[QnA] Taking screenshots of virtual consoles?

I am trying to find ways to take screenshots of virtual consoles. This article shows the method of taking screenshots from console using the ImageMagick. The author said that the method also works for consoles with the command as the follows

$ sudo chvt N; sleep T; import -display :0.0 -window root output.png; sudo chvt M

where N is the target console and T is the time in seconds. The last chvt command is just for returning the original working console.

After testing with the command, however, I found the png file was generated but the image itself is not what I expected. At the beginning I thought that might due to my framebuffer setting so I disabled the corresponding setting in the /boot/grub/menu.lst. Nothing has been improved and I still can only get the following useless image.

[QnA] FrameBuffer setting

Several months ago, I learned the way to view images in the virtual console. I happened to recall the framebuffer and want to know more about it, so I began to search related information again.

Here are several informative web pages:

1. Images and Videos on the Command Line? YES!
2. Using framebuffer devices on Intel platforms
3. Ubuntu wiki: FrameBuffer

In the 2nd web page, there is a table showing the values for different resolution as follows:

Colours   640x400 640x480 800x600 1024x768 1152x864 1280x1024 1600x1200
--------+--------------------------------------------------------------
 4 bits |    ?       ?     0x302      ?        ?        ?         ?
 8 bits |  0x300   0x301   0x303    0x305    0x161    0x307     0x31C
15 bits |    ?     0x310   0x313    0x316    0x162    0x319     0x31D
16 bits |    ?     0x311   0x314    0x317    0x163    0x31A     0x31E
24 bits |    ?     0x312   0x315    0x318      ?      0x31B     0x31F
32 bits |    ?       ?       ?        ?      0x164      ?

Furthermore, from the 3rd reference I found more useful setting such as

• ``vga=normal'', or ``nofb'', disables the framebuffer
• ``vga=ask'' will able you to set a value at each boot good for testing out the various modes.

[QnA] Sound volume control in command line

I've used wmii for several weeks, and it meets most of my need well. Sometimes, however, I want to control the volume but there is no the control panel as in the Gnome desktop environment.

Here is the solution: amixer (or alsamixer, which has the ncurses interface).

To use alsamixer is easier due to the straightforward interface. If you get the following error message when you type ``alsamixer'' in the command

alsamixer: function snd_ctl_open failed for default: Connection refused

then do the following steps:

$ rm ~/.asoundrc and then do
$ asoundconf list
$ asoundconf set-default-card foo

where the foo is one of the sound cards listed by `asoundconf list.'

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Ref:
http://ubuntuforums.org/showthread.php?t=597765
http://ubuntuforums.org/showpost.php?p=3631606&postcount=4

[SW] Big5 and utf-8 in Vim

To make Vim open big5 files properly, just set the following

set fileencodings=utf-8,big5,euc-jp,gbk,euc-kr,utf-bom,iso8859-1
set encoding=utf8
set tenc=utf8

---
Ref: http://wiki.debian.org.tw/index.php/Unicode#VIM

[Py] Equal sign

Python: Careful with equal sign

I found this article when I was searching for the information about comparisons in Python.

When we assign a variable to another, for example, a = 1; b = a, Python just passes the reference (of variable a) to the new one (i.e., the variable b) but not creates a new copy with new memory address.

>>> a = 1
>>> b = a
>>> id(a) == id(b)
>>> True

But if we change the value of b, then a new memory block will be used to store the new assigned value.

>>> b = 2
>>> id(a) == id(b)
>>> False

[Py] Comparisons -- ``=='' vs. ``is''

In Python, there two operators which check whether things are the same. One is ``=='' and another is ``is.'' They may produce identical results but actually they have different meanings.

I found an article talked about this: is is not the same as equal in Python

The simple guideline has been given by Eric:

You should really only use 'is' to check for object identity, and for any kind of value comparison, == is the way to go.

And an interesting example has been given by Kevin:

>>> "peter" == "peter"
>>> True
>>> "peter" is "peter"
>>> True

>>> "peter" is "peter1"[:-1]
>>> False
>>> "peter" == "peter1"[:-1]
>>>True

---
ref: Python built-in types: comparison

[Py] Guidelines for Python coding style

Here are two links about the Python coding style:

• Style Guide for Python Code (by Guido van Rossum and Barry Warsaw)
• Python Coding Guidelines (by Rob Knight)

One thing I've never noticed is the indentation problem. Python relies on consistent indentation of code blocks, so if the programmer mixed spaces and tabs in the code there could be problems when others open or edit the code with other editors with different tab setting.

The above links give many information that I cannot read throughly in limited time, but they have offered me some useful guidelines to follow in the future.

[QnA] Cannot mount disk -- you are not privileged to mount volume

One of my Windows XP disk partition happened to be unmountable and I totally didn't know why. I've set the auto mounting in /etc/fstab and it has worked well till today.

To solve this problem, use:
$sudo mount -t ntfs-3g /dev/yourdevice /media/yourfolder -o force

[QnA] GPG error -- the solution

When the Ubuntu users update and upgrade their system, there are, sometimes, GPG error messages shown in the GUI dialog or command line terminal.

Here are a solution I've found useful and easy (only two steps):

$ gpg --keyserver keyserver.ubuntu.com --recv put_the_last_8_digits_of_the_key_here
$ gpg --export --armor put_the_last_8_digits_of_the_key_here | sudo apt-key add -

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Some other related links (for backup and reference):
https://answers.launchpad.net/easyubuntu/+question/73458
https://answers.launchpad.net/ubuntu/+question/73171
http://kovyrin.net/2006/11/28/debian-problem-apt-get-update/