Err... what? It seems that twitter requires you to have Javascript enabled in order to view 140 characters of someone's worthless drivel. Otherwise you get a blank page. The mind boggles.

A little while ago, someone on Slashdot pointed me at the Sale of Goods Act in relation to purchased electronics. The act, for those unfamiliar with it, requires that goods be 'suitable for the purpose for which sold.' This is a fairly broad term, but it basically means that they must be able to do anything that the seller claims that they can do. Under this law, you have 6 years from the date of purchase to file a lawsuit if the item does not match the claims.

This was relevant to me because my MacBook Pro is now out of warranty and the battery is dying. Looking in the System Profiler, its full charge capacity was showing up as 1476mAh after 56 charges. When new, it was 5500mAh. These numbers don't mean anything by themselves, but Apple claims that their batteries retain 80% of their full charge capacity after 300 charge cycles. Claiming this means that a battery that does not retain 4400mAh after 300 charge cycles is not suitable for the purpose for which sold, and they are legally required to refund or replace it (irrespective of the time that has elapsed, although I can only sue them if they don't within 6 years of the time of sale).

I called their support line and was put through to an Indian woman, who explained that the warranty had expired. I quoted the relevant parts of law to her, and (after being kept on hold for a bit), was transferred to someone senior. He very quickly agreed to send out a replacement battery.

Interestingly, he did not ask that the original battery be sent out, nor that I provide a credit card number where I would be billed if the battery turned out not to be defective. I've had two batteries replaced in warranty, and this was standard procedure then, so apparently I get better service out of warranty. I don't have a great deal of use for a battery that only lasts about 35 minutes on a full charge, but I'll probably keep it as a spare.

As always, it pays to know the law. It's a shame that Apple, which claims to be a customer-focussed company, doesn't educate its support team about this though. Possibly the Indian call centre deals with people from everywhere English speaking, while the Irish one only deals with people in the UK and Ireland, so the people there are more familiar with British law, but if I had not quoted the relevant act then I would have been charged £99 for a battery, on top of the £1.50 it cost to call their support line for half an hour.

Once you've been around computers for a while, you get to recognise certain sounds. Such as the pop followed by the spinning down of fans, and the ominous silence that emanates from the box that's supposed to be your fileserver. Arse. I was off work yesterday due to a nasty cold, and the last thing I wanted to be doing was rebuilding the server. Fortunately, it turned out to be just the power supply. I'd been worried that it was going to have taken out the motherboard too. It did take a hard drive with it on the way out, but fortunately that wasn't fatal. The RAID rebuild ran OK overnight, and now we're back to normal.

Does anyone know of a good solution for zooming/panning static images for turning into a video? The so called Ken Burns effect? It must work on Linux, and should ideally be open source. The pan in openshot doesn't seem to work, and the zoom is too jerky to be useful. I can write my own fairly easily if I have to, but I'd rather not reinvent the wheel if I can avoid it.

Today I learned that my window manager hotkey to bring the focused window to the front doesn't work when the thing that's obscuring the window in question is a post-it note on the monitor. D'oh!

http://www.webmproject.org

It's what we were all hoping for, and I'm pleased that it's come to pass. It's not perfect, and I don't agree with all of their decisions. However, even an imperfect alternative to the current H.264 situation is a massive improvement. I'm pleased they've gone for a full stack solution of not only VP8 but also Matroska(-ish) and Vorbis, too. If nothing else, it's likely to mean that a) Vorbis will be shipped by default on most platforms[1], and b) hardware support for both VP8 and Vorbis should be widespread in the very near future. Further, there's a commitment to transcode all of the existing videos on YouTube. That's a massive endorsement. Of course, the risk with that is the reduced quality that will come from three or more lossy transforms, but given that they've announced it, they're clearly not too concerned about that. The future's looking very bright indeed.

[1] Or will it? I've yet to see any official response from Microsoft or Apple on this. But it's going to be hard for them to ship something that won't play YouTube videos by default. Of course, in the short and probably medium term, YouTube will continue to offer videos in other formats as well. But we'll see how it plays out in the long term.

I went to an interesting talk by Eng Lim Goh of SGI on Thursday, demonstrating their Ultraviolet systems. Very cool. While there are bigger and faster computers on the planet, they're all technically clusters rather than a single computer. The SGI machines can have 4096 CPUs and 16TB of RAM running under a single Linux kernel. Nice.

Also interesting to see the stats on when their systems were delivered to McLaren and Brawn, and where the performance of those cars was afterwards. I know there's more to F1 than CFD, but it certainly plays a large part these days.

Some time around 2005, Slashdot ran an article about a new hosting company, MacMiniColo that was taking advantage of the new machines that Apple had just released to offer cheap hosting. I got in contact with them, and a little while later, I had a Mac Mini, sitting in a rack somewhere, running OpenBSD and acting as my dedicated server. A 1.42GHz G4 CPU, 512MB of RAM, and an 80GB disk was (and still is) more than adequate for my needs. The biggest load on it is eJabberd, and even that only used under 1% of the CPU.

I had really great service from these people. The hard drive failed a little under a year after I bought the Mini, and Apple refused to honour the warranty because they couldn't find the records of the sale (then, a few weeks later, they could, but by then it was out of the warranty period). MacMiniColo replaced the disk for me at their own expense.

After five years with them, however, I had a little look around and noticed that VPS hosting has gone down in price a lot. I've written a book on Xen, so I thought I might try a Xen-based VPS now that FreeBSD has Xen support.

GigaTux only claims to offer Linux, but I dropped them an email and they were happy to install FreeBSD for me. I still haven't tried the Xen-enabled kernel yet; they installed the stock x86-64 kernel in an HVM domain for me and performance has been fantastic.

I'm sharing a server with 64 other guests and in spite of that performance tends to be better than my ageing Mac Mini. I was getting 1000IOPS while untaring the ports tree, which is far more than the Mini's old 2.5" laptop drive could handle, and is amazing considering that it's going via the slow, QEMU-derived, emulated device, rather than the fast PV driver. I've been installing software from ports, so everything is compiled on the machine, and even that has been fast.

And my Mini? They found someone else who wants it, and offered me about a third of what I paid for it originally - not bad depreciation after five years of constant use. Shipping it back to the UK would have cost almost as much as buying one on eBay, so I sold it on. Hopefully someone else will get some good use out of it.

As an aside, I've been really impressed by how well OpenBSD works on Mac/PowerPC hardware. If you've got an old Mac Mini lying around, chuck OpenBSD on it and you've got a reasonable low-volume server. The newer ones, of course, are x86 hardware, so will run just about anything.

The UK's Information Commissioner has ruled that research data must be made public. I have little sympathy for the likes of Keenan. But I have even less sympathy for so called scientists who refuse to make their data available for others to study. This isn't just about climate change, either, but about science in general. The recent spate of falsified results in Chinese and Korean papers should be ample evidence that data needs to be made public so that results can be independently verified. That's what science is all about.

There are two reasons why I don't use GNU/Linux: One is GNU, the other is Linux. Of these, the larger reason is GNU, and specifically the glibc part. The most recent reinforcement of this is Ulrich Drepper's inability to read the C specification.

For those not familiar with the C specification, all identifiers that start with an underscore are reserved for the implementation (see section 17.4.3.1.2). You should never use them in your own code, because your compiler is completely free to do whatever it wants with them. By convention, single underscores are used for global non-standard libc extensions and double underscores are used for compiler builtins.

You can find a number of these in existing compiler. Microsoft exposes SEH with keywords like __try. GCC provides __asm for inline assembly, ICC uses __cpuid for accessing the CPUID instruction, and so on. Clang added __block as a type specifier for their variables that are copied to the heap for use by blocks (closures).

Unfortunately, it turns out that the glibc headers use __block as a parameter name. There are several things wrong with this. One is that they use double underscores at all. By convention, these are reserved for the compiler, while single underscores are reserved for the libc. The second is that they used underscores at all in a parameter. Parameter names are not in the global scope, so they can be anything to prevent name clashes.

The result of this is that, if you use glibc, you can't also use blocks. This is a shame, because we (Etoile) were shipping a working blocks implementation six months before Apple. Well, working on *BSD and Solaris (and probably Windows, QNX and Symbian with PIPS, but not tested there). This problem means that it doesn't work on GNU/Linux.

No problem for me. I only use platforms with libc implementations written by people who can read specs. It may be a problem for some of you, if you use a broken platform with a libc maintained by someone who'd rather salvage his ego than fix a problem, and if it is then I'm sorry for you. My suggestion is that you remember that there are other options.

My backup failed last night, because the device was read only:

building file list ... done
rsync: delete_file: unlink "/backup/local/shared/camera/2009-08-24--foq/img_0507.jpg" failed: Read-only file system (30)
rsync: delete_file: unlink "/backup/local/shared/camera/2009-08-24--foq/.xvpics/img_0507.jpg" failed: Read-only file system (30)

That's never a good sign. Looking through the logs, I see a number of ATA errors, starting with a timeout, a device error, and a bunch of HSM violations. A few examples:

Mar 22 07:56:03 riva kernel: ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
Mar 22 07:56:03 riva kernel: ata2.00: cmd 25/00:00:87:d1:86/00:02:03:00:00/e0 tag 0 dma 262144 in
Mar 22 07:56:03 riva kernel: res 40/00:00:00:00:00/ff:ff:ff:ff:ff/00 Emask 0x4 (timeout)
Mar 22 07:56:03 riva kernel: ata2.00: status: { DRDY }
Mar 22 07:56:03 riva kernel: ata2: hard resetting link
Mar 22 07:56:03 riva kernel: ata2: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
Mar 22 07:56:03 riva kernel: ata2.00: configured for UDMA/33
Mar 22 07:56:03 riva kernel: ata2: EH complete
Mar 22 07:56:03 riva kernel: SCSI device sdb: 1465149168 512-byte hdwr sectors (750156 MB)
Mar 22 07:56:03 riva kernel: sdb: Write Protect is off
Mar 22 07:56:03 riva kernel: SCSI device sdb: drive cache: write back

Mar 22 07:59:05 riva kernel: ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Mar 22 07:59:05 riva kernel: ata2.00: BMDMA2 stat 0x6d0009
Mar 22 07:59:05 riva kernel: ata2.00: cmd 25/00:00:df:ce:87/00:02:03:00:00/e0 tag 0 dma 262144 in
Mar 22 07:59:05 riva kernel: res 51/04:80:5f:cf:87/00:01:03:00:00/e0 Emask 0x1 (device error)
Mar 22 07:59:05 riva kernel: ata2.00: status: { DRDY ERR }
Mar 22 07:59:05 riva kernel: ata2.00: error: { ABRT }
Mar 22 07:59:05 riva kernel: ata2.00: configured for UDMA/33
Mar 22 07:59:05 riva kernel: ata2: EH complete
Mar 22 07:59:05 riva kernel: SCSI device sdb: 1465149168 512-byte hdwr sectors (750156 MB)
Mar 22 07:59:05 riva kernel: sdb: Write Protect is off
Mar 22 07:59:05 riva kernel: SCSI device sdb: drive cache: write back

Mar 22 08:01:15 riva kernel: ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
Mar 22 08:01:15 riva kernel: ata2.00: cmd 25/00:00:ff:1e:88/00:02:03:00:00/e0 tag 0 dma 262144 in
Mar 22 08:01:15 riva kernel: res ff/ff:ff:ff:ff:ff/ff:ff:ff:ff:ff/ff Emask 0x2 (HSM violation)
Mar 22 08:01:15 riva kernel: ata2.00: status: { Busy }
Mar 22 08:01:15 riva kernel: ata2.00: error: { ICRC UNC IDNF ABRT }
Mar 22 08:01:15 riva kernel: ata2: hard resetting link
Mar 22 08:01:15 riva kernel: ata2: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
Mar 22 08:01:15 riva kernel: ata2.00: configured for UDMA/33
Mar 22 08:01:15 riva kernel: ata2: EH complete
Mar 22 08:01:15 riva kernel: SCSI device sdb: 1465149168 512-byte hdwr sectors (750156 MB)
Mar 22 08:01:15 riva kernel: sdb: Write Protect is off
Mar 22 08:01:15 riva kernel: SCSI device sdb: drive cache: write back

SMART doesn't seem to be much help here, with the device refusing to run anything but the mandatory offline test:

riva:~# smartctl --test=offline /dev/sdb
smartctl version 5.36 [i686-redhat-linux-gnu] Copyright (C) 2002-6 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

Default Self Test Successful
riva:~# smartctl --test=short /dev/sdb
smartctl version 5.36 [i686-redhat-linux-gnu] Copyright (C) 2002-6 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

Short offline self test failed [unsupported field in scsi command]
riva:~# smartctl --test=long /dev/sdb
smartctl version 5.36 [i686-redhat-linux-gnu] Copyright (C) 2002-6 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

Long (extended) offline self test failed [unsupported field in scsi command]

It's a Seagate drive:

Host: scsi1 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: ST3750528AS Rev: CC38
Type: Direct-Access ANSI SCSI revision: 05

I'm running 2.6.18-128.4.1.el5 on CentOS 5.

Any ideas? Does anyone know enough about the ATA spec to tell me what these errors actually mean? Is this a genuine hardware failure? If so, where's it likely to be? Drive? Controller? Cable? The drive is only a few weeks old, so while sometimes shit happens, I want to investigate the (probably more likely) alternatives as well.

How can I get a <td> to be a containing block? Section 10.1 of the spec implies that just giving it position: relative; should be sufficient. But that's completely bypassed, and the search carries on up the element hierarchy. I kludged it by putting a relatively positioned <div> inside the cell, but it's frustrating to have to resort to such workarounds. Anyone know why it didn't work? There's no mention in the spec of table elements being given special treatment when it comes to containing blocks. Indeed, it explicitly mentions that table cells should work. But they don't (in Firefox 3 and Opera 10, at least).

And why oh why doesn't <tbody> nest? I want to refer to part of a table and manipulate it with some Javascript (mostly just to show or hide it in response to user actions). But I can't just stick the relevant bits in a <tbody> and select by that because the table already contains several tbodies. Thus I'm once again stuck in workaround hell, trying to tag each tbody with an appropriate class, so I can iterate over them and check if I'm interested in each one. Further, because I'm dynamically adding and removing parts of the table, I need to check at the time I add to the table whether the bit I'm adding should be visible or not. Life would be so much easier if I could just stick it in an appropriate <tbody> further up the hierarchy, and then mark the whole lot visible or otherwise. But I guess that would be far too easy :-(

The time has come for a new laptop. But how do I find the right one? My requirements are minimal. Namely, I need a large screen, decent battery life and a low price. Surely there must be a laptop comparison site somewhere that lets me enter my specs and it'll give some recommendations, right? Yes, I can go to Toshiba's site and there's a great tool that does exactly that. Dell's and Acer's are adequate but not quite as good as Toshiba, and HP don't have one at all. But all of them are restricted to a single brand (as you'd expect). Where is the cross brand equivalent? Further, there are no doubt brands I've never heard of that I might be interested in, and without knowing who they are, I can't go to their web sites to check their offerings even if I wanted to.

Any CPU will be more than sufficient for my needs. The screen needs to be at least 17", and not gloss (which sadly seems to rule out the otherwise promising models from Samsung). I need 2GB RAM, and I don't want to be paying more than £500. A bit of digging reveals that all of the major players have models that meet those requirements. But I still have the nagging feeling that I'm missing out of the "right" model simply because I don't know about it. Where should I be looking?

Oh, and it won't have an Apple badge, so don't even consider suggesting that...

I don't know why, but I always get a warm feeling when I configure policy routing. Under Linux, iproute2 makes it almost trivially easy, so there isn't any real reason for it, but when I see my packets going off where I tell them to, I always seem to have a sense of accomplishment that's disproportionate to the amount of difficulty involved.

We had a power cut this morning. The second in two days (yesterday was at work, this one was at home). It was bigger than I thought, too, extending at least as far as the tube station, as I found out when I tried to go to work (trains weren't stopping due to the lack of power at the station). But it wasn't such a big deal. I went to work, reasonably confident that by the time I got home, the power would be restored. Sure enough, I returned home to find all the machines powered up. The main server was sitting waiting for a root password because the journal recovery had failed, and it needed an explicit fsck. Fair enough. But after fixing that, everything appeared to be back to normal. Except is seemed more than a little sluggish. You see, after the return of power, my ADSL router had decided to connect at a whopping 256Kb/s down[1]. Nor was it just a freak of the line state when the power returned. Disconnecting and reconnecting gives me exactly the same speed. Naturally, my utterly useless ISP is closed at times when it would actually be useful to call them. So I'll have to wait until tomorrow morning to get them to try testing the line, and generally failing to have a clue about anything, if past experiences with their technical support team are anything to go by :-(

[1] And 512Kb/s up, FWIW. The A in ADSL usually means you get much better bandwidth down than up. Not so here, it seems...