how to copy sd-card whithout copying the unallocated space

Question:

I have a 32Gb SD card and I want to make a light copy of my os to make it work on a 16Gb SDcard.

Answer - use image-backup

Perhaps the easiest way to do this is with the image-backup utility - part of image-utils. If you are running RPi OS, image-backup has these advantages:

• image-backup may be done on a "live" system: no need to shut down the system, or unmount the device.

• image-backup is fast: 3min:55sec elapsed time to create a bootable image on RPi 4B from a 32GB SD card; activities included in elapsed time:

  • Includes interactive dialog w/ image-backup & USB HDD I/O (USB-3 port).
  • Includes 3x resize2fs and e2fsck on the finished ext4 partition - part of image-backup
  • On a RPi 3B: 13min:42sec from a 16GB SD card to USB "thumb" drive (USB-2 port).
  • Elapsed times measured as follows:

  $ echo $(date) && sudo ./image-backup && echo $(date)  
  

• image-backup produces a small raw image file:

  • image file contains only actual data on SD card - not the entire partition (à la dd)
  • 32GB GB SD card --> 4.05GB
    For comparison:

  $ df -h
  Filesystem             Size  Used Avail Use% Mounted on
  /dev/root               29G  5.0G   23G  18% /
  /dev/mmcblk0p1         256M   47M  209M  19% /boot
  

• image-backup produces an .img file that can be flashed to another SD card, USB drive, etc using common tools such as etcher and rufus.

• image-backup is free (no cost) and open sourced bash script, currently less than 13kB in size. The author has not yet placed it under a "formal" license, instead stating recently, "Users are free to modify them for their personal use...".

As its name implies, the primary purpose of image-backup is making a live backup of an RPi. Coincidentally, it's also a good solution to shrinking the OS to fit on a smaller SD card.

You can download a copy of image-utils from this location. The instructions (in the README file) may be a bit fuzzy at first, but it's very simple to use. If you have problems, you can post questions to the author in the forum, or ask a specific question here. Alternatively, you can install on your RPi using git from here.

How will image-backup address my question?

Once you've "installed" it, you can make a complete backup of your entire system to an image file. By "image file", I mean a file that can be flashed to your (smaller) SD card using etcher or rufus (for example), and then booted in your RPi.

image-backup compresses the image file, and installing to a smaller (32GB->16GB) SD card will not be a problem based the info in your question.

Show me how...

There is no package for image-utils, so apt cannot be used to install it. However, image-utils is just a collection of scripts (text files), and very easy to install; you may install manually, or via git:

Manual installation of image-utils on your RPi:

Open a terminal window (or via SSH) in your RPi, and from your home directory (/home/pi):

$ mkdir image-utilities
$ cd image-utilities
$ wget -O image.zip https://www.raspberrypi.org/forums/download/file.php?id=39167
$ unzip ./image.zip 
$ chmod a+x image-*

run image-backup

At this point, image-backup is ready to use, but you will need to have a USB drive mounted (or any drive under /mnt) as a destination for the image file it will create. Once your USB drive is mounted, you may create the image file as follows:

$ sudo ./image-backup

• image-backup will prompt you for the options needed:

  Image file to create? /mnt/Passport2TB/img_backups/20210113_Pi4B_imagebackup.img
  

NOTE: A full path specification to the image file you want to create. The drive must be mounted under /mnt or /media. I have embedded a date & machine id in my filename. Then, ↵

Initial image file ROOT filesystem size (MB) [5933]?

NOTE: Accept default ( ↵ )

Added space for incremental updates after shrinking (MB) [0]?

NOTE: Accept default ( ↵ )

Create /mnt/Passport2TB/img_backups/20210113_Pi4B_imagebackup.img (y/n)? y

NOTE: Enter y, then ↵

Starting full backup (for incremental backups, run: ./image-backup /mnt/Passport2TB/img_backups/20210113_Pi4B_imagebackup.img)

NOTE: The instructions for making an incremental backup are N/A here because you are running image_backup on a one-time basis.
Additional output will show 3 iterations of resize2fs to reduce the image file to its smallest possible size, and upon completion, e2fsck will be run to verify the integrity of the filesystem.

• You should now have an image file that is ready to be flashed to your spare SD card.

Verify & inspect the image file

I have used an external drive mounted at /mnt/Passport2TB to store my backup image - in a folder named img_backups. Your external drive will likely be different than mine. You can verify your external drive is mounted by using the lsblk --fs command.

List the contents of /mnt/Passport2TB/img_backups to verify the image file is there, and check its size:

$ ls -l /mnt/Passport2TB/img_backups 
total 28533608

...

-rw-r--r-- 1 root root  3921674240 Jan 13 18:48 20210113_Pi4B_imagebackup.img

Note that the size of my image file is 3.92GB. Yours will likely be a different size based on which version of the OS you've installed (I use the Lite version of RPi OS). To provide some context for comparison, let's look at how much space is being used on my RPi 4B:

$ df -h -t ext4
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        29G  4.9G   23G  18% /

And so, in my case, image-backup reduced 4.9GB to a 3.92GB .img file - or about a 20% reduction.