Experimenting with GNU/Linux

Reduce the size of PDF files

noreply@blogger.com (madhu) — Wed, 31 May 2017 22:45:00 +0000

Reduce the size of PDF file using ghost script

https://tex.stackexchange.com/questions/73444/can-pdflatex-or-any-tex-package-automatically-rescale-included-images-which-ha

gswin64c.exe -sDEVICE=pdfwrite -dMaxSubsetPct=100 -dPDFSETTINGS=/ebook -dAutoFilterColorImages=false -dColorImageFilter=/FlateEncode -sOutputFile=" Thesis.pdf" -dNOPAUSE -dBATCH "PHD_Thesis_madhu.pdf "

Ghostscript resamples to a given dpi based on dPDFSETTINGS:

prepress = 300 dpi

printer = 300 dpi

ebook = 150 dpi

screen = 72 dpi

Pattern download wget

noreply@blogger.com (madhu) — Mon, 26 Sep 2016 05:05:00 +0000

Pattern "*1080*mov" with one level (red colour) down search

wget -A "*1080*mov" -r -np -nc -l1 --no-check-certificate -e robots=off http://www.example.com

link http://stackoverflow.com/questions/20927157/wget-accept-files-containing-pattern

Installing Torque on debian 7

noreply@blogger.com (madhu) — Tue, 21 Apr 2015 01:50:00 +0000

# DO the following after installation into default

# Configure the trqauthd daemon to start automatically at system boot

cp contrib/init.d/debian.trqauthd.in /etc/init.d/trqauthd.in

# Fix the server_name in /var/spool/torque/server_name

echo "$HOSTNAME" >/var/spool/torque/server_name

echo '/usr/local/lib' > /etc/ld.so.conf.d/torque.conf

ldconfig

cp contrib/init.d/debian.pbs_mom.in /etc/init.d/pbs_mom
update-rc.d pbs_mom defaults

cp contrib/init.d/debian.pbs_server.in /etc/init.d/pbs_server

update-rc.d pbs_server defaults

echo "\$pbsserver $HOSTNAME" | sudo tee /var/spool/torque/mom_priv/config

echo "$HOSTNAME np=`cat /proc/cpuinfo | grep processor | wc -l`" | sudo tee /var/spool/torque/server_priv/nodes

cp pbs_server pbs_mom pbs_sched /etc/init.d/

qterm

pbs_server

pbs_mom

pbs_sched

# see if nodes are available:
qnodes -a

# setup database

pbs_server -t create

# create queue and set server settings in database
Code:

qmgr
create queue batch
set queue batch queue_type = Execution
set queue batch max_running = 22
set queue batch resources_max.ncpus = 24
set queue batch resources_max.nodes = 1
set queue batch resources_default.ncpus = 1
set queue batch resources_default.neednodes = 1:ppn=24
set queue batch resources_default.walltime = 3600:00:00
set queue batch max_user_run = 6
set queue batch enabled = True
set queue batch started = True
set server default_queue = batch
set server scheduling = True

exit

# restart the server
trqauthd
qterm
pbs_server
pbs_sched # this will give some warning about missing files
pbs_mom

# important
sudo su # login to root
qterm -t quick
momctl -s % shutdown pbs_mom
killall pbs_sched % kill all sched
pbsnodes -a %% all should be free

qmgr -a -c 'set node cvraman state=free'

Rename files recursively in Linux

noreply@blogger.com (madhu) — Tue, 21 Apr 2015 01:41:00 +0000

copy folders between linux servers

rsync -avh ssh /home/foo jerry@openbsd.nixcraft.in:/home/madhu/

#In the specified directory

find /my/directory/ -name "*.jpeg" -exec rename s/.jpeg/.jpg/ {} ;

# In all subdirectories 

# Rename '.gz%0D' extension to '.gz' 

find . -name "*.gz%0D" -exec rename s/.gz%0D/.gz/ {} \;

# Unzip recursievly  in all subdirectories

find . -name "*.gz" | xargs gunzip

# find number of file in all subdirectories

find . -type f | wc -l

#  Delete files with specified extension in all subbirectories 

find . -name \*.tiff -type f -delete 

Delete ZIP files in all sub folders

find . -name "*.ZIP" -print0 | xargs -0 rm -rf

Unzip files in all sub folders

find . -name "*.ZIP" -exec sh -c 'unzip -d "${1%.*}" "$1"' _ {} \;

Find all files in sub directories and copy to desired folder

find <start directory> -iname "<all my files type>" -exec cp {} <target_dir> \;

# See this

$ rename 's/search/replace/;' file1 [file2 file3...]

$ rename 's/tutorial0/mymodel/;' *

Converting a space delimited file to tab delimited

noreply@blogger.com (UbuntuGuru) — Thu, 15 May 2014 05:53:00 +0000

try this one liner
cat file | tr ' ' '\t'

How to cut video using ffmpeg

noreply@blogger.com (UbuntuGuru) — Mon, 10 Jun 2013 10:43:00 +0000

You can cut a piece of video from a bigger video like this.

ffmpeg -ss 00:00:30 -t 00:00:05 -i source_video -vcodec copy -acodec copy newfilename

skype 4.2 j on debian wheezy behind proxy

noreply@blogger.com (Fermi Level) — Tue, 28 May 2013 05:11:00 +0000

The new skype 4.2 on linux machines do not offer a configuration screen when you start it for the first time. If you are behind a proxy, you are stuck.
Here is the quick solution.
Start skype. The EULA screen will come up. Accept it (at your own risk). The skype log in screen will come up. Press Cntrol + O . The configuration screen will come up.

Skype on debian Wheezy amd 64

noreply@blogger.com (Fermi Level) — Tue, 28 May 2013 04:56:00 +0000

Here are is what I did for installing skype on debian wheezy 64 bit.

1) Enable 32 bit repositories

# dpkg --add-architecture i386
# apt-get update

 2 Install  libpulse from i386 repository

   
# apt-get install libpulse0:i386

Download skype from skype.com. Choose debian wheezy package (multiartch)

# dpkg -i skype-debian_4.2.0.11-1_i386.deb

The package will fail to configure.

Install the dependencies by

 #apt-get install -f

Done :)

File format conversion made simple

noreply@blogger.com (UbuntuGuru) — Fri, 21 Dec 2012 17:19:00 +0000

Format Junkie is an Graphical application which gives you an easy file format manipulation facility on your desktop. The home page of Format Junkie is here . It is available in launch pad so that you can quickly install it on Ubuntu .
Some of the file conversion capabilities are

a) Audio: Conversion between the audio formats: mp3, mp2, wav, ogg, wma, flac, m4r, m4a and aac
b) Video: Conversion between the video formats: avi, ogv, vob, mp4, vob, flv, 3gp, mpg, mkv, wmv
c) Image: Conversion between the image formats: jpg, png, ico, bmp, svg, tif, pcx, pdf, tga, pnm
d) Iso|Cso Create an iso with selected files, convert iso to cso and vice versa.
e) Advanced Encode subtitles to an avi file.

Format Junkie Installation:
Add the ppa to your machine

sudo add-apt-repository ppa:format-junkie-team/release

Install format junkiee

sudo apt-get update
sudo apt-get install formatjunkie

After successful installation, you can open up the application from the Unity 'Dash' Here is a screen shot.

Command-Line Multitasking with Screen

noreply@blogger.com (UbuntuGuru) — Wed, 19 Dec 2012 17:50:00 +0000

Most modern Unix like operating systems (e.g. Linux, MacOS X, and BSD) come with ( or can be installed ) a little console-mode utility called GNU Screen. Even some of the power user who work exclusively on console are unaware of its existence.
What is screen ?
Screen is best described as a terminal multiplexer. That is any number of console applications can be run concurrently with in a single terminal and you can quickly switch back and forth between these applications. If you are logged to a remote server via ssh , you can run many applications in a single ssh session. The programs will be running even if you accidentally close the ssh connection.\

Starting screen: launching and switching between programs
Start screen just by typing screen at your favourite command shell prompt. You'll probably be greeted by a welcome message. Dismiss this and you'll have with an empty terminal containing a shell prompt, which is pretty much what you had before you started screen.

Every program running under screen runs in a window, and every window is identified by a unique number. Screen made a new window, numbered it 0, and started a command shell inside it.

Let us run ls command in this window or any other command so that we can recognise the window later on.

Now make another window; this will be window 1.

To do this, type C-a c; that is, type Ctrl-a and then type c

Now that you have two windows,

. To switch between windows , type C-a C-a, which will switch you to whichever window you were using before the current one. Here are some more window switching key sequences if you have many windows open under screen.

Use C-a n and C-a p to switch to the next or previous window in the list, by number.

Use C-a N, where N is a number from 0 to 9, to switch to the corresponding window.

Use C-a " to get a full-screen list of windows. You can navigate this list with the arrow keys (or vi-style, with j and k), and pick a window to activate by pressing Enter when it's highlighted. C-a w will give you a small, non-interactive list of windows.

A window can be given a name if you type C-a A    This name will be used in the window listing, and will help you remember what you're doing in each window when you start using a lot of windows.
Exiting the last program in a window will cause the window to disappear. You can also kill misbehaving programs with C-a K.

Terminal decoupling and re coupling
   You can detach from the screen session by pressing C-a d. This means the screen session will be decoupled from the   terminal in which you started it up. If you close the terminal in which screen is running , the session will be automatically detached.   Detaching a screen session does not terminate any of the programs running in that screen session .
Start up a new terminal emulator, and type screen -r . You'll be right back where you were when you detached.
   You can detach from a screen session at work, shell into the machine from home, and reattach.

Copying, pasting, and the scrollback buffer

Screen remembers a configurable number of scrollback lines, and you'll need them because you won't be able to use your terminal emulator's scroll features while running screen. You can access the scrollback buffer by entering "copy mode", which is accomplished by typing C-a [. You can mark text anywhere in the scrollback buffer and paste it with C-a ].

Monitoring for silence and activity
One of the disadvantages of running a bunch of programs within screen is that you can't keep an eye on all of them at the same time, since in general you can only see one at once. ) To help mitigate this problem, Screen has features that allow you to monitor a window for silence--useful for knowing when a compile has finished, for example--or activity--useful for knowing when someone is finally talking on your favourite IRC channel, for example.
To start or stop monitoring the current window for 30 seconds of silence, type C-a _; to start or stop monitoring a window for activity, type C-a M.
Config Files
   Screen looks for a startup configuration file named .screenrc in your home directory. Look in screen man pages for options.

Remote control your desktop with android phone

noreply@blogger.com (Fermi Level) — Fri, 14 Dec 2012 08:06:00 +0000

Gmote is a powerful program which allows your anddroid phone to act as a remote control for your Linux desktop. Gmote provides all standard remote control features such as play, pause, rewind, volume controls etc.

Gmote can also be used as a wireless Touchpad and keyboard, allowing you to control your computer at distance. Gmote has the ability to stream music from your computer to your phone!

Gmote has to be set up both on your computer and on your android phone.
Here are the steps.

Setting up the Gmote Server on PC

The Gmote Server requires the Java JVM version 1.6 or higher.
To determine your java version, go to terminal and type 'java -version'.
You can download the latest JVM from http://www.java.com/en/download/index.jsp

On the computer you wish to control, download and install the appropriate package for your Ubuntu Linux system - here, after successful installation, open the terminal and type following command:

tar -zxvf GmoteServerLinux2.0.0.tar.gz
cd GmoteServerLinux2.0.0/
./GmoteServer.sh

On starting you'll see a password prompt. This allows you to set a password so that only you can connect to the server from your phone. You'll be asked to enter this password once on the phone as well. You can change your password later by right clicking on the Gmote server icon (task bar) and selecting 'Change password'.

Finally Gmore server will get started on port 8889, make sure to adjust your firewall rules accordingly to allow connection on port 8889.

Setting up the Gmote Client:

The installation process for client is fairly simple. From your Android handset, download and install the Gmote client.

You need wifi or 3G connectivity between your phone and PC.
Launch Gmote from your phone, select the server to connect to, and enjoy.

sudo on ubuntu

noreply@blogger.com (Fermi Level) — Tue, 11 Dec 2012 10:15:00 +0000

Here are some sudo   variations I use. (Be careful :) )

    sudo command - run command as root
    sudo su – root shell open
    sudo su user – open shell as a user
    sudo -k – forget your password sudo
    gksudo command – sudo visual dialog (GNOME)
    kdesudo command – sudo visual dialog (KDE)
    sudo visudo – edit / etc / sudoers
    gksudo nautilus – root file manager (GNOME)
    kdesudo konqueror – root file manager (KDE)

How to customize the GRUB 2 in Ubuntu

noreply@blogger.com (Fermi Level) — Tue, 11 Dec 2012 10:12:00 +0000

GRUB 2 is the next generation of GNU GRUB. All recent versions of ubuntu come with GRUB 2. GRUB 2 cleaner, safer, more robust, more portable and more powerful.

If you're already familiar with older GRUB, GRUB 2 configuration file is similar in broad sense, but it varies in many finer details. Some times it can be a bit tricky too.

The main config file is /etc/default/grub . Open it using

$ sudo gedit /etc/default/grub

you will see some thing very similar to the following ....

# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.

GRUB_DEFAULT=0
#GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=7
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""

# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"

# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console

# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
GRUB_GFXMODE=640x480

# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true

# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_LINUX_RECOVERY="true"

# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"

Some of the important configuration options you can try changing are

Change default Timeout:
To change the default timeout option in GRUB 2, you just need to change the GRUB_TIMEOUT parameter. The value of this parameter is in sec, change this value as per your requirement.

Change the default boot option:
To change the default boot option in GRUB 2, you just need to change the GRUB_DEFAULT parameter. 0 is the first entry, so if you want Windows to be your default boot option which is, say at, 5th position in the grub menu, then you just need to change the GRUB_DEFAULT value to 4 and save the file and close it. Save the file after making all the required changes and from the terminal run the following command

sudo update-grub

How to disable a user account in linux

noreply@blogger.com (Fermi Level) — Tue, 11 Dec 2012 10:02:00 +0000

The easiest way to lock a user account on Linux machines is to use -l option to passwd command.
Open a terminal and acquire root

# passwd -l abc ( abc is the user you want to lock.)

You can unlock the account with -u option

#passwd -u abc

:)

Multimedia & Video Howto on Ubuntu 12.04

noreply@blogger.com (Fermi Level) — Sun, 24 Jun 2012 06:37:00 +0000

The easiest way to get most of the media format working on ubuntu 12.04 is to enable medibuntu repository and install couple of extra packages.

This can be done quickly as follows.
Copy the following line to a command prompt

sudo -E wget --output-document=/etc/apt/sources.list.d/medibuntu.list http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list && sudo sed -i "/^# deb .*partner/ s/^# //" /etc/apt/sources.list && sudo apt-get --quiet update && sudo apt-get -y --force-yes --quiet --allow-unauthenticated install medibuntu-keyring app-install-data-medibuntu apport-hooks-medibuntu && sudo apt-get update

Then install the packages.

sudo apt-get install ubuntu-restricted-extras non-free-codecs p7zip-rar acroread gimp inkscape blender smplayer vlc libdvdcss2 libdvdread4 faac faad audacious rubyripper cd-discid aacplusenc gtkpod lame cdrdao aacgain flac mp3gain normalize-audio vorbisgain arista soundconverter gnome-sushi exfalso winff devede openshot audacity cheese synaptic gconf-editor lsb-core

enjoy.

Dangerous commands you should not try

noreply@blogger.com (Fermi Level) — Sat, 23 Jun 2012 06:27:00 +0000

I was browsing through Ubuntu forums when I saw this list of dangerous commands. I am copying them for my own reference. Don't try them out.

1) Delete all files, delete current directory, and delete visible files in current directory.

rm -rf /
rm -rf .
rm -rf *

2) Reformat. This command will reformat your hard disk ( you may need superuser permission to run)

mkfs
mkfs.ext3
mkfs.anything

3) Block device manipulation . These commands manipulate underlying block device. ( here also you may need root permission)

any_command > /dev/sda
dd if=something of=/dev/sda

4) Forkbomb : This will spawn a number of processes and eventually your system will hang. ( This works for bash shell )

:(){:|:&};:

Transparent Proxy on Linux using redsocks

noreply@blogger.com (Fermi Level) — Fri, 27 Apr 2012 09:38:00 +0000

Adapted form http://pritambaral.com/2012/04/transparent-proxy-on-linux/

This post is targeted at those Linux users behind a network proxy but cannot set it in an app, or are just plain lazy to go about telling every app to use a proxy. I’ll give a quick rundown of the instructions for those in haste, with geeky details following towards the end. I’m assuming a fairly recent distro here, and I’m targeting the Ubuntu 12.04 release.

What we’ll need:

A Linux OS (obviously!)
redsocks (an app, check in your repos, or compile it yourself)
a text-editor

On Ubuntu, we have another package that we’ll need, iptables-persistent. But before we install it, let’s set some rules (iptables rules.) Don’t worry, it’s nothing but a bunch a lines in a text file.

*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A OUTPUT -d 10.0.0.0/8 -j RETURN
-A OUTPUT -d 127.0.0.0/8 -j RETURN
-A OUTPUT -d 192.168.0.0/16 -j RETURN
-A OUTPUT -o eth0 -p tcp -m tcp --dport 80 -j DNAT --to-destination 127.0.0.1:5123
-A OUTPUT -o eth0 -p tcp -m tcp --dport 443 -j DNAT --to-destination 127.0.0.1:5124
-A OUTPUT -o wlan0 -p tcp -m tcp --dport 80 -j DNAT --to-destination 127.0.0.1:5123
-A OUTPUT -o wlan0 -p tcp -m tcp --dport 443 -j DNAT --to-destination 127.0.0.1:5124
COMMIT

I saved it as redirect.rules and ran this command:

sudo iptables-restore ./redirect.rules

Now we shall install the package iptables-persitent. During the installation, it will ask you whether you want to save the current rules. Yes, you do. The redirection’s been set-up. Time to get the juicer running.
Install redsocks (if you haven’t already.) Save this in the file /etc/redsocks.conf

base {
 log_debug = off;

 log_info = off;

 log = "stderr";

 daemon = on;

 user = redsocks;
 group = redsocks;

 redirector = iptables;
}

redsocks {
 /* `local_ip' defaults to 127.0.0.1 for security reasons,
 * use 0.0.0.0 if you want to listen on every interface.
 * `local_*' are used as port to redirect to.
 */
 local_ip = 127.0.0.1;
 local_port = 5123;

// `ip' and `port' are IP and tcp-port of proxy-server
 ip = 10.201.13.50;
 port = 80;

// known types: socks4, socks5, http-connect, http-relay
 type = http-relay;

login = "LDAP ID HERE";
 password = "LDAP PASSWORD HERE";
}

redsocks {
 local_ip = 127.0.0.1;
 local_port = 5124;

ip = 10.201.13.50;
 port = 80;

type = http-connect;

login = "LDAP ID HERE TOO";
 password = "LDAP PASSWORD HERE TOO";
}

Make sure you feed your own LDAP IDs and passwords. AT BOTH LOCATIONS. Feed your password as-it-is, no matter what special character it has. (Unless, of course, it’s a double-quote itself! Bit of a soup there.)
Now either restart your system, or run sudo service redsocks start
Voila! You have the ultimate solution to proxy! You may (or may-not) set a proxy in Gnome, Firefox, wget, gedit, whatever; it will work. This will not interfere with what you have set in Chrome/Firefox/whatever. In fact, I recommend that you explicitly set a proxy wherever you can. You see, redsocks has a knack of getting in a bundle sometimes (too many pending requests…,) in which case, a simple sudo service redsocks restart should suffice.

This also “fixes” those apps which provide no method of setting a proxy whatsoever, e.g, Gwibber. Sadly, unsupported protocols still won’t work. Sorry, no Thunderbird, no torrents, no irc.
PS: This is the exact same method used by the Android app ProxyDroid to provide system-wide proxy on rooted Android devices.

How to restore missing gnome panel

noreply@blogger.com (UbuntuGuru) — Sun, 15 Apr 2012 14:24:00 +0000

Open a terminal and try

$gconftool --recursive-unset /apps/panel && killall gnome-panel

How to Convert MTS to AVI in Linux

noreply@blogger.com (UbuntuGuru) — Sun, 15 Apr 2012 14:22:00 +0000

Try this

$ ffmpeg -i InputFile.MTS -vcodec libxvid -b 18000k -acodec libmp3lame -ac 2-ab 320k -deinterlace -s 1440x1080 OutputFile.AVI

Setting up a NIS slave server

noreply@blogger.com (Fermi Level) — Fri, 03 Feb 2012 09:54:00 +0000

This note explains how to setup a nis slave server. It is assumed that you have a NIS server running .

Setup
Existing NIS server named mahalanobis on 10.107.35.1
The slave server is to be set up is named gauss on 10.107.35.6

Install ubuntu 10. 04 Lucid on gauss 10.107.35.6. Setup the network interface and make sure that it works as a standalone machine.

Install NIS software on Gauss

# apt-get install portmap nis

Setup the slave as a NIS client

Edit /etc/yp.conf and add

ypserver 127.0.0.1
Edit /etc/hosts on master ( Mahalanobis) and add an entry for slave

10.107.35.6 gauss
Edit /etc/hosts on slave ( Gauss) and add an entry for master
10.107.35.6 mahalanobis

Log on to the master server. Add the slave server to the master
server's database map by editing the /var/yp/ypservers file on the
master.
# File: /var/yp/ypservers
mahalanobis
gauss

The make file in the /var/yp directory defines how the NIS server will
build the database map and how the master will relate to the NIS slave.
Edit the make file to allow the master to push maps to the slave.

# File: /var/vp/Makefile

# Allow the master to do database pushes to the slave
#
NOPUSH=false

Run make command. (You must be in /var/yp )

Iniitialise slave database
# /usr/lib/yp/ypinit -s mahalanobis

On slave ( gauss) edit /etc/defaults/nis ) Change the flag NISSERVER to slave

# /etc/defaults/nis Configuration settings for the NIS daemons.
#

# Are we a NIS server and if so what kind (values: false, slave, master)?
NISSERVER=slave

Restart nis services on slave

#/etc/init.d/nis restart

Testing

On a client machine which is being authenticated by the master edit /etc/yp.conf and change the ypserv entry to point to the new slave machine.
Restart nis on that client machine and see if you are able to login.

Mount Ext4 partitios in Windows

noreply@blogger.com (UbuntuGuru) — Mon, 12 Dec 2011 03:11:00 +0000

Ubuntu partitions are incompatible with Windows, we can not read and write to them from widows. Ext4 partitions can be read from windows if you install a simple utility in Windows.
Download ext2fsd from

http://sourceforge.net/projects/ext2fsd/files/Ext2fsd/0.51/

Find out Ext2Fsd-0.51.exe from the above site and install it. The following screen shots are self explanatory.

how to clone ubuntu installation

noreply@blogger.com (UbuntuGuru) — Sun, 11 Dec 2011 16:23:00 +0000

Here is a quick way to build an exactly similar ubuntu installation on another computer.

Run
$ dpkg --get-selections >my_pakages

on the machine that you want to clone. Install a clean copy of Ubuntu on the target machine. Copy the file my_packages to the target machine.
Run the following command on the target machine.
$ sudo dpkg --set-selections < ./package_names
$ sudo apt-get -u dselect-upgrade

Done.

SSH Login Without Password

noreply@blogger.com (Fermi Level) — Sat, 26 Nov 2011 15:07:00 +0000

For this you required to generate your own personal set of private/public pair. ssh-keygen is used to generate that key pair for you.

On the user’s home directory, on the localhost, type

[local-host]$ ssh-keygen -t dsa

This will ask you a passphrase. A passphrase is a sequence of words or other text used to control access to a computer system, program or data. A passphrase is similar to a password in usage, but is generally longer for added security. Once entered the passphrase you will be prompted to enter the same passphrase again for confirmation.

The private key was saved in .ssh/id_dsa and the public key .ssh/id_dsa.pub.
Now, copy the public key to the remote machine

[local-host]$ ssh-copy-id -i ~/.ssh/id_dsa.pub user@remotehost

or if you don’t have ssh-copy-id script installed use

[local-host]$ cat ~/.ssh/id_dsa.pub | ssh user@remotehost "cat - >> ~/.ssh/authorized_keys"

Now on the localhost machine, on GNOME select System > Preferences > Sessions.
Select Startup Programs and add a new entry with this command.

eval `ssh-agent`

ssh-agent is a program that used together with OpenSSH or similar ssh programs provides a secure way of storing the passphrase of the private key.

Open terminal and run ssh-add without any arguments, it will ask your passphrase once.
ssh-add adds identities to the authentication agent, ssh-agent.

[local-host]$ ssh-add

Enter passphrase for /home/vinod/.ssh/id_dsa:
Identity added: /home/you/.ssh/id_dsa (/home/you/.ssh/id_dsa)
That’s it, now login to remote server it will not ask any password or passphrase.

NB: No one else must see the content of .ssh/id_dsa, as it is used to decrypt all correspondence encrypted with the public key.

Childsplay for kids

noreply@blogger.com (UbuntuGuru) — Fri, 08 Jul 2011 04:12:00 +0000

Childsplay is a collection of educational activities for young children and runs on Windows, OSX, and Linux. It can be used at home, kindergartens and pre-schools. Childsplay is a fun and save way to let young children use the computer and at the same time teach them a little math, letters of the alphabets, spelling, eye-hand coordination etc.

Childsplay is part of the schoolsplay.org project

Childsplay includes the following games:
* Numbers - Put the correct operator between two numbers.
* SoundNpic - A toy for young children with pictures and sounds.
* Packid - A pac-man game, try to catch the letters.
* Soundmemory - The classic memory game, with sounds.
* Fallingletter - Type them before the reach the ground.
* Findsound - Listen to a sound and find the image to which it belongs
* Findsound2 - The same as findsound, now with numbers and letters.
* Pong - The classic game, play alone or against another child.
* Billiards - Try to shoot the balls into the hole.

Childsplay installation:
On ubuntu open a terminal and type

sudo apt-get install childsplay

After installation you can open childsplay from Applications > Education > Childsplay

How to recover deleted files in Ubuntu/Linux

noreply@blogger.com (UbuntuGuru) — Wed, 29 Jun 2011 09:49:00 +0000

When a file is deleted, only the pointer to the file is overwritten and the original file will still reside in the blocks of the storage device and will be kept there until it is overwritten by another file. In a sense, you can always write a file but you can never delete it. So if you have ever faced the dilemma of trying to recover a deleted file in Ubuntu then look no further. Linux offers a wide range of tools for recovering deleted files. These tools work by retrieving the pointer to the deleted files.

The chief among the recovery tools would be Scalpel. Scalpel is a platform independent command based tool which is small yet very powerful. You can install the latest version of Scalpel (version 2.0) by doing a simple

sudo apt-get install scalpel

in the terminal.

After installation you need to go to the configuration file of scalpel which resides in

/etc/scalpel/scalpel.conf

Using an editor like gedit open the scalpel.conf file using the command.

sudo gedit /etc/scalpel/scalpel.conf

You will notice that that all the lines in the file are preceded by a comment (#) symbol. Remove the # symbol preceding the file you want to recover.

sudo scalpel "device name/Directoryname/file name" -o "output directory"

The output directory is the directory where you want to restore your deleted files. It should be empty before running the command, otherwise you will get an error. You can also input the deleted filename directly by using -i option.