Erasing GPT backup header block, if expr is good enough

xorriso-dd-target/xorriso-dd-target.info

@@ -50,7 +50,7 @@ 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,
+*Superuser power* is often 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.
@@ -157,10 +157,10 @@ File: xorriso-dd-target.info,  Node: Plugtest,  Next: Dowrite,  Prev: Givendevic
 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
+*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
@@ -224,9 +224,14 @@ Looking for mount points of sde:
 Unmounted: /dev/sde1
 Unmounted: /dev/sde2
 Performing:
-sudo /bin/dd if='debian-live-10.0.0-amd64-xfce.iso' of=/dev/sde bs=1M
-status=progress oflag=dsync ; sync
+sudo /bin/dd if=/dev/zero of=/dev/'sde' bs=512 seek='245759999'
+count=1 status=none
+sudo /bin/dd if='debian-live-10.0.0-amd64-xfce.iso' of=/dev/'sde'
+bs=1M status=progress oflag=dsync ; sync
 ...  dd messages ...
+The first dd run shall erase a possible GPT backup header.  It is
+performed only if the local program "expr" can deal with the byte size
+of the device.
 
 
 File: xorriso-dd-target.info,  Node: Unwise,  Next: Reasons,  Prev: Dowrite,  Up: Overview
@@ -263,8 +268,10 @@ 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' of=/dev/sdd bs=1M
-status=progress oflag=dsync ; sync
+sudo /bin/dd if=/dev/zero of=/dev/'sdd' bs=512 seek='7864318'
+count=1 status=none
+sudo /bin/dd if='debian-live-10.0.0-amd64-xfce.iso' of=/dev/sdd
+bs=1M status=progress oflag=dsync ; sync
 BE SMART. BE CAUTIOUS. BEWARE.
 
 
@@ -462,7 +469,7 @@ for libburnia-project.org
 14.2 Copyright
 ==============
 
-Copyright (c) 2019 Thomas Schmitt
+Copyright (c) 2019 - 2020 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
@@ -541,20 +548,20 @@ File: xorriso-dd-target.info,  Node: ConceptIdx,  Next: Top,  Prev: CommandIdx,
 Tag Table:
 Node: Top429
 Node: Overview996
-Node: Simplenames2792
-Node: Listall3516
-Node: Givendevices5089
-Node: Plugtest6053
-Node: Dowrite7954
-Node: Unwise9097
-Node: Reasons10637
-Node: Options13218
-Node: Examples16315
-Node: Files16488
-Node: Seealso16646
-Node: Bugreport16812
-Node: Legal17399
-Node: CommandIdx18103
-Node: ConceptIdx19369
+Node: Simplenames2789
+Node: Listall3513
+Node: Givendevices5086
+Node: Plugtest6050
+Node: Dowrite7955
+Node: Unwise9336
+Node: Reasons10958
+Node: Options13539
+Node: Examples16636
+Node: Files16809
+Node: Seealso16967
+Node: Bugreport17133
+Node: Legal17720
+Node: CommandIdx18431
+Node: ConceptIdx19697
 
 End Tag Table