I want to be notified by email upon restart of the remote server serving the HDD where I do the offsite backup of my data.

I used init in the past for such purpose, combined with a script that sends an email.

But init is gone and has been replaced by systemd in Ubuntu for a while now.

Yet, the same result can be achieved by creating a service in systemd and have it run only once.

Send an email¶

I'll create a script in my home directory that sends me an email: vi ~/scripts/notify_start.sh.

To prevent emails from stacking in the same conversation in Gmail, I'll include the current date and time in the subject (plus it's a useful information, in case emails are delayed).

Since restarts happen only so often, I'll include instructions in the body of what and how I should be doing manually upon restart, in case I forget.

I'll use ssmtp to send the email, see how to configure gmail with SSMTP on Ubuntu.

I'll use the braces + pipe trick and the echo command to send multiple lines to ssmtp (over the harder to read cat + delimiter, which I find harder to read and maintain).

#!/usr/bin/env bash

set -euo pipefail

DATE=$(date +"%Y-%m-%d-%H%M%S")
{
        echo "Subject: MyServer (re)started at $DATE"
        echo
        echo "This email is sent from systemd service notify_start.service on MyServer."
      echo "Check service logs with either 'sudo systemctl status notify_start.service' or 'journalctl -u notify_start.service'."
        echo "" 
        echo "Immediate actions to take:"
        echo " * mount and open HDD with '/blablabla/mount.sh'"
} | ssmtp me@gmail.com

Create the service¶

The unit of work in systemd is a unit. We will use one of type service, since systemd starts, stops and generally manages the lifecycle of those, and we can declare dependencies on other services (see below).

A unit is created with a configuration file. I'll use /etc/systemd/system as location since it prevails over any other and I have root access.

sudo vi /etc/systemd/system/notify_start.service

• I create and a description to the unit

  [Unit]
  Description=Send me an email when system starts
  

• the unit is a service

  [Service]
  

• the service calls the above script (upon starting):

  ExecStart=/home/phan/scripts/pidatabak_scripts/notify_start/notify_start.sh
  

• the service must be started only once (to run the script only once):

  Type=oneshot
  

• since the script sends an email, the service requires network to be available before running:

  After=network-online.target
  Wants=network-online.target
  

Side benefit: since the service just calls a script, it can be easily duplicated to serve other purpose.

Test the service¶

After testing the script, test the service with sudo systemctl start notify_start.service.

If service was already tested, stop it first: sudo systemctl stop notify_start.service.

Enable the service¶

To have the service managed by systemd, it needs to be enabled with sudo systemctl enable notify_start.service.

This fails with the following message:

The unit files have no installation config (WantedBy=, RequiredBy=, Also=,
Alias= settings in the [Install] section, and DefaultInstance= for template
units). This means they are not meant to be enabled using systemctl.

Possible reasons for having this kind of units are:
• A unit may be statically enabled by being symlinked from another unit's
  .wants/ or .requires/ directory.
• A unit's purpose may be to act as a helper for some other unit which has
  a requirement dependency on it.
• A unit may be started when needed via activation (socket, path, timer,
  D-Bus, udev, scripted systemctl call, ...).
• In case of template units, the unit is meant to be enabled with some
  instance name specified.

To fix this, add the following:

[Install]
WantedBy=multi-user.target

Monitor the service¶

• check logs with either sudo systemctl status notify_start.service or journalctl -u notify_start.service
• check status with sudo systemctl status notify_start.service

[Unit]
Description=Send me an email when system starts
# source: https://systemd.io/NETWORK_ONLINE/
After=network-online.target
Wants=network-online.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/home/phan/scripts/pidatabak_scripts/notify_start/notify_start.sh

[Install]
WantedBy=multi-user.target