success!
Normally, root should only be allowed to connect from 'localhost'.  This
ensures that someone cannot guess at the root password from the network.

Disallow root login remotely? [Y/n] y
... Success!

By default, MySQL comes with a database named 'test' that anyone can
access.  This is also intended only for testing, and should be removed
before moving into a production environment.

Remove test database and access to it? [Y/n] y
 - Dropping test database...
 ... Success!
 - Removing privileges on test database...
 ... Success!

Reloading the privilege tables will ensure that all changes made so far
will take effect immediately.

Reload privilege tables now? [Y/n] y
 ... Success!

Cleaning up...

All done!  If you've completed all of the above steps, your MySQL
installation should now be secure.

Thanks for using MySQL!
sudo yum install php php-mysql
sudo chkconfig httpd on sudo chkconfig mysqld on
sudo service httpd restart
yum install mysql mysql-server -y
service mysqld start 

Fix "device eth0 does not seem to be present" after migrating Virtual Server

Check network:

# ifconfig
lo        Link encap:Local Loopback
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

 Try to start Eth0 device

# ifup eth0
Device eth0 does not seem to be present, delaying initialisation

To Solve this :

Delete networking interface rules file so that it can be regenerated and reboot your CentOS system.

# rm /etc/udev/rules.d/70-persistent-net.rules
# reboot

New Mac address has been generated:

# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.
# PCI device 0x8086:0x100e (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="08:00:27:fe:c1:03", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

Now edit /etc/sysconfig/network-scripts/ifcfg-eth0,

Add   new  HWADDR generated or  remove it 
Remove UUID   line

Restart the networking service

# service network restart
Shutting down interface eth0:                              [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:  Determining if ip address is already in use for device eth0...
                                                           [  OK  ]
# ifconfig
eth0      Link encap:Ethernet  HWaddr 08:00:27:FE:C1:03
          inet addr:  Bcast:xxxxxxxx  Mask:
          inet6 addr: fe80::a00:27ff:fefe:c103/64 Scope:Link
          RX packets:4400 errors:0 dropped:0 overruns:0 frame:0
          TX packets:129 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:387597 (378.5 KiB)  TX bytes:19567 (19.1 KiB)


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