ops(scripts): add macOS ISO USB writer

Provide an interactive script that lists external disks, requires repeated device confirmation, and safely unmounts, writes, and ejects the target. Detect El Torito hybrid ISO support to recommend direct writing or convert non-hybrid images to UDRW before copying them with dd.
2026-10-27 16:32:49 -05:00 · 2026-08-13 21:14:50 -05:00
parent 6c7604b218
commit 3a05a40cfd
1 changed files with 135 additions and 0 deletions
@@ -0,0 +1,135 @@
+#!/usr/bin/env bash
+#
+# iso2usb-macos.sh - Write an ISO image to a USB drive on macOS.
+#
+# Usage:
+#   ./iso2usb-macos.sh [--prompt|-p] /path/to/input.iso
+#
+# Options:
+#   -p, --prompt   Skip El Torito auto-detection and go straight to the
+#                  direct-write Y/N prompt with no pre-selected default.
+#
+# Requires: hdiutil, diskutil, dd (all built into macOS). Must be run with
+# sudo privileges for the dd step (the script will prompt when needed).
+
+set -euo pipefail
+
+SKIP_DETECT=0
+ISO_PATH=""
+
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        -p|--prompt)
+            SKIP_DETECT=1
+            shift
+            ;;
+        -*)
+            echo "Unknown option: $1"
+            echo "Usage: $0 [--prompt|-p] /path/to/input.iso"
+            exit 1
+            ;;
+        *)
+            ISO_PATH="$1"
+            shift
+            ;;
+    esac
+done
+
+if [[ -z "$ISO_PATH" ]]; then
+    echo "Usage: $0 [--prompt|-p] /path/to/input.iso"
+    exit 1
+fi
+
+if [[ ! -f "$ISO_PATH" ]]; then
+    echo "Error: file not found: $ISO_PATH"
+    exit 1
+fi
+
+# List external/removable disks only, to reduce risk of selecting an internal drive.
+echo "Available external disks:"
+echo "--------------------------"
+diskutil list external
+
+echo ""
+read -rp "Enter the disk identifier to write to (e.g. disk4): " DISK_ID
+
+# Normalize input in case user includes /dev/ prefix.
+DISK_ID="${DISK_ID#/dev/}"
+DISK_PATH="/dev/${DISK_ID}"
+RDISK_PATH="/dev/r${DISK_ID}"
+
+if [[ ! -e "$DISK_PATH" ]]; then
+    echo "Error: $DISK_PATH does not exist."
+    exit 1
+fi
+
+DISK_INFO="$(diskutil info "$DISK_PATH")"
+DISK_SIZE="$(echo "$DISK_INFO" | grep "Disk Size" | sed -E 's/.*Disk Size:[[:space:]]*//; s/[[:space:]]*\(.*//')"
+# Not all diskutil info output includes a "Disk Size" field (varies by
+# identifier type, e.g. whole-disk vs partition). Fall back to "Total Size"
+# if the first lookup came back empty.
+[[ -z "$DISK_SIZE" ]] && DISK_SIZE="$(echo "$DISK_INFO" | grep "Total Size" | sed -E 's/.*Total Size:[[:space:]]*//; s/[[:space:]]*\(.*//')"
+
+echo ""
+echo "Selected device: $DISK_PATH (${DISK_SIZE:-unknown size})"
+echo "$DISK_INFO" | grep -E "Device / Media Name|Protocol|Total Size|Removable Media"
+
+echo ""
+echo "WARNING: all data on $DISK_PATH will be destroyed."
+read -rp "Type the disk identifier again to confirm (e.g. disk4): " CONFIRM_ID
+if [[ "$CONFIRM_ID" != "$DISK_ID" ]]; then
+    echo "Confirmation did not match. Aborting."
+    exit 1
+fi
+
+WORKDIR="$(mktemp -d)"
+trap 'rm -rf "$WORKDIR"' EXIT
+
+IMG_PATH=""
+
+# Check for an El Torito boot record to determine if the ISO is hybrid.
+# The boot record volume descriptor lives at sector 17 (byte offset 0x8800).
+# Byte 0 of that sector is 0x00 (boot record type), followed by the string
+# "CD001", followed by the boot system identifier. Hybrid/El Torito ISOs
+# carry "EL TORITO SPECIFICATION" in that identifier field.
+is_hybrid_iso() {
+    local iso="$1"
+    dd if="$iso" bs=1 skip=34823 count=23 2>/dev/null | grep -aq "EL TORITO SPECIFICATION"
+}
+
+DEFAULT_DIRECT=""
+if [[ "$SKIP_DETECT" -eq 1 ]]; then
+    echo "Skipping El Torito auto-detection (--prompt set)."
+else
+    echo "Inspecting ISO for El Torito hybrid boot support..."
+    if is_hybrid_iso "$ISO_PATH"; then
+        echo "Detected: hybrid El Torito/ISO9660 image. Direct dd write should work."
+        DEFAULT_DIRECT="Y"
+    else
+        echo "No El Torito boot record found. This ISO is likely not hybrid;"
+        echo "converting via hdiutil is recommended."
+        DEFAULT_DIRECT="N"
+    fi
+fi
+
+read -rp "Attempt direct write of the raw ISO without conversion? [${DEFAULT_DIRECT:-y/N}]: " DIRECT
+DIRECT="${DIRECT:-$DEFAULT_DIRECT}"
+if [[ "$DIRECT" =~ ^[Yy]$ ]]; then
+    IMG_PATH="$ISO_PATH"
+else
+    echo "Converting ISO to UDRW image..."
+    hdiutil convert -format UDRW -o "${WORKDIR}/output.img" "$ISO_PATH"
+    # hdiutil appends .dmg to the output filename even though it is raw content.
+    IMG_PATH="${WORKDIR}/output.img.dmg"
+fi
+
+echo "Unmounting $DISK_PATH..."
+diskutil unmountDisk "$DISK_PATH"
+
+echo "Writing image to $RDISK_PATH. This may take several minutes..."
+sudo dd if="$IMG_PATH" of="$RDISK_PATH" bs=1m status=progress
+
+echo "Ejecting $DISK_PATH..."
+diskutil eject "$DISK_PATH"
+
+echo "Done."