xorriso-dd-target -  Device evaluator and disk image copier for GNU/Linux

Copyright © 2019 Thomas Schmitt

     Permission is granted to distribute this text freely.

xorriso-dd-target 1.5.3
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xorriso-dd-target -  Device evaluator and disk image copier for GNU/Linux

Overview
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xorriso-dd-target evaluates block devices of the Linux kernel whether they are suitable targets for a disk image file and optionally copies the image file to one of them. It is specialized on the device names of the Linux kernel and uses the capabilities of util-linux program lsblk. Therefore it refuses to run on non-Linux kernels.

The main purpose of xorriso-dd-target is to inspect the device files of disk-like storage media and to judge whether they look like removable devices with disposable content. If a single plausible candidate is detected, then the program is willing to copy a disk image file onto it. This will overwrite or make inaccessible the previous partition table and all previous data content of the target device. Superuser power is normally needed for filesystem type identification, for possible unmounting, and for possible image writing. Option -with_sudo offers a way to gain this power only for those tasks and to run the program elsewise with a normal user's power. If a particular disk image file is intended as copy source, then its path should be given by option -image_file, so that its size can be used as decision criterion.

Following are use case descriptions with examples:

List plain device names
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The most simple and most boring use case is a program run without device names and without options -list_all, -plug_test, -DO_WRITE, -dummy_force. It prints on standard output (stdout) only the names of advisable devices without "/dev/" prefix. One name per line and without any reasoning text. The possible sudo password prompt, the message line about sudo, and the empty line after it do not go to stdout. Example: $ xorriso-dd-target -with_sudo Testing sudo to possibly get password prompting done now: [sudo] password for thomas: sudo /bin/lsblk seems ok.

sde

List all devices with reasoning
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For the more curious user, there is option -list_all which prints the evaluation of each disk-like device that is listed by program lsblk. Optical drives, floppy disks, RAM block devices, loop devices are excluded, though. Each device is shown by one line of the form name : advice : reasoning : info name is the device name without "/dev/" prefix. advice is either "YES" or "NO". "YES" indicates that the device appears to be pluggable disk-like, not used as system disk or sincere data storage, and - if tested - of sufficient or plausible size. reasoning is a blank separated list of words with either suffix '+' for an inviting device property or '-' for a prohibitive property. Normally a single '-' reason disqualifies the device from being advisable. Only if option -look_for_iso is given, a reason "has_XYZ-" can be overridden by the presence of an ISO 9660 filesystem on the device. info is composed from VENDOR and MODEL as told by lsblk. Option -list_long causes with each line an additional listing of the information provided by lsblk which led to the shown reasons. Example: $ xorriso-dd-target -with_sudo -list_all ... sda : NO  : not_usb- has_vfat+ has_ext4- : ATA Samsung SSD 850 sdb : NO  : not_usb- has_swap- has_ext4- : ATA WDC WD20EFRX-68A sdc : YES : usb+ has_iso9660+ has_vfat+ : Intenso Ultra Line sdd : NO  : usb+ has_iso9660+ has_vfat+ has_ext2- : SanDisk Cruzer

Evaluate particular given devices
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If device names are given instead of option -list_all, then only these devices are inspected. Their result gets listed without the ": info" part, unless option -with_vendor_model is given. Device names must not begin by '-' and must be single words composed of the characters [A-za-z0-9_/-]. They should not contain '/'. E.g. 'sdc' is valid, '/dev/sdc' is not valid. If one of the given device names gets not advised, the exit value is 1. It makes few sense to give device names which are not listed by -list_all. Examples: $ xorriso-dd-target -with_sudo sdc ... sdc : YES : usb+ has_iso9660+ has_vfat+ $ xorriso-dd-target -with_sudo -with_vendor_model sdc ... sdc : YES : usb+ has_iso9660+ has_vfat+ : Intenso Ultra Line $ xorriso-dd-target sdc sdc : NO  : usb+ no_fs_while_not_su-

Detect intended device by plugging
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Option -plug_test triggers an interactive method to unambiguously determine the intended target device candidate. It consists of 2 or 3 steps. Step 1 is to have the intended storage device unplugged and to confirm this by pressing the Enter key at the program's prompt. The program will then assess the list of not wanted devices. Step 2 is to plug in the intended storage device and to confirm this by pressing the Enter key a second time. The program will wait up to 10 seconds for a disk-like storage device which is not in the list of not wanted devices. The user may wait with key pressing until the device blinking looks like it is ready. Only if a single new device is found, the program will go on as if a single device name was given. Option -list_all and any device names given as arguments will be ignored. Step 3 happens only if options -DO_WRITE or -dummy_force are given. The program asks for a final input of the word 'yes' before real or simulated writing begins. Example: $ xorriso-dd-target -with_sudo -plug_test ... Caused by option -plug_test: Attempt to find the desired device by watching it appear after being plugged in. Step 1: Please make sure that the desired target device is plugged _out_ now. If it is currently plugged in, make sure to unmount all its fileystems and then unplug it. Press the Enter key when ready.

Found and noted as _not_ desired:  sda sdb sdc Step 2: Please plug in the desired target device and then press the Enter key.

Waiting up to 10 seconds for a new device to be listed ... found: sdd Now waiting 5 seconds to let it settle ......... Found and noted as desired device:  sdd

sdd : NO  : usb+ has_iso9660+ has_vfat+ has_ext2- : SanDisk Cruzer

Write image to an advised device
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Only if option -DO_WRITE is given and -list_all is not, and if exactly one advisable device is listed, it really gets overwritten by the file content of the given -image_file. In this case the exit value is zero if writing succeeded, non-zero else. Option -dummy prevents this kind of real action and rather shows the planned umount and dd commands on stdout. Example: $ xorriso-dd-target -with_sudo -plug_test -DO_WRITE \ -image_file debian-live-10.0.0-amd64-xfce.iso ... sudo messages and above plug test steps 1 and 2 ...

sde : YES : usb+ has_iso9660+ has_vfat+ Step 3: Last chance to abort. Enter the word 'yes' to start REAL WRITING. yes Looking for mount points of sde: /dev/sde1 on /mnt/iso type iso9660 (ro,relatime) /dev/sde2 on /mnt/fat type vfat (rw,...,errors=remount-ro) Unmounted: /dev/sde1 Unmounted: /dev/sde2 Performing: sudo /bin/dd if='debian-live-10.0.0-amd64-xfce.iso' bs=1M of=/dev/sde ; sync ... dd messages ...

Show commands for writing to a not advised device
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There should be no way to convince xorriso-dd-target of writing to a target device which it does not deem advisable. Please report any set of arguments that can be misused for that. The outmost complicity to potentially unwise actions is offered by option -dummy_force. If given together with a single device name or with option -plug_test it will act like -dummy -DO_WRITE with this device, even if it looks not advisable. I.e. it will show the shell commands which the program does not dare to perform. Example: $ xorriso-dd-target -with_sudo -list_long -dummy_force sdd \ -image_file debian-live-10.0.0-amd64-xfce.iso ... sdd : NO  : usb+ has_iso9660+ has_vfat+ has_ext2- NAME    SIZE FSTYPE  TRAN LABEL sdd     3.8G iso9660 usb  d-live 9.5.0 xf i386 |-sdd1  1.9G iso9660      d-live 9.5.0 xf i386 |-sdd2  320K vfat `-sdd3  512M ext2

Overriding any advice because of -dummy_force Looking for mount points of sdd: /dev/sdd1 on /mnt/iso type iso9660 (ro,relatime) /dev/sdd2 on /mnt/fat type vfat (rw,...,errors=remount-ro) /dev/sdd3 on /mnt/ext type ext2 (rw,relatime) AGAINST THE ADVICE BY THIS PROGRAM, a daring user could do: sudo /bin/umount /dev/sdd1 sudo /bin/umount /dev/sdd2 sudo /bin/umount /dev/sdd3 sudo /bin/dd if='debian-live-10.0.0-amd64-xfce.iso' bs=1M of=/dev/sdd ; sync BE SMART. BE CAUTIOUS. BEWARE.

Alphabetical list of positive and negative reasons
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As stated with use case "List all devices", reasons are words with either suffix '+' for an inviting device property or '-' for a prohibitive property. Normally a single '-' reason disqualifies the device from being advisable.

Reasons
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has_XYZ- A filesystem of type XYZ is detected on base device or partition and is spoiling the impression of a device with disposable content. has_iso9660+ An ISO 9660 filesystem is detected. has_vfat+ A FAT (MS-DOS-like) filesystem is detected. look_for_iso++ Option -look_for_iso is given and an ISO 9660 filesystem is detected. This reason overrides any "has_XYZ-" reason. looks_like_cd_drive- A given device name looks like the name of an optical drive: sr[0-9]*. Use program xorrecord for this kind of devices. looks_like_disk_partition- A given device name looks like the name of a partition. Expected are names of base devices, like "sde", not of their partitions, like "sde1". looks_like_floppy- A given device name looks like the name of a floppy disk drive: fd[0-9]*. looks_like_loopdev- A given device name looks like the name of a loop device: loop[0-9]*. looks_like_ramdev- A given device name looks like the name of a RAM block device: zram[0-9]*. lsblk_no_size- A size test is given by -max_size, -min_size, or -image_file but the size of the device cannot be inquired by lsblk. This is supposed to happen only with given inappropriate device names. mmcblk+ The device name looks like a directly connected memory card. name_with_slash- A given device name contains '/' characters. no_bus_info- The device is not a memory card and lsblk reports nothing about the way how it is connected to the computer. no_fs_while_not_su- No filesystem is reported by lsblk and the program does not believe to have run it with superuser powers. There is the risk that lsblk silently failed to detect existing filesystems. no_iso9660- Option -look_for_iso is given but no ISO 9660 filesystem is detected. not_usb- The device is not a memory card and lsblk reports that it is connected by something other than USB. size_too_large- Option -max_size is given with a size smaller than the size of the device. size_too_small- Option -min_size or -image_file is given with size or file size larger than the size of the device. usb+ The device is reported by lsblk to be connected via USB.

Options
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-plug_test
     Find the target device by asking the user to press the Enter key when the desired target is _not_ plugged in, to then plug it in, and to press Enter again. This overrides device names and option -list_all. The found device is then shown with advice, vendor, and model. Option -DO_WRITE is obeyed if given. In this case, the word 'yes' has to be entered to let unmounting and writing begin.

-list_all
     Print list of all found devices with advice, vendor and model. One per line. Ignore any device names. Ignore -DO_WRITE.

-list_long
     After each result line, which shows reasons, add an additional listing of the information provided by lsblk which led to the reasons and add an empty line.

-with_vendor_model
     Print vendor and model with each submitted device name.

-max_size n[M|G|T]
     Set the upper byte size limit for advisable devices. Plain numbers get rounded down to full millions. As suffix are recognized: M = million, G = billion, T = trillion. Be generous to avoid problems with GB < GiB.

-min_size n[M|G|T]
     Set the lower byte size limit for advisable devices. After processing like with -max_size, one million gets added to the size limit.

-look_for_iso
     Demand presence of an ISO 9660 filesystem. If so, then any further filesystem type is acceptable on that device. If this option is missing, only ISO 9660 and VFAT filesystems are accepted.

-with_sudo
     Run 'lsblk -o FSTYPE' by sudo. If no filesystems are detected on a device while the program has no superuser power, then the device is not advised. Option -with_sudo avoids this refusal without the need to run the whole program as superuser. If -DO_WRITE -with_sudo is given, then the programs umount and dd will be run by sudo, too.

-image_file PATH
     Set the path of the image file which shall be written to a device. Its size will be set as -min_size.

-DO_WRITE
     Write the given -image_file to the one advisable device that is found. If more than one such device is found, then they get listed but no writing happens. In this case, to get a real write run, consider unplugging unneeded devices, or using option -plug_test, or a re-run with one of the advised device names as additional argument.

-dummy
     Report the -DO_WRITE actions but do not perform them.

-dummy_force
     If a single device name is given, do a run of -dummy -DO_WRITE even against the advice of this program. This probably shows you ways to shoot your own foot.

-help
     Print the help text to stdout and then end the program.

Examples
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Examples are given in the above description of use cases.

Files
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For now, no files are defined for configuration.

See also
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lsblk(8), sudo(8), umount(8), dd(1), xorrecord(1)

Reporting bugs
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To report bugs, request help, or suggest enhancements for xorriso-dd-target, please send electronic mail to the public list bug-xorriso@gnu.org. If more privacy is desired, mail to scdbackup@gmx.net.

Please describe what you expect the program to do, the program arguments which you used, the messages of xorriso-dd-target, and the undesirable outcome of your program run.

Expect to get asked more questions before solutions can be proposed.

Author, Copyright, Credits
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Author
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Thomas Schmitt <scdbackup@gmx.net> for libburnia-project.org

Copyright
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Copyright (c) 2019 Thomas Schmitt Permission is granted to distribute this text freely. It shall only be modified in sync with the technical properties of xorriso-dd-target. If you make use of the license to derive modified versions of xorriso-dd-target then you are entitled to modify this text under that same license.

Credits
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xorriso-dd-target is developed in cooperation with Nio Wiklund alias sudodus.