interface_error_watch.sh

#!/usr/bin/env bash

set -euo pipefail

# interface_error_watch.sh
# Samples interface rx/tx error and drop counters from /sys/class/net.

usage() {
  cat <<'EOF'
Usage: ./interface_error_watch.sh [options]

Options:
  --interval N           Seconds between samples (default: 2)
  --samples N            Number of samples (default: 5)
  --only IFACE           Monitor only one interface (repeatable)
  --exclude IFACE        Exclude interface (repeatable)
  --show-loopback        Include loopback interface
  -h, --help             Show help
EOF
}

INTERVAL=2
SAMPLES=5
SHOW_LOOPBACK=false
ONLY_IFACES=()
EXCLUDE_IFACES=()

while [[ $# -gt 0 ]]; do
  case "$1" in
    --interval) INTERVAL="$2"; shift 2 ;;
    --samples) SAMPLES="$2"; shift 2 ;;
    --only) ONLY_IFACES+=("$2"); shift 2 ;;
    --exclude) EXCLUDE_IFACES+=("$2"); shift 2 ;;
    --show-loopback) SHOW_LOOPBACK=true; shift ;;
    -h|--help) usage; exit 0 ;;
    *) echo "Unknown option: $1"; usage; exit 1 ;;
  esac
done

if [[ ! -d /sys/class/net ]]; then
  echo "/sys/class/net not found"
  exit 1
fi

is_excluded_iface() {
  local iface="$1"
  local item

  if [[ "$iface" == "lo" && "$SHOW_LOOPBACK" == false ]]; then
    return 0
  fi

  if [[ "${#ONLY_IFACES[@]}" -gt 0 ]]; then
    local in_only=false
    for item in "${ONLY_IFACES[@]}"; do
      if [[ "$iface" == "$item" ]]; then
        in_only=true
        break
      fi
    done
    if [[ "$in_only" == false ]]; then
      return 0
    fi
  fi

  for item in "${EXCLUDE_IFACES[@]}"; do
    if [[ "$iface" == "$item" ]]; then
      return 0
    fi
  done

  return 1
}

list_ifaces() {
  local iface
  for iface_path in /sys/class/net/*; do
    iface="$(basename "$iface_path")"
    if is_excluded_iface "$iface"; then
      continue
    fi
    echo "$iface"
  done
}

read_stat() {
  local iface="$1"
  local stat="$2"
  local p="/sys/class/net/$iface/statistics/$stat"
  if [[ -r "$p" ]]; then
    cat "$p"
  else
    echo 0
  fi
}

ifaces=()
while IFS= read -r iface; do
  ifaces+=("$iface")
done < <(list_ifaces)

if [[ "${#ifaces[@]}" -eq 0 ]]; then
  echo "No interfaces matched selection."
  exit 1
fi

echo "Interface error watch timestamp: $(date -Iseconds)"
echo "interval=${INTERVAL}s samples=$SAMPLES"
echo "interfaces=${ifaces[*]}"
echo

declare -A prev_rx_err prev_tx_err prev_rx_drop prev_tx_drop

total_delta_events=0

for ((sample=1; sample<=SAMPLES; sample++)); do
  echo "=== Sample $sample/$SAMPLES ==="
  for iface in "${ifaces[@]}"; do
    rx_err=$(read_stat "$iface" rx_errors)
    tx_err=$(read_stat "$iface" tx_errors)
    rx_drop=$(read_stat "$iface" rx_dropped)
    tx_drop=$(read_stat "$iface" tx_dropped)

    if [[ "$sample" -eq 1 ]]; then
      drx_err=0
      dtx_err=0
      drx_drop=0
      dtx_drop=0
    else
      drx_err=$(( rx_err - ${prev_rx_err[$iface]} ))
      dtx_err=$(( tx_err - ${prev_tx_err[$iface]} ))
      drx_drop=$(( rx_drop - ${prev_rx_drop[$iface]} ))
      dtx_drop=$(( tx_drop - ${prev_tx_drop[$iface]} ))
    fi

    delta_sum=$(( drx_err + dtx_err + drx_drop + dtx_drop ))
    if [[ "$delta_sum" -gt 0 ]]; then
      total_delta_events=$(( total_delta_events + delta_sum ))
    fi

    printf '%-12s rx_err=%-8s tx_err=%-8s rx_drop=%-8s tx_drop=%-8s | delta rx_err=%-6s tx_err=%-6s rx_drop=%-6s tx_drop=%-6s\n' \
      "$iface" "$rx_err" "$tx_err" "$rx_drop" "$tx_drop" "$drx_err" "$dtx_err" "$drx_drop" "$dtx_drop"

    prev_rx_err[$iface]="$rx_err"
    prev_tx_err[$iface]="$tx_err"
    prev_rx_drop[$iface]="$rx_drop"
    prev_tx_drop[$iface]="$tx_drop"
  done

  echo
  if [[ "$sample" -lt "$SAMPLES" ]]; then
    sleep "$INTERVAL"
  fi
done

status="OK"
if [[ "$total_delta_events" -gt 0 ]]; then
  status="WARN"
fi

echo "Summary: status=$status total_delta_events=$total_delta_events"

if [[ "$status" == "WARN" ]]; then
  exit 2
fi

exit 0