Debian freezes randomly

Since about one year I own a ultrabook ‘Wortmann Terra Mobile 1450 II’ which I run on Linux.  The system contains a Intel Core i7-351U chip set and 8GB RAM. But this system shows a very strange problem on Linux (and as I guess maybe also on other operating systems): randomly the system freezes.

When the system freezes no mouse , no keyboard, no REISUB was possible. The screen is corrupted and did not update. The only key board functionality which is still possible is Fn+F9 (switch display on/off). So the only possibility was to to switch off the system hard.

The freeze occurs when the system runs on battery as also when it is plugged. It looked as if the errors occurs more frequently at high memory usage.

The memory…

A memory check (with memtest86+) indicates no problem. Therefore, I thought it had to do something with the kernel. See also the discussion here. But updating every week a new kernel version and playing around with several kernel boot options the problem still occurs.

Back to the idea that the problem comes from the RAM I installed the tool ‘memtester’. With this tool you can test memory when linux is running. For Example I started a test to check 7GB RAM with the following command:

memtester 7G 1

And now I was able to force the freeze. During such a test each time my system freezes. Also when I booted in kernel recovery mode the same situation – system freezes! So this indicated to me that the problem is with the memory.

The solution

If the memory seems to be ok in general (memtest86+ indicates no errors) but the system freezes in situations with heavy  memory usage (memtester) then it may have something to do with overclocking the memory?

In my BIOS settings () I found the following setting:

->Chipset
-> System Agent (SA) Configuration
-> Memory Configuration
-> Memory Frequency Limiter

This was defined as ‘AUTO’. What ever this means I changed the value to lowest available setting of ‘1067’ (other values where 1600, 1867, … up to 2667). With this setting I can not see any substantial impairment of the speed. But from now on my system runs without any more freezes!

So if you are also faced with the problem of random freezes, first try to control the overclocking of your memory. I hope this will help you too.

After all the last question is: Is my hardware to fast for linux or is linux to fast for my hardware 😉

 

WordPress – try to lock out hackers

WordPress is really a nice software. I use it for websites and blogs. The problem is that WordPress is so common used in the net that hackers aggressive try to enter your site and inject eval php code. This is really terrible and I suffered some times ago because such a hackers attach against main own web sites.

After all I think two things can help to lock out hackers from wordpress.

1) Wordfence Plugin

The Wordfence Plugin is – in my eyes  – really good software. You should install this plugin to understand if your wordpress is under attack.

2) Protect your directories

The important thing running WordPress is to protect your directories. Never allow the apache server to write into the WordPress instalation directory. I know this is for most people an essential feature because this allows to easily update WordPress, install Plugins and Themes. But this also allows hackers to inject bad php code into your installation. And the most secure way to protect your wordpress installation is to disallow the apache server to write into the installation code.

For Linux servers this means:

In your apache web directory create a folder for your WordPress installation and reduce the directory access to a minimum which means only your own linux user account should be the owner and allowed to change content.

ls -l /var/www/
drwxr-xr-x 5 youraccount youraccount 4096 Apr 16 21:12 wordpress

As you can see the apache user (e.g. www-data) can only read but not change directories. Any changes on the wp-config.php or the installation of plugins or themes can still be made by direct ssh access (in this example) from the user ‘youraccount’.

The only exception could be the wp-content/uploads folder which need to be writable from apache when you try to upload an image.

There are a lot of additional tipps and tricks how to protect your WordPress. But I think protecting the WordPress installation from modification by the apache server is the best way.

‘evbug’ auf die Blacklist setzen

Ich hatte das Problem das mein kern.log file mit Meldungen dieser Art geflutet wurde:

Sep 27 18:07:48 r-ultrabook kernel: [ 380.012332] evbug: Event. Dev: input6, Type: 0, Code: 0, Value: 0
Sep 27 18:07:48 r-ultrabook kernel: [ 380.028334] evbug: Event. Dev: input6, Type: 2, Code: 1, Value: -1
Sep 27 18:07:48 r-ultrabook kernel: [ 380.028343] evbug: Event. Dev: input6, Type: 0, Code: 0, Value: 0
Sep 27 18:07:48 r-ultrabook kernel: [ 380.044419] evbug: Event. Dev: input6, Type: 2, Code: 1, Value: -1
Sep 27 18:07:48 r-ultrabook kernel: [ 380.044430] evbug: Event. Dev: input6, Type: 0, Code: 0, Value: 0

Diese Meldungen werden wohl vom Modul  ‘evbug’ erzeugt und dienen als Debug Information. Das Modul sollte im Normalfall eigentlicht im Kernel geladen werden.

Um nun das Modul abzuschalten kann man es auf die blacklist setzen.

Dazu habe ich die (bei mir noch nicht vorhandene) Datei /etc/modprobe.d/blacklist.conf erstellt und folgenden Inhalt eingetragen:

# This file lists those modules which we don't want to be loaded by
# alias expansion, usually so some other driver will be loaded for the
# device instead.
# evbug is a debug tool that should be loaded explicitly
blacklist evbug

Dies führt dazu das das Modul beim nächsten booten nicht mehr geladen wird und die Meldungen verschwinden.

Debian – systemd

Debian Weezy verwendet in der aktuellen version immer noch den Init-Deamon System-V-init. Dieser kann durch den neueren deamon systemd ersetzt werden. Dieser erlaubt einen schnelleren  Bootvorgang, da beim booten mehrere dienste parallel gestartet werden können:

# apt-get update
# apt-get install systemd

 

Debian Installation

Hier folgen einige kurze Hilfestellungen zur Installation von Debian 7 (Wheezy)

Für die Installation von Debian wird die ‘Netzwerkinstallation‘ empfohlen. Es handelt sich dabei um ein ca. 200MB großes ISO Image welches von einem USB-Stick aus installiert werden kann. Sämtliche für die eigentliche Installation benötigten Komponenten werden werden später automatisch heruntergeladen. Continue reading “Debian Installation”

Character encoding de_DE on Linux Debian

On my debian server today I run into a problem with the encoding of XSL templates running on a GlassFish server. The problem was that German characters where not displayed correctly.

After a long time of searching, I figured out that the reason for that problem was not my MySQL database, nor my GlassFish installation. It was simply the missing German language support on my linux debian.

You can test the installed locales with the following command:

locale -a

In my case only ‘en_US.utf8’ was listed.

In debian you can simply add the german language support by changing the file /etc/locale.gen. Simply uncomment the lines:

de_DE ISO-8859-1
de_DE.UTF-8 UTF-8
de_DE@euro ISO-8859-15

and run the command:

locale-gen

After restarting my GlassFish server the xsl transformation works fine with german characters.

The command “locale -a” now displays the following locale:

C
de_DE
de_DE@euro
de_DE.iso88591
de_DE.iso885915@euro
de_DE.utf8
deutsch
en_US.utf8
german
POSIX