wrapdocker script capable of being used to run docker in docker (dind) with jenkins mesos-plugin

wrapdocker.sh

#!/bin/bash

echo "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -"
echo "                ABOUT TO START DOCKER  ...                         "
echo "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -"

# --------------------------------------------------------------------------
# primarily based on https://github.com/jpetazzo/dind/blob/master/wrapdocker
# --------------------------------------------------------------------------

# Ensure that all nodes in /dev/mapper correspond to mapped devices currently loaded by the device-mapper kernel driver
dmsetup mknodes

# First, make sure that cgroups are mounted correctly.
CGROUP=/sys/fs/cgroup
: {LOG:=stdio}

[ -d $CGROUP ] ||
	mkdir $CGROUP

mountpoint -q $CGROUP ||
	mount -n -t tmpfs -o uid=0,gid=0,mode=0755 cgroup $CGROUP || {
		echo "Could not make a tmpfs mount. Did you use --privileged?"
		exit 1
	}

if [ -d /sys/kernel/security ] && ! mountpoint -q /sys/kernel/security
then
    mount -t securityfs none /sys/kernel/security || {
        echo "Could not mount /sys/kernel/security."
        echo "AppArmor detection and --privileged mode might break."
    }
fi

# Mount the cgroup hierarchies exactly as they are in the parent system.
for SUBSYS in $(cut -d: -f2 /proc/1/cgroup)
do
        [ -d $CGROUP/$SUBSYS ] || mkdir $CGROUP/$SUBSYS
        mountpoint -q $CGROUP/$SUBSYS ||
                mount -n -t cgroup -o $SUBSYS cgroup $CGROUP/$SUBSYS

        # The two following sections address a bug which manifests itself
        # by a cryptic "lxc-start: no ns_cgroup option specified" when
        # trying to start containers withina container.
        # The bug seems to appear when the cgroup hierarchies are not
        # mounted on the exact same directories in the host, and in the
        # container.

        # Named, control-less cgroups are mounted with "-o name=foo"
        # (and appear as such under /proc/<pid>/cgroup) but are usually
        # mounted on a directory named "foo" (without the "name=" prefix).
        # Systemd and OpenRC (and possibly others) both create such a
        # cgroup. To avoid the aforementioned bug, we symlink "foo" to
        # "name=foo". This shouldn't have any adverse effect.
        echo $SUBSYS | grep -q ^name= && {
                NAME=$(echo $SUBSYS | sed s/^name=//)
                ln -s $SUBSYS $CGROUP/$NAME
        }

        # Likewise, on at least one system, it has been reported that
        # systemd would mount the CPU and CPU accounting controllers
        # (respectively "cpu" and "cpuacct") with "-o cpuacct,cpu"
        # but on a directory called "cpu,cpuacct" (note the inversion
        # in the order of the groups). This tries to work around it.
        [ $SUBSYS = cpuacct,cpu ] && ln -s $SUBSYS $CGROUP/cpu,cpuacct
done

# Note: as I write those lines, the LXC userland tools cannot setup
# a "sub-container" properly if the "devices" cgroup is not in its
# own hierarchy. Let's detect this and issue a warning.
grep -q :devices: /proc/1/cgroup ||
	echo "WARNING: the 'devices' cgroup should be in its own hierarchy."
grep -qw devices /proc/1/cgroup ||
	echo "WARNING: it looks like the 'devices' cgroup is not mounted."

# Now, close extraneous file descriptors.
pushd /proc/self/fd >/dev/null
for FD in *
do
	case "$FD" in
	# Keep stdin/stdout/stderr
	[012])
		;;
	# Nuke everything else
	*)
		eval exec "$FD>&-"
		;;
	esac
done
popd >/dev/null

# -------------------------------------------------------
#   START : Fix for running out of loopback devices
# FROM HERE https://github.com/jpetazzo/dind/issues/19
# -------------------------------------------------------

#!/bin/bash
ensure_loop(){
  num="$1"
  dev="/dev/loop$num"
  if test -b "$dev"; then
    echo "$dev is a usable loop device."
    return 0
  fi

  echo "Attempting to create $dev for docker ..."
  if ! mknod -m660 $dev b 7 $num; then
    echo "Failed to create $dev!" 1>&2
    return 3
  fi

  return 0
}

LOOP_A=$(losetup -f)
LOOP_A=${LOOP_A#/dev/loop}
LOOP_B=$(expr $LOOP_A + 1)

ensure_loop $LOOP_A
ensure_loop $LOOP_B

# -------------------------------------------------------
#   END : Fix for running out of loopback devices
# -------------------------------------------------------


# If a pidfile is still around (for example after a container restart),
# delete it so that docker can start.
rm -rf /var/run/docker.pid

# If we were given a PORT environment variable, start as a simple daemon;
if [ "$PORT" ]
then
	exec docker -d -H 0.0.0.0:$PORT -H unix:///var/run/docker.sock \
		$DOCKER_DAEMON_ARGS
else
	if [ "$LOG" == "file" ]
	then
		docker -d $DOCKER_DAEMON_ARGS &>/var/log/docker.log &
	else
		docker -d $DOCKER_DAEMON_ARGS &
	fi
	(( timeout = 60 + SECONDS ))
	until docker info >/dev/null 2>&1
	do
		if (( SECONDS >= timeout )); then
			echo 'Timed out trying to connect to internal docker host.' >&2
			break
		fi
		sleep 1
	done

fi

echo "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -"
echo "                   DOCKER STARTED !!!!                             "
echo "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -"

if [ "$#" -eq 0 ]
then
    # Start a bash shell
	/bin/bash
else
	echo "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -"
	echo "                   EXEC ADDITIONAL COMMANDS                        "
	echo "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -"
    echo "about to exec $@"
    exec /bin/bash -c "$@"
fi