The method I’m presenting is easy and effective. OpenSSH makes this a snap. Your web browsing packets will be routed via an encrypted connection to your server.

Create a SOCKS Proxy Connection on localhost

First, in a terminal, open a SOCKS connection to your server with OpenSSH. Just add “-D 9999″ to your normal SSH command. This will create a SOCKS proxy on localhost at port 9999.

ssh -D 9999 username@myserver.com

Depending on your configuration, you may need to enter your server account password. Whatever your normal authentication is for SSH. This will even open a normal SSH session, you will get a shell prompt on the server like normal. If you do not want a shell prompt, use “-ND” instead of “-D” and the

You now have a proxy on your local computer using SOCKS on port 9999. Now we just need to use it.

Install Switchy! in your Chrome browser

This can be easily found in the Chrome Web Store.

Use your Shiny New SOCKS Proxy

Open the Switchy! Options dialog. Type the a name for this proxy in Profile Name. On the SOCKS Host line, enter “localhost” in the first blank and “9999″ for the Port. Click the Save button. You are using a SOCKS proxy running on your localhost.

Then, select the proxy by clicking the Switchy! icon in Chrome and selecting the proxy name you just entered.

You are now using a secure connection to browse the web. Note that someone on the network where your server is hosted can still snoop your traffic, but not in the Starbucks where your are sitting.

$filename = 'something';
$file_path = '/somepath/to/the/file/';
$file_fullpath = $file_path . $filename;
//
//
if (!file_exists($file_fullpath)) {
    header("HTTP/1.0 404 Not Found");
    return;
}
//
// get the mime type
$finfo = finfo_open(FILEINFO_MIME_TYPE);
$mimeType = finfo_file($finfo, $file_fullpath);
//
// calc values for header
$size = filesize($file_fullpath);
$time = date('r', filemtime($file_fullpath));
$fm = @fopen($file_fullpath, 'rb');
if (!$fm) {
    header('HTTP/1.0 505 Internal server error');
    return;
}
$begin = 0;
$end = $size;
if (isset($_SERVER['HTTP_RANGE'])) {
    if (preg_match('/bytes=\h*(\d+)-(\d*)[\D.*]?/i', $_SERVER['HTTP_RANGE'], $matches)) {
        $begin = intval($matches[0]);
        if (!empty($matches[1])) $end = intval($matches[1]);
    }
}
//
// create http header
if ($begin > 0 || $end < $size) {
    header('HTTP/1.0 206 Partial Content');
}else {
    header('HTTP/1.0 200 OK');
}
header('HTTP/1.0 200 OK');
header("Content-Type: $mimeType");
header('Cache-Control: public, must-revalidate, max-age=0');
header('Pragma: no-cache');
header('Accept-Ranges: bytes');
header('Content-Length:' . ($end - $begin));
header("Content-Range: bytes $begin-$end/$size");
header("Content-Disposition: inline; filename=$filename");
header("Content-Transfer-Encoding: binary\n");
header("Last-Modified: $time");
header('Connection: close');
// output the file
$cur = $begin;
fseek($fm, $begin, 0);
while (!feof($fm) && $cur < $end && (connection_status() == 0)) {
    print fread($fm, min(1024 * 16, $end - $cur));
    $cur+= 1024 * 16;
}

There you have it. Your user can click the link for the file, which then runs this code. In my case, this is in a Kohana controller.

The files are not stored in a public directory, so unauthenticated users cannot access them.

If a file is created on the fly, like a PDF of an invoice, this will also work.

You can modify it for your specific requirements or grab some code for another use.

#!/usr/bin/perl -w
use strict;
use warnings;

use IPC::Open3;

# example
my $filename  = $ARGV[0];
my %videoInfo = videoInfo($filename);
print "duration: " . $videoInfo{'duration'} . "\n";
print "durationsecs: " . $videoInfo{'durationsecs'} . "\n";
print "bitrate: " . $videoInfo{'bitrate'} . "\n";
print "vcodec: " . $videoInfo{'vcodec'} . "\n";
print "vformat: " . $videoInfo{'vformat'} . "\n";
print "acodec: " . $videoInfo{'acodec'} . "\n";
print "asamplerate: " . $videoInfo{'asamplerate'} . "\n";
print "achannels: " . $videoInfo{'achannels'} . "\n";

#
# returns media information in a hash
sub videoInfo {
	# ffmpeg command
	my $ffmpeg = '/usr/local/bin/ffmpeg';

	my %finfo = (
				  'duration'     => "00:00:00.00",
				  'durationsecs' => "0",
				  'bitrate'      => "0",
				  'vcodec'       => "",
				  'vformat'      => "",
				  'acodec'       => "",
				  'asamplerate'   => "0",
				  'achannels'       => "0",
	);

	my $file = shift;

	# escaping characters
	$file =~ s/(\W)/\\$1/g;

	open3( "</dev/null", ">/dev/null", \*ERPH, "$ffmpeg -i $file" ) or die "can't run $ffmpeg\n";
	my @res = <ERPH>;

	# parse ffmpeg output
	foreach (@res) {
        print;

		# duration
		if (m!Duration: ([0-9][0-9]:[0-9][0-9]:[0-9][0-9].[0-9][0-9])!) {
			$finfo{'duration'} = $1;
		}

		# bitrate
		if (m!bitrate: (\d*) kb/s!) {
			$finfo{'bitrate'} = $1;
		}

		# vcodec and vformat
		if (/Video: (\w*), (\w*),/) {
			$finfo{'vcodec'}  = $1;
			$finfo{'vformat'} = $2;
		}

        # Stream #0.1(und): Audio: aac, 48000 Hz, 1 channels, s16, 64 kb/s

		# acodec, samplerate, stereo and audiorate
		if (m!Audio: (\w*), (\d*) Hz, (\d*)!) {
			$finfo{'acodec'}     = $1;
			$finfo{'asamplerate'} = $2;
			$finfo{'achannels'}     = $3;
		}
	}

	my $tenths  = substr( $finfo{'duration'}, 9, 2 );
	my $seconds = substr( $finfo{'duration'}, 6, 2 );
	my $minutes = substr( $finfo{'duration'}, 3, 2 );
	my $hours   = substr( $finfo{'duration'}, 0, 2 );
	$finfo{'durationsecs'} = ( $tenths * .01 ) + $seconds + ( $minutes * 60 ) + ( $hours * 360 );

	return %finfo;
}

I added a few niceties such as help, multiple source options and a listing of available languages.

Entering:

tranny -t de ‘I am a citizen of Berlin’

gets this result:

Ich bin ein Bürger von Berlin

and entering:

tranny ‘Ich bin ein Bürger von Berlin’

results:

I am a citizen of Berlin

I created a Google Code project for tranny at: http://code.google.com/p/tranny/

If you need a scriptable translator, give it a try. If you run into trouble or would like to suggest changes, leave comments here or at the project.

#!/usr/bin/perl
#
# what:      tranny, a language translator
# project:   https://code.google.com/p/tranny/
# copyright: Copyright 2010, Andrew Ault
# license:   This content is released under the  http://code.google.com/p/tranny/wiki/license MIT License.
#
# Uses the JSON module from CPAN. To install: "sudo cpan JSON"
#

use strict;
use warnings;
use POSIX;
use Getopt::Std;
use JSON;
use LWP;

require 'sys/ioctl.ph';
die "no TIOCGWINSZ " unless defined &TIOCGWINSZ;

my $original;
my $winsize;
my $has_tty = 1;
my ( $screen_rows, $screen_cols, $screen_xpixels, $screen_ypixels );

my %languages = (
				  'afrikaans'      => 'af',
				  'albanian'       => 'sq',
				  'amharic'        => 'am',
				  'arabic'         => 'ar',
				  'armenian'       => 'hy',
				  'azerbaijani'    => 'az',
				  'basque'         => 'eu',
				  'belarusian'     => 'be',
				  'bengali'        => 'bn',
				  'bihari'         => 'bh',
				  'breton'         => 'br',
				  'bulgarian'      => 'bg',
				  'burmese'        => 'my',
				  'catalan'        => 'ca',
				  'cherokee'       => 'chr',
				  'chinese'        => 'zh',
				  'chinese simp'   => 'zh-cn',
				  'chinese trad'   => 'zh-tw',
				  'corsican'       => 'co',
				  'croatian'       => 'hr',
				  'czech'          => 'cs',
				  'danish'         => 'da',
				  'dhivehi'        => 'dv',
				  'dutch'          => 'nl',
				  'english'        => 'en',
				  'esperanto'      => 'eo',
				  'estonian'       => 'et',
				  'faroese'        => 'fo',
				  'filipino'       => 'tl',
				  'finnish'        => 'fi',
				  'french'         => 'fr',
				  'frisian'        => 'fy',
				  'galician'       => 'gl',
				  'georgian'       => 'ka',
				  'german'         => 'de',
				  'greek'          => 'el',
				  'gujarati'       => 'gu',
				  'haitian creole' => 'ht',
				  'hebrew'         => 'iw',
				  'hindi'          => 'hi',
				  'hungarian'      => 'hu',
				  'icelandic'      => 'is',
				  'indonesian'     => 'id',
				  'inuktitut'      => 'iu',
				  'irish'          => 'ga',
				  'italian'        => 'it',
				  'japanese'       => 'ja',
				  'javanese'       => 'jw',
				  'kannada'        => 'kn',
				  'kazakh'         => 'kk',
				  'khmer'          => 'km',
				  'korean'         => 'ko',
				  'kurdish'        => 'ku',
				  'kyrgyz'         => 'ky',
				  'lao'            => 'lo',
				  'latin'          => 'la',
				  'latvian'        => 'lv',
				  'lithuanian'     => 'lt',
				  'luxembourgish'  => 'lb',
				  'macedonian'     => 'mk',
				  'malay'          => 'ms',
				  'malayalam'      => 'ml',
				  'maltese'        => 'mt',
				  'maori'          => 'mi',
				  'marathi'        => 'mr',
				  'mongolian'      => 'mn',
				  'nepali'         => 'ne',
				  'norwegian'      => 'no',
				  'occitan'        => 'oc',
				  'oriya'          => 'or',
				  'pashto'         => 'ps',
				  'persian'        => 'fa',
				  'polish'         => 'pl',
				  'portuguese'     => 'pt',
				  'punjabi'        => 'pa',
				  'quechua'        => 'qu',
				  'romanian'       => 'ro',
				  'russian'        => 'ru',
				  'sanskrit'       => 'sa',
				  'scots_gaelic'   => 'gd',
				  'serbian'        => 'sr',
				  'sindhi'         => 'sd',
				  'sinhalese'      => 'si',
				  'slovak'         => 'sk',
				  'slovenian'      => 'sl',
				  'spanish'        => 'es',
				  'sundanese'      => 'su',
				  'swahili'        => 'sw',
				  'swedish'        => 'sv',
				  'syriac'         => 'syr',
				  'tajik'          => 'tg',
				  'tamil'          => 'ta',
				  'tatar'          => 'tt',
				  'telugu'         => 'te',
				  'thai'           => 'th',
				  'tibetan'        => 'bo',
				  'tonga'          => 'to',
				  'turkish'        => 'tr',
				  'ukrainian'      => 'uk',
				  'urdu'           => 'ur',
				  'uzbek'          => 'uz',
				  'uighur'         => 'ug',
				  'vietnamese'     => 'vi',
				  'welsh'          => 'cy',
				  'yiddish'        => 'yi',
				  'yoruba'         => 'yo',
);

# get window size for country listing
open( TTY, "+</dev/tty" ) or $has_tty = 0;
if ($has_tty) {
	unless ( ioctl( TTY, &TIOCGWINSZ, $winsize = '' ) ) {
		die sprintf "$0: ioctl TIOCGWINSZ (%08x: $!)\n", &TIOCGWINSZ;
	}
	( $screen_rows, $screen_cols, $screen_xpixels, $screen_ypixels ) = unpack( 'S4', $winsize );
}

getopts( 'f:t:o:hl', \my %opts );
if ( defined $opts{h} && $opts{h} == 1 ) { usage() }
if ( defined $opts{l} && $opts{l} == 1 ) { usage() }
my ( $from, $to ) = ( $opts{f}, $opts{t} );
if ( !defined $opts{f} ) { $from = ''; }
if ( !defined $opts{t} ) { $to   = 'en'; }

# if text was passed on the command line
if ( defined $ARGV[0] ) {
	$original = $ARGV[0];
# text is from a file
} elsif ( defined $opts{o} ) {
	# slurp from file
	open FILE, $opts{o} or die "-o argument: couldn't open file: $!";
	local $/ = undef;
	$original = <FILE>;
	close FILE;
# text is from STDIN
} else {
	# slurp STDIN
	local $/ = undef;
	$original = <STDIN>;
}

my $ua = LWP::UserAgent->new;
$ua->agent("PGDict/1.0");
my $request =
  HTTP::Request->new( GET => "http://ajax.googleapis.com/ajax/services/language/translate?v=1.0&langpair=$from|$to&q=$original" );
my $response = $ua->request($request);

if ( $response->is_success ) {
	my $perl_res = from_json( $response->content );
	if ( $perl_res->{'responseStatus'} eq '200' ) {
		print $perl_res->{'responseData'}->{'translatedText'} . "\n";
	} else {
		warn "error " . $perl_res->{'responseDetails'} . "\n";
	}
} else {
	print $response->status_line . "\n";
}

sub usage {
	print "usage: ";
	print "\ttranny -f language_code -t language_code [original text]\n\n";
	print "-f language_code (optional)\n\n";
	print "-t language_code (optional)\n\n";
	print "-o original_file (optional)\n\n";
	print "-h this help\n\n";
	print "-l language list\n\n";
	print "Tranny uses Google Translate and requires an Internet connection to work.\n";
	print "Text is translated from STDIN, from the command line or a file with -o.\n\n";
	print "By default,the 'from' language is automatically detected and translated to English (en).\n\n";
	if ( defined $opts{l} && $opts{l} == 1 ) { list_languages() }
	exit;
}

sub list_languages {
	my $num_columns = ceil( $screen_cols / 23 );
	my $num_rows = ceil ( keys(%languages) /$num_columns );
	my $row = 0;
	my $col = 0;
	my @formatted_languages = ( );
	foreach my $key ( sort ( keys(%languages) ) ) {
		$row++;
		$formatted_languages[$col][$row] =  sprintf( "%-14s %-6s", $key, $languages{$key} );
		if ( $row == $num_rows ){
			$row = 0;
			$col++;
		}
	}
	for ($row = 0; $row <= $num_rows; $row++) {
		for ($col = 0; $col <= $num_columns; $col++) {
			if ( defined $formatted_languages[$col][$row] ){
				print $formatted_languages[$col][$row];
			}
		}
		print "\n";
	}
}

This has been tested on Ubuntu Lucid and Jaunty. This procedure will create a system with:

• Install a separate Dropbox client (daemon) for individual users
• Each user has a separate Dropbox account
• All the daemons will be managed together with normal daemon controls

This allows individuals to have their own Dropbox accounts, each with a separate process syncing their individual ~/Dropbox directory. With one command an admin can start or stop all the daemons at once.

Install Prerequisites

Later, we’ll need to read a sqlite3 database record, so install sqlite3.

sudo aptitude -y install sqlite3

Install Dropbox client for an individual user

This step is repeated for each user that wants a Dropbox client. Start by setting up your own account, then repeat for each user. This is run with a user’s own account. The changes made all take place in their home directory.

First, determine whether you have 32-bit or 64-bit Ubuntu Server. You must install the correct version, either 32 or 64 bit or it will not work. The following command will tell you which is installed:

uname -a | grep '_64' >/dev/null && echo 'A 64-bit OS is installed'; uname -a | grep '_64' >/dev/null || echo 'A 32-bit OS is installed'

Run the correct installation, based on whether a 32-bit or 64-bit OS is installed.

32-bit installation:

cd ~
wget -O dropbox.tar.gz http://www.dropbox.com/download/?plat=lnx.x86
tar -zxof dropbox.tar.gz

or

64-bit installation:

cd ~
wget -O dropbox.tar.gz http://www.dropbox.com/download/?plat=lnx.x86_64
tar -zxof dropbox.tar.gz

Link user’s Dropbox client to their Dropbox account:

wget http://dl.dropbox.com/u/6995/dbmakefakelib.py
python dbmakefakelib.py

The above will run for a little while without printing anything, then print “dropboxd ran for 15 seconds without quitting – success?”. When it does so, press control-c twice. Yes, it is unusual. What this does is populate a sqlite3 database with an ID from the Dropbox server. Next, we’ll extract that code and use it to link your Dropbox user account with this CLI Dropbox client instance.

On the server, via SSH

Get the URL with:

echo https://www.dropbox.com/cli_link?host_id=`echo '.dump config' | sqlite3 ~/.dropbox/dropbox.db | grep host_id | cut -d \' -f 4 | python -c 'print raw_input().decode("base64")' | grep '^V' | cut -b 2-`

On your local machine, in a web browser

Copy the URL that the above printed and paste it into a web browser. When you do so, Dropbox will register your client on the server with your Dropbox account.

At this point, Dropbox will not be quite working yet. The next steps will take care of that.

Create Dropbox daemon control

The next task is to create a system to start and stop the dropbox daemon for each user on the system that has Dropbox installed for his/her user account. The following daemon init script was lifted from: http://wiki.dropbox.com/TipsAndTricks/TextBasedLinuxInstall.

Of course, this is for the use of the system admin. This creates a normal daemon init start/stop script and installs it so the Dropbox daemons are started when the system boots. The admin can also use this to control the Dropbox daemons manually.

sudo vi /etc/init.d/dropbox

Paste in the following code. Then, modify line 3, replacing “user1 user2″ with your username. For future reference, additional user’s Dropbox daemons can be controlled with this one script – add additional username separated with spaces.

# dropbox service
# separate usernames in the following line with spaces.
DROPBOX_USERS="user1 user2"

DAEMON=.dropbox-dist/dropbox

start() {
    echo "Starting dropbox..."
    for dbuser in $DROPBOX_USERS; do
        HOMEDIR=`getent passwd $dbuser | cut -d: -f6`
        if [ -x $HOMEDIR/$DAEMON ]; then
            HOME="$HOMEDIR" start-stop-daemon -b -o -c $dbuser -S -u $dbuser -x $HOMEDIR/$DAEMON
        fi
    done
}

stop() {
    echo "Stopping dropbox..."
    for dbuser in $DROPBOX_USERS; do
        HOMEDIR=`getent passwd $dbuser | cut -d: -f6`
        if [ -x $HOMEDIR/$DAEMON ]; then
            start-stop-daemon -o -c $dbuser -K -u $dbuser -x $HOMEDIR/$DAEMON
        fi
    done
}

status() {
    for dbuser in $DROPBOX_USERS; do
        dbpid=`pgrep -u $dbuser dropbox`
        if [ -z $dbpid ] ; then
            echo "dropboxd for USER $dbuser: not running."
        else
            echo "dropboxd for USER $dbuser: running (pid $dbpid)"
        fi
    done
}

case "$1" in
  start)
    start
    ;;

  stop)
    stop
    ;;

  restart|reload|force-reload)
    stop
    start
    ;;

  status)
    status
    ;;

  *)
    echo "Usage: /etc/init.d/dropbox {start|stop|reload|force-reload|restart|status}"
    exit 1

esac

exit 0

Make the init script executable and restart the daemon:

sudo chmod +x /etc/init.d/dropbox
sudo /etc/init.d/dropbox restart

When you restart the daemon, it will be running correctly linked to your Dropbox account. It will create a Dropbox directory in your home directory and will start to populate it with files you have on Dropbox.

Have the daemon(s) run automatically at boot time:

sudo update-rc.d dropbox defaults

The above correctly copies links as needed so the daemon(s) start when the server boots.

Managing the Daemons

A separate daemon will be run for each user that has the Dropbox client installed – with only one command. This makes it easy for individual users to have separate Dropbox accounts, each syncing to ~/Dropbox for their user account. Here are the commands to manage these daemons:

Start Dropbox services for all users:

sudo /etc/init.d/dropbox start

Stop Dropbox services for all users:

sudo /etc/init.d/dropbox stop

Restart Dropbox services for all users:

sudo /etc/init.d/dropbox restart

Get service status for each user Dropbox service:

sudo /etc/init.d/dropbox status

#! /bin/bash

CODE="upc"
OWNER="myusername"
GROUP="mygroupname"
KOHANA_URL="http://dev.kohanaframework.org/attachments/download/1355/kohana-v2.3.4.zip"
KOHANA_ZIP="kohana-v2.3.4.zip"
SITESROOT="/usr/local/var/www"
URL="www.mysite.com"
# database.php parameters
DBUSER="mydbuser"
DBPWD="mydbpasswd"
DBHOST="localhost"
DBDATABASE="mydbname"

#
# make sure this is run as root
#
if [[ $UID -ne 0 ]]; then
    echo "Not running as root"
    exit
fi

if [ ! -d $SITESROOT ]; then
	echo "$SITESROOT directory does not exist"
	exit
fi

#
# change to the siteroot directory
#
cd $SITESROOT

if [ -d $URL ]; then
	echo "$SITESROOT/$URL directory already exists"
	exit
fi 

mkdir $URL
chown $OWNER:$GROUP $URL
cd $URL

#
# create kohana directory
#
echo creating kohana directory
mkdir kohana
chown $OWNER:$GROUP kohana
chmod g+ws kohana
wget "$KOHANA_URL"
unzip "$KOHANA_ZIP"
rm "$KOHANA_ZIP"
chown -R $OWNER:$GROUP kohana
chmod -R g+w kohana
chown $OWNER:www-data kohana/application/logs
rm kohana/example.htaccess
rm kohana/install.php
rm kohana/Kohana\ License.html
rm kohana/kohana.png

#
# create public directory
#
echo creating public directory
mkdir public
chown $OWNER:$GROUP public
chmod g+ws public
mv kohana/index.php public/
sed -i "s\\kohana_application =.*$\\kohana_application = '../kohana/application';\\" public/index.php
sed -i "s\\kohana_modules =.*$\\kohana_modules = '../kohana/modules';\\" public/index.php
sed -i "s\\kohana_system =.*$\\kohana_system = '../kohana/system';\\" public/index.php
echo "# turn on URL rewriting
RewriteEngine On
RewriteBase /
" > public/.htaccess

#
# create Apache logs directory
#
echo creating logs directory
mkdir logs
chown $OWNER:www-data logs
chmod g+ws logs
touch logs/error.log
touch logs/combined.log

#
# create utilties directory
#
echo creating utilties directory
mkdir utilities
chown $OWNER:$GROUP utilities
chmod g+ws utilities

#
# modify kohana/application/config/config.php
#
echo modifying kohana/application/config/config.php
sed -i "s\\'/kohana/'\\'$URL/'\\" kohana/application/config/config.php

#
# create kohana/application/config/database.php
#
echo creating kohana/application/config/database.php
cp kohana/system/config/database.php kohana/application/config/database.php
chown $OWNER:$GROUP kohana/application/config/database.php
chmod g+w kohana/application/config/database.php
sed -i "s\\'user'.*$\\'user'     => '$DBUSER',\\" kohana/application/config/database.php
sed -i "s\\'pass'.*$\\'pass'     => '$DBPWD',\\" kohana/application/config/database.php
sed -i "s\\'host'.*$\\'host'     => '$DBHOST',\\" kohana/application/config/database.php
sed -i "s\\'database'.*$\\'database' => '$DBDATABASE',\\" kohana/application/config/database.php

#
# create kohana/application/config/routes.php
#
echo creating kohana/application/config/routes.php
cp kohana/system/config/routes.php kohana/application/config/routes.php
chown $OWNER:$GROUP kohana/application/config/routes.php
chmod g+w kohana/application/config/routes.php
sed -i "s\\'welcome'\\'/index'\\" kohana/application/config/routes.php

#
# copy kohana/application/config/profiler.php
#
echo creating kohana/application/config/profiler.php
cp kohana/system/config/profiler.php kohana/application/config/profiler.php
chown $OWNER:$GROUP kohana/application/config/profiler.php
chmod g+w kohana/application/config/profiler.php

#
# create Apache virtual site
#
echo creating Apache virtual site file in /etc/apache2/sites-available
echo "<VirtualHost *:80>
	ServerName $URL
	DocumentRoot $SITESROOT/$URL/public
	DirectoryIndex index.php
	LogLevel warn
	ErrorLog $SITESROOT/$URL/logs/error.log
	CustomLog $SITESROOT/$URL/logs/combined.log combined
</VirtualHost>
" > /etc/apache2/sites-available/$URL

#
# finish up
#
echo "enable site with: sudo a2ensite $URL"
echo "restart Apache with: sudo /etc/init.d/apache2 restart"

• Wait for video files to be dropped via FTP and then process them
• Check for a recurring problem and report it to admin
• Monitor system load and report to the admin at a certain threshold

In this post we’ll take a look at how to create a Perl daemon script and how to get it to run as a daemon whenever the system is started. For the Perl script, a template will be created and for control of the daemon process, standard Debian facilities will be used.

What will be covered:

• Create the start/stop script in /etc/init.d
• Create the Perl daemon script in /usr/bin/
• Create the log file in /var/log/
• Get the daemon to start automatically when the system boots
• How to manage your daemon

The start/stop script starts and stops the daemon. It is also used by the system to start your daemon when the system starts.

The Perl daemon script contains your custom Perl code to run in the background. It executes your code every x number of seconds.

Create the Start/stop Script

Happily, Debian and therefore Ubuntu, supplies a template that uses the Debian start-stop-daemon command to start and stop daemons. It is only necessary to copy this template to a new file of the correct name and modify it for the purpose.

These scripts reside in the /etc/init.d/ directory. The script you create will have the exact same filename as the Perl daemon script you will create and the name cannot have a file extension – just the bare name.

Substitute your daemon’s name for “mydaemon” in the examples.

sudo cp /etc/init.d/skeleton /etc/init.d/mydaemon
sudo chmod +x /etc/init.d/mydaemon

sudo vi /etc/init.d/mydaemon

Make changes to your start/stop script. Locate the header in the script:

PATH=/sbin:/usr/sbin:/bin:/usr/bin
DESC="Description of the service"
NAME=daemonexecutablename
DAEMON=/usr/bin/$NAME
DAEMON_ARGS="--options args"
PIDFILE=/var/run/$NAME.pid
SCRIPTNAME=/etc/init.d/$NAME

Create the Perl Daemon Script

Use the Perl Daemon Script Template located at the end of this post. In the following, the script template is copied to /usr/bin/where executables specific to this system are located. Actually, you would copy the template to your home directory, make the changes and then copy the daemon script to /usr/bin/.

sudo cp daemon_template.pl /usr/bin/mydaemon
sudo vi /usr/bin/mydaemon
sudo chmod +x /usr/bin/mydaemon

The script template is commented with the changes that are needed. In particular, change the value of $daemonName to the exact name of your new daemon. Ten, add your custom code where # do something appears.

Prerequisites

The script uses File::Pid and POSIX from CPAN, so you’ll need to install that module:

sudo aptitude install cpan
sudo cpan POSIX
sudo cpan File::Pid

Create the Log File

We’ll create the log file so it has the correct ownership and permissions. The log fie has the daemon name appended with “.log”. It is located in the /var/log/ directory.

sudo touch /var/log/mydaemon.log
sudo chmod 640 /var/log/mydaemon.log
sudo chown root:adm /var/log/mydaemon.log

The permissions and ownership change allow adm group members to read the log, per convention. Add yourself to adm group to view logs.

Run your Daemon

As you have created a standard start/stop script for your daemon, you can start it the standard way:

sudo /etc/init.d/mydaemon start

Stop your Daemon

Similarly, your daemon is easy to stop and restart:

sudo /etc/init.d/mydaemon stop

sudo /etc/init.d/mydaemon restart

Automatically Start your Daemon

This command tells your system to start your daemon automatically when the system starts:

update-rc.d mydaemon defaults 99

To keep your daemon from starting, if needed:

update-rc.d -f mydaemon remove

Managing Daemons

List running daemons

Well-behaved daemons generally create a PID file in /var/run/. List that directory and your have a fair list of running daemons.

sudo ls /var/run/

Get PID for a particular daemon

If you know the name of a daemon and want to see if it is running and get its PID, use pgrep.

pgrep mydaemon

Also useful is the ps command, which list processes.

ps aux

The aux switch limits output to processes not associated with a terminal.

Show programs running as daemons

This line attempts to show programs that are running as daemons.

which `ps aux | cut -c 66- | cut -d\  -f 1` | sort | uniq

The Perl Daemon Script Template

#!/usr/bin/perl -w
#
# mydaemon.pl by Andrew Ault, www.andrewault.net
#
# Free software. Use this as you wish.
#
# Throughout this template "mydaemon" is used where the name of your daemon should
# be, replace occurrences of "mydaemon" with the name of your daemon.
#
# This name will also be the exact name to give this file (WITHOUT a ".pl" extension).
#
# It is also the exact name to give the start-stop script that will go into the
# /etc/init.d/ directory.
#
# It is also the name of the log file in the /var/log/ directory WITH a ".log"
# file extension.
#
# Replace "# do something" with your super useful code.
#
# Use "# logEntry("log something");" to log whatever your need to see in the log.
#
use strict;
use warnings;
use POSIX;
use File::Pid;

# make "mydaemon.log" file in /var/log/ with "chown root:adm mydaemon"

# TODO: change "mydaemon" to the exact name of your daemon.
my $daemonName    = "mydaemon";
#
my $dieNow        = 0;                                     # used for "infinte loop" construct - allows daemon mode to gracefully exit
my $sleepMainLoop = 120;                                    # number of seconds to wait between "do something" execution after queue is clear
my $logging       = 1;                                     # 1= logging is on
my $logFilePath   = "/var/log/";                           # log file path
my $logFile       = $logFilePath . $daemonName . ".log";
my $pidFilePath   = "/var/run/";                           # PID file path
my $pidFile       = $pidFilePath . $daemonName . ".pid";

# daemonize
use POSIX qw(setsid);
chdir '/';
umask 0;
open STDIN,  '/dev/null'   or die "Can't read /dev/null: $!";
open STDOUT, '>>/dev/null' or die "Can't write to /dev/null: $!";
open STDERR, '>>/dev/null' or die "Can't write to /dev/null: $!";
defined( my $pid = fork ) or die "Can't fork: $!";
exit if $pid;

# dissociate this process from the controlling terminal that started it and stop being part
# of whatever process group this process was a part of.
POSIX::setsid() or die "Can't start a new session.";

# callback signal handler for signals.
$SIG{INT} = $SIG{TERM} = $SIG{HUP} = \&signalHandler;
$SIG{PIPE} = 'ignore';

# create pid file in /var/run/
my $pidfile = File::Pid->new( { file => $pidFile, } );

$pidfile->write or die "Can't write PID file, /dev/null: $!";

# turn on logging
if ($logging) {
	open LOG, ">>$logFile";
	select((select(LOG), $|=1)[0]); # make the log file "hot" - turn off buffering
}

# "infinite" loop where some useful process happens
until ($dieNow) {
	sleep($sleepMainLoop);

	# TODO: put your custom code here!
	# do something

	# logEntry("log something"); # use this to log whatever you need to
}

# add a line to the log file
sub logEntry {
	my ($logText) = @_;
	my ( $sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst ) = localtime(time);
	my $dateTime = sprintf "%4d-%02d-%02d %02d:%02d:%02d", $year + 1900, $mon + 1, $mday, $hour, $min, $sec;
	if ($logging) {
		print LOG "$dateTime $logText\n";
	}
}

# catch signals and end the program if one is caught.
sub signalHandler {
	$dieNow = 1;    # this will cause the "infinite loop" to exit
}

# do this stuff when exit() is called.
END {
	if ($logging) { close LOG }
	$pidfile->remove if defined $pidfile;
}

UPDATE:

Looks like there’s a page in French about this post: http://www.duncane.net/2011/02/25/perl-daemon/. Merci Duncane!