How does Armbian self-expand?

[Meestor_X]

Armbian is written to a µSD card as a small file (a gig or two if I recall). If the card is 64gigs, the image is still just a few gigs written to that card. When booted on the device, though, it automatically expands the file system to the full size of the card.

How exactly does it do that?

And...

How do I do the reverse?

Take the file system from a working armbian install and create a small image that when written to a µSD card, will stay small, but then auto-expand when booted on a device?

[Werner]

I think it is this script: https://github.com/armbian/build/blob/main/packages/bsp/common/usr/lib/armbian/armbian-resize-filesystem

 

There might be a switch or option to prevent resize, need to check documentation.

 

Or do manually after expansion:

https://unix.stackexchange.com/questions/656836/how-do-i-shrink-a-partition-right-after-shrinking-its-filesystem-with-resize2fs

 

[laibsch]

• Be aware that the answer might depend on the filesystem you are using on your board
• Be aware that a resize operation can easily destroy your data or at least make it inaccessible
• have a look at shrink-backup for "reverse"