IT Notepad

Clone hard disk with VMware ESXi

nedwards — Wed, 18 May 2011 14:58:06 +0000

I have been using VMware ESXi (4.1) a lot recently and have been using disk clones so that I don’t have to do a new OS install every time.

The issue is that I am using thin provisioning and when you do a copy if you are using NFS then it will change and allocate all of the space in the resulting copy. Not helpful!

So to get around this you can use vmkfstools. You will need to perform the following on a hard disk that is part of an existing machine otherwise you will get the following error:

DiskLib_Check() failed for source disk The system cannot find the file specified (25). that the machine

Use the following to do a thin provisioned clone of a disk.
vmkfstools -i original.vmdk -d thin ../newmachine/copy.vmdk

What I tend to do is to do a snapshot after I have created the virtual machine (original). I can then do a clone on a running machine as everything after the snapshot will be written to a delta file that just contains the changes after the snapshot.

Using Clonezilla

nedwards — Thu, 04 Nov 2010 13:17:00 +0000

I have just had the task of configuring 50 netbooks for a specific purpose. As I had already done a few of these before I knew it would be a good idea to try to clone one of the disks and use this on the others.

I came across Clonezilla a while back, and basically it’s an open source alternative to Norton Ghost. You can run it as a server or on a cd or usb drive. I decided to use the server option as I had so many netbooks to setup.

The first thing I did was install on a Ubuntu 10.04 virtual machine using some helpful instructions from here.

After cloning a configured install, I connected the server to a separate 8 port gigabit switch. From what I could see it needs it’s own switch as the server needs to run dhcp. I was able to restore the image to multiple devices at once using the multicast option, meaning that the data stream is sent to all the devices at once.

All in all, I’m really impressed with Clonezilla and will definitely use it again if doing something similar.

NOTE: When doing the multicast restore the speed was around 14.5MB/s, a bit slower than I would have thought for a gigabit switch, but still plenty fast enough and there may have been some way to increase this.

ARP issue with xen bridge

nedwards — Mon, 23 Aug 2010 15:25:00 +0000

I have been using Xen with network bridging for a while and things have been working well. However I started to see strange behaviour on a specific new guest (domU). Connectivity on the public bridged interface would be intermittent. Up for a while and then down for a while. It turns out that some arp queries were not being answered and so the guest (domU) host did not know the mac address for a particular ip (the gateway) for a period of time. I then observed this on other hosts.

After much digging and looking at tcpdump output, I set the arp address manually on the affected guests. After a while though I decided to specify the network bridges in Debian, instead of letting the Xen scripts do their work as I had heard that they can cause issues.

So to add two bridge interfaces, one with an ip and one without, add the following to /etc/network/interfaces

auto br-eth0 iface br-eth0 inet static address 192.168.xxx.xxx netmask 255.255.255.0 gateway 192.168.xxx.xxx bridge_ports eth0


auto br-eth1

iface br-eth1 inet manual

  bridge_ports eth1

Now that I have done this the problem has not reappeared as yet. I still don’t know exactly why this was happening.

Use Keepass with Dropbox

nedwards — Fri, 18 Jun 2010 09:08:50 +0000

I have been using Keepass (KeepassX) for a while now (replacing Password Safe). It works well and does everything I need. There is even an Android app (KeePassDroid), along with ports for other platforms http://keepass.info/download.html.

Storing files on Dropbox, means they are always available on any computers that are linked to your Dropbox account. Dropbox also now has an Android client so you can view files on your phone.

Now to have your password file available you could just pop the file within your Dropbox folder, however for extra security you can create a key file for the password database. This then means that to open the password database you need not just the password but the key file also.

A good secure option then would be to store your password database in Dropbox and your key file on the computers or devices that need it.

For your password itself be sure to set a secure one of at least 8 mixed case alpha numeric characters.

Disown job

nedwards — Wed, 05 May 2010 15:47:55 +0000

Every so often I fire up and job and then need to end my ssh session for one reason or another. Until the other day I did not realise that you could leave an already existing process running (other than using screen or nohup).

Use disown.

Run your job.

CTRL+Z to stop the job.

To put it in the backgroud.
$ bg
Then to disown.
$ disown -h

Now logout (CTRL+D) and it will just keep on running!

Install Tomcat 6 on Debian Lenny with pinning

nedwards — Tue, 24 Nov 2009 10:39:36 +0000

I recently needed to install tomcat 6 on debian lenny, however it is not in the repository and there is no backport.

There were two options, either use the tar or install the debian testing package. I have opted for the testing package as it is a debian specific setup and integrates properly.

I am assuming that you already have the debian java 6 package installed. Run the following as root.

First set the release to stable:
echo 'APT::Default-Release "stable";' > /etc/apt/apt.conf
This is important and not setting this will cause issues.

Now add the testing repository:
cat </etc/apt/sources.list.d/squeeze.list # Repository for Squeeze, to get Tomcat6 deb http://ftp.uk.debian.org/debian squeeze main contrib non-free deb-src http://ftp.uk.debian.org/debian squeeze main contrib non-free EOF

Now pin the new packages:
cat </etc/apt/preferences Package: * Pin: release o=Debian,a=stable Pin-Priority: 990 Package: * Pin: release o=Debian,a=testing Pin-Priority: 500 Package: tomcat6,tomcat6-admin,tomcat6-common,libtomcat6-java,libservlet2.5-java Pin: release o=Debian,a=testing Pin-Priority: 990 EOF

The above with ensure that testing packages will only take the priority for the tomcat related packages. The higher pin priority takes precedence.

Now update the repositories and install tomcat 6.
aptitude update aptitude install tomcat6

Ref:

http://www.waltercedric.com/component/content/article/193-technical/1634-debian-lenny-how-to.html
Why no apt-pinning by release name?
http://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_tweaking_candidate_version

Convert Virtualbox disk (.vdi) to VMware disk (.vmdk)

nedwards — Thu, 22 Oct 2009 08:32:37 +0000

I needed to do this recently and found that the instructions on the net that told me to just use qemu did not work as the hard disk would not boot.

Then I found the following set of commands:

VBoxManage internalcommands converttoraw vb.vdi vb.raw && qemu-img convert -O vmdk vb.raw vb.vmdk && rm vb.raw

It worked at treat and I was up and running on VMware 2 Server.

http://www.commandlinefu.com/commands/view/3773/convert-vdi-to-vmdk-virtualbox-hard-disk-conversion-to-vmware-hard-disk-format

Update ARP cache on router

nedwards — Wed, 29 Jul 2009 14:16:33 +0000

A couple of times in the past I have had issues when migrating from one server to another behind a router. By this I mean bringing the interface of one server down and then assigning the same ip address to another server. So by doing this you do not have to change a dns records.

However there is sometimes as issue which is that the arp cache on the router is not updated with the new mac address, so the router is still looking for the old mac address.

In order to force an update on the router, run the following:

sudo arping -U -I eth1 xxx.xxx.xxx.xxx

On Debian Lenny this is in iputils-arping.

sudo aptitude install iputils-arping

SSH Timeout

nedwards — Fri, 26 Jun 2009 12:18:42 +0000

As I use ssh all the time. An issue that I sometimes get is that the vpn disconnects, and the ssh session just freezes and never disconnects. To combat this and to get the ssh client to disconnect if it does not receive anything from the server after a period of time, then add the following to /etc/ssh/ssh_config:

ServerAliveInterval 30

The above should mean that it will disconnect after 30 seconds, however it seems to be a bit longer than that. Anyway it works.

Postgres readonly access

nedwards — Wed, 22 Apr 2009 16:12:09 +0000

Having used MySQL quite a bit in the past. I have been used to being able to setup a read only user for a database. In PostgreSQL things work a bit differently. In order to allow read only access you need to assign SELECT access on each table to a role.

The following seems to work.

Login to database

psql database

Create readonly role

CREATE ROLE readonly;

Create readonly_for_database.sh

This will grant select access on every table.


#!/bin/sh

tables=$(psql database -A -t -c "SELECT table_name FROM information_schema.tables \
WHERE table_schema = 'public';")

for table in $tables
do
echo "Granting select to readonly on $table"
psql database -c "GRANT SELECT ON $table to readonly;"
done

Grant readonly role to existing user

GRANT readonly TO existinguser;

Once this is done you will be able to give users read only access to the database.