如何进入指定docker容器的namespace？

脚本如下：

#!/bin/sh
if [ -e $(dirname "$0")/nsenter ]; then
  # with boot2docker, nsenter is not in the PATH but it is in the same folder
  NSENTER=$(dirname "$0")/nsenter
else
  NSENTER=nsenter
fi
if [ -z "$1" ]; then
  echo "Usage: docker-enter.sh CONTAINER [COMMAND [ARG]...]"
  echo ""
  echo "Enters the Docker CONTAINER and executes the specified COMMAND."
  echo "If COMMAND is not specified, runs an interactive shell in CONTAINER."
else
  PID=$(docker inspect --format "{{.State.Pid}}" "$1")
  if [ -z "$PID" ]; then
    exit 1
  fi
  shift
  OPTS="--target $PID --mount --uts --ipc --net --pid --"
  if [ -z "$1" ]; then
    # No command given.
    # Use su to clear all host environment variables except for TERM,
    # initialize the environment variables HOME, SHELL, USER, LOGNAME, PATH,
    # and start a login shell.
    "$NSENTER" $OPTS su - root
  else
    # Use env to clear all host environment variables.
    "$NSENTER" $OPTS env --ignore-environment -- "$@"
  fi
fi