problem: apache2 crashing. fix by adding Restart=always into its systemd override file. systemctl edit apache2
[Service] Restart=always
Add email notifications for apache2 restarts:
vi /etc/systemd/system/notify-email@.service systemctl enable /etc/systemd/system/notify-email@.service and
systemctl edit apache2
and add
[Unit] OnFailure=notify-email@%i.service
and
systemctl daemon-reload
install mailutils
apt install mailutils