system-helpers/usr/local/bin/systemd_failure_notify

#!/usr/bin/env bash

# usage
usage() {
USAGE=$(cat <<EOF
Usage: systemd_failure_notify [CONFIG_FILE (absolute path)]

Notifies via mail when a service has failed. You need to place the following in the service which should be checked:

[Unit]
Description=...
OnFailure=systemd_failure_notify@%n.service
...

You should place the <scriptname>'s service into systemd's user and systemd's system folder so it can be used by global and user services.

If no CONFIG_FILE is given, HOME/.systemd_failure_notify.conf or /etc/systemd_failure_notify.conf is used. This fallback option
has to exist or the script will exit.

Configuration can be done in any file and any pre-defined variable can be overwritten.

The following are at least required for the script to work:
- SYSTEMD_FAILURE_NOTIFY_MAIL_ADDRESS="" // mail.rc has to be configured

You can copy this script to '/usr/local/bin' and use create a custom CONFIG_FILE as user. Examples can be found in '/usr/share/doc/<scriptname>'.
EOF
)
	echo "$USAGE";
}

set -e;

SYSTEMD_FAILURE_NOTFY_SERVICE=$1
if [ -z "$SYSTEMD_FAILURE_NOTFY_SERVICE" ]; then
	echo "No service given";
	echo "";
	usage;
	exit 1;
fi

SYSTEMD_FAILURE_NOTFY_HOSTNAME=$(hostname)
SYSTEMD_FAILURE_NOTFY_USER=$(whoami)
SYSTEMD_FAILURE_NOTIFY_MAIL_ADDRESS="";

# check for config file
apply_config() {
  local config=$1;

  if [[ ! -f "$config" ]]; then
      echo "No config file specified";
      echo "";
      usage;
      exit 1;
  fi

  set -a;
  # shellcheck disable=SC1090
  source "$config";
  set +a;
}

source_config() {
  local config=$1;
  local configFallback=$2;
  local configGlobalFallback=$3;

  if [[ -f "$config" ]]; then
    apply_config "$config";
    return;
  fi

  if [[ -f "$configFallback" ]]; then
    apply_config "$configFallback";
    return;
  fi

  if [[ -f "$configGlobalFallback" ]]; then
    apply_config "$configGlobalFallback";
    return;
  fi
}
source_config "$2" "$HOME/.systemd_failure_notify.conf" "/etc/systemd_failure_notify.conf"

SUBJECT="[systemd $SYSTEMD_FAILURE_NOTFY_HOSTNAME for $SYSTEMD_FAILURE_NOTFY_USER] $SYSTEMD_FAILURE_NOTFY_SERVICE RUN FAILED"
MESSAGE="$SYSTEMD_FAILURE_NOTFY_SERVICE run failed"
echo "$MESSAGE"|mailx -Ssendwait -s "$SUBJECT" "$SYSTEMD_FAILURE_NOTIFY_MAIL_ADDRESS";