Linux embedded Systems

Nice tutorial that concludes a series of tutorials on embedded Linux system development by noted ARM Linux kernel hackers Vincent Sanders and Daniel Silverstone, here

ASCII art

This is amazing stuff!!

 _   _             _                          _       
| | | |_   _ _ __ | |_ ___ _ ____      ____ _| | __ _ 
| |_| | | | | '_ \| __/ _ \ '__\ \ /\ / / _` | |/ _` |
|  _  | |_| | | | | ||  __/ |   \ V  V / (_| | | (_| |
|_| |_|\__,_|_| |_|\__\___|_|    \_/\_/ \__,_|_|\__,_|

OR

 _   _  __  __  _  _  ____  ____  ____  _    _    __    __      __   
( )_( )(  )(  )( \( )(_  _)( ___)(  _ \( \/\/ )  /__\  (  )    /__\  
 ) _ (  )(__)(  )  (   )(   )__)  )   / )    (  /(__)\  )(__  /(__)\ 
(_) (_)(______)(_)\_) (__) (____)(_)\_)(__/\__)(__)(__)(____)(__)(__)

Make you own and embed it in your source code :)
Click here to convert. They have various fonts as you see ;)

ping sweep

You have a machine on the subnet for which you know the MAC address but you don't know what IP address it got after a restart, use nmap and do a ping sweep:

sudo nmap -n -sP 192.168.1.0/24 | grep "00:11:22:33:44"

-n tells nmap not to never do reverse DNS resolution on the active IP address it finds. Makes scanning faster
-sP Only perform a ping scan (host discovery) and prints the results, go no further.

HTML editor

I am working on creating the website for my lab and I had to find a good open source alternative to Dreamweaver.

Bluefish Editor
It is a nice editor but it is not a WYSIWYG. One needs to go back to learning HTML and family and it becomes irritating after sometime.





Quanta Plus
Like Bluefish but more crappy and archaic. I would suggest installing software using aptitude rather than apt-get because it is easy to purge and clean the dependency chain that it creates.




KompoZer
This is best editor. Powered by Mozilla (even looks like Firefox) and is a WYSIWYG with powerful features like tag view, source view and preview. It provides easy layering (div) and properties. It took me 10 minutes to create the same page that took 1 hour in Bluefish. Winner!!!

[Book] Beginning Perl

Beginning Perl by Simon Cozens is available in PDF format online under the Creative Commons license. Nice resource, if you are starting from scratch.

link

[Image courtsey: http://www.amazon.com]

Changing the default size of gnome-terminal

The small window can be a pita sometimes.

Figure out what size you want to make the terminal. (If you have compiz enabled, while dragging the right bottom edge, you can get the size in the center of the screen, else trial-and-error)

Add gnome-terminal to the panel, change the properties and add the following to the command

gnome-terminal --geometry 152x55

(or whatever size you prefer)

[Book] Linux in a nutshell

This O'Reilly book is a good starter for people new to Linux. Here are the list of useful commands from the book.

[Image courtsey http://www.oreillynet.com]

Using cut and uniq

For some weird reason I had to do this, cut and uniq turned out to be quite handy and can be used along with sed

cat /proc/cpuinfo | grep "model name" | uniq | cut -d: -f2

So, instead of this
model name : Intel(R) Core(TM)2 Duo CPU E8500 @ 3.16GHz
model name : Intel(R) Core(TM)2 Duo CPU E8500 @ 3.16GHz

I get this
Intel(R) Core(TM)2 Duo CPU E8500 @ 3.16GHz

OK, another approach is to use awk
cat /proc/cpuinfo | grep "model name" | uniq | awk -F: '{print($2)}'

Emacs command list

Sometimes I tend to forget some of these :D :P

C = Control
M = Meta = Alt|Esc

Basics
C-x C-f "find" file i.e. open/create a file in buffer
C-x C-s save the file
C-x C-w write the text to an alternate name
C-x C-v find alternate file
C-x i insert file at cursor position
C-x b create/switch buffers
C-x C-b show buffer list
C-x k kill buffer
C-z suspend emacs
C-X C-c close down emacs

Basic movement
C-f forward char
C-b backward char
C-p previous line
C-n next line
M-f forward one word
M-b backward one word
C-a beginning of line
C-e end of line
C-v one page up
M-v scroll down one page
M-< beginning of text
M-> end of text

Editing
M-n repeat the following command n times
C-u repeat the following command 4 times
C-u n repeat n times
C-d delete a char
M-d delete word
M-Del delete word backwards
C-k kill line

C-Space Set beginning mark (for region marking for example)
C-W "kill" (delete) the marked region region
M-W copy the marked region
C-y "yank" (paste) the copied/killed region/line
M-y yank earlier text (cycle through kill buffer)
C-x C-x exchange cursor and mark

C-t transpose two chars
M-t transpose two words
C-x C-t transpose lines
M-u make letters uppercase in word from cursor position to end
M-c simply make first letter in word uppercase
M-l opposite to M-u

Important
C-g quit the running/entered command
C-x u undo previous action
M-x revert-buffer RETURN (insert like this) undo all changes since last save
M-x recover-file RETURN Recover text from an autosave-file
M-x recover-session RETURN if you edited several files

Online-Help
C-h c which command does this keystroke invoke
C-h k which command does this keystroke invoke and what does it do?
C-h l what were my last 100 typed keys
C-h w what key-combo does this command have?
C-h f what does this function do
C-h v what's this variable and what is it's value
C-h b show all keycommands for this buffer
C-h t start the emacs tutorial
C-h i start the info reader
C-h C-k start up info reader and go to a certain key-combo point
C-h F show the emacs FAQ
C-h p show infos about the Elisp package on this machine

Search/Replace
C-s Search forward
C-r search backward
C-g return to where search started (if you are still in search mode)
M-% query replace

Space or y replace this occurrence
Del or n don't replace
. only replace this and exit (replace)
, replace and pause (resume with Space or y)
! replace all following occurrences
^ back to previous match
RETURN or q quit replace


Search/Replace with regular expressions
Characters to use in regular expressions:
^ beginning of line
$ end of line
. single char
.* group or null of chars
\< beginning of a word
\> end of a word
[] every char inside the backets (for example [a-z] means every small letter)

M C-s RETURN search for regular expression forward
M C-r RETURN search for regular expression backward
M C-s incremental search
C-s repeat incremental search
M C-r incremental search backwards
C-r repeat backwards
M-x query-replace-regexp search and replace

Window-Commands
C-x 2 split window vertically
C-x o change to other window
C-x 0 delete window
C-x 1 close all windows except the one the cursors in
C-x ^ enlarge window
M-x shrink-window command says it ;-)
M C-v scroll other window
C-x 4 f find file in other window
C-x 4 o change to other window
C-x 4 0 kill buffer and window
C-x 5 2 make new frame
C-x 5 f find file in other frame
C-x 5 o change to other frame
C-x 5 0 close this frame

Bookmark commands
C-x r m set a bookmark at current cursor pos
C-x r b jump to bookmark
M-x bookmark-rename says it
M-x bookmark-delete "
M-x bookmark-save "
C-x r l list bookmarks

d mark bookmark for deletion
r rename bookmark
s save all listed bookmarks
f show bookmark the cursor is over
m mark bookmarks to be shown in multiple window
v show marked bookmarks (or the one the cursor is over)
t toggle listing of the corresponding paths
w " path to this file
x delete marked bookmarks
Del ?
q quit bookmark list

M-x bookmark-write write all bookmarks in given file
M-x bookmark-load load bookmark from given file

Shell
M-x shell starts shell modus
C-c C-c same as C-c under unix (stop running job)
C-d delete char forward
C-c C-d Send EOF
C-c C-z suspend job (C-z under unix)
M-p show previous commands

DIRectory EDitor (dired)
C-x d start up dired
C (large C) copy
d mark for erase
D delete right away
e or f open file or directory
g reread directory structure from file
G change group permissions (chgrp)
k delete line from listing on screen (don't actually delete)
m mark with *
n move to next line
o open file in other window and go there
C-o open file in other window but don't change there
P print file
q quit dired
Q do query-replace in marked files
R rename file
u remove mark
v view file content
x delete files marked with D
z compress file
M-Del remove all marks (whatever kind)
~ mark backup files (name~ files) for deletion
# mark auto-save files (#name#) for deletion
*/ mark directory with * (C-u * removes that mark again)
= compare this file with marked file
M-= compare this file with it's backup file
! apply shell command to this file
M-} change to the next file marked with * od D
M-{ " previous "
% d mark files described through regular expression for deletion
% m " (with *)
+ create directory
> changed to next dir
< change to previous dir
s toggle between sorting by name or date
M-x speedbar starts up a separate window with a directory view

Telnet
M-x telnet starts up telnet-modus
C-d either delete char or send EOF
C-c C-c stop running job (similar to C-c under unix)
C-c C-d send EOF
C-c C-o clear output of last command
C-c C-z suspend execution of command
C-c C-u kill line backwards
M-p recall previous command

Text
Works only in text mode
M-s center line
M-S center paragraph
M-x center-region name says

Macro-commands
C-x ( start macro definition
C-x ) end of macro definition
C-x e execute last definied macro
M-n C-x e execute last defined macro n times
M-x name-last-kbd-macro give name to macro (for saving)
M-x insert-keyboard-macro save named macro into file
M-x load-file load macro
M-x macroname execute macroname

Programming
M C-\ indent region between cursor and mark
M-m move to first (non-space) char in this line
M-^ attach this line to previous
M-; formatize and indent comment
C, C++ and Java Modes
M-a beginning of statement
M-e end of statement
M C-a beginning of function
M C-e end of function
C-c RETURN Set cursor to beginning of function and mark at the end
C-c C-q indent the whole function according to indention style
C-c C-a toggle modus in which after electric signs (like {}:';./*) emacs does the indention
C-c C-d toggle auto hungry mode in which emacs deletes groups of spaces with one del-press
C-c C-u go to beginning of this preprocessor statement
C-c C-c comment out marked area
M-x outline-minor-mode collapses function definitions in a file to a mere {...}
M-x show-subtree If you are in one of the collapsed functions, this un-collapses it

In order to achive some of the feats coming up now you have to run etags *.c *.h *.cpp (or what ever ending you source files have) in the source directory

M-. (Thats Meta dot) If you are in a function call, this will take you to it's definition
M-x tags-search ENTER Searches through all you etaged
M-, (Meta comma) jumps to the next occurence for tags-search
M-x tags-query-replace yum. This lets you replace some text in all the tagged files

GDB (Debugger)
M-x gdb starts up gdm in an extra window

Version Control
C-x v d show all registered files in this dir
C-x v = show diff between versions
C-x v u remove all changes since last checkin
C-x v ~ show certain version in different window
C-x v l print log
C-x v i mark file for version control add
C-x v h insert version control header into file
C-x v r check out named snapshot
C-x v s create named snapshot
C-x v a create changelog file in gnu-style

(Reference: http://lpn.rnbhq.org/tools/xemacs/emacs_ref.html)

Mounting an ISO

sudo mount -t iso9660 -o loop /path/to/the/iso /folder/to/mount/into

In case you are getting errors like ISOFS: Unable to identify CD-ROM format., do a file /path/to/the/iso and confirm that the file that you think is an ISO, actually is.

Using ssh, scp, sftp

SSH
The server node should be running the SSH server

sudo aptitude install openssh-server

Connect to the server

ssh username@ipaddress:port

Connect to the server with X enabled

ssh username@ipaddress:port

Note: specify port only if the default 22 is not being used.

SCP
scp can be used to transfer the files between the nodes (works on top of SSH)

From remote node to local node

cd local_folder
scp username@ipaddress:port:/home/username/path/to/folder_file .

From local node to remote node

scp /path/to/local/folder_file username@ipaddress:port:/home/username/path

SFTP
If you have a luxury of a GUI, you can copy using sftp.

Open nautilus (if using Gnome) and type in the location bar the address to the server.

nautilus --no-dektop --browser
Location Bar: sftp://username@ipaddress:port/home/username

Although you can go to the root folder as well, but is not a good practice to screw around in that area