Debian IPsec tunnel

Assume we have two servers in different subnets that we want to connect through IPsec.

# Alice
206.36.46.56
10.20.10.10  # local IP

# Bob
207.37.47.57
10.20.20.10  # local IP

Ubuntu - install Sun Java and browser plugin

Install Java

Since Oracle Java is no longer currently available in a supported Ubuntu repository, one should go to Java download page and download tgz archive. Currently the latest version is 7 update 51.

Assuming you downloaded it to ~/Download/jre-7u51-linux-x64.tar.gz:

sudo mkdir -p /usr/lib/jdk/
cd /usr/lib/jdk/
sudo tar xzf ~/Download/jre-7u51-linux-x64.tar.gz
sudo update-alternatives --install "/usr/bin/java"   "java"   "/usr/lib/jdk/jdk1.7.0_51/bin/java"   0
sudo update-alternatives --install "/usr/bin/javac"  "javac"  "/usr/lib/jdk/jdk1.7.0_51/bin/javac"  0
sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jdk/jdk1.7.0_51/bin/javaws" 0

You may also need to configure java alternatives (in case you have several java versions installed):

sudo update-alternatives --config java
sudo update-alternatives --config javac
sudo update-alternatives --config javaws

Install browser (chrome) plugin

See official page for up-to-date instructions or perform these commands:

1. Become the root user by running the su command and then enter the super-user password.

   sudo -s

2. Create a directory called plugins if you do not have it.

   mkdir -p /opt/google/chrome/plugins

3. Go to Google chrome plugins directory before you make the symbolic link.

   cd /opt/google/chrome/plugins

4. Create a symbolic link.

   ln -s /usr/lib/jdk/jdk1.7.0_51/jre/lib/amd64/libnpjp2.so .

5. Restart your browser and test Java

Open jnlp files from webpages with javaws

Go to the webpage with jnlp application. Start the application and the browser will download the jnlp file. Click the arrow next to the file button in the downloads bar and select "Always open files of this type". Start the application again to see the effect.

Extract audio with silence from video with ffmpeg

Usually excracting audio track from video file is not a problem and can be done using ffmpeg:

ffmpeg -i video.avi -vn result_audio_track.wav

But if you have video where audio track has silent parts, the command above will extract and concatenate only the parts where audio is not silent. So the result audio track will be shorter than the original. To overcome this the additional parameters should be set:

ffmpeg -i video.avi -vn -af \
    aresample=min_comp=0.001:min_hard_comp=0.100000 \
    result_audio_track.wav

These options prevent ffmpeg from dropping silent parts of audio track:

• aresample resamples the input audio to the specified parameters.
• min_comp sets the minimum difference between timestamps and audio data (in seconds) to trigger stretching/squeezing/filling or trimming of the data to make it match the timestamps.
• min_hard_comp sets the minimum difference between timestamps and audio data (in seconds) to trigger adding/dropping samples to make it match the timestamps.

Multiline regex

The simplest solution would be to use pcregrep, that is grep using the pcre library. Use the flag -M for multiline search:

pcregrep -M 'expression1\nexpression2' filename

if you'd like more 'native' solution without installing additional packages, there's a Python one-liner that will do the job:

alias mlgrep='python -c '\''import re, sys; \
    sys.exit("Usage: mlgrep PATTERN") if len(sys.argv) != 2 else True; \
    match = re.findall(r".*" + sys.argv[1] + r".*", sys.stdin.read().strip(), re.MULTILINE); \
    print("\n".join([x.strip() for x in match])) if match else sys.exit(1)'\'''

add this line to your ~/.bashrc file and use it as:

cat filename | mlgrep "expression1\nexpression2"

Python: set network interface for urllib2

The problem is that urllib2 is based on httplib library which doesn't have such functionality. The best solution I found was this “monkey patch” from Alex Martelli posted on Stack Overflow:

import socket
true_socket = socket.socket
def bound_socket(*a, **k):
    sock = true_socket(*a, **k)
    sock.bind((sourceIP, 0))
    return sock
socket.socket = bound_socket

Simply run this block of code before using urllib2 functions.

Zabbix + Nginx + PostgresDB

Assuming you already have running nginx and postgres and are going to install Zabbix server. Download and install Zabbix. Then you'll need to install FastCGI for PHP support and several additional packages:

# apt-get install zabbix-server-pgsql zabbix-frontend-php \
    php5-pgsql php5-fpm

You should be prompted to configure postgres database for zabbix during the installation. If not, refer to the documentation on how to do it manually.

Lets proceed to adding PHP support to Nginx for Zabbix. Add the following block to your 'server' in nginx.conf:

location /zabbix {
    if ($scheme ~ ^http:){
        rewrite ^(.*)$  https://$host$1 permanent;
    }
    
    alias               /usr/share;
    index               index.php;
    error_page          403 404 502 503 504  /zabbix/index.php;

    location ~ \.php$ {
        if (!-f $request_filename) { return 404; }
        expires         epoch;
        include         /usr/local/nginx/conf/fastcgi_params;
        fastcgi_param   SCRIPT_FILENAME  $document_root$fastcgi_script_name;
        fastcgi_index   index.php;
        fastcgi_pass    127.0.0.1:9000;
    }

    location ~ \.(jpg|jpeg|gif|png|ico)$ {
        access_log      off;
        expires         33d;
    }
}

Modify 'include' directive to point to your nginx configuration directory and 'alias' - to zabbix installation dir. Note that if zabbix is installed into

/usr/share/zabbix

set alias to

/usr/share

Now set fastcgi to run on port 9000 and not using socket. Modify

/etc/php5/fpm/pool.d/www.conf

and set:

listen = 127.0.0.1:9000

Now Zabbix page can be opened in your browser: http://<server_ip_or_name>/zabbix. In case it doesn't check all the settings above and nginx and fastcgi logs to fix the problem. Once done proceed with installation steps on the opened page.

Screencast recording in Linux with ffmpeg

Screencast recording can be performed in HQ using ffmpeg x11grab and pulseaudio:

ffmpeg -f alsa -ac 2 -ab 160k -i pulse -acodec pcm_s16le \
    -f x11grab -r 25 -s 1280x1024 -i :0.0+0,0 -aspect 4:3 \
    -vcodec libx264 -vpre lossless_ultrafast -threads 0 \
    screencast.mkv

options:
-s - recording size
-i - display index + start coords (0,0 - upper left corner)

Run

$ x264 --help

to see all available -vpre options.

ffmpeg should be configured as follows:

./configure --prefix=/usr/local/share/ffmpeg/ --enable-x11grab \
    --enable-gpl --disable-ffplay --disable-ffserver \
    --enable-small --disable-debug --disable-yasm \
    --disable-ffprobe --enable-libx264 --enable-shared