Build [asuswrt-merlin](https://github.com/RMerl/asuswrt-merlin#readme) using Vagrant. This is just works-for-me, and not an officially supported mechanism

build.sh

#! /usr/bin/env bash
set -e
if [[ -z "$GIT_DIR" ]]; then
  echo 'You will want $GIT_DIR' >&2
  exit 1
elif [[ ! -d "$GIT_DIR" ]]; then
  echo "It seems git-dir \"$GIT_DIR\" is 404" >&2
  exit 1
fi
dir=`dirname $0`
dir=`cd $dir && pwd`

build_dir=$dir/release/src-rt-6.x

cd $build_dir

PATH=$dir/tools/brcm/hndtools-mipsel-uclibc/bin:$PATH

if [[ -z "$MAKE_JOBS" ]]; then
  MAKE_JOBS=$(nproc)
fi

# just documenting the reason
rc4_h_err=<<'RC4ERR'
make[6]: *** No rule to make target `../../include/openssl/rc4.h', needed by `eng_openssl.o'.  Stop.
make[6]: Leaving directory `/home/vagrant/asuswrt-merlin/release/src/router/openssl/crypto/engine'
make[5]: *** [subdirs] Error 1
RC4ERR
if [[ ! -e ../src/router/openssl/include/openssl/rc4.h ]]; then
  echo 'I am fixing up an ssl include dumbness' >&2
  sleep 2
  ln -s ../../crypto/rc4/rc4.h  ../src/router/openssl/include/openssl/rc4.h
fi

# just a comment showing what we are working around
bogus_err=<<'ERR'
make -C tor -j`grep -c '^processor' /proc/cpuinfo`
make[4]: Entering directory `/home/vagrant/asuswrt-merlin/release/src/router/tor'
CDPATH="${ZSH_VERSION+.}:" && cd . && aclocal-1.15 -I m4
/bin/bash: aclocal-1.15: command not found
ERR
# :point_up: :point_down:
for i in libogg tor wget; do
  cd ../src/router/${i}
  if grep -iq gettext configure.??; then
    gettextize --force
  fi
  autoreconf -fvis
  cd $OLDPWD
done

rc=0
# using a function makes the || syntax less wonky in the if
make_rt_n66u() {
  make V=1 VERBOSE=1 -j${MAKE_JOBS} rt-n66u || rc=$?
}
t0=`date +%s`
if ! make_rt_n66u; then
  echo "MAKE.RC=$rc" >&2
fi

t1=`date +%s`
tt=$(( $t1 - $t0 ))

mv -iv $build_dir/image/*.trx /vagrant/

if [[ -f nohup.out ]] && [[ ! -s nohup.out ]]; then
  mv -iv nohup.out /vagrant/build-`date +%s`.log
else
  logf=`/bin/ls -1 build-*.out`
fi
if [[ "$logf" ]] && [[ -f "$logf" ]]; then
  mv -iv $logf /vagrant/
fi
echo "OK: $rc in $tt seconds"
exit $rc

Vagrantfile

# -*- mode: ruby -*-
# vi: set ft=ruby :

Vagrant.configure("2") do |config|
  # the resulting image won't be 64 bit,
  # so adding that into the mix just makes life painful
  config.vm.box = "ubuntu/trusty32"
  config.vm.boot_timeout = 3600

  config.vm.provider "virtualbox" do |vb|
    vb.cpus = 8
    vb.memory = 4 * 1024
  end
  # this needs to be a file on the machine so we can re-exec
  # into it as "vagrant" after the priviledged operations are over
  config.vm.provision :file,
                      :source => "Vagrantfile.sh",
                      :destination => "/tmp/provision.sh"
  config.vm.provision :shell,
                      :inline => "/tmp/provision.sh",
                      :privileged => true
end

Vagrantfile.sh

#! /usr/bin/env bash
set -e
if [[ 0 == `id -u` ]]; then
    # set -x
    export DEBIAN_FRONTEND=noninteractive
    apt_cache_tar=/vagrant/var_cache_apt.tar
    tar_cmd=c
    if [[ -f   $apt_cache_tar ]]; then
      tar -xvf $apt_cache_tar -C /
      tar_cmd=u
    fi
    apt-get update
    _apt_get() {
      for i in 1 2 3; do
          apt-get "$@" && return 0
      done
      return 1
    }
    # set them to download first, then install them
    apt_extra='-d'
    for x in 1 2; do
      if [[ $x == 2 ]]; then
        cd /
        tar -${tar_cmd}vf $apt_cache_tar var/cache/apt var/lib/dpkg var/lib/apt
      fi
      _apt_get --no-install-recommends install -y \
        $apt_extra \
        autoconf automake bash bison bzip2 diffutils file flex g++ gawk \
        gcc-multilib gettext gperf groff-base libncurses-dev libexpat1-dev \
        libslang2 libssl-dev libtool libxml-parser-perl make patch perl pkg-config \
        python sed shtool tar texinfo unzip zlib1g zlib1g-dev \
        git-core \
        libstdc++6 automake1.11 intltool autopoint \
        libelf-dev:i386 libelf1:i386
      apt_extra=''
    done
    echo '==='
    echo '=== Switching to the vagrant user for the build...'
    echo '==='
    exec sudo -i -u vagrant bash -x "$0" "$@"
fi

VER="${1:-380.69}"

cd ~vagrant

# set this so the git info will be available to "make"
export GIT_DIR=/vagrant/.git
if [[ ! -d "$GIT_DIR" ]]; then
  echo "EGAD, git-dir \"$GIT_DIR\" is 404" >&2
  exit 1
fi

mkdir -p asuswrt-merlin
cd asuswrt-merlin

cp /vagrant/build.sh .

git checkout --force $VER
git reset --hard $VER
ls -la
# we have to disown this since this script is running in :provision
nohup bash -xc "./build.sh &>build-${VER}.out" &
ls -la
ps -efw
disown