Archive for Linux


I’ve just started using BackupPC to backup my file server. It’s a disk-based solution – so if you want to archive to removable media such as DVD-R or tape, you need a separate archive step.

The advantage of BackupPC is supposed to be that it can do remote backups of every machine on your network, without needing special software to be loaded on each client machine. That’s true, but a little misleading. If you want to maintain security, then you need to do a little bit of setup on each client.

Configuration seemed unnecessarily awkward. Here’s what I did. Read the rest of this entry »

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I’ve been Joe-jobbed.

Some low-life spammer has started forging messages from my domain. My mail server is receiving many deliveries per second, all bounces for users that don’t exist at my domain. Unfortunately I have (had) a catch-all alias that put mails for all unknown users into my mailbox. Ooops.

I’m in the habit of making up e-mail addresses within my domain, in order to keep track of where people get hold of my e-mail address. So if Amazon want my e-mail address, I’ll tell them it’s That mail will still get to me because of my catch-all alias, but I’ll be able to tell that something fishy’s going on if somebody else starts to send me mails to that address. Read the rest of this entry »

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The linkfile and SUID mystery.

How does linkfile(1) know what the original user ID was, when it’s run from inside a SUID program? Well, it’s a mystery to me anyway.

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Using OSX Mail with Exim

My laptop is usually connected behind a restrictive firewall. Since port 25 is blocked, I can’t send mail the normal way. Instead I just build a tunnel to my mail server using ssh -Nf -L25025:localhost:25 mailhost and configure Mail’s SMTP server to point to localhost port 25025. Usually this works fine, but sometimes I get unexplained connection failures.

Finally, I have unearthed the cause of the problem. Read the rest of this entry »

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Building Debian Packages from Source

This is already well documented in the Debian FAQ, but here goes…

To get the source to the current directory:

$ apt-get source PACKAGE

Read the rest of this entry »

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Spam Blocking

I use Exim version 4 on Debian Sarge, and I want to start using a “Real-time Black-hole List” (RBL) service. How the hell do I do that? Read the rest of this entry »

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Recording from Realplayer

One of the great things about Linux is that it’s an open platform, so you can get round stupid DRM nonsense. The BBC produces lots of great stuff in real media format, but some of it isn’t made available to people outside the UK. I want to review some of this material, and I want my review to be available outside the UK.

So, I need to take some of the audio from a RealPlayer stream and store it as MP3. Read the rest of this entry »

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Dual Boot Windows with Grub

Here’s the magic formula to boot into a Windows (slave) hard drive from Grub. Windows thinks that it’s installed on the master, but I’ve moved it over to the slave position. Sadly it refused to boot from there. The trick is to tell the BIOS to remap the drives, and thereby fool Windows into thinking it’s on the master. Read the rest of this entry »

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dig: segmentation fault on UML

The ‘Native Posix Thread Library’ (NPTL) is not supported by User Mode Linux (UML). NPTL is the much-vaunted ‘new’ threading implementation in the Linux 2.6.x kernels. There can be many symptoms of this problem, but the one I seem to always get is a crash whenever a program tries to resolve a host name. Whatever the symptoms, you will only see problems with a 2.6.x UML kernel – the same filesystem will work correctly when you boot it with a 2.4.x UML kernel.

The solution: Disable the new threading by renaming /lib/tls to /lib/tls.DISABLED on the guest, and reboot UML.

Although this solution is simple, it’s not permanent (at least on Debian). apt will continue to re-create the /lib/tls directory whenever it is updated. Then you’ll start to see crashes again when you next reboot.

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