Public bug reported: Speaking about this line in unmkinitramfs:
113: dd < "$initramfs" skip=$start count=$((end - start)) iflag=skip_bytes 2> /dev/null | dd's block size is 512 by default. iflag=skip_bytes does not change that. Both $end and $start are byte-offsets. Hence the count is ($end-$start) blocks or ($end-$start)*512 bytes which is wrong. Anyways, the script just works because the count is unneeded: dd's output is piped into cpio which stops on the first end-of-archive marker, no matter how much data it is fed with. I think it is the best to just drop the count option (the patch is attached). If there is still a need to explicitly limit data fed to cpio, dd is impractical in this case. The only way to count= in bytes is bs=1, which makes dd extremely slow on lengthy data chunks. For example ubuntu-23.10.1-desktop-amd64.iso contains initrd with embedded uncompressed cpio archives of such sizes: 77312 7200768 78615040 A combo of dd+head could be used intead to skip and count respectively: 113: dd < "$initramfs" skip=$start iflag=skip_bytes 2> /dev/null | head -c$((end - start)) Or even tail+head: 113: tail -c+$((start+1)) "$initramfs" | head -c$((end - start)) ** Affects: initramfs-tools (Ubuntu) Importance: Undecided Status: New ** Patch added: "dd-count.patch" https://bugs.launchpad.net/bugs/2055055/+attachment/5749511/+files/dd-count.patch -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2055055 Title: unmkinitramfs: wrong and unneeded count= in a dd call To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/initramfs-tools/+bug/2055055/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs