Monit

if installed with apt systemd file is already in.

sudo nano /etc/monit/monitrc

changed:

set alert ractive74@gmail.com

set mailserver smtp.gmail.com port 587

   username "MYUSER" password "MYPASSWORD"
   using tlsv12

  check system $HOST
    if loadavg (1min) > 4 then alert
    if loadavg (5min) > 2 then alert
    if cpu usage > 95% for 10 cycles then alert
    if memory usage > 75% then alert
    if swap usage > 25% then alert

 check network public with interface eth0
   if failed link then alert

sudo systemctl restart monit

sudo monit -t

sudo monit start all

sudo monit status

Systemd .service file

# This file is systemd template for monit service. To
# register monit with systemd, place the monit.service file
# to the /lib/systemd/system/ directory and then start it
# using systemctl (see bellow).
#
# Enable monit to start on boot: 
#         systemctl enable monit.service
#
# Start monit immediately: 
#         systemctl start monit.service
#
# Stop monit:
#         systemctl stop monit.service
#
# Status:
#         systemctl status monit.service

[Unit]
Description=Pro-active monitoring utility for unix systems
After=network.target

[Service]
Type=simple
KillMode=process
ExecStart=/usr/local/bin/monit -I
ExecStop=/usr/local/bin/monit quit
ExecReload=/usr/local/bin/monit reload
Restart = on-abnormal

[Install]
WantedBy=multi-user.target