CentOS – update / install PHP 5.2
CentOS 5.x comes with PHP 5.1, which is too old for some applications.
Here is a quickie on how to update it using CentOS development / testing repository.
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Cipher benchmark for dm-crypt / LUKS
Do you have a netbook, laptop, desktop or a server which uses dm-crypt to encrypt data on your disks? If yes, you will probably find that raw hard disk performance is better than encrypted disk performance. You will notice that especially on slow machines (i.e. netbooks), but also high-performance servers, because of the current dm-crypt design.
What cipher in the Linux kernel provides you with the best performance?
Setting up DKIMproxy with Exim for DKIM and DomainKeys signing
Was your mail ever rejected or tagged as spam because it didn’t have a DKIM signature? You could enable DKIM-signing in Exim, but then, some older mail systems may still use DomainKeys.
Currently, Exim does not support signing mails with both DomainKeys and DKIM. You have to pick one of them, unless you do some tricks with patching Exim or connecting back to itself.
Still though, such setup is not perfect: Exim does not wrap its DomainKeys signature, which may result in SpamAssassin installations tagging your mail with HEAD_LONG rule (“Message headers are very long”) and assigning it 2.5 spam points.
So how to sign mail with DKIM and DomainKeys without negative consequences of being tagged by SpamAssassin for very long headers? DKIMproxy to the rescue!
Exim configuration
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DRDB and link compression
Recently I was setting up DRBD (in short: “block devices designed as a building block to form high availability (HA) clusters”) between two data centers.
DRBD doesn’t apply any form of compression on the data that is replicated; is it a good idea to enable compression in the VPN link if you replicate your data with DRBD over Internet? Here is a quick test.
Linux and Lumix digital cameras
Do you happen to be running a Linux distribution and have Panasonic Lumix digital camera?
If yes, you may have problems downloading photos from it – depending on your kernel and udev settings, or more generally, on Linux distribution used.
The tips from below may help you.
Accessing Windows console remotely from Linux
Have you ever needed to execute a command or to connect to an interactive text console on a remote Windows station?
Probably several times, and usually, you had to log in using either VNC or RDP (Remote Desktop Protocol – Microsoft Terminal Services). If you’re used to SSH, you may wonder why the overhead of a complete desktop is needed just to start a few text commands.
Of course, there are free and commercial SSH servers for Windows, but one problem with them is that they have to be installed separately. Which may be too much work for a one-off task now and then. Are there any other methods of accessing a remote Window text console from your Linux station?
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HP loves Linux the Windows way
Quite recently, HP announced a new line of thin clients with Debian Etch 4.0 preinstalled. That’s certainly good news for Linux, but why HP’s Linux support is Windows only?
New wave of Blogspot spam
Did you also notice an increase of unwanted “Blogspot messages” either in your inbox or spam folder? These messages contain a link to http://<some_random_letters_and_numbers>.blogspot.com, but in the end, you end up on entirely different page – why? Let’s try to analyse the page and find out.
CPUfreq and dm-crypt performance problems
Is using CPU frequency scaling on a server a good idea? After all, some servers don’t do very much at night, so why shouldn’t we scale CPU frequency down when servers are idle?
Unfortunately, simple tests revealed serious performance problems when reading from a drive encrypted with dm-crypt / LUKS – here is why (with a simple solution).
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Using fault injection
Lately, I was playing with logfs, a scalable flash filesystem. It’s interesting because of at least three reasons:
- it can compress data transparently,
- it provides wear levelling,
- it works with block devices.
In other words, a perfect filesystem to use for all flash-based devices, like USB-sticks.
Any filesystem should aim for high reliability, no doubt about it. But how to test it? Linux kernel provides a nice feature called “fault injection”. If Documentation/fault-injection/fault-injection.txt isn’t clear for you after the first read, here’s a quick help.