this post was submitted on 15 Aug 2026
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There's a way to do it without shrinking the partition and dd until last used block.
I use this to copy my Linux setup for a nas down to a 4 gig ISO for redeploy.
Have to check my notes...
Edit: Checked Notes
#Use-case of fdisk taking the approach that fdisk is used, and assumption is your "sudo fdisk -l " produced:
The two things you should take note of are
In this case you have cylinders that are equal to 8225280 Bytes. In the "End" column sda8 terminates at 525 (which is 525[units] * 16065 * 512 = ~4.3GB)
dd can do a lot of things, such as starting after an offset, or stopping after a specific number of blocks. We will do the latter using the count option in dd. The command would appear as follows:
sudo dd if=/dev/sda of=/your_directory/image_name.iso bs=8225280 count=526Where -bs is the block size (it is easiest to use the unit that fdisk uses, but any unit will do so long as the count option is declared in these units), and count is the number of units we want to copy Note that we increment the count by 1 to capture the last block).
Note to display units in cylinders:
fdisk -l -u=cylinders /dev/sdaNote for newbies of dd that of= can be a device you write to i.e. /dev/sdc, rather than a path to an iso image.