Is VPSLink Out of Business?

Yes... From all indications, VPSLink is out of business:
* Their phones lines do not work.
* E-mails are unanswered.
* New support tickets cannot be opened.
* New forum threads cannot be created.

They will let you open a new account.  They will continue to bill your credit card.  If you have a functioning VM, it will continue to operate. If you have any trouble with your service or account, their is no avenue for support.

As a result, my only available course of action was to cancel my account.

IPtables Blocking KVM Bridge

Recently, I've been having problems with VM networking on RHEL KVM hosts. The initial symptom is the VM cannot get a DHCP address from the physical network, through a bridged virtual NIC. I've determined the problem is the with the FORWARD chain of IPtables.

Assuming a bridged ethernet called br0, I've added the following rules:

iptables -I FORWARD -i br0 -o br0 \
  -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -I FORWARD -i br0 -o br0 \
  -m state --state NEW -j ACCEPT

This will allow UDP, TCP, and ICMP initiated from the physical network to be routed to VMs attached to the br0 bridge.

This configuration is that it route all traffic, which some might consider bad form. If the KVM host only ran a fixed set of VMs, it might be wise to lock down specific ports. In a dynamic environment (like my lab) the level of effort to support IPtables on the host exceeds the risk, as the VMs are all running IPtables themselves.

Auqaponic System

I've constructed a small auqaponics system in my backyard green house. Here's a video of the first iteration. I have been impressed at how little water loss I'm experiencing in the system. Admittedly, the system is over-engineered, but that is normal for a prototype.

It's better to put too much into a test system, and introduce incremental cost savings over time, then to cut corners that might lead to total failure.

BeagleBone Black Console Cable

I recently got a BeagleBone Black from Adafruit. Immediate access was easy using the USB interface:

sudo screen /dev/ttyACM0 115200

To disconnect, press [Ctrl][A], followed by [k], and respond [y].

I wanted to watch boot sequence, but the USB does not come online until the end of the init process. I had purchased a USB to serial adapter, but did not find an obvious path between the "Prolific Technology PL2303" converter, and the serial header on the BeagleBone. The lack of documentation should not have been a surprise: most people have no interest in this feature.

To make matters more interesting, the picture on the Adafruit website was off by one pin. Luckily, Google Images was able to find the blog of Christophe Blaess, who had posted a picture of the correct pin-out:

The blog is written in French, which I don't speak, but a picture is worth a thousand words.

KVM Network Bridge

Finally, a simple way to configure a bridged network for a KVM server:

virsh iface-bridge eth2 br0

PVM, aka Beowulf Cluster

I stumbled upon a little project this weekend and found myself without a Beowulf cluster to help out.  It had been several years since I'd built a computational cluster, so I noticed a few "new" gothchas.  But... before we get to the fun stuff, let's review:

• No, Beowulf is not "dead technology"
• No, Hadoop is not the perfect tool for every job

That which was once called a Beowulf cluster is actually the use of a Message Passing Interface (MPI) that when deployed across nodes, create a Parallel Virtual Machine (PVM).  Ready for this-- the current generation of Hadoop (et al) clusters, are actually MPIs, and thus PVMs.  Given network attached storage, a map-reduce cluster is, in theory, Beowulf compliant.

To set up the absolute simplest PVM, we need two nodes, with an NFS share, and a user account.  The user needs an SSH key pair distributed to all nodes such that the user can login to any machine, from any machine.  Each node's hostname must be able to resolve via DNS or /etc/hosts.  Each node's hostname and address must be statically configured, and cannot be "localhost".

The first step is to install the base package from an EPEL repo.  (I'm using Scientific Linux 6.)  The package is delivered as source and must be compiled with a minimal set of options:

yum install -y pvm --nogpgcheck
rpm -ql pvm | grep -m1 pvm3
/usr/share/pvm3

This shows us where the RPM installed the source.  The issue with this incarnation is that it is still configured for RSH rather than SSH:

export PVM_ROOT=/usr/share/pvm3/
cd $PVM_ROOT
find . -type f -exec sed -i "s~bin/rsh~bin/ssh~g" {} \;
make; make install

Unfortunately, there are still hard-coded references to RSH in some of the binary libraries, so we spoof the references with a symlink:

ln -s /usr/bin/ssh /usr/bin/rsh

Repeat these steps on all (both) nodes.

On only one of the nodes (it doesn't matter which one) validate that PVM is not running, configure the PVM_ROOT variable, and start the first instance as the non-root user:

ps -ef | awk '!/awk/ && /pvm/'
echo "export PVM_ROOT=/usr/share/pvm3" >> ~/.bashrc
echo id | pvm
pvm> id
t40001
Console: exit handler called
pvmd still running.
ps -ef | awk '!/awk/ && /pvm/'
compute <snip> /usr/share/pvm3/lib/LINUXX86_64/pvmd3

Notice that the PVM deamon launched and remained resident.  Individual commands can be piped to PVM, or an interactive console can be used.  From the same node, remotely configure the next node:

ssh pvm2 'echo "export PVM_ROOT=/usr/share/pvm3" \
                >> ~/.bashrc'
# should not prompt for a password
ssh pvm2 'echo $PVM_ROOT'
/usr/share/pvm3
ssh pvm2 'rm -f /tmp/pvm*'

The last line is the very, very, important.  From the first node, remotely start the second node:

pvm
pvmd already running.
pvm> conf
conf
1 host, 1 data format
   HOST     DTID     ARCH   SPEED       DSIG
   pvm1    40000 LINUXX86_64    1000 0x00408c41
pvm> add pvm2
add pvm2
1 successful
   HOST     DTID
   pvm2    80000
pvm> conf
conf
2 hosts, 1 data format
   HOST     DTID     ARCH   SPEED       DSIG
   pvm1    40000 LINUXX86_64    1000 0x00408c41
   pvm2    80000 LINUXX86_64    1000 0x00408c41

In this sequence, we have accessed the console on pvm1 to view the clusters configuration (conf).  Next, we started the second node.  It is now displayed in the cluster's conf.

Just for fun, let's throw it the simplest of compute jobs:

pvm> spawn -4 -> /bin/hostname
4 successful
t8000b
t8000c
t4000c
t4000d
pvm>
[3:t4000d] pvm1
[3:t4000c] pvm1
[3:t4000c] EOF
[3:t4000d] EOF
[3:t8000b] pvm2
[3:t8000b] EOF
[3:t8000c] pvm2
[3:t8000c] EOF
[3] finished

There are a few things to notice about the output:

1. The command asked the cluster to spawn the command "/bin/hostname" four times.
2. The "->" option indicates we wanted the output returned to the console, which is completely abnormal... we only do this for testing.
3. The prompt returned before the output.  The assumption is that our compute jobs will take an extended period of time.
4. The responses were not displayed correctly.  They were displayed as they returned, because all this magic is happening asynchronously.
5. Each job's responses, from each node, could be grep'ed from the output using a unique serial number, automatically assigned to the job.

To leave the console and return to the command prompt issue the quit command.  All started nodes will continue to run.  To shutdown the compute cluster, execute:

echo halt | pvm

Finally, remember this one last thing: The cluster is a peer-to-peer grid.  Any node can manage any other, any node can schedule jobs, and any node can issue a halt.

Fun with Unicode Characters

Whenever I am tasked with creating a web page, it ends up being the absolute bare minimum.  (If you don't believe me, just visit dougbunger.com!)  Of course I do it in the interest of fast rendering and bandwidth conservation... because I am a good Internet citizen.  So here are some fun unicode graphics that can be used as web page icons.  There are thousands of characters, but these seem to be a good cross platform sub-set.

And by the way: Excuse the font.

This -->  &
...is an ampersand.

←	←	↑	↑	→	→	↓	↓
↔	↔	↕	↕
⇐	⇐	⇑	⇑	⇒	⇓	⇓	⇓
⇔	⇔	⌂	⌂
■	■	□	□	▪	▪	▫	▫
▲	▲	►	►	▼	▼	◄	◄
○	○	●	●	◖	◖	◘	◘
✇	✇	✈	✈	✓	✓	❥	❥
➲	➲	➳	➳	➸	➸	➼	➼

Removing Old Linux Kernels

Today, I had trouble removing an obsolete kernel from my workstation. It should have been simple enough, but I tried to use yum erase rather than rpm -e, and kept running into errors. That is obviously the bad news, so let's make sure to report the good news: YUM is such an improvement over RPM alone, that it is smart enough to know which kernels are obsolete. For instance:

# rpm -qa kernel
kernel-2.6.32-279.el6.x86_64
kernel-2.6.32-279.19.1.el6.x86_64
kernel-2.6.32-279.22.1.el6.x86_64
# uname -r
2.6.32-279.22.1.el6.x86_64
# yum erase kernel
<snip>
Removing:
kernel   x86_64   2.6.32-279.el6
kernel   x86_64   2.6.32-279.19.1.el6
Is this ok [y/N]:

First, we determine the machine has three kernels. Second, we see that that it is running the most recent version, dot-22. Finally, YUM demonstrates that it is smart enough to erase the two old kernels, but not the current kernel.

One small problem: I don't want to remove dot-19 because I have a driver problem with dot-22. I only want to remove dot-null. Here's the trick:

# yum list kernel
Loaded plugins: refresh-packagekit, security
Installed Packages
kernel.x86_64   2.6.32-279.el6
kernel.x86_64   2.6.32-279.19.1.el6
kernel.x86_64   2.6.32-279.22.1.el6
# yum erase kernel-2.6.32-279.el6

The critical success factors are to drop the arch and t0 add a dash(-) between the package name and the version number.

RHEL6 Udev Rules

I recently moved my home workstation from Fedora to Scientific Linux 6, on the grounds that Fedora has diverged too far from the current RedHat distribution.  Sure, bleeding edge is cool, but as a self professed Linux mercenary, I need to be in sync with what the real world is doing... not what it might be doing.

After the move, I've found myself annoyed by the way the Gnome desktop handles removable media, in particular media cards such as Flash and Secure Digital (SD).  One trick I learned a while back, was to make sure to assign an e2label to cards formatted with an ext filesystem.  This way, when Gnome automounts the media and places an icon on the desktop, the name is the e2label.  Without an e2label, the icon's text is the device size.  This is also true of FAT devices.

The real problem, however, is the fact that the device is owned by root.  Since the desktop is running as an unprivileged user (because we never login the GUI as root... right?) we are faced with an icon for an device that we can't drop-and-drag to.  Doh! Here's how I used Udev to trick the system into allowing my GUI account to use these devices.

First, insert the device, allow it to automount, and appear on the desktop.  (We won't worry with how the kernel, udev, fuse, and the desktop is accomplishing this.)  Assuming an ext device, it was probably mounted to a dynamic mountpoint under /media; in this case, we ended up with:

# mount | grep media
/dev/sdb1 on /media/Flash_1GB type ext3
   (rw,nosuid,nodev,uhelper=udisks)
# ls -ld /media/Flash_1GB
drwxr-xr-x. 4 root root 4096 Feb  9 15:55 /media/Flash_1GB/

The goal is to modify a few mount options and change the ownership of the device.  To accomplish this, we need to tell Udev to watch for a given device and respond in a specific manner.  This requires isolating a unique aspect of the device that can be used a s trigger.  The command to manage Udev changed with RHEL6:

# udevadm info --query=all --attribute-walk --name=/dev/sdb
<snip>
looking at device '/devices/<snip>/6:0:0:0/block/sdb':
    KERNEL=="sdb"
    SUBSYSTEM=="block"
    DRIVER==""
    ATTR{range}=="16"
    ATTR{ext_range}=="256"
    ATTR{removable}=="1"
    ATTR{ro}=="0"
    ATTR{size}=="2001888"
    <snip>
  looking at parent device '/devices/<snip>/6:0:0:0':
    KERNELS=="6:0:0:0"
    SUBSYSTEMS=="scsi"
    DRIVERS=="sd"
    <snip>
    ATTRS{vendor}=="Generic-"
    ATTRS{model}=="Compact Flash   "
    <snip>

There are a few things to notice about this output.  On the command line, the name is the disk, not the mounted partition.  The top most block is the device, blocks that follow are upstream devices.  We are most interested in the ATTR fields.  Don't be seduced by the first directive, "KERNEL=="sdb"... we all know that Linux is notorious for changing device letters on reboot.

Second, Udev rules are created as code snippets in the /etc/udev/rules.d dir.  For simplicity sake, create a file called 99-local.rules and add all machine specific rules to this one file.  Each rule is one line.  There are many sophisticated and elegant things that can be done by Udev, but my example is a simple sledgehammer:

SUBSYSTEMS=="scsi", 
ATTRS{model}=="Compact Flash   ",
ATTR{size}=="2001888",
RUN+="/bin/sh -c 'mount /media/Flash_1GB
   -o remount,noatime,nodiratime,async;
   chown doug:doug /media/Flash_1GB' "

The first directive tells the machine that we're dealing with a disk (we could have used "block".)  The second directive is an attribute that was listed for the device (notice the spaces: it has to exactly match the output from udevadm.)  The third attribute is the device size, so this rule applies just to this card, or atleast to cards with exactly this number of sectors.  The last part of the rule is the RUN command, which executes a set of bash commands.  In this case, I'm changing the default mount options, then I'm changing the mount point ownership.  Using the RUN feature provides infinite flexibility.

Eclipse Plugins For RedHat

You know how they say you shouldn't look at the sun during an eclipse or you'll go blind?  If there was any truth to that, why aren't there villages full of blind people in third world nations.  Why aren't there myths about the time that everyone on Earth went blind?  Think about it...  There had to be a first eclipse.  Who told the first dude not to look at it or he'd go blind?  Read on for the answer.

In the mean time, I've been beating myself up for a few days trying to get the Epic plugin for the Eclipse IDE installed.  I've got it on my Fedora desktop at home, and wanted it for a Linux machine at work, but the eclipse-epic RPM wasn't on Satellite. Simple enough: download it and install it from Epic-IDE.org... and spend the next several days wonder why it doesn't work.

The first issue is that the documentation has not been updated in several revisions, so the instructions for Epic are completely out of line with Eclipse 3.x.  Every time I would try follow a path through the point an click menus that seemed reasonable, I would get a message such as "could not find jar" or "no software site found at jar".  The obvious problem would be permissions, but all files and paths were world read-able.

The next obvious choice was to start hacking under the hood.  I looked at the Fedora eclipse-epic RPM and compared it to the Eclipse install tree.  I thought what seemed like a promising option when I found a plugins directory, but I could never get the machine to pickup the files.

Then, I tried something soooo stupid, it had to work.  I entered some arbitrary text into an unrelated field.  Of course it immediately launched exactly as expected.  The trick is to understand that which undocumented fields are required, but not checked by the application.  So, on Eclipse 3.x on RedHat Linux, to add a plugin:

Extract (unzip) the plugin
Launch Eclipse
Help / Install New Software...
Click Add... and Local...
Browse to (not into) the extracted directory
Click OK
*** In the Name field, provide some text ***
Click OK

The plugin options should appear in the pop-up window.  From this point, it should just be a case of checking boxes and accepting defaults.  Right?  Wrong!  Now we get dozens of lines of Java-esque errors, which for those of you who have ever worked with Java is line after line of completely useless garbage.  Take for instance the line:

No repository found containing: osgi.bundle,

A reasonable person might think that this and the fifty lines that follow it are telling you that there is a missing dependency.  Obviously, what that means is that the only way to install the plugin is to be root.

Remember those permission problems from earlier?  Its not that we didn't have permission to the files we just installed, its that we don't have permission to the Eclipse installation tree.  So...

Exit Eclipse
Open a terminal window and su to root
Launch Eclipse from the command line
Help / Install New Software...
Select "Available Software Sites"
Highlight the failed plugin
Click Remove and OK

Continue from "Click Add..." in the step above.

As for why the first human didn't go blind during the first eclipse?  He was too busy trying to figure out why his wheel wouldn't roll, because the instructions didn't mention that it had to be upright.

Defeating Facial Recognition

I saw a web advertisement from Merrill Edge Investments (not to be confused with Merrill Lynch... a risk latent, greedy, delusional, Wall Street investment firm that helped firm cheat millions of people out of their retirement earnings) for a new investment tool called Face Retirement.  The concept of the ad campaign is based on the work of Daniel Goldstein, PhD, who says people fail to invest for retirement is because they "can't see themselves as old."  His research indicated that if you showed someone a picture of what they would look like at age 65, it would motivate them to spend the next 15, 25, 35 years preparing for reaching that age.

I didn't believe it when I heard him say it the first time, but I salute him for managing to bilk the Wall Street suits out of the money to implement this as a web app.  I'll tell you why its a stupid idea in a few minutes, but first the fun stuff.

Merrill Edge implemented a facial recognition system that implements an aging feature.  You are suppose to use your web cam to center your face in an oval and snap a picture of yourself.  I decided to use this to demonstrate why facial recognition is not implemented in the wild.  You see, the basic concept that most people fail to understand about facial recognition is the question: What is a face?  Consider our first example.

As is obvious, this is a face-- it just happens to be the face of a dog (and not even a real dog, at that.)  The software successfully denied access, on the grounds that the face was not properly formatted.  In the second example, the application was presented with a "more" human face.

Again the software successfully denied access.  It did specifically recommend I remove my hat. 

Option number three was also a failure, thought this is a properly formatted, obviously human face.  Unfortunately, it is not a "real" face, but a picture from an AllState Insurance brochure.  If I owned stock in a facial recognition company, I might stop here, trumpeting how well the product had discarded this obvious attempt at trickery.  But I don't own any stock.  I can't remember why not... Oh, yes, thieving Wall Street scum bags.

But I digress.  Attempt number four:

Success!  I was granted access, using a photo of face.  Why did face three fail, but face four succeed?  Notice that face number three is not looking into the camera, but face four is a full frontal view.  This allowed the software to properly align the eyes, nose, and mouth.  The senorita from the cover of the "Instant Immersion Spanish" box does not have ears, but male model did not have eyes (they are closed.)

The fun thing about facial recognition is that most can be tricked by a photograph and the few that cannot, are usually tricked by a mask.  In all production quality systems, additional safeguards (heat sensors, echo location) have to be implemented to override these simple hacks.

As for why this idea of showing someone an aged image of themselves is stupid...  Its a short run fix.  Goldstein researches a favorite subject of mine, decision theory.  He indicates that we postpone long range decisions, because we do not see them as relevant.  By demonstrating aging, he hopes to bring a sense of reality to the abstract concept of time.  This works only until the car needs new tires or the muffler replaced.  No one is going to sit on the side of the road, replacing a bald, dry-rotted, flat tire, and say to themselves:

I've got one spare tire.  If this tire blew, the others are bound to go at any minute.  I can spend $500 on four new tires, or I can put the $500 toward retirement.  Would I rather have a safe car that I can drive to work, or I can make life better for "future me".

No.  The decision is simple: Replace the tires, screw "future me".  Short run always wins over long run, because "In the long run, we are all dead."  Which raises the question as to why Merrill Edge would spend the money on such a tool?  Are they altruistically trying to change human nature?

No.  Like I said... Its a short run fix.  The purpose of the tool is to "help you make a long run decision", knowing full well that short run realities will overcome the tool's effectiveness.  But by then, they've got what long run money you had available at that short run moment.

At isn't that what really matters.  That... and using stuffed dog puppets to validate new technology.

No Reserved Words in XML

Or so goes the mantra, but if that's true then why can't I use this syntax:

<?xml version="1.0"?>
<parse>
    <rule id="1">
      <type>pattern</type>
      <description>might be time value</description>
    </rule>
</parse>

It passes all my tests for well formed XML.  Why can't I use it?

Well, obviously, I can... so here's the story.  I've got some Perl code that I've used dozens of times before, but all of a sudden didn't work with this data.  After scoring the code and the the internet for a reason that this data structure wouldn't work, I finally changed the data to read , and everything worked fine.  This would seem to be a happy ending except for on small detail:  Its not my data.

To better understand what's going on, let me explain "doesn't work."  There is a Perl module called XML::Simple.  It combines dozens of steps into three lines:

use XML::Simple;
my $xml = new XML::Simple;
my $data = $xml->XMLin("file.xml");

These lines open the file, read the lines, parse out the tags, and assign the values into a dynamically allocated hash.  By adding a call to a Data::Dumper, we can look at the hash structure of the XML data:

$VAR1 = {
  'rule' => [
    {
      'id' => '1',
      'type' => 'pattern',
      'description' => 'might be time value',
    },

Or that's how it should break out.  Instead, it breaks out like this:

$VAR1 = {
  'rule' => [
       '1' => {
           'type' => 'pattern',
           'description' => 'might be time value',
        },

Which broke my normal subroutines.  Yet, if I change "id" to "item", everything works as expected.  So if its true that there are no reserved words in XML, why doesn't it work?

It turns out, for some bizarre, undocumented reason, the Perl XML::Simple module has decided that there are reserved words in XML.  And those words are name, key, and id.  If those words are found as tags in an XML structure, they are promoted to elements. Though CPAN does not explain why this is the case, they do provide a solution:

my $data = $xml->XMLin("file.xml",KeyAttr=>[]);

By setting the option KeyAttr to "none", the parser behaves as it should.

dracut: FATAL: initial SELinux policy load failed

Here's an obnoxious install failure: Using the RHEL/Scientific Linux 6.3 DVD, it is possible for an install to crash on first boot with an SELinux error.  The problem is a bug in the post of the target policy RPM.  The bug is immediately fixed by running yum update... assuming you can figure out how to get the machine booted.  Luckily, the error is nice enough to tell you how move forward.

Reboot, and at the GRUB menu, append "selinux=0" to boot into Permissive mode.  From the root prompt:

ls /etc/selinux/targeted/policy/policy.24
ls: cannot access /etc/selinux/targeted/policy/policy.24:
No such file or directory

If possible, issue: yum update selinux-policy-*

If the machine is not network connected, the problem can be resolved by restoring the file policy.24 from install media.  And it it were that simple, you wouldn't need me.  You will have to force install two RPMs:

rpm -ivh --force selinux-policy-3.7.19-*
rpm -ivh --force selinux-policy-targeted-3.7.19-*

The second force install will take several minutes to complete.

Regardless of how the issue is resolved, it is best to relabel the filesystem:

touch /.autorelabel

RHEL Cluster Anti-Affinity Configuration

I'm often amused by how vendors define "High Availability", aka HA.  Customers always talk about Five Nines, but "off the shelf" HA solutions seldom achieve 99% availability.  In the case of RedHat's HA cluster service, the default configuration might provide unattended failover within 60 seconds.  Given that Five Nines only allows 25.9 seconds per month, a single failure can blow away a service level agreement.

To counter the real-world lag of application failover, an system must be load balanced across a cluster.  A real HA environment would be at least three nodes, running two instances of the service.  If one node fails, the load balancer will redirect everything to the second instance, while the service is recovered on the third node.

There is an HA problem that VMware has addressed in their HA solution, that RedHat has not, known as the anti-affinity rule.  Affinity is when two "processes" favor the same resource.  An example would be when running a web and database instance on the same machine improve performance.  In the case of redundant services, running them on the same machine is pointless, if the machine fails.  To prevent this, we need an anti-affinity rule that requires the two processes to never be on the same machine.

RedHat cluster suite provides affinity in the form of child services.  If the cluster moves the web service to another node, the database has to follow.  What they don't provide is an anti-affinity rule to prevent the load balanced services from trying to run on a single node.  As a matter of fact, by default, all services will start on the same cluster node.  (It will be the node with the lowest number.)

I found I could implement anti-affinity from with in the service,s init.d script.  First, we add an /etc/sysconfig/ file for the process, with the following variables:

CLUST_ENABLED="true"
CLUST_MYSERVICE="service:bark"
CLUST_COLLISION="service:meow service:moo"

A collision is when the presence of a service prevents this service from starting on this node.  The names should be listed exactly as they appear in clustat.  Make sure the script sources the config file:

# source sysconfig file
[ -f /etc/sysconfig/$prog ] && . /etc/sysconfig/$prog

Next, add a new subroutine to the existing init.d script:

cluster(){
  # look for other services on this host
  K=$(for J in $CLUST_COLLISION; do \
          clustat | grep "$J.*$HOSTNAME.*started" \
          >/dev/null; \
          [ $? == 0 ] && echo "$J "; \
          done)
  if [ $K ]; then
    # show service names
    echo -n "Cluster, collision $prog: $K"
    # fail, but with a success return code
    failure; echo; exit 0
  fi
  # look for this service running on other nodes
  K=$(clustat | grep "$CLUST_MYSERVICE.*started" | \
          awk '{print $2}')
  if [ $K ]; then
    # show hostname of other instance
    echo -n "Cluster, $prog exists: `echo $K | cut -d. -f1`"
    # fail but with a success return code
    failure; echo; exit 0
  fi
}

Finally, add a reference to the cluster sub in the start sub:

start(){
  if [ $(ps -C cluster-$prog.sh | grep -c $prog) == 0 ]; then
    # only check cluster status if enabled
    [ "$CLUST_ENABLED" == "true" ] && cluster
    echo -n "Starting $prog"

Here's what happens in the case of a collision:

• rgmanager issues a start
• the cluster sub recognizes the collision, but tells rgmanage that it started successfully (exit 0)
• rgmanager shows the service as running
• 30 seconds pass
• rgmanager issues a status against the service, which fails, since the init.d script lied about the service running
• the cluster orders a relocation of the service
• rgmanager issues a start... on a different node
• there is no collision this time, so the init.d runs as expected

RHEL 6 Clustering, VM Fencing

I recently retasked one of my lab machines as a RedHat virtualization server, which RedHat calls RHEV, but is really KVM.  One of this machine's tasks is to support a test cluster of VMs.  Under normal circumstances, clustering would require a remote management interface such as an ILO, DRAC, or RMM.

As usual, I was disappointed with how difficult this was.  To make matters more difficult, for you, I won't be covering clustering in the article.  This document's scope will be limited setting up to RHEV VM fencing.

On the host machine, we need to install the fence daemon.  Considering this is very lightweight, the I'm going to do a shotgun install:

yum install fence-virtd-*

On my machine, this loaded four packages: the daemon, the interface between the daemon and the hypervisor, and two "plugins".  (The serial plugin is probably not needed.)

The base RPM will provide the /etc/fence_virt.conf file.  Modify it to look like this:

listeners {
  multicast {
    family = "ipv4";
    interface = "virbr0";
    address = "225.0.0.12";
    port = "1229";
    key_file = "/etc/cluster/fence_xvm.key";
  }
}
fence_virtd {
  module_path = "/usr/lib64/fence-virt";
  backend = "libvirt";
  listener = "multicast";
}
backends {
  libvirt {
    uri = "qemu:///system";
  }
}

Two things to notice about the config file.  The key_file option is little more than a password in a text file, which is going to have to be duplicated on all the VMs in the cluster.  The "theory" is that only a device with the password will be able to fence other nodes.  This brings us to the second point, the multicast option.  If a cluster node issues a fence command, the symmetric authentication key will be multicast on the network in the clear.  Thus, the reality is that the key_file provides no real security.

Which brings us to a second issue with the multicast.  Per RedHat, cross host fencing is not supported.  As such, all cluster nodes have to exist on the same physical machine, rending real world VM clustering pretty much worthless.  Here's the reality of cross host fencing: It is not supported because of the security concerns of multicasting the clear text fencing password and the fact that RedHat cannot guarantee the multicast configuration of the switch infrastructure.  Given properly configured switches, a dedicated host NIC and virtual bridge in each host, cross host fencing works.  In this lab configuration, however, it is not a concern.

After creating a key_file, open the fenced port in IPtables:

-A INPUT -s 192.168.122.0/24 -m tcp -p tcp --dport 1229 -j ACCEPT

Copy the key_file to each clustered VM (they don't need the config file) and add the opposite IPtables rule:

-A OUTPUT -d 225.0.0.12 -m tcp -p tcp --dport 1229 -j ACCEPT

On the host, chkconfig and start fence_virtd.  Running netstat should show the host listening on 1229.  What it is listening "for" is the name of a VM to "destroy" (power off.)  This means the names of the cluster nodes and VMs recognized by KVM/QEMU have to match.  On the host, display the status of the VMs using: 

watch virsh list

Given a two node cluster, on node1 issue:

fence_node node2

On the host, the status of node2 should change from running to inactive, and a moment later, back to running.  For testing purposes, the fence_node command can be installed on the host, without the host being part of the cluster.  If you try this using yum, you'll get the entire cluster suite.  Instead, force these three RPMs:

rpm -ivh clusterlib-*.x86_64.rpm  --nodeps
rpm -ivh corosynclib-*.x86_64.rpm  --nodeps
rpm -ivh cman-*.x86_64.rpm  --nodeps

 Truthfully, the better choice is to build a VM to manage the cluster using Luci.

Kickstart from Hard Drive ISO

I'm building a machine that may need to be remotely re-imaged, without the benefit a kickstart server.  I've always heard that you can kick a machine from itself, but had never tried it.  Truthfully, it's probably more trouble than its worth.  The best option would be to install a DVD drive with media, but configure the BIOS such that DVD is after the main drive.  Since I didn't want an optical drive on this machine, here's how to kickstart a machine from a hard drive.

Let's do this backwards.  Get the machine to image off an HTTP server and then change the ks.cfg:

#url --url http://1.2.3.4/rhel6
harddrive --partition=/dev/sdb1 --dir=/

Notice that I'm telling the machine that its image is on sdb, not sda.  Providing two drives is safer that trying to image off the boot/root drive, but it could be a partition on the same drive.  Besides, I've got dozens of little drives laying around doing nothing.  Further down in the file, I also indicated:

#clearpart --all
clearpart --drives=sda

Next, we mount the second drive and copy the ISO into the root of the drive.  To clarify:

mount /dev/sdb1 /mnt
cp rhel-6-x86_64-dvd.iso /mnt/

When kickstarting from a local drive, we use the ISO file itself... not an extracted or loop mounted filesystem.  Looking back at the first change we made to the ks.cfg, we indicated --dir=/, so we are telling the installer that the ISO is on the top level of the drive.

As a matter of convenience, mount the ISO, because we need a few files from it:

mkdir /mnt/rhel6
mount rhel-6-x86_64-dvd.iso /mnt/rhel6 -o loop

Copy three files:

mkdir /mnt/images
cp /mnt/rhel6/images/install.img /mnt/images
cp /mnt/rhel6/isolinux/vmlinuz /mnt/images
cp /mnt/rhel6/isolinux/initrd.img /mnt/images

If you were going to allow the machine to rebuild different versions (or distros) you would want to add a version number to each file.

To initiate the rebuild, we will use the tried and true Grub rebuild hack:

cd /boot
cp /mnt/images/vmlinuz /boot
cp /mnt/images/initrd.img /boot
cat >> /boot/grub/grub.conf << EOF
title Rebuild
  root (hd0,0)
  kernel /vmlinuz ramdisk_size=8192 ks=hd:sdb1/ks/ks.cfg
  initrd /initrd.img
EOF

Many docs indicate that the second drive has to be made bootable.  In this case, we are still booting off the primary drive, but only long enough to read the ks.cfg from sdb and switch to install.img.  Once install.img has control, it will read the clearpart command, wipe sda, and reinstall from sdb.

There is a "gotcha" I've not quite worked out yet.  As we all know, Linux is notorious for renaming drive letters at boot time.  It is possible that  the machine might confuse sda and sdb.  This could be disastrous if the machine crashed, and while trying to rebuild, it wiped the image drive!  The good news is that the installer reports that it can't find the image and kickstart file, and fails.  Just reboot until it finds the correct drive.

* It would seem that either a UUID or LABEL could be used in both Grub and the kickstart file.  I'll add checking those possibilities to my ToDo list.  Or you could figure that part out and let me know which works.  Its only fair: I've already done the hard part for you.

Citrix Xenserver: Apply Multiple Updates

As a result of reorganizing the servers in my lab, I had to reinstall Citrix Xenserver.  I should have downloaded 6.1, but decided to keep it at 6.0 and apply the updates that I already had on the NAS.  All went well with the install, I moved all my VMs and templates to this machine, and retasked the other machine.

When I went to load the updates, a funny thing happened... It refused to load more than one, and expected to reboot after each.  After a moment of thought, I realized that I had probably never tried to load two at a time before.  It seems like something that should be simple, but the procedure is not obvious.

Here's how:

1. Highlight a server, click the "General" tab, and expand the "Updates" pane.
2. In the "Updates" pane, notice which updates have already been applied.
3. On the menu bar, click "Tools", "Install Software Update", and "Next".
4. Click the "Add" button, select the lowest numbered update, and click "Open".
5. At this point, its tempting to add another update, but don't: yet.
6. Click "Next", select one or more servers, and click "Next".
7. A check will be run against the update.

If the check succeeds, click "Previous", "Previous", and repeat from step 4.

If the check fails, then two things.  First, click "Cancel" and start the entire procedure over again, but don't add the update that failed the test.  Second, don't blame me-- I didn't create the interface.

Once you've added all the relevant updates, click "Next".  You'll have the choice of performing post install steps automatically or manually.  What this really means is reboot now or later.  If you select manually (reboot later,) it is possible that some of the updates will fail, but that's actually okay.  When an update succeeds, it appears in the "Updates" pane as Applied.  If it fails, it appears as Not applied.

To get activate the not applied updates, repeat steps 1, 2, and 3, but instead of step 4, highlight the not applied update.  Continue through the rest of the steps, making sure to do automatic, as recommended.

Linux KVM Disk Drivers

I was having a problem with storage device names on virtual machines running on a RedHat KVM host.  Occasionally, I'd build a VM and the storage device would be named /dev/sda and other times /dev/xvda.  I quickly found that if I created the VM using virt-install, I got a xvda device, and if I used virt-manager (the GUI app), I got the sda device. After some investigation, I've discovered where things went wrong.

First, the syntax of the virt-install command changed in RHEL 6, and I was still using the RHEL 5 command.  Rather than complaining, RHEL 6 would guess what it thought I meant.  Here's the wrong command:

virt-install -n server -r 512 -w bridge=virbr0 \
-f /var/lib/libvirt/images/server.img -s 10

The -f/-s options says to create an image file the is 10GB.
Here's what was implemented:

virt-install -n server -r 512 -w bridge=virbr0 \
-disk path=/var/lib/libvirt/images/server.img,\
bus=ide,size=10

Rather than complaining that the -f/-s options were deprecated, it invoked the new syntax and assumed I wanted an IDE drive, which on RHEL 6, is named as if it were an SCSI device.  We can force the paravirt driver by using the correct command:

virt-install -n server -r 512 -w bridge=virbr0 \
-disk path=/var/lib/libvirt/images/server.img,\
bus=virtio,size=10

Second, the GUI does not allow a VM's disk type to be selected from the install wizard-- it always defaults to the paravirt driver.  To force a specific driver, on the last screen of the wizard, check the box for "Customize configuration before install".

This will open a new window listing the VM's hardware.  Select "Add Hardware", select "storage", and configure a second disk the same size as the first.  At this point, there is a pull down menu that will specify the driver.  Once the second disk is in place, remove the first.  Removing the first disk before the adding the replacement disk can cause problems.

Hint: Once you've modified the hardware, there is not "Apply" option.  Just close the window and the VM will launch.

Kitchen is Getting Close

Got the cabinets-- waiting on the counter top.

Turns out installation was not included with the vent hood, like that makes sense. What's that you say? "Nickel and dime"? Yep.

Certified Ethical Hacker

I recently took the Certified Ethical Hacker (CEH) class and certification exam.  First, I passed.  Second, I was a little disappointed with the class.

Let's take a look at the first item: I passed the test.  How can anyone reasonably complain about passing a certification test?  Let me contrast the certification test with three other tests. 

RedHat certification tests are all hands on:  Here's a broken computer, fix it.  Generally speaking, if you have at least one year of experience with Linux, take a RedHat class, understand the hands-on labs, you can pass the test.  The ITIL advanced certifications are almost the opposite.  Unless you have several years of workplace experience making IT management decisions, the class is of little help with the certification exams.  In the case of ITIL's advanced certifications, the proctored, paper exams test your ability to apply their methods to your real-world experience.  And then there is VMware, whose certification is a multiple choice, computer based test.  A quick breeze through the VMware docs, and just about anyone can pass the test.  As such, VMware requires you to take their class before you can get the certification, which makes the VCP little more than an indicator of class attendance.

The CEH is a multiple choice, computer based, exam, like VMware's.  The difference, however, is that (having taken the class) I'm not certain I could have passed the test based only on what I learned in the class.  Even though the class is structured like a RedHat class, with lecture and hands-on labs, I feel the exam required some real world experience.

Don't get me wrong... I'm not saying that "simply" taking the class should be enough.  I do agree that a candidate should have some experience in the area of study, but I feel that the purpose of the class and labs should be to solidify what they've seen, fill the gaps in what they haven't, and help them identify where they are weak.

And this brings me to the class.

Every class starts the same way-- introduce yourself and say what you hope to get out of this class.  Most people say something like "I'm John, and I want to pass the test."  This time, I said:

I'm Doug, and for the last ten years customers have insisted that I implement obscure security protocols, but I've never seen someone demonstrate that they can successfully breach a properly configured system.  I'm hoping this class will provide some validation that there really is a threat more sophisticated than scripts looking for default passwords.

What did I learn from the class?  Three things:  Windows sucks, Linux is invincible, and once a month 10% of users should all be shot.

At this point, let me interject that the CEH course material was the highest quality training material I have ever seen.  They had color graphics, high quality artwork, no diagrams stolen from vendor brochures, the books event had spines... like a real book that you'd buy at a book store.  We got six disks worth of tools.  And goodies like a backpack and a T-shirt!  The first half hour of class was like being six years old on Christmas day.  The rest of the class was like the feeling you have after you've opened all the Christmas presents, and you realize that the its all over.

Some of the labs were interesting, but there are only so many times you can demonstrate that Microsoft has sacrificed security for usability.  After a couple days, the fact that insiders and stupid users are allowing access to the network was well worn.  There really was no need for more than one lab demonstrating that organizations expose too much information to Google and Netcraft.

I'm going to end with one last thought, and this really doesn't have anything to do with CEH.  Human beings can learn anything from books, but we like to be taught by other human beings.  An instructor provides three basic services in a class:

1. Focus the student's attention on what is really important in the book, and identify the fluff and filler.
2. When a student indicates they do not understand the book, they offer more detail or alternate examples.
3. Provide value-add in the form of real world examples or relevant material outside of the book.

If you ever find yourself as a technical instructor, pay heed to what I'm about to say next:  If you can't fulfil at least one of the services above, simply being [ cool | fun | entertaining ] isn't enough.