How to change boot order in GRUB2?

With Ubuntu 9.10 (Karmic Koala), GRUB2 is the default boot loader.
How to change boot order in GRUB2?

1.
$ cat /etc/grub/grub.cfg
see the order of the wanted kernel. Starts from 0.

2.
$ vi /etc/default/grub
change GRUB_DEFAULT=0 value to wanted kernel

3. run
$ update-grub
to update

4. reboot and check with
$ uname -r
to see if correct kernel selected.

Find Biggest Files/Directories

Since ls does not give correct size on disk, better to
use du command.

$ du /path/to/dir | sort -nr

I hope above
command will give you the proper result you wanted.



Note: The above command may take large time, depending on

number of files in /path/to/dir . You can use depth(say 2) in
that dir.

$ du --max-depth=2 /path/to/dir | sort -nr 

Newer Yahoo! Messenger Protocol on Pidgin on Debian Lenny 5.0

Yahoo! has changed authentication method of Yahoo! messenger protocol, which is not supported in Pidgin (Version <>= 2.5.7) supports newer Yahoo! Messenger Protocol. But Debian 5.0 Lenny repository has older pidgin (2.4.3). We can install newer pidgin, in the following steps:

## download latest pidgin from pidgin.im (at this time 2.6.3 is latest)
$ wget http://sourceforge.net/projects/pidgin/files/Pidgin/pidgin-2.6.3.tar.bz2

## extract files using tar
$ tar -zxvf pidgin-2.6.3.tar.bz2

$ cd pidgin-2.6.3

## Configure, Compile, and make
$ ./configure --disable-screensaver --disable-vv --disable-avahi --disable-tcl --disable-tk --prefix=/usr 
$ make
$ sudo make install

Now you can use newer pidgin with newer Yahoo! Messenger. :)
Enjoy Yahoo!

Find Files Created Between 2 Times

In order to find files created between two times (start hour and end hour). The required hours are hours from current time. For example,

Current time = 2 PM = 14:00

If you want file created between 9 AM and 12 PM today, the start hour and end hour are:

Start Hour = (14 - 9) = 5
End Hour = (14 - 12) = 2

Hence required command is:

$  ./find_files_between_times.pl /path/to/dir 5 2

The Perl script which does this is given below:-

#!/usr/bin/perl -w
#===============================================================================
#
#         FILE:  find_files_between_times.pl
#
#        USAGE:  ./find_files_between_times.pl <dir> <start_hour> <end_hour>
#
#  DESCRIPTION:  
#
#      OPTIONS:  ---
# REQUIREMENTS:  ---
#         BUGS:  ---
#        NOTES:  ---
#       AUTHOR:  Mitesh Singh Jat (mitesh), <mitesh[at]yahoo-inc[dot]com>
#      COMPANY:  Yahoo Inc, India
#      VERSION:  1.0
#      CREATED:  11/13/2009 10:00:02 PM IST
#     REVISION:  ---
#===============================================================================

use strict;
use warnings;

if (@ARGV != 3)
{
    print STDERR "Usage: $0 <dir> <start_hour> <end_hour>\n";
    exit(-1);
}

my $dir = $ARGV[0];
## Calculate current_hour - given_hour
#my $start_time = `/bin/date "+\%H"`;
my $start_time = $ARGV[1];
#chomp($start_time);
my $end_time = $ARGV[2];
$end_time = time - ($end_time * 60 * 60);
#$end_time = $start_time - $end_time;
#$start_time = $start_time - $ARGV[0];

if ($start_time > $end_time)
{
    ($start_time, $end_time) = ($end_time, $start_time);
}

my $cmd = "find $dir -ctime -$start_time";
print "Running $cmd\n";
my @files = `$cmd`;
foreach my $file (@files) # (`find $dir -ctime $start_time`)
{
    chomp($file);
    my ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
                           $atime,$mtime,$ctime,$blksize,$blocks) 
        = stat($file);

    if ($ctime > $end_time)
    {
        next;
    }
    print "$file\n";
}


exit(0);

Better Console Calculator Using bc

If we use expr for mathematical calculations on console (terminal), it is frustrating, and hard to remember syntax and escape sequences used in expr. :( This small tip will help us.

Just add following line in your .bashrc file (~/.bashrc).

function calc
{
echo "${1}" | bc -l;
}

Then update the shell environment by:

$ source ~/.bashrc

"calc" from the shell will work as follows:

$ calc 2+3
5
$ calc 1+2*3
7
$ calc 1.1*2
2.2
$ calc "(1+2)*3"
9
$ calc "(1+2)^3"
27
$ calc "s(.5)"
.47942553860420300027

Checking Network Services Using Telnet

Suppose we want to check whether the web server(port 80) or any other network service is running or not, but we do not have any browsers (lynx, Firefox, IE, Netscape, ...), then there is a simple way of doing that. Just telnet to that machine on the http port (port no. 80 in general).

$ telnet <ip_addr> <port_no>

And then, give command "get /" (without quotes). If the webserver is running, it displays the HTML script of the homepage or basic info and closes the connection to the remote host.

$ telnet wordpress.com 80 
Trying 76.74.254.126...
Connected to wordpress.com.
Escape character is '^]'.
get /
<html>
<head><title>400 Bad Request</title></head>
<body bgcolor="white">
<center><h1>400 Bad Request</h1></center>
<hr><center>nginx</center>
</body>
</html>
Connection closed by foreign host.

Joining Multiple Videos into One Using Mplayer

In order to join multiple video files, into a single video file, you just need to issue following command:

$ mencoder -oac copy -ovc copy -o joined_single_video.avi video1.avi video2.avi video3.avi

Even you can use wild cards (*, ?) too.

$ mencoder -oac copy -ovc copy -o joined_single_video.avi video*.avi

PS. In place of 'avi', you can give whatever file format is available.