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Even with today massive disk drives it’s so easy to run out of disk space. This can be a real pain if you happen to run out of space on your root volume.

So, you fancy doing some spring cleaning and want to track down where all of your space has gone.

Here’s a quick run through using nothing more than the command prompt -

To show all of your filesystems with the -m showing used/free space in megabytes

So I’m using 718 MB of my disk space but where?

For the next bit we’re going to need to be root (or root equivalent)

That will list the size in MB of all of the folders in root (/) with the largest last.

So my /usr folder is using 513MB. Now I can drill down into the folders running the same command again.

and so on.

Obviously you only want to be deleting files when you’re absolutely positive what they are used for and what impact deleting them will have on your system!

There are a whole bunch of utilities for both Windows and linux to make this process easier and prettier! Here’s a couple -

Linux - http://treesize.sourceforge.net/
Windows - http://sourceforge.net/projects/windirstat/

I’ve always been pretty confident just using denyhosts to prevent people running brute force ssh login attempts against my servers but now with this from securityfocus - http://www.securityfocus.com/news/11518 - I think I’ll also be changing the port number that SSH is listening on.

The report says that there are now large distributed brute force ssh attempts coming from multiple IP addresses. This means that utilities that are blocking login attempts from hosts that have made multiple failed attempts are not going to help.

Here’s a quick and easy way to get a CentOS Xen dom0 and domU up and running

1 - Boot using the CentOS CD

2 - When prompted for the package bundle selection just choose “Virtulization”

3 - Log into your new CentOS install as root

4 - Install the ftp server vsftpd. We’ll use this to install CentOS on our domU

5 - Mount our CentOS CD so we can access it via FTP

Continue reading ‘10 steps to a Xen domU’ »

If you’ve ever had a slow, unable connection to a server it could be that you’re suffering from some packet loss between you and the server.

This might not be noticeable for web browsing or e-mail but if you’re doing any sort or VOIP or gaming it can be critical to know the quality of the connection between 2 points.

A simple tool for this is mtr. This is normally included in modern Linux ditros - if you’re a RedHat/CentOS/Fedora person just run -

Now you can fire it up by running -

Continue reading ‘Where are my packets going?’ »

I’ve been looking round for a small, simple helpdesk system that I can use for keep track of contact with my customers.

I want something that can create tickets via e-mail, something that’s easy to manage and, because I’m just starting out, something that’s free!

I’ve decided to give Trellis Desk from Accord5 a go. I’ve not seen it talked about much but it was pretty easy to install and looks really nice.

Check out Trellis Desk for yourself here

SSH is extremely versatile and can be used to both mange your server and copy files to your server. Unless you have a real good reason to be using FTP still you really shouldn’t be (and you certainly shouldn’t be using telnet any more!)

It’s certainly worth taking some time to make sure your SSH service is secure and there is plenty you can do to accomplish this.

Here’s what I do with my servers plus some links to other things that you can do.

1 - Make sure you are running the latest version of the SSH daemon software

2 - Install denyhosts

Denyhosts can be configured to stop accepting connections from IP addresses that have made too many failed login attempts. It is configurable so you can specify how many failed login attempts to allow before the host is blocked, how long the host is blocked for … 

Continue reading ‘Making your SSH service secure’ »

Here are several areas you should consider when looking for a VPS - I’m sure there are others! Please let me know if you think of any and I’ll add them to the list

Memory: When I first started looking for a VPS I was shocked at how little memory you got. 256MB sounds like a ridiculous amount - however, you have to remember that a lot of the memory that the Linux kernel is using does not come out of your allocation. Also, programs these days expect there to be a lot of memory available on the server. If you’ve only got a small amount then you can tweak the configuration files (of apache, mysql, etc …) to use less memory. Sometimes this will degrade performance to an unacceptable level but often not.

Continue reading ‘What to consider when you’re looking for a VPS?’ »

Virtual Private Server (VPS) or Virtual Dedicated Server (VDS) are two terms that describe the same thing - a share (or slice) of a physical server. VPS’s are becoming very popular amongst web hosters and developers who’s sites requirements are greater than a shared hosting supplier can provide, but do not yet demand their own dedicated server.

With shared hosting you get some web space that you can run your site on, however, problems can arise if your site is too busy (it can affect other users with that shared hosting provider) or, if the software that you want to run (mailserver, web blog, picture gallery, bulletin …) has certain requirements that a shared hosting provider does not provide.

Continue reading ‘What is a Virtual Private Server (VPS)?’ »

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 …

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.

I’ve got a few DDI numbers from CallCentric all around the world (UK, US, Australia) and couldn’t figure our how to setup an ‘Inbound Route’ in FreePBX that used the number that had been dialled to route the call.

It turns out that you need to extract the number from the ‘SIP header’ information and there’s no setting in FreePBX to do this so it means hacking at the Asterisk config files just a little.

Continue reading ‘Getting the DID number from a CallCentric SIP trunk for FreePBX’ »