user@sandbox:~$ systemctl list-unit-files --type=service |grep mongo
mongod.service                         disabled

dpkg -L mongodb-org-server
/.
------8<----------------
/lib
/lib/systemd
/lib/systemd/system
/lib/systemd/system/mongod.service

#!/bin/sh
# postinst script for mongodb
#
# see: dh_installdeb(1)

set -e

# summary of how this script can be called:
#        * <postinst> `configure' <most-recently-configured-version>
#        * <old-postinst> `abort-upgrade' <new version>
#        * <conflictor's-postinst> `abort-remove' `in-favour' <package>
#          <new-version>
#        * <postinst> `abort-remove'
#        * <deconfigured's-postinst> `abort-deconfigure' `in-favour'
#          <failed-install-package> <version> `removing'
#          <conflicting-package> <version>
# for details, see http://www.debian.org/doc/debian-policy/ or
# the debian-policy package


case "$1" in
    configure)
	# create a mongodb group and user
        if ! getent passwd mongodb >/dev/null 2>&1; then
		adduser --system --no-create-home mongodb
		addgroup --system mongodb
		adduser mongodb mongodb
        fi

	# create db -- note: this should agree with dbpath in mongod.conf
	mkdir -p /var/lib/mongodb
	chown -R mongodb:mongodb /var/lib/mongodb

	# create logdir -- note: this should agree with logpath in mongod.conf
	mkdir -p /var/log/mongodb
	chown -R mongodb:mongodb /var/log/mongodb
    ;;

    abort-upgrade|abort-remove|abort-deconfigure)
    ;;

    *)
        echo "postinst called with unknown argument \`$1'" >&2
        exit 1
    ;;
esac

# dh_installdeb will replace this with shell code automatically
# generated by other debhelper scripts.

# Automatically added by dh_installinit
if [ -x "/etc/init.d/mongod" ]; then
	update-rc.d mongod defaults >/dev/null
	invoke-rc.d mongod start || exit $?
fi
# End automatically added section


exit 0

+if [ -f "/lib/systemd/system/mongod.service" ]; then
+        systemctl --system daemon-reload >/dev/null || true
+	systemctl enable mongod.service >/dev/null
+	systemctl start mongod.service|| exit $?
+fi

user@sandbox:~$ sudo apt-get remove --purge mongodb-org-server
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  mongodb-org-mongos mongodb-org-shell mongodb-org-tools
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  mongodb-org* mongodb-org-server*
0 upgraded, 0 newly installed, 2 to remove and 22 not upgraded.
After this operation, 54.5 MB disk space will be freed.
Do you want to continue? [Y/n]
(Reading database ... 40192 files and directories currently installed.)
Removing mongodb-org (3.4.2) ...
Purging configuration files for mongodb-org (3.4.2) ...
dpkg: warning: while removing mongodb-org, directory '/var/lib/mongodb' not empty so not removed
Removing mongodb-org-server (3.4.2) ...
Purging configuration files for mongodb-org-server (3.4.2) ...
Processing triggers for man-db (2.7.0.2-5) ...
user@sandbox:~$ mongo
MongoDB shell version v3.4.2
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.4.2
Server has startup warnings:
2017-02-17T15:14:31.249+0100 I STORAGE  [initandlisten]
2017-02-17T15:14:31.249+0100 I STORAGE  [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine
2017-02-17T15:14:31.249+0100 I STORAGE  [initandlisten] **          See http://dochub.mongodb.org/core/prodnotes-filesystem
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten]
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten]
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten]
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
2017-02-17T15:14:31.917+0100 I CONTROL  [initandlisten]
>

cat prerm 
#!/bin/sh
set -e
# Automatically added by dh_installinit
if [ -x "/etc/init.d/mongod" ]; then
	invoke-rc.d mongod stop || exit $?
fi
# End automatically added section

+if [ -f "/lib/systemd/system/mongod.service" ]; then
+	systemctl stop mongod.service|| exit $?
+      systemctl disable mongod.service > /dev/null
+fi