2010

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AC3 audio with pulseaudio in Ubuntu Lucid

2010-05-09 12:58 +00:00 | 2 comments

Update 2010-10-14 – This problem has been resolved since pulseaudio 1:0.9.22~0.9.21+stable-queue-32-g8478-0ubuntu14. You can now play AC3 audio with the Lucid packages.

Since upgrading my media PC to Ubuntu 10.04 “Lucid Lynx”, pulseaudio can’t play files with AC3 audio. Unfortunately this includes all of my ripped DVDs, which were encoded with AC3 pass-through audio. If I play such a file in Miro, the video hangs after a few seconds. If I play it in Totem, the same happens but a pop-up is also displayed: “pa_stream_writable_size() failed: Connection terminated”.

I fixed it by downgrading Pulseaudio to the karmic version. Here is how.

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Moving an existing BackupPC partition to LVM

2010-05-06 20:39 +00:00 | 6 comments

I recently discussed how to use LVM to make a live copy of a BackupPC pool. That guide covers how to set up LVM on a new server with no data. But what if you already have a working BackupPC install, and you want to move your existing pool to LVM?

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The new mouse

2010-05-04 18:57 +00:00 | 2 comments

I’ve just bought a Logitech M205 wireless notebook mouse. Like my older MX650, this mouse uses the 27 MHz spectrum. The wheel doesn’t tilt, but it has a power switch and you can stow the receiver on the underside of the mouse. So far I’m very happy with it as a travel mouse. I’ll keep the MX650 for my regular work desk.

It seems Logitech is going entirely to 2.4 GHz for their mice. This is very disappointing, as the spectrum is so crowded. I’d love to switch, but the interference problems with wifi are horrible. The tiny “unifying receiver” used by their new devices is pretty slick too, but I doubt you could put an effective 27 MHz antenna in such a small dongle. Does anyone make a modern mouse which doesn’t use 2.4 GHz or bluetooth?

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Using LVM to make a live copy of a BackupPC pool

2010-04-23 20:32 +00:00 | 4 comments

“How do I backup my BackupPC pool” is perhaps the most common topic of discussion on the backuppc-users mailing list. BackupPC stores all files in a common compressed pool (cpool, although I’ll use simply “pool” for this discussion), and maintains trees of hardlinks into the pool for each backup host. Therefore BackupPC requires a Linux/Unix filesystem. If you want to back up the BackupPC server itself, you must duplicate the pool, and the hardlinks to it.

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Troubleshooting path MTU problems

2010-04-08 20:26 +00:00 | 1 comment

Not long ago we started having very unusual issues our email servers. Mail would be inexplicably held for delivery, bounce back, or fail to send for hours and then send without issue later. Some users couldn’t fetch email by POP until they restarted their mail client. We investigated the mail software, but weeks of investigation turned up nothing.

Around the same time, we also experienced intermittent problems logging in to MSN Messenger, and some users complained of issues accessing certain web pages, including a lot of HTTPS links. I began to suspect these were related.

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Firefox extension: Open With

2010-03-30 07:12 +00:00 | No comments

Some time ago I released a simple Firefox extension, Open With Konqueror. In the time since I released it, a new version of KDE and the Crystal icon set have been released, as well as a slew of new “Open With X”-type extensions. Open With Konqueror is simply obsolete.

I recommend you install Open With, a generic extension capable of opening the current page or selected link with any application. KDE users can simply open the extension preferences, select the “Manual Entries” tab, select “Add”, and enter “/usr/bin/konqueror”.

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iptables firewall templates

2010-03-29 18:39 +00:00 | 2 comments

I use iptables firewalls on every server I administer, including all of our core routers (which run Linux too). There are lots of tools to easily configure a firewall. For simple tasks, Ubuntu now installs ufw by default, which has both command-line and GUI tools. For servers, consider Webmin.

If you want to do something more complicated, or prefer editing iptables rules yourself, you’ll have to do it by hand. When I first started doing this I found a template online and edited it to suit my need. Over time I’ve learned a lot more about iptables, and my templates have evolved.

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Flying without a net: safe techniques for working remotely

2010-02-28 22:16 +00:00 | No comments

I try to post a few times each month, but somehow January (and most of February) fell through the cracks. Lately I’ve been busy with operational tasks, which hasn’t left me much room for engineering. I haven’t solved any particularly hard or unusual problems, which is usually what I write about. Instead, I’ll write about a routine problem that is nonetheless tricky enough to warrant discussion.

Most of the time I’m not in the same country as the servers I administer. Which means I can’t just drive down and fix something when it goes wrong. It also means that making changes to the network is particularly dangerous. So is updating the kernel, initrd, or GRUB configuration. It is possible to leave a server in a state that requires you to be physically present to fix it. I call this kind of work “flying without a net”. Here are my techniques for safely working without console access.

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VLANs, bridges, and virtual machines

2010-02-20 12:44 +00:00 | 13 comments

We run several virtual machine host servers on a network with multiple VLANs. The virtual machines are members of different VLANs, but are not themselves aware of the VLAN. This is how we did it.

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