This program will auto mount USB device and count number when systme power on.

#/bin/bash
# Program:
#       This program will auto mount USB device and count number when systme power on.
# History:
# 2013/09/24 Mace First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

#test file path
file_path="/tmp"

# Open an file to save fdisk information.
touch /mnt/information

# Store fdisk -l info to file information.
fdisk -l | grep "FAT32" > /mnt/information

# cut dev path to dev_path.
dev_path="`head /mnt/information | tr -s ' ' | cut -f1 -d' '` "

# Judge USB device is on plug.
if [ "$dev_path" == " " ];then
  echo "Can't found USB device." 
  exit 0
else
  echo "Found USB device at: "$dev_path
fi

# mount USB to /tmp folder.
mount -t vfat $dev_path $file_path

if [ -f "$file_path"/test ];then
  count_num="`head $file_path/test`"
  echo "$count_num"
else
  echo "file not found. Create test file init number to 0."
  touch $file_path/test
fi

if [ "$count_num" == " " ];then
  count_num=0
  echo "test file is empty. init count_unm=0"
else
  count_num=$(($count_num + 1))
  #echo "$count_num"
  echo $count_num > $file_path/test
fi 

#umount USB device.
umount "$file_path"
 
exit 0

How to make linux run on RamDisk

        This topic is talking about making Linux run on Ramdisk and create your own file system.

        Also we can run script after system initialed.

We need prepare some tool and device as below:

1.      USB device with FAT format. We can use format tool “HPUSBFW”.

2.      Syslinux: Help us to loader Linux kernel and file system and also kernel boot up parameter, like: Console, Kernel file name..

3.      Busybox: Busybox include Linux most common use command and help you to generate file system.

========================================================================

There 4 part in this topic:

First: Create a bootable Linux USB device.

1.      Download syslinux(v6.01) tool and unzip to USB device. URL: https://www.kernel.org/pub/linux/utils/boot/syslinux/

2.      Open cmd with administer.

3.      Find your USB device disc number my example is “F:”

4.      Enter “FF:\syslinux-6.01\bios\win32” folder and type command: “syslinx.exe –ma F:”

       For the DOS and Windows installers, the -m and -a options can be used on hard drives to write a Master Boot Record (MBR), and to mark the specific partition active. On boot time, by default, the kernel will be loaded from the image named LINUX on the boot floppy.

5.      Now finished the first part. We can found more information on syslinux.

Web: http://www.syslinux.org/wiki/index.php/The_Syslinux_Project

6.      Create and configure syslinux.cfg.

TIMEOUT 200

serial 0 115200

default linux (Auto search kernel file: “linux”, if can’t find linux we need enter file name.)

LABEL linux

KERNEL linux (*Kernel file name must same as KERNEL “linux”)

APPEND ro initrd=root.gz rootfstype=ext2 root=/dev/ram0 rw init=/linuxrc console=tty0 console=tty0,115200n8 acpi=off raid=noautodetect

========================================================================

Second: Configure Kernel and build image.

1.      Check Linux system version and download kernel source.

2.      For example:”uname –a” get the kernel version. Like: Linux localhost.localdomain 2.6.32-358.el6.i686 #1..

3.      Download Kernel source: “wget https://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.32.18.tar.gz /usr/src/kernels”

4.      tar kernel source: “tar -xvjf linux-2.6.32.18.tar.gz .”

5.      Enter folder configure make menu: “make menuconfig”.

è Enter Genernal setup: Set 

[*] enable deprecated sysfs features which may confuse old userspace tools

[*] Initial RAM filesystem and RAM disk (initramfs/initrd) support

è Enter Device Drivers 

---> Generic Driver Options  --->

[*] Create a kernel maintained /dev tmpfs (EXPERIMENTAL)

[*]   Automount devtmpfs at /dev

--->[*] Block devices  --->

           <*>   RAM block device support 

           (16)    Default number of RAM disks     

(16384) Default RAM disk size (kbytes)

è Enter Executable file formats / Emulations  --->

            [*] Kernel support for ELF binaries

            [*] Write ELF core dumps with partial segments   

            <*> Kernel support for a.out and ECOFF binaries  

<*> Kernel support for MISC binaries  

è Enter  File systems  --->  

       <*> Second extended fs support                 

         [*]   Ext2 extended attributes                

         [*]   Ext2 POSIX Access Control Lists          

         [*]   Ext2 Security Labels        

         [*]   Ext2 execute in place support 

       DOS/FAT/NT Filesystems  --->

         <*> MSDOS fs support

         <*> VFAT (Windows-95) fs support      

         (437) Default codepage for FAT        

         (ascii) Default iocharset for FAT        

         < > NTFS file system support 

6.      Exit & Save config

7.      make clean

8.      make bzImage.

9.      Find bzImage in the /arch/x86/boot/bzImage

10.  Change file name to “linux” and copy to USB device.

========================================================================

Third: Create Ext2 Block space to generator filesystem.

1.      Download Busybox tool. Example: busybox-1.20.2, URL: http://www.busybox.net/

2.      tar busybox file to linux. /root/Desktop/

3.      Create an empty file that you can format as a filesystem:

   cd /tmp/

          mkdir initrd | chmod 755 initrd                   ß Create empty folder under /tmp/.

          dd if=/dev/zero of=rootfs bs=4k count=4000       ß Create 16M empty file that you can format as a filesystem

      mke2fs -i 4096 -m 0 -F /tmp/rootfs               ß Format the rootfs file with a filesystem

      mount -o loop rootfs initrd/                  ß Mount the file on a mountpoint so we can place files in it

      cd initrd/ 

mkdir dev etc etc/rc.d bin proc mnt tmp var     ß Making necessary folder

chmod 755 dev etc  etc/rc.d bin mnt tmp var

chmod 555 proc

4.      Enter Busybox folder and find /examples/bootfloppy/bootfloppy.txt to start making a root file system. You may find the tools at /examples/bootfloppy/

5.      Make device files in /dev: This can be done by running the 'mkdevs.sh' script. If you want the gory

        details, you can read the script.

6.      Make necessary files in /etc: For this, just cp -a the etc/ directory onto rootfs. Again, if you want all the details, you can just look at the files in the dir.

7.      Modify /etc/inittab as below:

    ::sysinit:/etc/init.d/rcS

::respawn:-/bin/sh

::restart:/sbin/init

::ctrlaltdel:/sbin/reboot

::shutdown:/bin/umount -a –r

8.      Modify /etc/fstab

    poc             /proc    proc    defaults    0   0

/dev/ram0       /        ext2    defaults    0   0

========================================================================

Fourth: busybox compiler and install.

1.      Enter Busybox folder: make menuconfig

Busybox Settings  --->

  General Configuration  --->

     [*] Don't use /usr

Build Options  ---> 

   [*] Build BusyBox as a static binary (no shared libs)

      [*] Build with Large File Support (for accessing files > 2 GB)  

   ()  Cross Compiler prefix (*If you use another compiler tool please assign the path. )

Coreutils  ---> Select all items.

Debian Utilities  ---> Select all items.

Editors  --->  Don’t need

   [ ]   Allow vi to display 8-bit chars (otherwise shows dots)

   [ ]     Enable regex in search and replace

Finding Utilities  ---> Select all items.

Init Utilities  --->

     [*]   Support reading an inittab file

Linux System Utilities >

[*] mount

[*] umount

[*] Support loopback mounts

[*] Support for the old /etc/mtab file

       Miscellaneous Utilities  --->

            [*] devfsd (obsolete)

       Shells  --->

            [*] ash

      

2.      Exit & Save config.

3.      “make clean”

4.      “make CONFIG_PREFIXED=/tmp/initrd install”

5.      “umount initrd”

6.      “gzip -9 –c rootfs > root.gz”

7.      Copy root.gz to USB device

8.      Check USB device include files: linux, root.gz, syslinux.cfg

=================================================================================================

Troubleshooting:

1.      Make menuconfig Error !!

yum -y install ncurses ncurses-devel

2.      Need compiler busybox in static, we need install gcc compiler patch for this.

yum -y install glibc-devel.i686 glibc-devel

sudo yum install glibc-static libstdc++-static

3.      Kernel panic problem: can’t mount root unknow device.

   Please make sure kernel configure is correct and kernel image file name must be same as syslinux.cfg item: KERNEL XXXX.

4.      Kernel panic problem: can’t access init=/linuxrc.

   Please use same compiler to build kernel and busybox.

Linux command tar

常用tar指令整理:
壓縮: tar -jcv -f filename.tar.bz2 要被壓縮的檔案或目錄名稱。

[root@mylinux tmp]# tar -jcv -f /tmp/vitest.tar.bz2 /tmp/vitest

Note: 此案例是給定絕對位置所以，壓縮後檔案位置會放到/tmp裡面，並觀察到解壓縮路徑會包括/tmp/vitest。
如果只要打包到/vitest資料夾則需要移除/tmp，並且在tmp目錄裡面做打包動作。

=======================================================================
查詢: tar -jtv -f filename.tar.bz2。

[root@mylinux tmp]# tar -jtv -f /tmp/vitest.tar.bz2

Note: 解壓縮前先觀察路徑。

=======================================================================
解壓縮: tar -jxv -f filename.tar.bz2 -C 欲解壓縮的目錄。

[root@mylinux tmp]# tar -jxv -f vitest.tar.bz2 -C /

Note:給定解壓縮目錄的路徑，須注意所在目錄，此案例是在/tmp裡面解壓縮所以只要給定/，如果所在位置不同請給絕對位置。

Linux command wget

An sample example to used wget to download an file from HTTP.

[root@mylinux /]# wget -P /tmp/vitest/ http://linux.vbird.org/linux_basic/0310vi/vi.big5
  [Parameter]:
  -P: Save file to directory.

An 'array' with 5 elements which is a pointer

期望印出Array[5]中的數值:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
 int n =5;
 int *Array,*aptr;
 
 Array = (int*)malloc(n*sizeof(int));
 memset(Array,0,5);
 aptr = Array;
 for(n = 0; n < 5; n++)
 {
  *aptr = n;
  aptr++;
 }
 aptr = &Array[0];
 for(n = 0; n < 5; n++)
 { 
  printf("show array vaule = [%d]\n", (*aptr)++; 
 }
  free(Array); 
  system("PAUSE"); 
  return 0;
}

Result of this program.

上例中乍看是正確的輸出Array中的值但是其實不然，請看下例解釋:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
 int n =5;
 int *Array,*aptr;
 
 Array = (int*)malloc(n*sizeof(int));
 memset(Array,0,5);
 aptr = Array;
 for(n = 0; n < 5; n++)
 {
  *aptr = n*2;
  aptr++;
 }
 aptr = &Array[0];
 for(n = 0; n < 5; n++)
 { 
   printf("show array vaule = [%d]\n", (*aptr)++; 
 }
  free(Array); 
  system("PAUSE"); 
  return 0;
}

上例中我們期望可以列印出Array中的值[0][2][4][6][8],但是列印出來的值卻是[0][1][2][3][4]。這是因為(*aptr)++是針對Array[0]裡面的值先輸出在遞增，而不是改變pointer的位址。

那要如何列印出Array中的值[0][2][4][6][8]請看下例:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
 int n =5;
 int *Array,*aptr;
  
 Array = (int*)malloc(n*sizeof(int));
 memset(Array,0,5);
 aptr = Array;
 for(n = 0; n < 5; n++)
 {
  *aptr = n*2;
  aptr++;
 }
 aptr = &Array[0];
 for(n = 0; n < 5; n++)
 {   
  printf("show array vaule = [%d]\n", *aptr++; 
 }
  free(Array); 
  system("PAUSE"); 
  return 0;
}

取消括號以後才是對aptr位址做增加，順利得到我們要的值。

接下來再嘗試將++換到aptr前面看看會發生甚麼事情。

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
 int n =5;
 int *Array,*aptr;
  
 Array = (int*)malloc(n*sizeof(int));
 memset(Array,0,5);
 aptr = Array;
 for(n = 0; n < 5; n++)
 {
  *aptr = n*2;
  aptr++;
 }
 aptr = &Array[0];
 for(n = 0; n < 5; n++)
 {   
  printf("show array vaule = [%d]\n", ++*aptr); 
 }
  free(Array); 
  system("PAUSE"); 
  return 0;
}

將程式改成++*aptr，代表Array[0]裡面的值先做遞增再輸出，測試結果列印出來為[1][2][3][4][5]。

另外如果加上括號++(*aptr)，測試輸出結果列印出來與上例相同。:

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