https://github.com/openstatusHQ/openstatus

install nagios plugins

# apt install nagios-plugins-common nagios-plugins-basic

/opt/server-status

#!/bin/sh
NAGIOS=/usr/lib/nagios/plugins
#SERVER_name will be used as a prefix for the filenames
SERVER_NAME="katerina"
ROOT_WEB=/home/katerina/public_html/status

# If free disk space under 25%, warning, if under 10% critical
$NAGIOS/check_disk -w 25% -c 10% > $ROOT_WEB/$SERVER_NAME-disk

# If load > 3 (1 minute), 2 (5 minutes), 1 (15 minutes), warning, if load > 6 (1'), 4 (5'), 2 (15'), critical
$NAGIOS/check_load -w 3,2,1 -c 6,4,2 > $ROOT_WEB/$SERVER_NAME-load

# If mysql process doesn't exist, critical
$NAGIOS/check_procs -c 1:1 -C mysqld > $ROOT_WEB/$SERVER_NAME-mysql

# If apache process doesn't exit or above 35 processes, critical
$NAGIOS/check_procs -w 1:25 -c 1:35 -C apache2 > $ROOT_WEB/$SERVER_NAME-apache

# If nginx process doesn't exit or above 35 processes, critical
$NAGIOS/check_procs -w 1:25 -c 1:35 -C nginx > $ROOT_WEB/$SERVER_NAME-nginx

chmod +x /opt/server-status

crontab

*/3 * * * * /opt/server-status > /dev/null 2>> /var/log/server-status.log