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This website runs in a  virtual machine under vmware server. It is clustered between two servers using heartbeat and DRBD.
 
When VMware server starts up a virtual machine it generates a uuid (unique id) based on the machine it is running on and stores this in the .vmx file.
 
When heartbeat switches from slave to master, it will start VMware server (which is setup as a resource in the haresources file).
 
Virtual machines that you want started automatically when you start VMware server will not start because the uuid changes between the master and backup systems. To get around this problem always do the following:
  • edit the .vmx file and add the following line

    uuid.action = "keep"
If this is not done then everytime you try to run the virtual machine on the backup system in your cluster, VMware server will complain that the virtual machine has been copied or moved and it will not start it.
  • set the virtual machine to power off when vmware is stopped. Do not set this to "suspend" or it will not restart on the backup machine.
This will allow the virtual machine to start properly on the backup machine.
 
 
 
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I am a fan of the previous incarnation of the PlugComputer so I was excited to see that Marvell have unveiled a new PlugComputer dubbed imaginatively "PlugComputer 3.0."

PlugComputer 3.0 Features:

Smaller sleeker design,
More powerful CPU - 2gz Armanda 300 CPU,
120GB 1.8-inch SATA hard drive,
Wifi,
Bluetooth,
10/100/1000 wired Ethernet,
USB 2.0
.
512MB of RAM
512MB of Flash memory


I for one would like to see an additional Ethernet port added to increase application flexibility, for some applications where you are using clustered plugs or even for routing, having multiple Ethernet ports is a must.

Even without multiple ethernet ports, these low power consumption devices really could have a place in SME environments, replacing large cumbersome legacy hardware with compact Linux plug servers.

More information about the PlugComputer can be found here
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Many motherboards nowadays have integrated gigabit ethernet that use the Realtek NIC chipset.

The Realtek r8168B network card does not work out of the box in Redhat/Centos 5.3: instead of loading the r8168 driver, modprobe loads the r8169 driver, which is broken as can be seen with ifconfig which shows large amounts of dropped packets. A solution is to download the r8168 driver from the Realtek website and install it using the following steps:

Check whether the built-in driver, r8169.ko (or r8169.o for kernel 2.4.x), is installed.

# lsmod | grep r8169

If it is installed remove it.

# rmmod r8169

Download the R8168B linux driver from here into /root.

Unpack the tarball :

# cd /root
# tar vjxf r8168-8.012.00.tar.bz2

Change to the directory:

# cd r8168-8.012.00

If you are running the target kernel, then you should be able to do :

# make clean modules   
# make install
# depmod -a
# insmod ./src/r8168.ko (or r8168.o in linux kernel 2.4.x)

make sure modprobe knows not to use r8169, and that depmod doesn’t find the r8169 module.

# echo "blacklist r8169" >> /etc/modprobe.d/blacklist
# mv /lib/modules/`uname -r`/kernel/drivers/net/r8169.ko   \ /lib/modules/`uname -r`/kernel/drivers/net/r8169.ko.bak

You can check whether the driver is loaded by using the following commands.

# lsmod | grep r8168
# ifconfig -a

If there is a device name, ethX, shown on the monitor, the linux driver is loaded. Then, you can use the following command to activate it.

# ifconfig ethX up

After this you should not see any more dropped packets reported.

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The Openfiler NAS/SAN Appliance (NSA) is a Storage Management Operating System / NAS Appliance distribution. It is powered by the Linux 2.6 kernel and Open Source applications such as Apache, Samba, LVM2, ext3, Linux NFS and iSCSI Enterprise Target. Openfiler combines these ubiquitous technologies into a small, easy to manage solution fronted by a powerful web-based management interface. Openfiler allows you to build a Network Attached Storage (NAS) and/or Storage Area Network (SAN) appliance, using industry-standard hardware, in less than 10 minutes of installation time.

Building upon the popularity of server virtualization technologies such as VMware, Virtual Iron, and Xen, Openfiler can also be deployed as a virtual machine instance or on  a bare metal machine.

This deployment flexibility of Openfiler ensures that storage administrators are able to make the best use of system performance and storage capacity resources when allocating and managing networked storage in a multi-platform environment.

Openfiler is ideally suited for use with High Availability Recital applications as it incorporates:

  • Heartbeat cluster manager
  • drbd disk replication
  • CIFS
  • NFS
  • Software and hardware RAID
  • FTP
  • rsync
  • HTTP/DAV
  • iSCSI
  • LVM2
  • Multiple NIC bonding for High Availability
  • Powerful web-based GUI

 

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To insert code samples into your articles in joomla, you use the pre tag like this:

<pre xml:lang="xxx"> your code goes here </pre>

You can use any of the following languages for colorizing your code in articles. 
 

recital, abap, dos, lotusscript, rails, actionscript3, dot, lscript, reg, actionscript, d, lua, robots, ada, eiffel, m68k, ruby, apache, email, make, sas, applescript, fortran, matlab, scala, apt_sources, freebasic, mirc, scheme, asm, genero, mpasm, scilab, asp, gettext, mxml, sdlbasic, autoit, glsl, mysql, smalltalk, avisynth, gml, nsis, smarty, bash, gnuplot, objc, sql, basic4gl, groovy,

ocaml-brieftcl, bf, haskell, ocaml, teraterm, blitzbasic, hq9plus, oobas, text, bnf, html4strict, oracle11, thinbasic, boo, idl, oracle8, tsql, caddcl, index.html, pascal, typoscript, cadlisp, ini, perl, vbnet, cfdg, inno, per, vb, cfm, intercal, php-brief, verilog, cil, io, php, vhdl, c_mac, java5, pic16, vim, cobol, java, pixelbender, visualfoxpro, c, javascript, plsql, visualprolog, cpp, kixtart, povray, whitespace, cpp-qt, klonec, powershell, winbatch, csharp, klonecpp, progress, xml, css, latex, prolog, xorg_conf, delphi, lisp, providex, xpp, diff, lolcode, python, z80, div, lotusformulas, qbasic

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Opening SSH to the outside world is a security risk. Here is how to restrict SSH access to certain IP addresses on a machine.

  1. Edit the /etc/hosts.allow file to include these lines, assuming your machine is on the 192.168.2.x nonrouting IP block, and you want to enable an external address of 217.40.111.121 IP block: Remember to add the period on the end of each incomplete IP number. If you have another complete IP address or range, add a space and that range on the end.

    sshd,sshdfwd-X11: 192.168.2. 217.40.111.121
  2. Edit your /etc/hosts.deny file to include this line:

    sshd,sshdfwd-X11:ALL 
  3. These lines refuse SSH connections from anyone not in the IP address blocks listed.

Additionally you can restrict SSH access by username.

  1. Edit the /etc/ssh/sshd_config file and add the following lines

    PermitRootLogin no
    AllowUsers      user1 user2 user3 etc
    PasswordAuthentication yes

Now restart the ssh daemon for these changes to take effect

service sshd restart




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Recital 10 enhances the SQL optimizer. Now, production indexes with a FOR <conditions> will be used to optimize SQL SELECT statements. If a WHERE <condition> on a SELECT statement matches a FOR <condition> on an index tag, this index will be used to optimize the query. The WHERE <condition> must be an exact match with the  FOR <condition>.  For example;
USE accounts 
INDEX on account_no TAG outstanding FOR balance  > 0
EXPLAIN SELECT * FROM accounts WHERE balance  > 0
  Optimized using for condition on tag 'OUTSTANDING'
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If you have software packages which you wish to share with others or simply between your own personal machines, a neat and easy solution is to create your own YUM repository and provide your .repo file for download.

YUM is by far the easiest method of installing software on Red hat, Centos and Fedora. Not only does it mean you don't need to trawl the web looking for somewhere to download the packages, YUM does a great job of satisfying any package dependencies. As long as the required packages are available in the enabled repositories on your system, YUM will go out and get everything you need.

To create your own YUM repository, you will need to install the yum-utils and createrepo packages:

yum install yum-utils createrepo

yum-utils contains the tools you will need to manage your soon to be created repository, and createrepo is used to create the xml based rpm metadata you will require for your repository.

Once you have installed these required tools, create a directory in your chosen web server's document root e.g:

mkdir -p /var/www/html/repo/recital/updates

Copy the rpm's you wish to host into this newly created directory.

The next step is to create the xml based rpm metadata. To create this use the createrepo program we installed earlier.

At the shell type the following command:

createrepo -v -s md5 /var/www/html/repo/recital/updates


This will create the required metadata in the repodata directory of your /var/www/html/repo/recital/updates directory.

root@test repodata]# ls -l
rwotal 44
-rw-r--r-- 1 root root 28996 Jan 13 21:42 filelists.xml.gz
-rw-r--r-- 1 root root   284 Jan 13 21:42 other.xml.gz
-rw-r--r-- 1 root root  1082 Jan 13 21:42 primary.xml.gz
-rw-r--r-- 1 root root   951 Jan 13 21:42 repomd.xml

To do a final consistency check on your repository run the following command:

verifytree /var/www/html/repo/recital/updates

We now have a fully functioning YUM repository for our hosted rpm packages.
The next process is to create a .repo file in the client systems /etc/yum.repos.d directory.

Navigate to the /etc/yum.repos.d directory on your system as root.

Using your preferred text editor to create the .repo file. In this example I will call it recital.repo.
Now paste in the following lines:

[Recital]
name=Recital Update Server
baseurl=http://ftp.recitalsoftware.com/repo/recital/updates
enabled=1
gpgcheck=1

Once that is saved, at the shell prompt on the same machine (YUM client system).

$ yum repolist
Loaded plugins: presto, refresh-packagekit
repo id                  repo name                                 status
Recital                  Recital Update Server                     enabled:      1
adobe-linux-i386         Adobe Systems Incorporated                enabled:     17
fedora                   Fedora 12 - i386                          enabled: 15,366

As you can see the Recital repo is now being picked up and we have access to all the packages it is hosting.

See how easy that was!

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