guivi

This is a copy past from another person you can find the original blog here:
https://ep.gnt.md/index.php/how-to-clone-raspberry-pi-sd-card-on-linux-and-shrink-it-to-actual-size/
I am making a copy here is I can find it easy and in case the original disappear of the web.

On Linux you can use dd to make a backup from SD card. Reverse if and of (i.e. to where they point – source and destination) afterwards to restore, but be careful not to restore to a wrong disk. It will be destroyed without a warning!!!

First use fdisk to get the device id of you SD card (check the size)

fdisk -l

then use dd to make a diskimage (change /dev/sdb with what you found with fdisk -l):

dd bs=4M if=/dev/sdb of=image1-`date +%d%m%y`.img

or this to make a compressed image:

dd bs=4M if=/dev/sdb | gzip > image1-`date +%d%m%y`.img.gz

The process will take some time. After the image is created you will notice that it’s too big(size of a SD card). To shrink it we will use a perfect script that I found on github here https://github.com/Drewsif/PiShrink.git called PiShrink.

PiShrink is a bash script that automatically shrink a pi image that will then resize to the max size of the SD card on boot. This will make putting the image back onto the SD card faster and the shrunk images will compress better.

Installation

wget https://raw.githubusercontent.com/Drewsif/PiShrink/master/pishrink.sh
chmod +x pishrink.sh
sudo mv pishrink.sh /usr/local/bin

Usage example

$ sudo pishrink.sh pi.img
e2fsck 1.42.9 (28-Dec-2013)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/loop1: 88262/1929536 files (0.2% non-contiguous), 842728/7717632 blocks
resize2fs 1.42.9 (28-Dec-2013)
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/loop1 to 773603 (4k) blocks.
Begin pass 2 (max = 100387)
Relocating blocks             XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Begin pass 3 (max = 236)
Scanning inode table          XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Begin pass 4 (max = 7348)
Updating inode references     XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
The filesystem on /dev/loop1 is now 773603 blocks long.

Shrunk pi.img from 30G to 3.1G

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

//#define _DEBUG

const char data[] = "adssdfl;jk$OTAQ1#adssdfl;jk$OTAQ1#123,command,command"
"*FFFF1234\r\nadssdfl;jk$OTAQ1#adssdfl;jk$OTAQ1#123,command,command*FFFF1234";    // Simulated serial string.
const char initial_token = '$'; // Start token on the datastring for our formated string. The format is "$....*FFFF".
const int max_size = 64;        // Maximum niber of bytes which can be part of a message.
char buffer[256];               // Temporary buffer to keep track of date from the serial port.
//char mesage[256];               // Message if any is found with the structure as described above.
bool initial_flag = false;      // Flag to indicate if an initial token has been found.
int counter = 0;                // counter to keep trak of the position in the buffer.

// Parses the messge into its components
void Parse(char* message)
{
    char limits[] = "$#,*";     // Use '$', '#', ',' and '*' are the parsing. 
    char* token = strtok(message, limits);
    while (token != NULL)
    {
        printf("%s\r\n", token);
        token = strtok(NULL, limits);
    }
}

// Identify the message from the strings of char's
void ReadMessage(char c)
{
    // if initialization flag is true then add teh character to teh buffer
        if (initial_flag)
        {
            buffer[counter] = c;    // Add the current character to the buffer.
            counter++;              // increase counter.
            char sum[5] = {0};
            char message[256] = {0};
#ifdef _DEBUG
            printf("%s\r\n", buffer);
#endif
            if(sscanf(buffer, "$%[^*]*%4s", message, sum) == 2){
                int _size  = strlen(sum);
#ifdef _DEBUG 
                printf("number of chars in sum %d\r\n", _size);
#endif
                if (_size == 4) // We have dound some data with the desired format.
                {    
                    // Do something with the string
                    printf("Check sum is: %s\r\n", buffer);
                    printf("Message is: %s\r\n", message);
                    Parse(buffer);
                    initial_flag = false;
                }
            }
        }
        // Check if enconter initial chracter. If this is found at any time reinitialize buffer. and set flag accordingly.
        if (c == initial_token)
        {
            printf("Initial token encounter\r\n");
            initial_flag = true;        // Set initialisation flag to true.s
            memset(buffer, 0, 255);     // Setbuffer data to 0.
            buffer[0] = initial_token;  // Put initial toekn in the buffer.
            counter = 1;                // initialize counter to 1 as 0 zero position has already been initialized.
        }
        if (counter >= max_size)        // If number of character in buffer is maximum the de-initialize the flag.
            initial_flag = false;
}

// Main
int main()
{
    int length = strlen(data);              // Get the dta length on the "serial" buffer. Is just for simulation.
    printf("Reading %d from data string\r\n", length);  // Print the length of data for awareness.
    for (size_t i = 0; i < length; i++) {   // Simulated readint one one caracter at the time from the serial port.
        char c = data[i];                   // Get the char form the buffer.
        ReadMessage(c);                     // Add the char to the message buffer and check it it can be parsed.
    }

}

void CDialog::SelectComPort()
{
	TCHAR lpTargetPath[5000]; // buffer to store the path of the COMPORTS
	DWORD test;
	bool gotPort = 0; // in case the port is not found
	m_serialList.ResetContent();

	for (int i = 0; i < 255; i++) // checking ports from COM0 to COM255
	{
		CString str;
		str.Format(_T("%d"), i);
		CString ComName = CString("COM") + CString(str); // converting to COM0, COM1, COM2

		test = QueryDosDevice(ComName, lpTargetPath, 5000);

		// Test the return value and error if any
		if (test != 0) //QueryDosDevice returns zero if it didn't find an object
		{
			m_serialList.AddString((CString)ComName); // add to the ComboBox
			
			gotPort = 1; // found port
		}

		if (::GetLastError() == ERROR_INSUFFICIENT_BUFFER)
		{
			lpTargetPath[10000]; // in case the buffer got filled, increase size of the buffer.
			continue;
		}

	}

	if (!gotPort) // if not port
		m_serialList.AddString((CString)"No Active Ports Found"); // to display error message incase no ports found

}

BEGIN_MESSAGE_MAP(CDialog, CDialogEx)
	ON_WM_DEVICECHANGE()
END_MESSAGE_MAP()

BOOL CDialog::OnDeviceChange( UINT wParam, DWORD_PTR  lParam)
{

}