Posted by gmendoza on December 9, 2009 under Tech Tips | 
If you’re running the Gnome desktop environment and would like to have GnuPG context menu options in Nautilus to encrypt, decrypt, and digitally sign files, simply install the Seahorse plugins package available in your favorite Linux distribution repositories. If using Debian or Ubuntu, it’s as easy as an apt-get install.
sudo apt-get install seahorse-plugins
After installing the package, go to System -> Preferences -> Encryption and Keyrings, select a default key to use and decide whether you want to include your own key by default when encrypting files. This is sometimes a good idea if you ever want to open a file you encrypted to someone else. Below are some screenshots of the Seahorse preferences.
Here are some screen shots of the context menu options that appear when you right click on files in Nautilus.
When you choose to encrypt a file, you can select as many public keys as you’d like. Here’s an example of the dialogue.
Using PGP has never been easier. There are still some improvements to the UI I would like to see completed, but overall the most important features are there.
Posted by gmendoza on June 21, 2009 under Tech Tips |
I recently needed to organize a large number of old digital photos that had the wrong date embedded in their EXIF tag data. The camera I used many years ago would often lose track of time and would sometimes be set to the wrong year. Applications I now use to organize photos read this data and made my albums difficult to navigate. I came across a Linux command line utility called jhead that allows you to modify this information to whatever you wish, and its easy to use in scripts as well. Installing was easy, because it’s currently in most repositories, including Ubuntu’s.
To read existing EXIF tag data, simply run jhead against an image without any options. As you can see from the example below, my date is set to the year 2022.
jhead image.jpg
File name : image.jpg
File size : 159390 bytes
File date : 2004:01:12 07:35:23
Camera make : Samsung
Camera model : Digimax 200
Date/Time : 2022:02:12 04:04:17
Resolution : 800 x 600
Flash used : Yes
Exposure time: 0.045 s (1/22)
Aperture : f/2.8
To clear all EXIF data from the file, use the -de option. Then recreate the EXIF fields with the -mkexif option, and check the data again. Notice the new Date/Time is set to the timestamp on the file.
jhead -de image.jpg
Modified: image.jpg
jhead -mkexif image.jpg
Modified: image.jpg
jhead image.jpg
File name : image.jpg
File size : 147751 bytes
File date : 2004:01:12 07:35:23
Date/Time : 2004:01:12 07:35:23
Resolution : 800 x 600
To change the entire timestamp manually, use the -ts option. Notice, there is no space between the -ts and the option. I could not trust the month and day, so I simply chaged the date to midnight on January 1, 2003.
jhead -ts2003:01:01-00:00:00 image.jpg
Modified: image.jpg
jhead image.jpg
File name : image.jpg
File size : 147751 bytes
File date : 2004:01:12 07:35:23
Date/Time : 2003:01:01 00:00:00
Resolution : 800 x 600
For many more options, check out the man page or visit the jhead site for more info.
Posted by gmendoza on October 19, 2008 under Tech Tips |
Here’s a simple tutorial on how to backup a list of all your installed repository applications, and restore them to another machine, perhaps even the same machine after a clean installation. This can save you an incredible amount of time, especially when this task must be repeated often. Of course, being that Ubuntu is based on Debian, this will work for any Debian based platform.
First, from a computer with all the applications preinstalled, retrieve your installed package list and redirect the output to a file called packages.txt. Save this package list somewhere so that you can use it for the restore process.
sudo dpkg --get-selections > packages.txt
To restore all the applications from your list, you must follow a three step process very carefully.
sudo dpkg --clear-selections
sudo dpkg --set-selections < packages.txt
sudo aptitude install
You will be prompted to install all the new applications in the list.
Another example of what this process allows you to do is create a baseline of all the applications after a clean installation of Ubuntu. Let’s say you would like to remove any applications installed since the clean install, perform the exact same process, and any package not defined in that list will be removed.
sudo dpkg --get-selections > clean-install-package-list.txt
sudo dpkg --clear-selections
sudo dpkg --set-selections < clean-install-package-list.txt
sudo aptitude install
The very first command of “–clear-selections” marks all currently installed packages to the state “deinstall”. When you restore the list of applications using “–set-selections”, only packages ommited from the list will remain in the “deinstall” state. Aptitude will honor the deinstall state and remove the extra packages, leaving you only with packages from the list. Most excellent. :-)