Category Archives: Linux

Linux and Unix

Permission troubles with Xen?

Thought I’d post a quick message about something that kept me busy for way too long!

If you get any permission errors while trying to setup Xen along the lines of …

Access denied ...

Unable to access ...

Device xxx (vbd) could not be connected ...

... does not exist

then it may be worth checking if you’ve got selinux enabled. Check the file /etc/selinux/config and try changing




and reboot to see if that cures your problems. If it does then you can either leave selinux disabled (ensure you know the consequences of doing this) or grant the required permissions for selinux.

Dell/MediaDirect wiped my data!

I’ve used Dell laptops for a while and when I was looking for a new one about a month ago I was interested in a Dell Vostro as I’d read good things. One of the good things I’d read was that you could order it without all the crapware that comes installed on most machines these days.

So I brought a Vostro 1400 and was pretty pleased with it. One of the first things I did was *wipe all the partitions* on the drive and set it up to dual boot between Windows Vista and Ubuntu – with a nice big partition to store my data. This could then be accessed from both Vista and Ubuntu – ideal.

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Compiz Fusion: Such a sucker for eye candy

Compiz is a 3D desktop environment (that used to be called Beryl) that can be a very nice place to work. I’m a sucker for Screenshot-3eye-candy, true, but even with most of it switched off the result can be a pleasant, and maybe even more productive, place to be. There are literally hundreds of videos on YouTube to give you an idea of what Compiz looks like – see here. One of the most noticeable effects is the ‘wobbly windows’. This give the windows some ‘flexibility’ and also gives the desktop some ‘friction’ The effect is quite stunning, especially as the contents of the windows update while they are being dragged.

OK, that looks nice but it’s not really that useful – one thing that is useful though is the desktop ‘cube’ effect. Your desktop can have up to 16 faces that are rotated in 3D. Now, I must admit that I also have dual monitors, so I have a lot of ‘desktop real estate’ already, but having the ability to have different ‘cube faces’ with work tasks grouped on them is great. I very rarely press Alt-Tab any more (even though the 3D application switcher effect is quite nice also) because my applications don’t stack on top of each other very often – they’re on different cube faces. I’ve also got my mouse setup so that if I rotate the mouse wheel while at the edge of the screen the cube rotates. This makes quickly switching between different applications very fast.

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Backing up a VPS with duplicity?

I’ve got a total of 3 VPS’s from different providers now and I’ve been trying to decide the best way to back them all up. Plus I’ve got about 7GB of documents, photos and videos on my home PC and if everything could be backed up to the same place then even better.

For the past month I’ve been using Amazon’s S3 along with Duplicity.

There are a few really good points to using this method –

  • the later versions of duplicity are built to work with S3, it’s one of the many options
  • duplicity only sends files that have changed since the last backup reducing the bandwidth you use
  • S3 is pretty cheap and you would hope, being Amazon, that your data is pretty secure
  • although not mountable as a filesystem yet you can access S3 through a plugin in firefox
  • it is possible to encrypt your data on S3

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Monitoring a VPS with munin

I’ve been looking round for something simple and light-weight to monitor my 2 VPS’s. I wanted to see cpu, memory, disk usage output to a web page with graphs.

Munin looks quite good so I though I’d have a go at installing that.

Installation on Ubuntu couldn’t have been easier, just –

apt-get install munin-node munin

and it was done.

That created a folder called /var/www/munin so this has to be accessible through your current web server config or you might need to change a few things.

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Forgotten Hyperic password

I setup Hyperic a while ago and rather stupidly forgot the hqadmin password!

If the same happens to you it’s fairly easy to reset it. This assumes you’re using the default postgres database  –

cd to your Hyperic server’s bin directory

cd ~/hyperic/server-3.1.1/bin

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PXE boot WinPE 2 (Vista) using Linux as the PXE Server

Spent a little while trying to get WinPE2 (Vista) to boot via PXE from a linux server and thought it could be useful to someone. We already had our Red Hat stuff booting from there and it seemed like a good idea to keep it in one place!

Some of the stuff could be useful for booting via PXE from a Windows box too

Windows XP was used for WAIK stuff
Fedora Core 6 was used for PXE Server
Both running on VMWare Server along with a blank VMWare machine as the PXE client
* Note – there’s a bug in RHEL5 that’s stop’s the tftpd.remap file working. Not sure how many versions this affects

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Installing Mysql and Apache [part3]

Now we’re going to install mysql and apache and make a few changes so that they run OK in limited memory. I’m going to use the package manager to install them. You can compile and install them from source to get exactly what you want but be prepared to update them manually as bug and vulnerabilities are fixed.

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Securing my Ubuntu VPS [part2]

Now we’re updated to Gutsy it’s time to secure our system a little

First a firewall. Linux comes with a command called iptables for setting up firewall rules. It can be fairly complicated to use but we only want to do something nice and simple so we can just write the rules by hand.

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