A script to remove rootfs verification and install an openssh server - needs to be run twice with two reboots.

etc-setup.sh

#!/usr/bin/env bash

###
APPLICATION="${0##*/}"
ARCHIVE=''
CURRENTROOT="$(rootdev -s)"
GO=''
HOM=$HOME
NUM='0'
SUDO=''
TMOUT='5'
ret=0

## Exits the script with exit code $1, spitting out message $@ to stderr
error() {
    local ecode="$1"
    shift
    echo "$*" 1>&2
    exit "$ecode"
}

####
#### If we're not running as root, restart as root.
if [ ${UID:-$(id -u)} -ne 0 ]; then
#  echo "...elevating $USER to superuser..."
#  echo
#  exec sudo /bin/sh "$0" "$@"
### If we're not running as root, use sudo
   echo "...elevating $USER to superuser via 'sudo'..."
   echo
   SUDO='sudo'
fi

###
### Check to see if rootfs is read-write
if ${SUDO} mount -i -o remount,rw / 2>/dev/null; then
  echo "Your rootfs (${CURRENTROOT}) is mounted read-write ..."
  echo "*** $(mount | grep ' / ') ***"; echo
else
  ## Check for bootcache fix ...
  ret=$(grep -iq bootcache /usr/share/vboot/bin/make_dev_ssd.sh; echo $?)
  if [ "$ret" -gt 0 ]; then
    echo "$ret: No 'bootcache' fix appplied yet. :("
    error 2 "Not safe to continue, exiting..."
  else echo "$ret: The 'bootcache' fix has been appplied - yay. :)"
    echo "You can now run 'rw-rootfs' safely."
  fi
  echo "Making your rootfs read-write ..."
  if grep -q CHROMEOS_RELEASE_BOARD=chromeover64 /etc/lsb-release; then
    echo "...using CloudReady, disabling verity."
    echo "$SUDO disable_verity" 1>&2
    $SUDO disable_verity || ret=$?
  else
    echo "$SUDO /usr/libexec/debugd/helpers/dev_features_rootfs_verification" 1>&2
    $SUDO /usr/libexec/debugd/helpers/dev_features_rootfs_verification || ret=$?
  fi
  if [ "$ret" -gt 0 ]; then
    error 2 "Sorry but REMOVAL of rootfs verification failed."
  else
    echo
    echo "*** Rebooting in $TMOUT seconds to make changes effective ***" 1>&2
    read -t $TMOUT -p "... ENTER 'a' TO ABORT! " GO
    if [ -n "${GO}" ]; then error 0 "Okay, ABORTING ..."; fi
    $SUDO reboot && exit $ret
  fi
fi

###
### Check for crouton functions file ( for mounting custom partitions )
crouton_mount='/var/crouton'
linux_mount='/var/linux'
if [ -s /usr/local/bin/cros_funcs ]; then
  . /usr/local/bin/cros_funcs
  ## mount Linux partition if it exists
  mountlinux $linux_mount && echo "...a LINUX partition is${PRIOR} mounted on '$MOUNTLINUX'."
# ${SUDO} mount -B  /var/linux/ /mnt/stateful_partition/crouton/shared/linux/
  ## mount CROUTON partition if it exists
  mountcrouton   $crouton_mount   && echo "...a CROUTON partition is${PRIOR} mounted on '$MOUNTCROUTON'."
else
  ROOTDEVICE="`rootdev -d -s`"
  ## mount Linux partition if it exists
  linuxpart="`${SUDO} cgpt find -n -l ROOT-C "$ROOTDEVICE" 2>/dev/null`"
  if [ -n "$linuxpart" ]; then
    if [ "`${SUDO} cgpt show -i "$linuxpart" -s "$ROOTDEVICE"`" -gt 1 ]; then
       [ ! -d $linux_mount ] && ${SUDO} mkdir -p $linux_mount 2>/dev/null
       [   -d $linux_mount ] && ${SUDO} mount ${ROOTDEVICE}/$linuxpart $linux_mount 2>/dev/null
       [   -d ${linux_mount}/crouton ] && ${SUDO} mount -o bind ${linuxpart}/crouton $crouton_mount 2>/dev/null
    fi
  fi
  ## mount crouton partition if it exists
  croutonpart="`${SUDO} cgpt find -n -l CROUTON "$ROOTDEVICE" 2>/dev/null`"
  if [ -n "$croutonpart" ]; then
    if [ "`${SUDO} cgpt show -i "$croutonpart" -s "$ROOTDEVICE"`" -gt 1 ]; then
       [ ! -d $crouton_mount ] && ${SUDO} mkdir -p $crouton_mount 2>/dev/null
       [   -d $crouton_mount ] && ${SUDO} mount ${ROOTDEVICE}/$croutonpart $crouton_mount 2>/dev/null
    fi
  fi
fi

# ###
# ### Make chronos/user HOME
# if [ $SUDO_USER=chronos ]; then
#   HOM="/home/chronos/user"
# fi
# 
###
### CHECKING FOR ARCHIVE FOLDER
ARCHIVE=/var/crouton/archive
if [ ! -d $ARCHIVE ]; then
  echo "Standard location of folder $ARCHIVE not found..."
  if [ -d ${HOM}/Downloads/archive ]; then
    echo -n "Found one... "
    ARCHIVE="${HOM}/Downloads/archive"
    echo "Using $ARCHIVE ..."
  elif [ -d /var/linux/archive ]; then
    echo -n "Found one... "
    ARCHIVE="/var/linux/archive"
    echo "Using $ARCHIVE ..."
  elif [ -r ./$APPLICATION ]; then
    echo -n "Found one... "
    ARCHIVE="`pwd`"
    echo "Using $ARCHIVE ..."
  else
    echo "Sorry, an archive folder could not be found..."
    error 1 "Aborting..."
  fi
else
  echo "Using $ARCHIVE ..."
fi

###
### ROUTINE TO INSTALL CONF FILES IF NEEDED
INIT=/etc/init
OPENSSH=0
cd $ARCHIVE
echo "Checking upstart files in /etc/init."
for CONF in *.conf
do
  if [ ! -s ${INIT}/$CONF ]; then
    echo -n"file "
    if ${SUDO} cp -v $ARCHIVE/$CONF $INIT; then 
      echo "installed..."
      NUM=$(($NUM+1))
    else
      ret=1
    fi
  elif ! diff ${INIT}/$CONF ${ARCHIVE}/$CONF 2>/dev/null 1>&2; then
    echo -n "file "
    if ${SUDO} cp -v ${ARCHIVE}/$CONF $INIT; then
      echo "updated..."
      NUM=$(($NUM+1))
    else
      ret=1
    fi
  else
    echo "file '${INIT}/$CONF' previously installed..."
  fi

# if [ "$CONF" = "openssh-server.conf" ]; then
#   OPENSSH=1
# fi
# echo "ret is $ret"

  if [ "$ret" -gt 0 ]; then
    echo "$ret: Copying to /etc/init/ has failed.:("
    error 2 "No point in continuing, exiting..."
  fi
done
# 
# ###
# ### CHANGE chromeos-boot-alert script delay from 30 seconds to 3 seconds
# SBIN=/sbin
# if ! diff ${SBIN}/chromeos-boot-alert ${ARCHIVE}/chromeos-boot-alert 2>/dev/null 1>&2; then
#   echo "file `${SUDO} cp -v ${ARCHIVE}/chromeos-boot-alert $SBIN` updated..."
#   ${SUDO} chmod +x ${SBIN}/chromeos-boot-alert 2>/dev/null
#   NUM=$(($NUM+1))
# else
#   echo "file '${SBIN}/chromeos-boot-alert' not present or previously installed..."
# fi

###
### Check for openssh server setup
echo
if ! /usr/libexec/debugd/helpers/dev_features_ssh --q ; then
  ###
  ### Setup openssh-server
  echo "Setting up new openssh server ..."
  ${SUDO} /usr/libexec/debugd/helpers/dev_features_ssh
  NUM=$(($NUM+1))
  echo "'openssh' server will start in /etc/init ..."
else
  echo "An openssh server was previously setup ..."
  ls -Ll /etc/init/openssh-server.conf
fi

###
### Reboot if needed.
echo 
if [ "$NUM" -gt 0 ]; then
  echo "NOTE: Reboot for $NUM changes to be applied."
  echo "*** Rebooting in $TMOUT seconds to make changes effective ***" 1>&2
  read -t $TMOUT -p "... ENTER 'a' TO ABORT! " GO
  if [ -n "${GO}" ]; then error 0 "Okay, ABORTING ..."; fi
  $SUDO reboot && exit $ret
else
  echo "### No changes needed/made."
fi

Revision 2: add CloudReady detection, restore archive scripts, use sudo.

Revision 3: Minor changes.