Monthly Archives: August 2009

CentOS install and configure NTP to synchronize the system clock

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Type the following command to install ntp:

[root@myServer ~] # yum install ntp

Turn on the service

[root@myServer ~] # chkconfig ntpd on

Synchronize the system clock with pool.ntp.org server:

[root@myServer ~] # ntpdate pool.ntp.org

Start the ntp:

[root@myServer ~] # /etc/init.d/ntpd start

Check the time:

[root@myServer ~] # date

Check if the bios clock matches the system clock:

[root@myServer ~] # hwclock

Set the bios clock to match the system clock

[root@myServer ~] #hwclock --systohc

Set the ntp time servers in the file /etc/ntp.conf (the ntp servers will begin with: server)

CentOS Firewall

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Activating the IPTables Service

The firewall rules are only active if the iptables service is running. To manually start the service, use the following command:

[root@myServer ~] # service iptables restart

To ensure that iptables starts when the system is booted, use the following command:

[root@myServer ~] # chkconfig --level 345 iptables on

The ipchains service is not included in Red Hat Enterprise Linux. However, if ipchains is installed (for example, an upgrade was performed and the system had ipchains previously installed), the ipchains and iptables services should not be activated simultaneously. To make sure the ipchains service is disabled and configured not to start at boot time, use the following two commands:

[root@myServer ~] # service ipchains stop
[root@myServer ~] # chkconfig --level 345 ipchains off

 

Using IPTables

The first step in using iptables is to start the iptables service. Use the following command to start the iptables service:

[root@myServer ~] # service iptables start

 

Show current IPTables config

To show all current settings in the IPTables program, execute the following command:

[root@myServer ~] # iptables –L

 

IPTables Command Syntax

The following sample iptables command illustrates the basic command syntax:

[root@myServer ~ ] # iptables -A <chain> -j <target>

The -A option specifies that the rule be appended to <chain>. Each chain is comprised of one or more rules, and is therefore also known as a ruleset.

The three built-in chains are INPUT, OUTPUT, and FORWARD. These chains are permanent and cannot be deleted. The chain specifies the point at which a packet is manipulated.

The -j <target> option specifies the target of the rule; i.e., what to do if the packet matches the rule. Examples of built-in targets are ACCEPT, DROP, and REJECT.

Important

When creating an iptables ruleset, order is important.

If a rule specifies that any packets from the 192.168.100.0/24 subnet be dropped, and this is followed by a rule that allows packets from 192.168.100.13 (which is within the dropped subnet), then the second rule is ignored.

The rule to allow packets from 192.168.100.13 must precede the rule that drops the remainder of the subnet.

To insert a rule in a specific location in an existing chain, use the -I option. For example:

[root@myServer ~ ] # iptables -I INPUT 1 -i lo -p all -j ACCEPT

This rule is inserted as the first rule in the INPUT chain to allow local loopback device traffic.

 

Saving and Restoring IPTables Rules

Changes to iptables are transitory; if the system is rebooted or if the iptables service is restarted, the rules are automatically flushed and reset. To save the rules so that they are loaded when the iptables service is started, use the following command:

[root@myServer ~ ] # service iptables save

The rules are stored in the file /etc/sysconfig/iptables and are applied whenever the service is started or the machine is rebooted.

Documentation

IPTables: http://wiki.centos.org/HowTos/Network/IPTables

Firewalls: http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-fw.html

Linux: Setup as DNS Client / Name Server IP Address

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Many new Linux user finds it difficult to setup / modify new name server address (NS1 / NS2).

Local name resolution is done via /etc/hosts file. If you have small network, use /etc/hosts file. DNS (domain name service is accountable for associating domain names with ip address, for example domain yahoo.com is easy to remember than IP address 202.66.66.12) provides better name resolution. To configure Linux as DNS client you need to edit or modify /etc/resolv.conf file. This file defines which name servers to use. You want to setup Linux to browse net or run network services like www or smtp; then you need to point out to correct ISP DNS servers:

/etc/resolv.conf file

In Linux and Unix like computer operating systems, the /etc/resolv.conf configuration file contains information that allows a computer connected to the Internet to convert alpha-numeric names into the numeric IP addresses that are required for access to external network resources on the Internet. The process of converting domain names to IP addresses is called “resolving.”

The resolv.conf file typically contains the IP addresses of nameservers (DNS name resolvers) that attempt to translate names into addresses for any node available on the network.

Setup DNS Name resolution

Steps to configure Linux as DNS client, first login as a root user (use su command):

Step # 1: Open /etc/resolv.conf file:

# vi /etc/resolv.conf

Step #2: Add your ISP nameserver as follows:

search isp.com
nameserver 202.54.1.110
nameserver 202.54.1.112
nameserver 202.54.1.115

Note Max. three nameserver can be used/defined at a time.

Step # 3:Test setup nslookup, dig or host command:

# dig www.google.com
# nslookup www.google.com
# host www.google.com

CentOS Configuring Proxy Server Access for Yum

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To enable all yum operations to use a proxy server, specify the proxy server details in /etc/yum.conf. The proxy setting must specify the proxy server as a complete URL, including the TCP port number. If your proxy server requires a username and password, specify these by adding proxy_username and proxy_password settings.

The settings below enable yum to use the proxy server mycache.mydomain.com, connecting to port 3128, with the username yum-user and the password qwerty.

# The proxy server - proxy server:port number
proxy=http://mycache.mydomain.com:3128
# The account details for yum connections
proxy_username=yum-user
proxy_password=qwerty

Howto Install vmware tools in Ubuntu

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source: http://www.ubuntugeek.com/howto-install-vmware-tools-in-ubuntu.html

We have already discussed about VMware server setup in gutsy.Now It is very important that you install VMware Tools in the guest operating system.With the VMware Tools SVGA driver installed, Workstation supports significantly faster graphics performance.The VMware Tools package provides support required for shared folders and for drag and drop operations.

Other tools in the package support synchronization of time in the guest operating system with time on the host, automatic grabbing and releasing of the mouse cursor, copying and pasting between guest and host, and improved mouse performance in some guest operating systems.

Click on VM in the top menu of the VMware Server console and select Install VMware Tools.

 Now you should be able see the following screen here click on install

 Now you should see similar to the following screen on your desktop

 First copy the VMware Tools from the mounted iso to the temporary folder

cp /media/cdrom/VMwareTools-1.0.3-44356.tar.gz /tmp/

Afterwards switch to the temporary folder and unpack the VMware Tools:

cd /tmp/

tar xvfz VMwareTools-1.0.3-44356.tar.gz

Next switch to the folder with the unpacked files and execute the installer:

cd vmware-tools-distrib/

sudo ./vmware-install.pl

Now you will be asked a few questions relating to installation paths etc. Choose the default value every time (simply hit enter).

 After the installation/configuration finished you have to start the VMware Tools:

vmware-toolbox &

Once it opens you should be able to see similar to the following screen

Vmware tools version details

Note: If you close the VMware Tools window, the VMware Tools will be disabled immediately.

VMware ESX and ESXi Comparison

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source: http://kb.vmware.com/kb/1006543

VMware ESX and ESXi Comparison

Purpose

This article provides a detailed comparison of VMware ESX and VMware ESXi. The article is separated in to capabilities or features and compared at that level.

Resolution

Capability

VMware ESX

VMware ESXi
Service Console Service Console is a standard Linux environment through which a user has privileged access to the VMware ESX kernel. This Linux-based privileged access allows you to highly customize your environment by installing agents and drivers and executing scripts and other Linux-environment code. VMware ESXi is designed to make the server a computing appliance. Accordingly, VMware ESXi behaves more like firmware than traditional software. To provide hardware-like security and reliability, VMware ESXi does not support a privileged access environment like the Service Console of VMware ESX. To enable interaction with agents, VMware has provisioned CIM Providers through which monitoring and management tasks – traditionally done through Service Console agents – can be performed. VMware has provisioned RCLI to allow the execution of scripts.
Remote CLI VMware ESX Service Console has a host CLI command through which VMware ESX can be configured. ESX 3.5 Update 2 supports RCLI. VMware ESX Service Console CLI has been ported to a Remote CLI (RCLI) for VMware ESXi. RCLI is a virtual appliance that interacts with VMware ESXi hosts to enable host configuration through scripts or specific commands. Note: 

  • RCLI is limited to read-only access for the free version of VMware ESXi. To enable full functionality of RCLI on a VMware ESXi host, the host must be licensed with VI Foundation, VI Standard, or VI Enterprise.
  • The VMware Infrastructure toolkit for Windows and the Perl toolkit access ESXi through the same API as RCLI. Similarly, these toolkits are limited to read-only access for the free version of VMware ESXi. When the host is upgraded to VI Foundation, VI Standard, or VI Enterprise, these toolkits have write-access and provide a scriptable method for managing ESXi hosts.
  • The following Service Console CLI commands have not been implemented in RCLI:
  • ESXcfg-info
  • ESXcfg-resgrp
  • ESXcfg-swiscsi 
Scriptable Installation VMware ESX supports scriptable installations through utilities like KickStart. VMware ESXi Installable does not support scriptable installations in the manner ESX does, at this time. VMware ESXi does provide support for post installation configuration script using RCLI-based configuration scripts.
Boot from SAN VMware ESX supports boot from SAN. Booting from SAN requires one dedicated LUN per server. VMware ESXi may be deployed as an embedded hypervisor or installed on a hard disk.   In most enterprise settings, VMware ESXi is deployed as an embedded hypervisor directly on the server. This operational model does not require any local storage and no SAN booting is required because the hypervisor image is directly on the server.

 

The installable version of VMware ESXi does not support booting from SAN.
Serial Cable Connectivity VMware ESX supports interaction through direct-attached serial cable to the VMware ESX host. VMware ESXi does not support interaction through direct-attached serial cable to the VMware ESXi host at this time.
SNMP VMware ESX supports SNMP. VMware ESXi supports SNMP when licensed to a VI Foundation, VI Standard, or VI Enterprise edition. The free version of VMware ESXi does not support SNMP.
Active Directory Integration VMware ESX supports Active Directory integration through third-party agents installed on the Service Console. VMware ESXi with a Virtual Infrastructure license and in conjunction with VirtualCenter allows users to be authenticated via Active Directory. In this configuration, users can log in directly to an ESXi host and authenticate using a local username and password. The free version of VMware ESXi does not support Active Directory integration at this time.
HW Instrumentation Service Console agents provide a range of HW instrumentation on VMware ESX. VMware ESXi provides HW instrumentation through CIM Providers. Standards-based CIM Providers are distributed with all versions of VMware ESXi. VMware partners may inject their own proprietary CIM Providers in customized versions of VMware ESXi. To obtain a customized version of VMware ESXi, you typically have to purchase a server with embedded VMware ESXi through a server vendor. At this time, HP also offers its customized VMware ESXi Installable on www.vmware.com. Dell, IBM, and FSC will soon offer their customized version of VMware ESXi on www.vmware.com.

 

Remote console applications like Dell DRAC, HP iLO, IBM RSA, and FSC iRMC S2 are supported with ESXi.

 

Note: COS agents have a longer lineage than CIM Providers and are therefore more mature. VMware is actively working with its 250+ partners to close the CIM Provider–Service Console agent gap.
Software Patches and Updates VMware ESX software patches and upgrades behave like traditional Linux based patches and upgrades. The installation of a software patch or upgrade may require multiple system boots as the patch or upgrade may have dependencies on previous patches or upgrades. VMware ESXi patches and updates behave like firmware patches and updates. Any given patch or update is all-inclusive of previous patches and updates. That is, installing patch version “n” includes all updates included in patch versions n-1, n-2, and so forth.
VI Web Access VMware ESX supports managing your virtual machines through VI Web Access. You can use the VI Web Access to connect directly to the ESX host or to the VMware Infrastructure Client. VMware ESXi does not support web access at this time.
Licensing VMware ESX hosts can be licensed as part of a VMware Infrastructure 3 Foundation, Standard, or Enterprise suite.  VMware ESXi hosts can be individually licensed (for free) or licensed as part of a VMware Infrastructure 3 Foundation, Standard, or Enterprise suite. Individually licensed ESXi hosts offer a subset of management capabilities (see SNMP and Remote CLI).

 

 

ESXi – Free License

(ESX not available without VI)

VI Foundation

(with ESX or ESXi)

VI Standard

(with ESX or ESXi)

VI Enterprise

(with ESX or ESXi)
Core hypervisor functionality

Yes

Yes

Yes

Yes
Virtual SMP

Yes

Yes

Yes

Yes
VMFS

Yes

Yes

Yes

Yes
VirtualCenter Agent

 

Yes

Yes

Yes
Update Manager

 

Yes

Yes

Yes
Consolidated Backup

 

Yes

Yes

Yes
High Availability

 

 

Yes

Yes
VMotion

 

 

 

Yes
Storage VMotion

 

 

 

Yes
DRS

 

 

 

Yes
DPM

 

 

 

Yes

Errors when gathering disk information during a physical to virtual conversion

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KB Article: 1010341

Symptoms

When gathering disk information during a physical to virtual conversion, you may see the following errors:

  • Fatal error occurred. The most common reason for this is loss of network connection.
  • The wizard will now be closed.
  • Please check your network connection and try again.
  • Exception getting Disks and Volumes
  • sourceStorageInfo is missing

Purpose

This article provides troubleshooting steps for converting a physical Windows source computer to a virtual machine. It assists you in eliminating common causes for this issue by verifying that networking is still in place between the Converter server and the the Windows source, and that the Windows source is not using any virtual disks.

Resolution

Please validate that each troubleshooting step below is true for your environment. Each step will provide instructions or a link to a document, in order to eliminate possible causes and take corrective action as necessary. The steps are ordered in the most appropriate sequence to isolate the issue and identify the proper resolution. Please do not skip a step.

Note: If you perform corrective action in any of the following steps, attempt the conversion again.

  1. Verify that networking is still in place between the Converter server and the source computer. For more information, see Required VMware vCenter Converter ports (1010056).
  2. Confirm that there are no virtual disks appearing as disk devices in the Disk Management utility.
    1. Click Start > Run.
    2. Type diskmgmt.msc and press Enter.
    3. Review the list of drive letters and devices in the bottom window. If there is a drive that is not associated with a physical device then remove it.

      Note:  You must determine what software process has mounted this virtual drive and consult with its product documentation.

Note: If your problem still exists after trying the steps in this article, please: