netns_wrapper.sh

#!/bin/bash

# runs a command in the same network namespaces as a process pid

set -e

function usage {
    test -n "$*" & echo "$*"
    echo "usage: $0 PID COMMAND [ARG...]" >&2
    exit 1
}

test $# -lt 2 && usage

PID=$1
shift

test -e /proc/$PID || usage "invalid PID $PID"

NETNS_DIR=/var/run/netns
mkdir -p $NETNS_DIR

TMP=$(mktemp -u $NETNS_DIR/netns.XXXXXXX)
trap 'test -e $TMP && rm -v $TMP' EXIT
NAME=$(basename "$TMP")

# ip netns expects a file in $NETNS_DIR
ln -sf "/proc/$PID/ns/net" "$NETNS_DIR/$NAME"
ip netns exec "$NAME" "$@"