./martijn

tweetbot2flickr

2012-05-30T19:31:27Z

If your using both Tweetbot and Flickr, you might like my tweetbot2flickr webservice.

Plus addressing with Postfix

2012-05-01T19:05:43Z

Using “user+foo@example.com” style addresses seems to be disabled in Postfix by default. One single parameter called the recipient_delimiter parameter needs to be set to make use of this kind of addressing in Postfix. Just add this to the main.cf file and reload Postfix:

recipient_delimiter = +

Alternatively, some other characters like ‘-’ or ‘_’ can be used here.

Nice to know when using .forward files in email-delivery; When using a ”user+foo@example.com” style address, the system will first check if there is a .forward+foo file before checking for a .forward file.

PaulPaulito.com Linux training

2012-04-10T19:15:09Z

Just gave PaulPaulito.com a try. All I can say is that it is a great way to learn Linux or prepare for the LPIC-1 exam. The screencasts PaulPaulito.com offers are in exceptional quality and are a great method to learn Linux.
If your looking for a good resource to learn Linux you should definitely give it a go!

Prepare voor RHCE Certification

2012-04-10T19:06:28Z

Red Hat’s RHCE certification is one of the most popular certifications in the IT market at the moment. There are different method in preparing for both the RHCSA en RHCE exams. Which works best depends on the individual. I decided to go for self-study, using several study resources. In this post, I’ll describe the resources I’ve used in preparation for the Red Hat ex200 and ex300 exams. And yes, I’ve passed both exams with a very decent score, which makes this a proven method of preparation .

For starters, the objectives for both RHCSA and the RHCE exams can be found on the Red Hat website. Make sure you know them. Red Hat also offers a free skills assessment, which is good to use as a baseline measurement.

Make sure you have a good lab environment. A laptop with sufficient memory and diskspace to house a minimum of three (RHEL 6, CentOS 6 or Scientific Linux 6) virtual machines. To study for the Virtualization/KVM objective, you’ll to run on bare-metal hardware that supports virtualization (eg. vmx on Intel CPU’s).

Next up, OpenRHCE is a public collaborative to create RHCE study-materials based on Red Hat published objectives – not on exam experiences or actual exam contents!
It’s a good resource for exam preparation. Make a check-out of the project on GitHub. You’ll find example labs and a broad coverage of the exam objectives.

What helped me probably most is the RHCSA/RHCE book by Michael Jang. Is a great book which covers all RHCSA/RHCE exam objectives in a clear way. The first half of the book covers preparation for the RHCSA exam, the second part the preparation for the RHCE exam.
The book comes with good knowledge tests at the beginning and end of each chapter and useful example materials and example labs on a DVD.

Good luck! .. and feel free to drop any questions about preparation for these Red Hat exams.

DVB-C via analoge TV bij Concepts. (Dutch)

2012-04-06T08:58:59Z

Mocht je beschikken over een FTTH (Glasvezel) aansluiting, dan is Concepts ICT een uitstekende Provider. Naast het digitale televisie aanbod, is het ook mogelijk om ‘ouderwets’ analoge TV te gebruiken. Er zit een Coax-aansluiting op het Genexys modem waarop het analoge signaal wordt uitgezonden.

Op het analoge TV net worden de standaard zenders ook digitaal aangeboden. Mocht je beschikken over een TV (of decoder) met DVB-C tuner, kun je de onderstaande gegevens gebruiken om de standaard zenders in SD kwaliteit digitaal te kijken.

Network-id : 07461
Fequency   : 304000 MHz
Modulation : 64 QAM
Scan freq. : 6875k/s

Resize an encrypted LVM logical volume

2012-03-13T22:54:22Z

Recently I had the challenge to resize an (dm-crypt, cryptsetup) encrypted LVM Logical Volume on Linux. While resizing a ‘plain’ Logical Volumes can’t get any easier, resizing an encrypted volumes involves a couple of more actions. Also, in contrast to un-encrypted Logical Volumes, the resizing of an encrypted volume can’t be done online – at certain moments an unmount is required.

These are the steps that worked out successfully for me; YMMV

First step – Determine the volume to be resized:

[root]# mount
(..)
/dev/mapper/crypt_srv on /srv type ext4 (rw)

Stop related services, unmount the mount point and run a filesystem check:

[root]# umount /srv
[root]# fsck.ext4 /dev/mapper/crypt_srv

Close the volume in dm-crypt:

[root]# cryptsetup luksClose /dev/mapper/crypt_srv

Perform the extend:

[root]# lvextend -l +1024 /dev/mapper/vg00-lv_srv

Re-open the volume in dm-crypt and make dm-crypt aware of the new blocks:

[root]# cryptsetup luksOpen /dev/mapper/vg00-lv_srv crypt_srv
[root]# cryptsetup --verbose resize crypt_srv

Check if it is possible to mount the volume, unmount again and perform a filesystem check:

[root]# mount /dev/mapper/crypt_srv /srv/
[root]# umount /srv
[root]# e2fsck -f /dev/mapper/crypt_srv

Now resize the filesystem itself (can also be done online), and mount the resized filesystem:

[root]# resize2fs /dev/mapper/crypt_srv
[root]# mount /dev/mapper/crypt_srv /srv

That’s all there is to it! Drop a comment to let me know how it worked out for you!

Vim anti-patterns

2012-03-18T20:15:57Z

Even if you think you can write a book on vim (or maybe you did), there’s always something new to learn.

http://blog.sanctum.geek.nz/vim-anti-patterns/

ownCloud 3.0

2012-02-04T18:43:38Z

The ownCloud project just released ownCloud 3.0. A feature-rich solution for personal file storage, sharing and personal information management.

ownCloud is written in PHP and uses a MySQL or SQLite backend. Setting up ownCloud on your own server or hosting-space is a matter of minutes.

ownCloud 3.0 Release Announcement

Fix “IPv6 addrconf: prefix with wrong length” messages in Linux

2012-01-24T19:31:27Z

Glancing trough the system-logging of one of my Internet VPS nodes, I noticed that the Kernel Ring Buffer (dmesg) was quite noisy with IPv6 Router Advertisement messages as:

"IPv6 addrconf: prefix with wrong length 48"

Some research learned me that this isn’t a harmful error – more a cosmetic one. It’s root cause are IPv6 RA’s from a device on the network that is advertising something indifferent than your host is configured to.

If you maintain a more static configured IPv6 setup, and your IPv6 setup is working as designed for you network, you can safely choose to disable those detections. Here’s how to disable IPv6 to accept Router Advertisements and IPv6 Auto-configuration at runtime:

echo 0 > /proc/sys/net/ipv6/conf/all/accept_ra
echo 0 > /proc/sys/net/ipv6/conf/all/autoconf

Or per interface:

echo 0 > /proc/sys/net/ipv6/conf/eth0/accept_ra
echo 0 > /proc/sys/net/ipv6/conf/eth0/autoconf

To make this setting survive a reboot, you can make it permanent with:

net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.all.autoconf = 0

Or again, per interface:

net.ipv6.conf.eth0.accept_ra = 0
net.ipv6.conf.eth0.autoconf = 0

If you’re running RHEL or CentOS, like my VPS was, you can add these options to “/etc/sysctl.conf”.

Migrate Apple Time Capsules

2012-01-14T20:33:57Z

Just replaced my Apple Time Capsule with a newer one. Here’s what I found to be the best approach in moving data and time-machine backups to the new unit.

Hook-up your Mac to an ethernet-port of the old time-capsule. You can use Network Utility or ifconfig to verify gigabit connectivity. This is something you do not want to do over the wireless network.
Second step is connecting a switch-port of the old time-capsule to a switch-port of the new unit. You can use both a straight or crossed networkcable.

Disable time-machine on your Mac (Time Machine in System Preferences) and make use no machine in the network is using the disk of the old unit.

Mount both time-capsules on you Mac from Finder. Just click the volumes on both units. Browse to the root of the data-volume on the old unit. Select and drag the time-machine images from the old unit to the new unit.
You can copy the remaining data to the new unit in one or multiple batches.

Next step is optional. It’s resizing the Time Machine sparse-bundle (eg., backup disk-image). If you upgrade from, let’s say, a 1TB Time Capsule to a 2TB unit you Time Machine sparse-bundle is max. 1TB in size. If you expect a large Time Machine backup you can use the command ‘sudo hdiutil resize -size 1024g /Volumes/<time capsule name>/machinename.sparsebundle’ from Terminal.app to resize the sparse-bundle.

Apple FileVault 2 on older Mac’s with SSD

2011-10-22T06:20:23Z

Apple’s FileVault2 is a valuable addition to OS X Lion. It offers full disk-encryption which I find to be something mandatory on notebooks these days.

On ‘newer’ Apple MacBooks, say since the Intel i5 and i7 architecture, FileVault 2 has barely no impact on disk I/O performance. OS X Daily has a fairly excessive benchmark report in which this is pointed out. I use a mid-2011 MacBook Air with an Intel i7 CPU, which benchmarks 200+ MB/s on both write and read with FileVault 2 turned on. Quite impressive speeds.

BlackMagic Disk Speed Test – a free Mac App Store app.

On ‘older’ types of MacBooks, say Intel Core 2 Duo architecture, FileVault 2 has a bigger impact on disk I/O performance.

In my case, I’ve enabled FileVault 2 on a late-2008 MacBook Pro (Intel Core 2 Duo CPU) with an OCZ Vertex 2 SSD disk. Without disk-encryption this SSD reaches over 200MB/s in both read and write speeds in OS X Lion. With FileVault2 enabled both speeds are seriously affected. Write speeds is impacted by 50% and Read speed with about 25%.

Still, very acceptable speeds. But definitely a factor when considering to use FileVault 2 on older types of MacBooks.

Resources:

FileVault 2 Benchmarks Show Full Disk Encryption is Faster Than Ever in OS X Lion
MacBook Air SSD Benchmarks: 2010 vs 2011 vs Lion Encryption