Erasing GPT backup header block, if expr is good enough

xorriso-dd-target/xorriso-dd-target

@@ -15,7 +15,7 @@
 # announces.
 
 xdt_print_version() {
-  echo "xorriso-dd-target , version 1.5.3 , 2020.01.06.204949"
+  echo "xorriso-dd-target , version 1.5.3 , 2020.01.07.123808"
 }
 
 
@@ -225,6 +225,10 @@ xdt_reset_job() {
   xdt_sudo_cmd=
   xdt_have_su_power=
   xdt_end_after_setup=
+  xdt_dev_bytes=
+  xdt_dev_end=
+  xdt_dd_bs="bs=1M"
+  xdt_dd_silent=
 
   return 0
 }
@@ -350,7 +354,9 @@ xdt_arg_interpreter() {
   done
   xdt_predict_su_power || return "$?"
   # Prepare for using dd pacifier if desired and available
+  # Prepare for using silent dd with GPT backup erasure if available
   xdt_dd_bs="bs=1M"
+  xdt_dd_silent=
   if test -n "$xdt_dd_cmd"
   then
     if test -z "$xdt_no_pacifier" && \
@@ -359,6 +365,11 @@ xdt_arg_interpreter() {
     then
       xdt_dd_bs="bs=1M status=progress oflag=dsync"
     fi
+    if "$xdt_dd_cmd" if=/dev/zero of=/dev/null count=1 bs=512 status=none \
+                     2>/dev/null
+    then
+      xdt_dd_silent="status=none"
+    fi
   fi
   return 0
 }
@@ -615,8 +626,8 @@ xdt_list_devices() {
     # Optional tests for size
     if test -n "$xdt_max_size" || test -n "$xdt_min_size"
     then
-      xdt_size=$("$xdt_lsblk_cmd" -n -b -o SIZE /dev/"$xdt_name" \
+      xdt_dev_bytes=$("$xdt_lsblk_cmd" -n -b -o SIZE /dev/"$xdt_name" | head -1)
-                     | head -1 | xdt_round_down_div_million)
+      xdt_size=$(echo "$xdt_dev_bytes" | xdt_round_down_div_million)
       if test -z "$xdt_size"
       then
         xdt_yucky=y
@@ -752,12 +763,37 @@ xdt_write_image() {
     echo "No executable program dd found in: $xdt_sudo_x_dir_list" >&2
     return 6
   fi
+
+  # Erase possible GPT backup table at end of device
+  # if expr can properly divide device size by 512
+  if test -n "$xdt_dev_bytes"
+  then
+    xdt_dev_end=$(expr "$xdt_dev_bytes" / 512 2>/dev/null)
+    if test "$(expr "$xdt_dev_end" '*' 512 2>/dev/null)" = "$xdt_dev_bytes"
+    then
+      xdt_dev_end=$(expr "$xdt_dev_end" - 1)
+    else
+      xdt_dev_end=
+    fi
+  fi
+  xdt_gpt_erase_line="$xdt_sudo_cmd $xdt_dd_cmd if=/dev/zero of=/dev/'${2}' bs=512 seek='$xdt_dev_end' count=1 $xdt_dd_silent"
+
+  xdt_copy_line="$xdt_sudo_cmd $xdt_dd_cmd if='${1}' of=/dev/'${2}' $xdt_dd_bs ; sync"
   if test -n "$xdt_dummy_run"
   then
-    echo "  $xdt_sudo_cmd $xdt_dd_cmd if='${1}' of=/dev/'${2}' $xdt_dd_bs ; sync"
+    if test -n "$xdt_dev_end"
+    then
+      echo "  $xdt_gpt_erase_line"
+    fi
+    echo "  $xdt_copy_line"
   else
     echo "Performing:"
-    echo "  $xdt_sudo_cmd $xdt_dd_cmd if='${1}' of=/dev/'${2}' $xdt_dd_bs ; sync"
+    if test -n "$xdt_dev_end"
+    then
+      echo "  $xdt_gpt_erase_line"
+      $xdt_sudo_cmd "$xdt_dd_cmd" if=/dev/zero of=/dev/"${2}" bs=512 seek="$xdt_dev_end" count=1 $xdt_dd_silent
+    fi
+    echo "  $xdt_copy_line"
     $xdt_sudo_cmd "$xdt_dd_cmd" if="${1}" of=/dev/"${2}" $xdt_dd_bs
     xdt_ret="$?"
     sync
@@ -768,8 +804,6 @@ xdt_write_image() {
     fi
   fi
 
-  # >>> ??? Erase possible GPT backup table at end of device ?
-
   if test -n "$xdt_dummy_force"
   then
     echo "BE SMART. BE CAUTIOUS. BEWARE."

xorriso-dd-target/xorriso-dd-target.1

@@ -9,7 +9,7 @@
 .\" First parameter, NAME, should be all caps
 .\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
 .\" other parameters are allowed: see man(7), man(1)
-.TH XORRISO-DD-TARGET 1 "Version 1.5.3, Jan 6, 2020"
+.TH XORRISO-DD-TARGET 1 "Version 1.5.3, Jan 7, 2020"
 .\" Please adjust this date whenever revising the manpage.
 .\"
 .\" Some roff macros, for reference:
@@ -48,7 +48,7 @@ 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.
 .br
-\fBSuperuser power\fR is normally needed for filesystem type identification,
+\fBSuperuser power\fR is often needed for filesystem type identification,
 for possible unmounting, and for possible image writing.
 Option \fB\-with_sudo\fR offers a way to gain this power only for those
 tasks and to run the program elsewise with a normal user's power.
@@ -173,13 +173,14 @@ sdc : NO  : usb+ no_fs_while_not_su\-
 Option \fB\-plug_test\fR triggers an interactive method to unambiguously
 determine the intended target device candidate. It consists of 2 or 3 steps.
 .br
-\fBStep 1\fR is to have the intended storage device unplugged and
+\fBStep 1\fR is to have the intended storage device \fBunplugged\fR 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.
 .br
-\fBStep 2\fR is to plug in the intended storage device and to confirm this
+\fBStep 2\fR is to \fBplug in\fR the intended storage device and to
-by pressing the Enter key a second time. The program will wait up to 10 seconds
+confirm this by pressing the Enter key a second time. The program will wait
-for a disk\-like storage device which is not in the list of not wanted devices.
+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.
 .br
@@ -270,9 +271,18 @@ Unmounted: /dev/sde2
 .br
 Performing:
 .br
-  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'
+.br
+               count=1 status=none
+.br
+  sudo /bin/dd if='debian\-live\-10.0.0\-amd64\-xfce.iso' of=/dev/'sde'
+.br
+               bs=1M status=progress oflag=dsync ; sync
 .br
  ... dd messages ...
+.br
+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.
 .SS
 \fBShow commands for writing to a not advised device:\fR
 .br
@@ -326,7 +336,13 @@ AGAINST THE ADVICE BY THIS PROGRAM, a daring user could do:
 .br
   sudo /bin/umount /dev/sdd3
 .br
-  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'
+.br
+               count=1 status=none
+.br
+  sudo /bin/dd if='debian\-live\-10.0.0\-amd64\-xfce.iso' of=/dev/sdd
+.br
+               bs=1M status=progress oflag=dsync ; sync
 .br
 BE SMART. BE CAUTIOUS. BEWARE.
 .SS
@@ -538,7 +554,7 @@ Thomas Schmitt <scdbackup@gmx.net>
 .br
 for libburnia\-project.org
 .SH COPYRIGHT
-Copyright (c) 2019 Thomas Schmitt
+Copyright (c) 2019 \- 2020 Thomas Schmitt
 .br
 Permission is granted to distribute this text freely. It shall only be
 modified in sync with the technical properties of xorriso\-dd\-target.

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
+*Step 1* is to have the intended storage device *unplugged* and to
-this by pressing the Enter key at the program's prompt.  The program
+confirm this by pressing the Enter key at the program's prompt.  The
-will then assess the list of not wanted devices.
+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 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
+sudo /bin/dd if=/dev/zero of=/dev/'sde' bs=512 seek='245759999'
-status=progress oflag=dsync ; sync
+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
+sudo /bin/dd if=/dev/zero of=/dev/'sdd' bs=512 seek='7864318'
-status=progress oflag=dsync ; sync
+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: Simplenames2789
-Node: Listall3516
+Node: Listall3513
-Node: Givendevices5089
+Node: Givendevices5086
-Node: Plugtest6053
+Node: Plugtest6050
-Node: Dowrite7954
+Node: Dowrite7955
-Node: Unwise9097
+Node: Unwise9336
-Node: Reasons10637
+Node: Reasons10958
-Node: Options13218
+Node: Options13539
-Node: Examples16315
+Node: Examples16636
-Node: Files16488
+Node: Files16809
-Node: Seealso16646
+Node: Seealso16967
-Node: Bugreport16812
+Node: Bugreport17133
-Node: Legal17399
+Node: Legal17720
-Node: CommandIdx18103
+Node: CommandIdx18431
-Node: ConceptIdx19369
+Node: ConceptIdx19697
 
 End Tag Table

xorriso-dd-target/xorriso-dd-target.texi

@@ -50,7 +50,7 @@
 @c man .\" First parameter, NAME, should be all caps
 @c man .\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
 @c man .\" other parameters are allowed: see man(7), man(1)
-@c man .TH XORRISO-DD-TARGET 1 "Version 1.5.3, Jan 6, 2020"
+@c man .TH XORRISO-DD-TARGET 1 "Version 1.5.3, Jan 7, 2020"
 @c man .\" Please adjust this date whenever revising the manpage.
 @c man .\"
 @c man .\" Some roff macros, for reference:
@@ -128,7 +128,7 @@ 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.
 @*
-@strong{Superuser power} is normally needed for filesystem type identification,
+@strong{Superuser power} is often needed for filesystem type identification,
 for possible unmounting, and for possible image writing.
 Option @strong{-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.
@@ -275,13 +275,14 @@ sdc : NO  : usb+ no_fs_while_not_su-
 Option @strong{-plug_test} triggers an interactive method to unambiguously
 determine the intended target device candidate. It consists of 2 or 3 steps.
 @*
-@strong{Step 1} is to have the intended storage device unplugged and
+@strong{Step 1} is to have the intended storage device @strong{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.
 @*
-@strong{Step 2} is to plug in the intended storage device and to confirm this
+@strong{Step 2} is to @strong{plug in} the intended storage device and to
-by pressing the Enter key a second time. The program will wait up to 10 seconds
+confirm this by pressing the Enter key a second time. The program will wait
-for a disk-like storage device which is not in the list of not wanted devices.
+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.
 @*
@@ -375,9 +376,18 @@ 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.
 @c man .SS
 @node Unwise, Reasons, Dowrite, Overview
 @chapter Show commands for writing to a not advised device
@@ -434,7 +444,13 @@ AGAINST THE ADVICE BY THIS PROGRAM, a daring user could do:
 @*
   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.
 @c man .SS
@@ -704,7 +720,7 @@ Thomas Schmitt <scdbackup@@gmx.net>
 for libburnia-project.org
 @c man .SH COPYRIGHT
 @section 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.