Systemd Cron Task Example w/Email

README.md

Goals:

• Run as root with a full bash env
• Notify on failure via SNS email
• Make this a good boilerplate

Sources:

• https://www.blunix.com/blog/ultimate-tutorial-about-systemd-timers.html

env.template

# Timer/Service Impl
SERVICE_NAME=""
SNS_TOPIC=""

# Script-specific

install.sh

#!/bin/bash

chmod 700 script.sh

# Ensure config has been set up
ENV_FILE="$(dirname $0)/env"
if [ ! -f "${ENV_FILE}" ]; then
  echo "File ${ENV_FILE} does not exist - please create before installing by copying from env.template and filling out!"
  exit 1
else
  echo "File ${ENV_FILE} exists."
fi

source "${ENV_FILE}"

# Update unit path and name
cp "$(dirname $0)/script.service" "$(dirname $0)/${SERVICE_NAME}.service"
cp "$(dirname $0)/script.timer" "$(dirname $0)/${SERVICE_NAME}.timer"
sed -i "s|^ExecStart=.*|ExecStart=/bin/bash $(dirname $0)/script.sh|" "$(dirname $0)/${SERVICE_NAME}.service"
sed -i "s|SERVICE_NAME|${SERVICE_NAME}|g" "$(dirname $0)/${SERVICE_NAME}.service"
sed -i "s|SERVICE_NAME|${SERVICE_NAME}|g" "$(dirname $0)/${SERVICE_NAME}.timer"

# Apply units
sudo mv "$(dirname $0)/${SERVICE_NAME}.service" "/etc/systemd/system/${SERVICE_NAME}.service"
sudo chmod 644 "/etc/systemd/system/${SERVICE_NAME}.service"
sudo mv "$(dirname $0)/${SERVICE_NAME}.timer" "/etc/systemd/system/${SERVICE_NAME}.timer"
sudo chmod 644 "/etc/systemd/system/${SERVICE_NAME}.timer"
sudo systemctl daemon-reload
sudo systemctl enable "${SERVICE_NAME}.timer"

script.service

[Unit]
Description=Execute a bash script for SERVICE_NAME

[Service]
Type=oneshot
ExecStart=

script.sh

#!/bin/bash

source "$(dirname $0)/env"

notify() {
  # Send notification
  aws sns publish --topic-arn "${SNS_TOPIC}" --message "$1"
}

handle_error() {
  notify "ERROR: ${SERVICE_NAME} failed on line ${LINENO}!"
  exit 1
}

trap handle_error ERR

# Example: 50/50 Success/Failure
random_byte=$(od -An -N1 -t u1 /dev/urandom)
if (( random_byte % 2 == 0 )); then
  result="True - Worked"
else
  result="ERROR - False - Failed"
  exit 1
fi

notify "OK: ${SERVICE_NAME} completed OK!"

script.timer

[Unit]
Description=Start the matching Systemd SERVICE_NAME.service on schedule

[Timer]
OnCalendar="Mon,Wed,Fri 1:0"
Persistent=true

[Install]
WantedBy=timers.target