Find and fix veth pairs that aren't connected to LXC containers anymore

fix-veths.sh

#!/usr/bin/env bash

# Create associative arrays
declare -A interior=()
declare -A exterior=()

# Make sure ethtool is installed on this host
apt-get install -y ethtool

# For each container
for container in $(lxc-ls)
do
  # For each list of ifindex:ifname pairs
  for items in $(awk -F': ' '{print $1 ":" $2}' < <(lxc-attach -n $container -- ip -o l | sort -n | tail -n+2))
  do
    # For each ifindex:ifname pairs
    for item in "${items[@]}"
    do
      # Split into ifindex and ifname
      index=$(echo $item | awk -F':' '{print $1}')
      name=$(echo $item | awk -F':' '{print $2}')

      # Add entry keyed on ifindex => ifname and container name
      interior+=([$index]="$name $container")
    done
  done
done

# For each ifindex:ifname pair
for item in $(ip -o l | grep veth | awk -F': ' '{print $1 ":" $2}')
do
  # Split into ifindex and ifname
  index=$(echo $item | awk -F':' '{print $1}')
  name=$(echo $item | awk -F':' '{print $2}')

  # Extract peer ifindex from ethtool
  peer=$(ethtool -S $name | awk '/peer_ifindex/ {print $2}')

  # Add entry keyed on interior peer's ifindex => ifname
  exterior+=([$peer]=$name)
done

# For each peer (interior) ifindex
for peer in "${!exterior[@]}"
do
  # Store exterior ifname for this veth pair
  extname=${exterior[$peer]}

  # If this peer ifindex was also found inside the container
  if [[ -n ${interior[$peer]} ]]
  then
    # Split out values into ifname and container name
    items=(${interior[$peer]})
    name="${items[0]}"
    container="${items[1]}"
    echo "Found peer for interface $extname => $peer:$name in $container"
  # Otherwise the exterior veth is dangling; delete it!
  else
    # This section redirects to stderr only
    # You can filter just for them with: $script 1>/dev/null
    echo "Peer $peer for interface $extname not in a container!" >&2
    echo "======= Deleting $extname =======" >&2
    ip link del $extname >&2
  fi
done