CentOS is different!

udevd-experiment.sh

#!/bin/bash

# Try with:
#     sudo $PWD/udevd-experiment.sh

THIS_SCRIPT=$0

if [ "$1" = "udevd1" ] ; then
  unshare --propagation unchanged -m $THIS_SCRIPT udevd2
  exit 0
fi

if [ "$1" = "udevd2" ] ; then
  mount --make-rslave /
  mount --make-rshared /
  sleep 5000
  exit 0
fi

$THIS_SCRIPT udevd1 &
sleep 1

DIR=/tmp/udevd-experiment-$RANDOM

mkdir $DIR
cd $DIR

mkdir s1
mount -t tmpfs tmpfs $DIR/s1
mkdir s1/rootfs
mount -t tmpfs tmpfs $DIR/s1/rootfs

echo In the host namespace:
cat /proc/self/mountinfo|grep udevd  || true

echo In the udevd namespace:
cat /proc/$(pidof sleep)/mountinfo|grep udevd || true

echo Simulating GC...

mount --make-private $DIR/s1/rootfs

mount --make-private $DIR/s1

umount $DIR/s1/rootfs

umount $DIR/s1

rm -rf $DIR/s1

echo In the host namespace:
cat /proc/self/mountinfo|grep udevd || true

echo In the udevd namespace:
cat /proc/$(pidof sleep)/mountinfo|grep udevd || true

# Cleanup
killall sleep