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Using NX with Linux Mint

paul@dwerryhouse.com.au (Paul) — Wed, 11 Apr 2012 08:31:10 +1000

Attempting to use the NX remote desktop client to log onto a Linux Mint server results in the error 'Failed to load session "ubuntu"'. This can be fixed by editing the /usr/NX/etc/node.cfg file, and changing the CommandStartGnome to the following:

CommandStartGnome = "/usr/bin/gnome-session --session=gnome-fallback"

After this, run:

/usr/NX/bin/nxserver --restart

Logging in using NX will now give you the Linux Mint Gnome Classic desktop.

SYNCDHCP with FreeBSD

paul@dwerryhouse.com.au (Paul) — Wed, 21 Mar 2012 07:17:45 +1100

When upgrading to FreeBSD 8.2, I found that my host would no longer get an IP address via DHCP. It appears that the startup sequence has changed, and that the system no longer waits to get an IP address while booting.

This can be fixed by changing "DHCP" to "SYNCDHCP" in /etc/rc.conf:

ifconfig_ed1="SYNCDHCP"

Redirecting TCP and UDP traffic to the Android emulator

paul@dwerryhouse.com.au (Paul) — Fri, 24 Feb 2012 09:56:00 +1100

If you're writing Android network code and need test it with the Android emulator, you'll quickly run a problem: the emulator doesn't have a 'real' network interface, and cannot be reached from the outside world. Fortunately, there's a way to resolve this.

To forward a tcp port to the emulator, use:

adb forward tcp:sourceport tcp:destport

For example, to forward port 8000 on the host to port 8500 on the emulator, use:

adb forward tcp:8000 tcp:8500

To redirect a UDP port, telnet to the emulator's port (usually 5554) and then use redir:

telnet localhost 5554

redir add udp:sourceport:destport

Emacs keybindings with XFCE

paul@dwerryhouse.com.au (Paul) — Tue, 18 Oct 2011 11:56:00 +1100

If like me, you can't stand Unity or Gnome 3, and have migrated to XFCE, you'll have found that (once again) you've lost your Emacs keybindings.

Run the following command to get them back again:

xfconf-query -c xsettings -p /Gtk/KeyThemeName -s Emacs

Building a redundant mailstore with DRBD and GFS

paul@dwerryhouse.com.au (Paul) — Sun, 18 Sep 2011 16:17:00 +1000

I've recently been asked to build a redundant mailstore, using two server-class machines that are running Ubuntu. The caveat, however, is that no additional hardware will be purchased, so this rules out using any external filestorage, such as a SAN. I've been investigating the use of DRBD in a primary/primary configuration, to mirror a block device between the two servers, and then put GFS2 over the top of it, so that the filesystem can be mounted on both servers at once.

While a set-up like this is more complex and fragile than using ext4 and DRBD in primary/secondary mode and clustering scripts to ensure that the filesystem is only ever mounted on one server at a time, it's likely that there will be a requirement for GFS on the same two servers for another purpose, in the near future, so it makes sense to use the same method of clustering for both.

The following guide details how to get this going on Ubuntu 10.04 LTS (lucid). It won't work on any version older than this - the servers that this is destined for were originally running 9.04 (Jaunty), however, I've tested DRBD+GFS on that release, and there's a problem that prevents it from working. As far as I'm concerned, production servers should not be run on non-LTS Ubuntu releases, anyway, because the support lifecycle is far too short. This guide should also work fine for Debian 6.0 (squeeze), although I haven't tested it, yet.

Continue reading "Building a redundant mailstore with DRBD and GFS"

Run a local DNS resolver with OpenWRT

paul@dwerryhouse.com.au (Paul) — Mon, 29 Aug 2011 11:03:00 +1000

OpenWRT is a fantastic open source distribution for embedded devices, such as the Linksys WRT-54G series of wireless routers. One of its many features is the use of dnsmasq, a combined DNS and DHCP server, useful on small networks that are sitting behind a NAT connection.

The downside of dnsmasq on OpenWRT, however, is that the default configuration uses your ISP's DNS servers, which can be problematic, if your ISP, like many others, is adopting bad habits of redirecting non-existent domains to their servers, or is blacklisting / censoring websites without asking you.

For this, and for so many other reasons, it's a much better idea to run your own local DNS resolver. Unfortunately, dnsmasq isn't cable of doing this, so it's necessary to install a DNS server that can do this on its own. In this article, I describe how to do this.

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Avoiding tests when building Debian packages

paul@dwerryhouse.com.au (Paul) — Wed, 27 Jul 2011 07:48:00 +1000

Ever had a situation where you need to rebuild a Debian or Ubuntu package on a regular basis, but it takes an incredibly long time because it's running automatic tests - tests that you don't need until your final build?

For many of these packages, there's a simple way to disable the tests, by setting the DEB_BUILD_OPTIONS to "nocheck", before you build the package:

apt-get source openldap cd openldap-2.4.21 DEB_BUILD_OPTIONS=nocheck dpkg-buildpackage -rfakeroot

Not all packages support this, however, and some packages might use 'notest' instead.

There are a number of other values that can be used with DEB_BUILD_OPTIONS, too, if the package supports them:

noopt - turn off optimisation

nodocs - don't build documentation

nostrip - do not strip debugging symbols from binaries

parallel=n - use n parallel processes to build the package

Rate limiting with sch_htb

paul@dwerryhouse.com.au (Paul) — Wed, 06 Jul 2011 11:37:00 +1000

Ever had a user who uses up far too much bandwidth on your network? The Linux Advanced Routing and Traffic Control Guide gives a good example of rate-limiting a single machine on your network, using the sch_cbq module; however, I wanted to do this on a Linksys WRT54-GS router running OpenWRT, and sch_cbq is not available on there.

Fortunately, sch_htb, the Hierarchical Token Bucket is available on OpenWRT, which can do the same thing, but it's a lot more complicated to configure.

The following script will rate limit the single IP address of 192.168.0.67 to 128kbps. All other addresses on the network will remain unlimited. Set the name of the inside interface on your Linux router in DEV, the IP address in IP, the maximum rate on your inside network in MAXRATE and the limit that you want to apply in LIMIT.

#!/bin/sh DEV="br-lan" IP="192.168.0.67" MAXRATE="100mbps" LIMIT="128kbps" tc qdisc add dev $DEV root handle 1: htb default 11 tc class add dev $DEV parent 1: classid 1:1 htb rate $MAXRATE ceil $MAXRATE tc class add dev $DEV parent 1:1 classid 1:10 htb rate $LIMIT ceil $LIMIT tc class add dev $DEV parent 1:1 classid 1:11 htb rate $MAXRATE ceil $MAXRATE tc filter add dev $DEV protocol ip parent 1:0 prio 1 u32 match ip dst $IP flowid 1:10 tc qdisc add dev $DEV parent 1:10 handle 20: pfifo limit 5 tc qdisc add dev $DEV parent 1:11 handle 30: sfq perturb 10

Demoronising Ubuntu Natty

paul@dwerryhouse.com.au (Paul) — Sun, 12 Jun 2011 11:24:00 +1000

I don't know what it is with the Ubuntu developers; they seem to be going out of their way to make their distribution as unpleasant to use as is humanly possible. If it wasn't bad enough that they slow it down by running the default desktop with pointless animations, and playing annoying drumbeats at boot time, they disable potentially useful features like menu tearoffs and then move everyone's titlebar buttons across to the left side, ignoring their previous defaults.

Here's a script to fix up these inanities:

#!/bin/sh # Put the buttons on the right, where they should be gconftool-2 --type string --set /apps/metacity/general/button_layout ":minimize,maximize,close" # Disable annoying animations gconftool-2 --type bool --set /desktop/gnome/interface/enable_animations false # Give us back tear-off menus gconftool-2 --type bool --set /desktop/gnome/interface/menus_have_tearoff true # Kill that irritating drumbeat forever sudo su gdm -c "gconftool-2 --type bool --set /desktop/gnome/sound/event_sounds false" # Stop asking us if we want to empty the trash. Of course we want to. gconftool-2 --type bool --set /apps/nautilus/preferences/confirm_trash false # Windows already have a maximise button, so do something useful with the titlebar double-click gconftool-2 --type string --set /apps/metacity/general/action_double_click_titlebar toggle_shade

The Huawei e169 mobile broadband modem and Ubuntu lucid

paul@dwerryhouse.com.au (Paul) — Sat, 19 Mar 2011 08:28:00 +1100

Every new release of Ubuntu seems to break something that was working on my systems, and it was no different with the 10.04 release of Ubuntu: my Huawei e169 mobile broadband modem, which can be used in Australia on the Optus, Vodafone and Virgin mobile networks, and in Europe almost everywhere, stopped working.

The device would appear in the filesystem, but no matter what I did, it refused to connect.

It's quite easy to fix this, in fact. Firstly, install the usb-modeswitch package:

sudo apt-get install usb-modeswitch

Then create the file /etc/udev/rules.d/75-e169.rules with the following contents:

ATTRS{idVendor}=="12d1", ATTRS{idProduct}=="1001", RUN+="modem-modeswitch -v 0x% s{idVendor} -p 0x%s{idProduct} -t option-zerocd"

Restart udev, or reboot, and after that, you'll find your modem works reliably.

Using a Virgin Mobile USA Broadband adaptor on Ubuntu 9.10

paul@dwerryhouse.com.au (Paul) — Wed, 26 May 2010 04:01:00 +1000

Virgin Mobile USA has a nifty prepaid mobile broadband plan called Broadband2Go. The adaptor costs US$99, and the rates are quite competitive.

However, Ubuntu 9.10 did not see the adaptor when I plugged it in. The following is a guide to getting it running:

First, install usb-modeswitch:

apt-get install usb-modeswitch

Then, edit the /etc/usb_modeswitch.conf file and add the following lines to the end of it:

DefaultVendor= 0x1410 DefaultProduct= 0x5031 TargetVendor= 0x1410 TargetProduct= 0x6002 MessageContent="5553424312345678000000000000061b000000020000000000000000000000"

Now, you can test this by plugging the adaptor into your PC and running usb_modeswitch as root:

# usb_modeswitch

The device should now be visible as /dev/ttyUSB0.

At this point, you should be able to configure Network Manager to connect to it; select the "Virgin Mobile/Helio" connection.

Automatic installations of Ubuntu with preseeding

paul@dwerryhouse.com.au (Paul) — Sat, 20 Jun 2009 20:38:00 +1000

It's a common scenario: you've been given the task of rolling out dozens of Linux boxes, but you'd rather not have to go through the pain of installing every one them manually. Automated installations with Redhat are well documented, but what about Ubuntu?

Ubuntu inherits Debian's ability to preseed the answers to its installation questions, but the instructions for this are rather haphazard and seems to quickly become out of date as newer versions are released.

In this article, we'll look at setting up automated installations for Ubuntu Jaunty, entirely from the network. We'll start out with one assumption however - that the workstation being used has the ability to perform network boots using PXE. Most modern workstations and servers have this feature, which is usually enabled via the BIOS. If your computer doesn't have this, then you will most likely need to initial your boots from a CDROM, floppy disk drive or USB key.

Continue reading "Automatic installations of Ubuntu with preseeding"

Five great ways to annoy telemarketers with Asterisk

paul@dwerryhouse.com.au (Paul) — Wed, 23 Jul 2008 22:17:00 +1000

I'm not going to mince words here: I can't stand telemarketers. I don't care whether they are charities, political organisations or just run-of-the-mill salespeople, I simply have neither the time, interest nor will to waste my own neurons talking to them. It particularly infuriates me that technology - auto-diallers and voice-over-IP - combined with minimum wage staff, has made it so easy for telemarketers to misuse my time, while making a fortune from it. Even being on a do-not-call list hasn't fixed the problem completely; there's so many exemptions that I still find I get unsolicited calls far too often.

Of course, technology can be fought with more technology, and fortunately those of us who move in the free-software sphere have been graced with the marvelous gift of Asterisk, which presents many opportunities to waste the time of these people, as they try to waste ours. The equipment needed to run this is all fairly basic, by today's standards: I have a Snom-300 IP phone on my desk, a Linksys SPA-3000 adaptor to connect my PSTN line into my household ethernet (and can also drive a standard PSTN phone) and finally an old-whitebox PC as my Asterisk server.

So if you're being driven insane by students reading from canned scripts wanting your money, here's five ways to use Asterisk to get rid of them and maybe even slow them down in the process...

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Checking out Opensolaris 2008.05

paul@dwerryhouse.com.au (Paul) — Sun, 20 Jul 2008 21:13:00 +1000

Author: Paul Dwerryhouse <paul@dwerryhouse.com.au>

OpenSolaris 2008.05, Sun's community-developed open-source Solaris distribution, was released in May of this year, to much fanfare. While I began my system administration career in the Solaris field, I've found myself more and more in the Linux arena in the last few years, and haven't had a good look at Sun's flagship product since back in 2005, when Solaris 10 was released. With this in mind, I decided to pull down an ISO and see just how much going open-source has improved the product.

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Starting out with Lighttpd

paul@dwerryhouse.com.au (Paul) — Wed, 11 Apr 2007 08:51:00 +1000

While a large proportion of the world's webservers are currently using Apache, a competitor has been steadily gaining popularity on many high-usage sites. Lighttpd, pronounced "lighty", is a small-footprint, high-speed webserver, and is notably used by sites such as Sourceforge, YouTube and MiniNova. Netcraft state that Lighttpd is currently being used on 1.38 million sites, and is steadily gaining on Sun's share of the market. This introductory article provides a guide to getting Lighttpd installed and configured.

Continue reading "Starting out with Lighttpd"