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I have a USB stick with a live system. One file in this has got the wrong md5 sum. The ISO image from which it was made had the right md5 sum.

I want to rename the broken file such that it does not harm any longer and put a known good replacement into the same directory.

Of course I could make a new stick from the onset. But my special stick has more than one partition and I want to keep the other partitions unchanged. Also there are some other files in the live system, which I would like to modify (and of course adapt the entries with the md5sums of the file md5sum.txt to the changed files). So my first question is just a practice for the second step.

I have already tried to mount the device (/dev/sdb1 in my case) in -w mode, but it refuses to do so because of the iso9660 filesystem.

Adalbert Hanßen
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    "iso9660" is not writable, by definition. – ChanganAuto Dec 28 '21 at 00:37
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    Generally one cannot modify an ISO9660 file system as that defeats the purpose of an immutable medium. This answer from a few years ago has a bit more info. – matigo Dec 28 '21 at 00:43
  • @ChanganAuto: Apparently the ISO9660 file system has been written to the thumbdrive, When in the writing process did it become unwritable? There are irreversible operations: when I close the door and it falls into the lock, for example, but with the right key you can get it open again... But I could also repartition the stick, then it would be rewritable again - fortunately! At https://askubuntu.com/questions/9262/change-liveusb-default-boot-options someone describes that he changes single files on the installed stick and I remember to have done that before and that it worked then. – Adalbert Hanßen Dec 28 '21 at 08:02
  • You're very confused. Your link has nothing to do with changing an immutable file system but with adding different Grub parameters once booted from that medium. Please read again and understand what was answered in Matigo's link. Namely understand that "iso9660" is originally a optical drive (CD/DVD) file system, read-only by definition. That later it was possible to use it to make bootable USB drives, by "emulating" an optical drive in a flash mass storage device doesn't change its characteristics. Of course the media itself is re-writable but NOT the file system insie as you wan do. – ChanganAuto Dec 28 '21 at 14:30
  • "live media with persistence" allows the use of the remaining space in a given USB flash by adding an additional user accessible rw file system. – ChanganAuto Dec 28 '21 at 14:32
  • My Xubuntu 20.04 from a downloaded https://cdimage.ubuntu.com/xubuntu/releases/20.04/release/xubuntu-20.04.3-desktop-amd64.iso adds a third partition labelled "writable" when booted. - Three times after several boots from the stick, it produced a message that a file is broken. md5sum -c --quiet md5sum.txt always report ./boot/grub/efi.img as wrong! This also happened with other new sticks. Before using the stick all md5sums were right. Before using the downloaded isofile, its overall checksum was also ok. Really strange for an immutable file system! – Adalbert Hanßen Dec 30 '21 at 11:37
  • Perhaps try PM'ing sudodus at Ubuntu Forums. He tried to explain the process to me several years ago, but it is a little too complex for my tired old brain. – C.S.Cameron Dec 30 '21 at 23:35

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