Ubuntu: Fixing NO_PUBKEY error from apt-get

Posted by daniel on 11 January, 2015
Category General

This error is likely to appear when you added an extra repository to your sources (e.g., ppa.launchpad.net). In my case, it was due to Gnome3.

After running apt-get update, I received the following error message:

W: GPG error: http://ppa.launchpad.net trusty Release: The following signature couldn't be verified because the publix key is not available: NO_PUBKEY ≪SIGNATURE≫

Where ≪SIGNATURE≫ was the source signature and consisted of a hexadecimal representation of a large number.

The reason for that error is that I had added the repository, but not its public key. My system couldn't verify it was dealing with the right repository and not a fake one.

To fix it, we have to get the key from some source that we trust. In my case, I got it from Ubuntu. (I am using their system, so I kind of trust them anyway.)

The command to add the key is as follows:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys ≪SIGNATURE≫
sudo apt-get update

The last command I used just to confirm everything was right. ;)

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Last night, I attended to a really interesting talk, given by one of the most recognizable alumni of the University of Calgary: James Gosling, a.k.a., the "Father of Java". He talked about his more recent work, and the talk even included robots in the ocean being attacked by huge sharks. He also showed to be a really approachable person, welcoming any questions he received... And it was a lot, in particular after the talk.

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Microsoft: Meet the company

Posted by daniel on 26 September, 2012
Category General

Quick note: Tonight (or last night), at the university, we had a little talk from Microsoft. The idea was "inviting" students to apply for a job at that company. The highlight that I have to share: at the beginning of the presentation, the Powerpoint froze. They had to call the task manager. The talk was delayed by about 10 minutes. The presenters were visibly embarrassed. Everyone was laughing. And I thought these problems in presentations were pure legend. hehehe

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Now, Xoom™ing with Ice Cream Sandwich

Posted by daniel on 22 June, 2012
Category General

I have recently starting using a Motorola Xoom™ with Android 4.0 (Ice Cream Sandwich).

My cellphone has Froyo (Android 2.2) installed and, comparing to that version of Android, the ICS came a long way and it's a lot better. First thing I noticed was that we can now organize the home screen putting Icons into "folders", just by moving an icon over another one. While I used all the five home screens in my cellphone and feel I needed more, with this feature, I don't use more than 2 home screens in the Xoom.

What I didn't like much was the camera. I have tried to take pictures of my daughter and I barely can get one that is not blurred. (Granted, my daughter simply can't be still for a picture... too much energy!) On a good side, I really like the landscape option for the camera. It worked nicely... Now I just need to get an opportunity to find a nice landscape to photograph.

In terms of performance, I don't know if it's because of the limited number of applications I am using, but I really find the tablet to be quite fast and battery has lasted a bit more than one day (with moderate use, which I find it to be acceptable.

Also, I liked the fact it has 32GB of internal storage (which is a lot compared to other products) and still accepts micro-SD card.

My favorite apps for it, so far, are:
- ConnectBot: a SSH client for Android
- Hacker's Keyboard: A substitute for the original keyboard that gives you a PC keyboard on screen (with numbers over the first row of letters, for example).
- Apex Launcher: "Launcher" is the android equivalent to Windows Managers in Linux. This one is quite light and provides some nice customization options, including number of home screens and animations.

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I used to keep some work files (keep in mind that I am still a student) at Dropbox. The idea was that I could work from home or from the university without having to bring my laptop back and forth and not having to worry about copying stuff before going home.
The problem became when my wife decided to use it to share photos with family. My 2GB space vanished quickly. There is another little problem, I can keep an updated version of my work, but I cannot roll back versions (as if I was using CVS, SVN or git). But having my code in sync with work is helpful enough (and I still can use SVN to control versions once in a while).

A while ago, I tried Unison, by Benjamin Pierce at the University of Pennsylvania. It's an open source software that allow you to implement your own "Dropbox". You have to set up your server machine on the internet, preferably 24x7. That was not the main problem with unison, though. The synchronization does not work so well with multiple users.

Recently, I looked for other alternatives and found Ubuntu One. It gives you up to 5GB for free, and you have a bit more granularity if you want to add extra space (so it's possible to spend less money than with Dropbox). For now, I am keeping work in Ubuntu One and personal stuff in Dropbox.

Now, when sharing this with a friend (Jon), he mentioned yet another alternative. It's called Sparkleshare, that performs synchronization, but using git. So, it's possible to have some version control at the same time as we have automatic synchronization. As Unison, I still have to set up a server (I could use Githup, but I don't like the idea of having my unfinished work open to the public).

I really find this Sparkleshare quite promising. I haven't used it yet, but I will soon be configuring a Git server and check how this thing works. More on this in a future post.

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In 2011/2012, I think that the best application I have tried (so far) is called Synergy. Synergy allows users to share the same keyboard and mouse between different computers, even with different operating systems.

Synergy consists of a server (installed on the machine you'd be physically using the keyboard and mouse) and a client (installed on the other machines). To change between systems, you just need to move the mouse to left or right (just like if you had a dual monitor system).

Just to give a hint of what we can do, in one moment, I was running some experiments in two other computers (other than my laptop). That's right! I was sharing my laptop's mouse and keyboard with two other computers. So, instead of having to manually switch from one keyboard to another, I just moved my mouse to the respective screen and started typing.

Anyone who has to work with multiple computers (for whatever reason) should give Synergy a try.


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