Category Archives: Linux

Tales of my climb up the Linux learning curve, on both desktop and server.

British Gas find a new way to annoy me…

As if they weren’t an inefficient enough organisation to deal with in other respects, today a division of British Gas asked me to send them a remittance advice to:

CardiffC&MFinance@centrica.com

Yes, that really is an ampersand in the local part. Sufficiently unusual that trying to send to it upset my default-configured installation of Exim:

rejected RCPT <CardiffC&MFinance@centrica.com>: restricted characters in address

You can tone down the (perfectly reasonable) check for these iffy characters by exempting centrica.com from it: edit /etc/exim4/conf.d/acl/30_exim4-config_check_rcpt and edit the domains line of the second ‘restricted characters in address’ ACL to read:

domains = !+local_domains : !centrica.com

India diary, day 5

In June/July 2010 I spent ten days travelling in Rajasthan, India with friends; this is my diary of the trip (full list of entries here).

I was quite ill today and spent it in the hotel feeling sorry for myself. Still; I had company – K also feeling pretty ropey. Happily we were both feeling a bit better by evening and resolved to press on in the morning for the third leg provided we felt no worse.

Slow outbound e-mail?

I’d noticed for years that sending outbound e-mail from Thunderbird to my server on port 587 took far longer than it should have – about six seconds of staring at the progress bar.

Today, I was finally bored enough to work out the cause: Exim is configured to perform ident checks, which take 5 seconds to time out. Since port 587 only accepts mail from authenticated users, we can disable the ident checks for it:

rfc1413_hosts = ${if eq{$interface_port}{25}{*}{! $sender_host_address}}

If you’re running Debian, change the above in /etc/exim4/conf.d/main/02_exim4-config_options.

A smartphone named Desire

After years of thinking about it, and even writing about it, I’ve finally bought myself a smartphone.

As I write, I’m coming to the end of my third week with my new HTC Desire S. And it hasn’t disappointed.

Carrying it around has proved less arduous than I imagined – although it weighs more than my clunky old Nokia 1100, it’s thinner and flatter, so it fits nicely in my shirt pocket. It gets quite warm when under heavy use (e.g. acting as a WiFi hotspot), but not unpleasantly so.

They’ve packed quite a lot into such a small case – in no particular order, we have FM radio, a 5 megapixel camera with LED flash which works quite well for basic snaps, a second front-facing camera for video calling (makes me look awful, but friends insist it’s accurate), GPS, a half-decent speaker, a headphone jack, a nice big touchscreen, and I’m told it also has a phone.

Typing on the on-screen keyboard has proven easier than I anticipated – even with my fat fingers, I can peck out a short e-mail with reasonable ease. The predictive/corrective text is actually surprisingly helpful here.

The built-in e-mail client is OK, if a little basic. It wouldn’t send outgoing mail via my Exim 4 server over TLS (a TLS packet with unexpected length was received), but I suspect that’s Debian’s fault for insisting that GNUTLS actually, er, works. I ditched the default client in favour of K9-Mail, which boasts PGP integration and is much more customizable. Apart from a few niggles with the UI, it does the job very well.

The browser works much as one would expect – even sites without a mobile option are surprisingly usable – the screen is a decent resolution for its size, and the usual gestures for zoom work well.

The music player worked straight out of the box when I copied some MP3s over, and the supplied headphones aren’t too shabby.

The ability to read bar codes and search online for the cheapest available version of the barcoded thing has proved endlessly amusing.

Irssi Connectbot deserves special mention for making IRC on the go dead easy.

One of the main reasons for opting for an Android phone were the tethering capabilities – with a couple of well-chosen taps, the phone can share its 3G internet connection by turning itself into a WiFi hotspot. This is one of the operations that makes it a bit warm, but it’s very handy if you’ve got a bigger computer with you, but no internet.

Battery life isn’t too bad given the capabilities of the device – it lasts a heavy day’s usage, and charges over USB from almost anything. They also throw in a standard wall-socket adapter too.

Android claims some IPv6 support, which I’ll report back on when my home IPv6 is raised from the dead. I’ve also got a few ideas for app development, so watch this space!

update-grub not working on your Debian Squeeze domU?

We‘ve been having a spot of bother with update-grub not working on our Debian Xen guests since upgrading them to squeeze.

The symptom: update-grub (as run after the installation of a new kernel package) fails because it’s ‘unable to find [a] GRUB drive for /dev/sda2 – check your device.map’. This happens using both grub-legacy and the new grub-pc package.

You’ll probably have run into this if your guests were created using xen-tools.

Skipping over the related bugs, the long and short of it seems to be:

  • The way Xen pokes /dev/sda1 and /dev/sda2 (which are probably LVMs on your dom0) into your guests without a corresponding block device confuses grub
  • grub used to be dumb enough to ignore the mysterious presence of ‘partitions’ with no block device and carry on anyway
  • The versions in Debian Squeeze are just clever enough to be dangerous and fall over in this situation

Happily, we’ve worked out the fix. Grub is hard-coded to do the right thing in this situation if your disk devices are called ‘/dev/xvd[a-z]’, so you need to:

  1. Fix all references to ‘/dev/sda2′ to read ‘/dev/xvda’ (and /dev/sda1 to /dev/xvdb). In practice this means grub’s menu.lst and possibly your /etc/fstab if that isn’t by UUID
  2. Edit the /etc/xen/guest-name file on the dom0 to rename the partitions (change the ‘root’ specifier and the lines in the ‘disk’ list)
  3. Destroy (sudo xm destroy) your guest. Note that you must destroy and recreate it; rebooting won’t give Xen a chance to rename the devices.
  4. Bring it up again with xm create -c config-file
  5. Profit.

When Sixxs met BytemarkDNS

Edit: Those of you coming across this post by googling for ‘Sixxs rDNS’ should note that Bytemark’s DNS service isn’t free unless you already have a server with them, but there are a number of free alternatives out there.

With IPv4 address space exhaustion practically upon us, I decided it was high time my house got IPv6. This is quite easy to do even if your ISP, like ours, doesn’t support it natively. Get a Sixxs tunnel, apply for a subnet, set up radvd on the Linux box behind your sofa (you do have one, right?) and there you are.

Even Windows XP can be trivially prodded into IPv6ing itself up, and my router seems not to mangle the radvd broadcasts so even wireless clients can have v6 if they support it.

What really impressed me, though, was what happened when I wanted to set up reverse DNS for my new Sixxs subnet. I’ve been assigned 2a01:348:1af::/48 and the Sixxs page tells you that you’ll need your own DNS server to host the necessary records. I don’t run my own DNS; I use Bytemark’s content DNS service.

I wasn’t expecting Bytemark to support adding rDNS records for random IPv6 /64s, however as it turns out, once you work out what the TinyDNS file needs to look like:

# IPv6 rDNS authority for Sixxs subnet 2a01:348:1af::/48

.f.a.1.0.8.4.3.0.1.0.a.2.ip6.arpa::a.ns.bytemark.co.uk
.f.a.1.0.8.4.3.0.1.0.a.2.ip6.arpa::b.ns.bytemark.co.uk
.f.a.1.0.8.4.3.0.1.0.a.2.ip6.arpa::c.ns.bytemark.co.uk

# Machines in the first /64 (home network)
6router.ipv6.dnorth.net:2a01034801af00000000000000000001:8640

… it Just Works:

$ host 2a01:348:1af::1
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.f.a.1.0.8.4.3.0.1.0.a.2.ip6.arpa domain name pointer router.ipv6.dnorth.net.

Nice one, Bytemark!

2011 geek wishlist

In no particular order…

  • That Debian Squeeze will release in Q1 2011
  • That I’ll discover a J2EE Servlet Container which isn’t totally horrible
  • That some kind of reconciliation between the JCP and Apache will occur
  • That Java 7 won’t be delayed forever
  • That Python 3 will get adopted faster than PHP 5 or Java 1.5 did
  • That we’ll finally see some major UK ISPs offering IPv6

Leave a comment if you can see anything I’ve missed, and we’ll check on them all at the end of the year…

Converting Word documents to PDF with OpenOffice and Python

The problem

A word document (plain old .doc, not 2007) should be received by e-mail, fed to a script, turned into a PDF and published on a website.

At my disposal

My server running Debian ‘Lenny’, which does not have a display of any kind.

How hard can it be?

Harder than it should have been, as ever. Here are my steps:

# aptitude install python-uno xvfb openoffice.org-java-common openoffice.org-writer unoconv

You’ll note the inclusion of Xvfb there, because it turns out that “headless” mode in OpenOffice isn’t really headless at all. Sigh. Also sigh some more at the broken dependencies of the unoconv Debian package.

Now we can write our script to do the actual conversion. Shame it took twice as long as it should have…

Fun with CurrentCost

Five years after the cool kids first started jumping on the bandwagon, I’ve got myself a CurrentCost CC128 (Southern Electric send them to some customers for free, it seems – e.g. my granddad who didn’t want it).

So, with the addition of an eight quid data cable and the Linux box running in my lounge, may I present my electricity usage graphs. Bear in mind that these are (at the time of writing) for a five-bedroom house in central Oxford.

The parser for the XML output of the device I’m using is this one – just swap “COM20″ for “/dev/ttyUSB0″ in their testrun script and fix it to ignore empty lines read from the serial port, and you’re in business. I then hackdapted this RRDTool tutorial to plot the graphs.

Spotify on Linux problems?

Dear lazyweb, does anyone else find that Spotify mysteriously hangs at the “logging in” stage when run under Wine? This suddenly happend on both my Linux boxes after it had been working fine for weeks.

Various posts on the Ubuntu forums suggested firewall issues, but nothing had changed, and Spotify continue to work on Windows on both machines.

In the end, I applied the nuclear fix of

$ mv ~/.wine ~/.wine-with-broken-spotify

and reinstalling Spotify from scratch, which worked. Might not be so handy for anyone with other apps under Wine, though.