The following example will look for files in a directory hierarchy on a FreeBSD operating system and list files, that has a file size of more than 50 MB. It uses “find” and “du”. The list will be sorted.

su -
find -s /usr/home -size +50M -exec du -h {} \;

The following example will perform the same search on an Ubuntu operating system. This list will not be sorted.

sudo find /home -size +50M -exec du -h {} \;

The implementation of “find” can be different in other operating systems. However, this command will work on other Linux and Unix-like operating systems.

Removing black borders can be done with a video editor, such as FFmpeg, which is a complete, cross-platform solution to record, convert and stream audio and video.

In our example, the size of each black border is guessed and the borders are removed from our input example of 720×576 pixels and resized to 320×288 pixels by FFmpeg.

ffmpeg -i example-input.mpg -croptop 76 -cropright 96 -cropbottom 76 -cropleft 96 -s 360x288 example-output.mpg

Do you need help with video editing? Contact Open Tech SmbA by mail at opentech@opentech.dk or call Open Tech SmbA at +45 43 62 22 88.

In the following example, the default command line prompt for a user on an Ubuntu operating system is configured for local usage and remote usage. The same procedure can be used for FreeBSD and similar operating systems.

nano -w ~/.bashrc
PS1='$ '; export PS1
nano -w ~/.profile
PS1='$ '; export PS1

There are also system wide configuration files for bash, sh and other shells on the Ubuntu operating system. However, configuring the default command line prompt for users and administrator does not seem to be taken into effect on the Ubuntu operating system.

/etc/profile
/etc/bash.bashrc

The system wide profile for shells should source in the bash system wide initialization file and configure the command line prompt for users and administrator (user 0).

In this example, we will install a Brother HL 4050 CDN network laser printer in the Ubuntu 10.04 operating system.

We visit the homepage for Official Ubuntu Documentation. We click Ubuntu 10.04 LTS. We click Printing and Faxing. We click Printing. We find the section for network printing. Here, we find the procedure for installing a network printer.

We open System, Administration and Printing. We click New and expand Network Printer. We follow the guide, go through the settings and print a test page. It works.

We also test printing from the browser and one of the office tools. It works.

This procedure can be used with other operating systems and file systems as well.

We attach the harddisk to a computer, that support the harddisk interface, and boot the computer with a Back Track Live CD.

Back Track is a Linux operating system, that can boot from CD. Back Tracks mounts file systems automatically. Back Track comes with a huge amount of tools, ready to use.

We can now access the client data.

ls /mnt/hda1

In order to write the client data to CD, we need to transfer the files to a FreeBSD network file system from which, an Ubuntu computer, that has a CD writer, can access the files. We use secure copy (scp) to transfer the files.

scp -r /mnt/hda1 starnix@starnix:temporary

In order to preserve file names and support multiple CD’s, we archive and split the data using zip.

cd temporary
zip -s 670m -r disk hda1
ls -ld disk.z*

The result is a number of zip archives, that has been split into the necessary number of archives in order to fit each CD media. We can now write the data to CD’s. We do this by inserting an empty CD media into the Ubuntu computer. Brasero disc writer offers to write our data to the CD. We drag the first archive and writes the data to disc. Note, that the first split archive is the z01 and the last is the zip.

The client can now copy the archives from the CD’s, unzip the archives and restore the files as necessary.

The solution is to enable the desktop delete feature.

Press Alt and F2. Run gconf-editor. Open apps, nautilus and preferences. Find enable_delete and set it. Close the dialogue. That’s it. We can now right click a file and delete it.

Note, that secure remove (srm) should be used to delete private files.

The delete function in most operating systems simply marks the space occupied by the file as reusable (removes the pointer to the file) without immediately removing any of its contents. At this point the file can be fairly easily recovered by numerous recovery applications. However, once the space is overwritten with other data, there is no known way to recover it.

srm is a secure file removal utility for Unix and Unix-like computer systems, such as Mac OS X or Linux respectively. It is a command line utility which exercises the Gutmann 35-pass algorithm for secure file deletion.

Let us test this. In our example, we want to have the password for a non privileged user changed.

We boot up an Ubuntu 9.10 operating system. We log on as a non privileged user. We click System and then click “Users and Groups”. We click our user account. We click “Change password”. We type in our current password and authenticate. We type in our new password. We retype the new password. We click “Change password”. The dialogue confirm, that our password has been changed. This seems good! We click Close. However, now a dialogue appear. It want us to authenticate again. We type in our new password. This fails. We end up with an error message, that say “The configuration could not be saved. An unknown error occured”. We log out and must try a different approach.

It seems, that changing password is an untested feature in Ubuntu.

We log on as a privileged user. Click System. Click “Users and Groups”. We click the keys to make changes and enter our password. We click the user. We click Properties. We enter the new password. We take a look at his privileges. Close. Now, we are back at the “Users and Groups” dialogue. We close that as well. We log out and log on as the non privileged user.

It worked. It seems, that only privileged users can change password for non privileged users.

There are a number of online tools, that can do that. However, it can be a security problem to use these as PDFs will have to be transmitted over the internet in unencrypted format. There are also a number of downloadable applications. We recommend PDFsam.

In our test of PDFsam on the Ubuntu 9.10 operating system, we want to split a multipaged PDF into single PDFs and then merge a number of single PDFs into a single PDF.

We install PDFsam from Ubuntu Software Center. When installed, we launch it by clicking Applications, Office and pdfsam.

We open the Split plugin, add our multipaged PDF, choose Burst, choose same destination as source and then run the plugin. The splitted PDFs are written as expected. We open the Merge plugin, add our PDFs, move the pages up or down as necessary, set our destination file and run the plugin. The new multipaged PDF is written as expected.

Raw pictures can have non-efficient file names from the digital camera. This makes them hard to organize and list. Raw pictures can be huge in file size. This is a problem for storage, backup, transfer, upload and download. Raw pictures can contain hidden data from your camera, camera software and picture editing software. The hidden data can include automatic data, such as timestamps, face identification and software details. That can be a security problem.

Therefore, you might want to prepare raw pictures for sharing over the internet.

In the following example, we will prepare a number of raw pictures from a digital camera for sharing over the internet.

The pictures are rotated according to their orientation data in Exchangeable Image File Format (EXIF). The orientation data in EXIF is then reset. The pictures are renamed according to the timestamp in EXIF. The pictures will have their EXIF header removed for security reasons. All this is done using jhead, which a JPEG EXIF header manipulation tool, that is perfect for this task.

jhead -autorot -ft -nf%Y-%m-%d-%H-%M-%S -purejpg *.JPG

The pictures are resized. This makes them smaller in file size and makes them fit the target. In this example, we will prepare pictures for sharing on Facebook, which uses a maximum size of 720 pixels. This is done using mogrify, which is perfect command line processing tool for this task. mogrify is a part of ImageMagick. If the picture is horizontal, the picture is resized to a maximum width of 720 pixels. If the picture is vertical, the picture is resized to a maximum height of 720 pixels. The aspect ratio remains the same.

mogrify -resize 720x720 *.jpg

If needed, we can apply grey scaling and then a blue tint. This effect will make all pictures appear blue.

mogrify -modulate 100,0,100 -fill 'blue' -tint 25 *.jpg

If needed, we can add a watermark. In this example, we will set the font type to the Kompakt TrueType font, the font size to 36, the place to bottom right, the font outline color to white, the transparency to 30% (0.3), the font RGB color code to 200,0,200 (pink), the transparency to 30%, the location to 5,0 (a little more space to the right edge) and our website address as the watermark.

mogrify -font /usr/share/fonts/truetype/opentech/kompakt.ttf -pointsize 36 -draw "gravity southeast stroke rgba(255,255,255,0.3) fill rgba(200,0,200,0.3) text 5,0 'www.opentech.dk'" *.jpg

Open Tech SmbA can help your company automate picture and image processing. Contact Open Tech SmbA by mail at opentech@opentech.dk or call Open Tech SmbA at +45 43 62 22 88.

Privat Digital Signatur er din personlige underskrift på internettet. Du kan blandt andet bruge signaturen til at ordne selvangivelsen, logge på e-boks, søge SU, skrive dit barn ind i en daginstitution, se dine sundhedsdata og meget mere. Du kan underskrive dokumenter og blanketter online.

Erhverv Digital Signatur giver virksomhederne mulighed for at lave indberetninger, udfylde og sende blanketter, fortrolige dokumenter, kontrakter og meget mere direkte over nettet. Det hele kan sendes krypteret, så ingen uvedkommende kan få adgang til informationerne.

I dette eksempel vil vi installere Erhverv Digital Signatur på en computer med Ubuntu 9.10 og Firefox 3.5.8.

Bestilling

Vi besøger hjemmesiden for DanID, vælger Erhverv Digital Signatur, vælger gratis medarbejdersignatur, udfylder felterne og udskriver aftalen om oprettelse af lokaladministrator (LRA) til udstedelse af medarbejdersignaturer og virksomhedssignaturer. Vi underskriver aftalen, sender aftalen per fax til DanID og afventer herefter den midlertidige kode, der skal bruges til installationen (installationskode).

Vi modtager samme dag en velkomst per elektronisk post fra DanID. I den findes en unik URL, der skal benyttes sammen med ovenstående installationskode. Vi modtagere endvidere en velkomst til Digital Signatur LRA, der er et system, der efter installation kan bruges til administration af vores brugere.

Vi modtager to dage efter ovenstående installationskode og en spærrekode fra DanID. Vi gemmer spærrekoden et sikkert sted.

Udstedelse af digitale signatur

Vi er nu klar til udstedelsen af vores nye digitale signatur. Vi starter åbner den URL, vi modtog fra DanID. Vi kommer ind på en side hos DanID med overskriften “Installation af Digital Signatur”. Vi læser og accepterer betingelserne. Vi accepterer endvidere, at der installeres software. Vi angiver den fremsendte installationskode. Vi opretter en adgangskode. Denne adgangskode vil blive knyttet til vores nye digitale signatur og skal således bruges fremover. Vi gemmer vores digitale signatur lokalt. Formatet er HTML, der er DanID’s eget beskyttede format. Hjemmesiden kvitterer for udstedelsen af vores digitale signatur og viser detaljerede oplysninger, herunder indehaveren, udstederen, udløbsdato og adresse. Vi noterer os udløbsdatoen. Vi kopierer endvidere den digitale signatur til et sikkert sted.

Eksport af digital signatur til standarden Public Key Cryptography Standards (PKCS) 12

Før vi kan få importeret den digitale signatur til browseren Firefox, skal vi have den gemt i et standard format. Vi åbner den digitale signatur fra før. Browseren viser overskriften “Digital Signatur sikkerhedskopi” og tilbyder indlæsning. Vi angiver stien til vores digitale signatur. Der fremkommer herefter en rød dialog, der siger, at vores browser-installation ikke blev genkendt. Det ser umiddelbart ikke lovende ud, men, dialogen tilbyder, at gemme vores digitale signatur igen – uden beskyttelse af DanID. Formatet er denne gang PKCS 12, hvilket er den standard og det format, vi er interesseret i. Vi kopierer endvidere den digitale signatur i dette format til et sikkert sted. Det er denne fil, vi skal bruge fremover.

Import af digital signatur til browseren Firefox

Vi kan nu importere vores digitale signatur i vores browser Firefox. Vi vælger Edit, Preferences, Advanced, Encryption, View Certificates, Your Certificates og “Import…”. Der kommer en dialog, der umiddelbart burde vise PKCS12-filer. Det gør den dog ikke. Vi skifter til visning af alle filer og åbner vores digitale signatur i PKCS12-format. Firefox kvitterer med dialogen “Successfully restored your security certificate(s) and private key(s)”. I listen over certifikater ses nu vores digitale signatur og vi kan genkende de detaljerede oplysninger fra udstedelsen.

Anvendelse

Vi åbner hjemmesiden for Skat. Dette er en af de hjemmesider, der understøtter sikker selvbetjening ved brug af digital signatur. Vi vælger, at logge ind med digital signatur. Vi skal nu vælge, hvilken digital signatur, vi vil logge på med. Vi vælger, at gennemse, hvorefter vi vælger vores digitale signatur i PKCS12-formatet fra før. Vi angiver vores adgangskode. Vi er herefter logget ind og kan betjene os selv på sikker vis.