Julian Kessel's Blog

Horde 4 Calendar Export

Julian Kessel — Fri, 18 May 2012 17:42:46 +0000

Just a quick note on exporting a user’s Calendar from Horde 4.
Unlike every site I stumbled upon searching for this solution suggests, the right way to accomplish it is a bit hidden:
https://your_horde_install/kronolith/#calendar => left Sidebar “My Calendars” => triangle pointing right => popup’s tabbar => “Export” Tab

My experience with FTP backups using lftp

Julian Kessel — Sat, 14 Apr 2012 09:41:34 +0000

What I learned from the situation of doing a admittedly huge backup over FTP:

do NOT use lftp (v 3.1.3 at least) for backing up large sites (≈28M files) in my case

My experience with it was very bad: after having about 90% of the data transferred over multiple days, lftp’s CPU usage went to 99% and the only message below the line of invocation was:
... Cache:...
I couldn’t find information to that error anywhere, so I cancelled the process (which was not responding to SIGTERM anymore) sending a SIGKILL and started rsync.
Too bad that I still don’t know at which file lftp was crashing, since it did its \r and overwrote the line already as I mentioned…
Then came the next problem: the rsync version 2.6.4 (the newest release is 3.0.9) does not support –append or –append-verify so I was unable to check automatically if the file (or even a whole write-buffer) was not written correctly or, which would be bad, partly.

What I can definitely say: If you absolutely not have to use FTP, don’t use it for the following reasons:

Transferring many small files reqires a too big overhead (since the control commands eat up time and bandwidth)
AFAIK the basic ftp client installed with almost any linux does not support recursive transfer
It’s transfers and authentication are unencrypted
you don’t have even basic checksumming

An alternative in my opinion is sftp/rsync+ssh. Both are relatively simple to use, and provide useful flags specifically for backing up stuff (preserve permissions, etc.).

Don’t use Virtualmin!

Julian Kessel — Mon, 02 Apr 2012 21:49:39 +0000

I’m really upset about the situation that you result in when someone installed virtualmin on a system later administered by you.
I just want to state that at the latest when you get that administration is a job for which you should have a decent knowledge of you systems, you will regret having to use a construct like virtualmin/webmin.

Here are a few reasons why Web-/Virtualmins support conditions (they provide a ton of standart packages including httpd, proftpd, etc. via their repo) are extremely poor:

there are no release notes, and changelogs via mail or web (just bad-to-follow and not regularly released forum-posts)
you don’t know if a package is up to date, because there is no sign of patching of the packages
this is extremely critical if you want to know if a piece of software has still a security issue
you are forced to use many standard packages packaged by virtualmin – a company underlying US-law
on other distros than centos (like debian) those packagages are maintained by the community
you authenticate with you root password over https by default, come on… do it like every other web-frontend and create seperate users

In my opinion, rpmforge and knowledge and documentation is the better alternative for administration, please consider it when setting up a new system.

BackupPC cfg and path change on ArchLinux

Julian Kessel — Wed, 29 Feb 2012 13:10:09 +0000

About one week ago, AL released a new verion of BackupPC via the official repos, but w/o mentioning there were massive cfg changes which lead me into an empty webfrontent not knowing what happened.
Just to document, these are the points you have to consider:

You can see they also changed the cfg dir to lowercase, that’s also why the frontend runs, but does not show any hosts…
old:
$Conf{TopDir} = '/var/opt/BackupPC'; #is your mountpoint / storage pool $Conf{ConfDir} = '/etc/BackupPC'; $Conf{LogDir} = '/var/log/BackupPC'; $Conf{InstallDir} = '/opt/BackupPC'; $Conf{CgiDir} = '/opt/BackupPC/www/cgi-bin';

new:
$Conf{TopDir} = '/var/lib/backuppc'; $Conf{ConfDir} = '/etc/backuppc'; $Conf{LogDir} = '/var/log/backuppc'; $Conf{InstallDir} = '/usr/share/backuppc'; $Conf{CgiDir} = '/usr/share/backuppc/cgi-bin';

You should also replace your notification email addr to a valid one if you use that feature. That should be enough if you don’t have further customized bpc.
Just remount your pool and restart the service, then you’re ready to go :)

Fully enabling HTTPS on WordPress

admin — Wed, 16 Nov 2011 21:02:28 +0000

If you want to get WordPress to support HTTPS without any unencrypted content being transferred to the client and included from the browser, you have to force WordPress to change the siteUrl depening on the request schema which comes from the client.
The basis for my small addition below is this post: https://prosauce.org/blog/2010/08/enable-complete-support-for-ssl-on-wordpress/
It explains how to do the changes described briefly above.

What’s still left is that for whatever reason, WP doesn’t make the pingback URL relative to the site_url we did set with the trick in the post, so we have to change that little line to in wp-includes/general-template.php to the following.
case 'pingback_url': $output = /*get_option('siteurl') */ site_url().'/xmlrpc.php'; break;

Gnuplottex – rotate y-axis label with LaTeX

Julian Kessel — Wed, 31 Aug 2011 17:26:40 +0000

A known caveat of the latex gnuplot terminal is the missing functionality to rotate text, which especially hurts for the ylabel.

Here's one dirty way to workaround this:

set ylabel "\\begin{sideways}YAXIS [$ms$]\\end{sideways}"

Getting LaTeX commands to work in Gnuplot(tex)

Julian Kessel — Wed, 31 Aug 2011 16:35:04 +0000

This time I was writing a gnuplot script for embedding the graphic in a latex document, with the help of gnuplottex package, no problem I thought.

But unfortunately my script names an axis like

set xlabel "Temperatur an $R_1$ [$^{\degree}C$]"

You'll notice that degree is displayed as a string and not executed to produce "°" as intended.

You have to escape the backslash so it will not be processed by gnuplot but rather by latex, success :)

set xlabel "Temperatur an $R_1$ [$^{\\degree}C$]";

A second failure I made writing log(1/3), while gnuplot, like C does, implicitly uses integer operations for an expression without a fp value, this leads to a silent error. (gnuplot skips dat file with no valid points)

For the protocol:

f(r) = (((log(1.0/3.0)*r*(47e-6))*-1)*1000)

is the right way to do it

QnD: fixing evolution-exported addressbook data to include “display name”

Julian Kessel — Tue, 23 Aug 2011 18:25:38 +0000

I'll keep it short: Export your AB via evolution, import it into TB, export it as csv, run the following script:

awk -F"," '{printf("%s,%s,%s %s,", $1,$2,$1,$2); for(i=4;i<36;i++) printf("%s,",$i); printf("\n")}' in.csv > out.csv

import the new csv into TB. You can also shorten this way via modding my one-liner and directly transforming evolution's output (it just makes double qoutes around the values) and import it then.

Productively using KmPlot for School Analysis

Julian Kessel — Tue, 23 Aug 2011 17:13:25 +0000

I has been a rather long time searching for a decent plotter application for linux. Though as a gnome user I usually defer kde apps because of their deps, but this time I found no alternative available which provided all stuff kmplot features.

Besides all cool features which can be discovered by clicking around in the UI, kmplot learnt me to split a parameterized function like x³-2tx² in two functions which describe the x-axis and y-axis seperately and controlling the values of t with a slider.

First, you have to get used to the fact that we call out functions f_x and f_y now, and not f as usual actually meaning f_y. That's because you just require f_x (the function generating x-values) to be e.g. f_x(x) = x (linear slope @1).

The function f(x)= x³-2tx² splits up in f_x(x) = x and f_y(t,k)=t³-2kt² while k is the parameter controlled by the slider (check "slider" and choose one from the list).

While this makes sense for being able to modify f_x later It's also possible to choose a regular cartesian plot.

Restoring an iPod Classic (GPT) from VirtualBox VM on linux

Julian Kessel — Fri, 12 Aug 2011 20:03:42 +0000

While testing several states (gpt,mbr,formatted,unformatted) I ran over a couple of weird errors including 1429 and a message that complained about that other programs would hold a write lock on the fs.

The final solution was the option in Vbox to turn on the USB 2.0 EHCI controller which needs the extension pack installed. On Archlinux you get it in the AUR, but you have to register it in the vbox prefs since the install script doesn’t handle this.
Instead, you can dl the extension a second time from the site, open in w/ vbox. It will register the previously installed one and give you an error because of conflicting files which is ok. After this, you can enable the EHCI controller and restoring/syncing will work fine :)