loadYOURSELF

Some domain’s serve under multiple ip addresses for example google.com

if you want to query this ip addresses then you can use this code block

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char **argv) {
 if (argc < 2) {
   fprintf(stderr,"Usage: ./app www.google.com\n");
   exit(1);
 }

 struct hostent *hp = gethostbyname(argv[1]);

 if (hp == NULL) {
   fprintf(stderr,"query failed\n");
   exit(1);
 } else {
   unsigned int i=0;
   while ( hp -> h_addr_list[i] != NULL) {
     printf( "%d -> %s ",i, inet_ntoa( *( struct in_addr*)( hp -> h_addr_list[i])));
     i++;
   }
   exit(0);
 }
}

This script counts one by one every time the user runs the script. “./scriptname reset” reset the counter.


!/bin/bash
if [ "$1" = "reset" ]
then
rm -rf fstore
fi
sayi=0
if [ -f fstore ]
then
sayi=`cat fstore`
fi
let sayi=$sayi+1
echo "INCREMENTING"
echo $sayi > fstore
echo -e -n "CURRENT="
echo $sayi


uses fstore file to remember the previous number.

If you have high cpu usage problem for your vmware application which runs on linux and the virtual machine files in NTFS partition,

you have to add:


mainMem.useNamedFile= FALSE"

to your .vmx file of you virtual machine.

this will solve the high cpu usage of mount.ntfs-3g.

You can backup your system partition table with sfdisk which you can also inlude extended partitions.

backup partition table

sfdisk -d /dev/sda > my-sda.sf


restore partition table

sfdisk /dev/sda < my-sda.sf --force


you can download the sfdisk source from

ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/v2.15/


and you can compile it for your desktop PC or for your embedded device. (cross compiling)

Ext3 is a linux filesystem and used by most of the linux systems. This article shows and example ext3 image usage situation.

we will create and use 20MB ext3 image. 1024×20480 bytes.

first we create an empty file with dd block size 1024

dd if=/dev/zero of=disk1.image bs=1024 count=20480


then we format that image

mkfs.ext3 -F -b 1024 disk1.image 20480


this will give an empty filesystem whose type is ext3.

if [ -f filename ]
then
echo "file exist"
else
echo "Sorry, file does not exist"
fi

if [ -d directory ]
then
echo "directory exist"
else
echo "Sorry, directory does not exist"
fi

MBR is the master boot record of your disks. It includes also partition table. If you want to create one to one partition table and don’t want to copy all your disk you can use the commands below

to backup your mbr

dd if=/dev/sdX of=mbr.bin bs=512 count=1

to restore back your mbr

dd if=mbr.bin of=/dev/sdX bs=1 count=64 skip=446 seek=446

SIGPIPE signal is sent by kernel to programs whose remote end closes or shuts down the socket and your program still tries to send/write operations on closed connection. The default signal handler terminates your program at this situation because of default behavior.

Solution 1:

Ignore the signal using ’signal(SIGPIPE, SIG_IGN)’

then catch the EPIPE error which will return from the send/write operation due to a broken pipe.

Solution 2:

Pass MSG_NOSIGNAL flag to send(). This is results as same as solution 1

You can use mplayer as a YUV player with the example command below.

mplayer foreman.qcif -demuxer rawvideo -rawvideo qcif

mplayer “yuv filename” -demuxer rawvideo -rawvideo “qcif,cif”

This entry gives a way to find active computers on a LAN with Linux machine.
We can use nmap port scanning tool for that.

You can install nmap with
yum install nmap
or
apt-get install nmap
Example:
nmap -sP 192.168.200.0/23

searches 192.168.200.x & 192.168.201.x sub networks. And lists active computers.

nmap -v -sP 192.168.200.0/23 gives more verbose.