How to search block device for text?

Strangely to me google had not returned any relevant (IMO) links in top results.

I want to edit iso9660.

Here How is it easier to make a persistent live drive with Ubuntu 19.10? I've read

sed 's/quiet splash/persistent  /' lubuntu-19.10-desktop-amd64.iso > persistent-lubuntu-19.10-desktop-amd64.iso  # yes, sed works with binary files

Then I thought, I have already made USB stick, why not try to edit it. dd works, but sed: couldn't edit /dev/sdb: not a regular file, so short of dumping all partition to file I better seek position of text to replace.

Any utilities to search within block file/device?

I expand Martian's answer to make it automatic. I'm using /dev/mapper/vgmint-root which is the root volume of my Linux Mint's LVM volume group with Ext4 filesystem):

sudo grep --only-matching --byte-offset --max-count=1 --text 'unique\.str \
    /dev/mapper/vgmint-root | cut -d: -f1 | xargs -I{} -- sh -xc \
    'sudo dd count=1 skip=$(echo "{} / 512" | bc) if=/dev/mapper/vgmint-root \
        | xxd -c 32'

This is actually a useful undelete command, at least for small plain text files. You can increase --max-count=1 if you want to see more matches, and count=1 if you expect a file longer than 512 bytes.

If you found what you're looking for, copy the xxd output into a file and run, and voila!

xxd -c 32 -r the_xxd_output_to_reverse

I think what you are trying to accomplish two seperate things,

The First is scanning an entire partition for a specific string.

You shouldn't try to edit/read block devices, rather try mounting them first! with

sudo mkdir /media/iso
sudo mount -o loop path/to/iso/file/YOUR_ISO_FILE.ISO /media/iso 

in your case. Source

Then you can use the mentioned sed command.

Now the actual thing you're trying to accomplish (as far as I understand) is making a persistant live Installation. This can be done two ways: Installing Ubuntu to the USB drive itself OR Iso-booting with persistant storage.

You are probably trying to boot the ISO with persistant storage so your changes dont get lost upon reboot!

Now This article is a little old and in german, though it has worked for me and you are probably able to follow the command snippets of it after using google translate on the site :)

My Grub-script for persistant live boot is as follows, you can install it like seen here.

insmod part_gpt
insmod ext2
set root='(hd0,2)'
set isofile='/iso/ubuntu-21.10-desktop-amd64.iso'

if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,msdos2  4e3de29b-008c-4063-9376-c52f34c87225
else
  search --no-floppy --fs-uuid --set=root 4e3de29b-008c-4063-9376-c52f34c87225
fi

loopback loop $isofile
linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile persistent quiet splash noeject
initrd (loop)/casper/initrd

The cryptic Text 4e3de29b-008c-4063-9376-c52f34c87225 is the UUID of the partition, the ISO is on. You can find yours using gnome-disks, g-parted or blkid /dev/sdX I hope I could help you!

$ sudo grep --only-matching --byte-offset --max-count=1 --text "quiet splash" /dev/sdb
1927125977:quiet splash

So this outputs offset in bytes, then divide by 512 (default dd block size) and then

sudo dd count=1 skip=3763917 if=/dev/sdb | hd


000001c0  69 6e 69 74 72 64 3d 2f  63 61 73 70 65 72 2f 69  |initrd=/casper/i|
000001d0  6e 69 74 72 64 2e 6c 7a  20 71 75 69 65 74 20 73  |nitrd.lz quiet s|
000001e0  70 6c 61 73 68 20 2d 2d  0a 6d 65 6e 75 20 64 65  |plash --.menu de|
000001f0  66 61 75 6c 74 0a 6c 61  62 65 6c 20 78 66 6f 72  |fault.label xfor|

Pattern located.