autoUSBmountHeadless

#!/usr/bin/env bash
set -euo pipefail

# Fixed mountpoint (login-independent)
MOUNTPOINT="/media/mcp/device"

# Optional: if set, only mount a filesystem with this label (leave empty to accept any)
WANTED_LABEL=""

# Optional: for vfat/exfat/ntfs, force ownership to this uid:gid
OWNER_USER="mcp"
OWNER_GROUP="mcp"

LOG_TAG="usb-auto-mount"

log() {
  logger -t "$LOG_TAG" -- "$*"
  echo "[$(date '+%F %T')] $*"
}

ensure_mountpoint() {
  mkdir -p "$MOUNTPOINT"
}

uid_of() { id -u "$OWNER_USER"; }
gid_of() { id -g "$OWNER_GROUP"; }

# Return 0 if MOUNTPOINT is currently mounted
is_mounted() {
  findmnt -rno TARGET "$MOUNTPOINT" >/dev/null 2>&1
}

# If mounted, unmount it
do_unmount() {
  if is_mounted; then
    local src
    src="$(findmnt -rno SOURCE "$MOUNTPOINT" || true)"
    log "Unmounting $MOUNTPOINT (source: ${src:-unknown})"
    umount -l "$MOUNTPOINT" || umount "$MOUNTPOINT" || true
  fi
}

# Pick a USB partition device node to mount, e.g. /dev/sda1
# Strategy:
#  1) look at /dev/disk/by-id/usb-* symlinks
#  2) resolve to kernel device
#  3) choose a PARTITION if present; else use whole-disk block if it has a filesystem
pick_usb_partition() {
  local byid dev kname part

  # Prefer stable USB by-id names
  for byid in /dev/disk/by-id/usb-*; do
    [[ -e "$byid" ]] || continue
    dev="$(readlink -f "$byid" || true)"
    [[ -b "$dev" ]] || continue

    # Get kernel name (e.g. sda, sdb)
    kname="$(lsblk -no KNAME "$dev" 2>/dev/null | head -n1 || true)"
    [[ -n "$kname" ]] || continue

    # Prefer first partition on that disk (e.g. /dev/sda1)
    part="/dev/${kname}1"
    if [[ -b "$part" ]]; then
      echo "$part"
      return 0
    fi

    # Otherwise, if the whole device has a filesystem, allow it (rare but possible)
    if lsblk -no FSTYPE "$dev" 2>/dev/null | grep -qE '.+'; then
      echo "$dev"
      return 0
    fi
  done

  return 1
}

# Get filesystem type and label
fstype_of() { lsblk -no FSTYPE "$1" 2>/dev/null | head -n1 || true; }
label_of()  { lsblk -no LABEL  "$1" 2>/dev/null | head -n1 || true; }

# Mount with sane options per filesystem
do_mount() {
  local dev="$1"
  local fstype label opts uid gid

  fstype="$(fstype_of "$dev")"
  label="$(label_of "$dev")"

  if [[ -z "$fstype" ]]; then
    log "Device $dev has no detectable filesystem (skipping)"
    return 1
  fi

  if [[ -n "$WANTED_LABEL" && "$label" != "$WANTED_LABEL" ]]; then
    log "Device $dev label '$label' != wanted '$WANTED_LABEL' (skipping)"
    return 1
  fi

  uid="$(uid_of)"
  gid="$(gid_of)"

  # Default mount options
  opts="rw,nosuid,nodev,noatime"

  # For non-POSIX fs, set ownership/masks so mcp can write
  case "$fstype" in
    vfat|fat|msdos)
      opts="$opts,uid=$uid,gid=$gid,fmask=0022,dmask=0002,utf8=1"
      ;;
    exfat)
      opts="$opts,uid=$uid,gid=$gid,fmask=0022,dmask=0002"
      ;;
    ntfs|ntfs3)
      opts="$opts,uid=$uid,gid=$gid,umask=0002"
      ;;
    ext4|ext3|ext2|xfs|btrfs)
      # ownership handled by filesystem permissions
      ;;
    *)
      log "Filesystem type '$fstype' on $dev is unhandled; trying generic mount"
      ;;
  esac

  log "Mounting $dev (fstype=$fstype label='${label:-}' ) -> $MOUNTPOINT"
  mount -t "$fstype" -o "$opts" "$dev" "$MOUNTPOINT"
}

# Try to mount if nothing is mounted
try_mount_once() {
  ensure_mountpoint

  if is_mounted; then
    return 0
  fi

  local dev=""
  if dev="$(pick_usb_partition)"; then
    do_mount "$dev" || true
  else
    # No USB devices currently visible
    :
  fi
}

main() {
  ensure_mountpoint

  # Serialize (avoid multiple instances fighting)
  exec 9>/run/usb-auto-mount.lock
  if ! flock -n 9; then
    log "Another instance is running; exiting."
    exit 0
  fi

  # Initial attempt in case USB is already plugged in
  try_mount_once

  log "Watching udev for USB block add/remove events..."

  # Monitor udev events for block devices.
  # We'll react to add/remove and re-check state each time.
  udevadm monitor --udev --subsystem-match=block | while IFS= read -r line; do
    # We react on lines that contain "add" or "remove"
    if grep -qE '\b(add|remove)\b' <<<"$line"; then
      # Small settle to let partitions appear/disappear
      udevadm settle --timeout=5 || true

      # If current mount source disappeared, unmount
      if is_mounted; then
        local src
        src="$(findmnt -rno SOURCE "$MOUNTPOINT" || true)"
        if [[ -n "$src" && ! -b "$src" ]]; then
          log "Mounted source $src no longer exists; unmounting."
          do_unmount
        fi
      fi

      # If not mounted, try mounting
      try_mount_once
    fi
  done
}

trap 'log "Shutting down; unmounting."; do_unmount' INT TERM
main