blog/_posts/2019-07-04-from-crontabs-to-systemd-timers.md

---
title: From crontabs to Systemd timers
tags: [bash, shell, crontab, cronie, systemd, timer]
updated: 2021-03-01 17:57
description: The steps I followed to migrate from crontabs to systemd timers.
---

## Introduction

<!--excerpt_start-->
Since I started my own server at home I have always use crontabs to handle
recurring tasks such as backups.
<!--excerpt-end-->

*Please note that every step described here is directly related to the
[automated-tasks](https://github.com/frnmst/automated-tasks) repository.*

The problem of this method is that you cannot
easily control running processes and you are not provided with a uniform interface.
Systemd service and timer unit files seem to solve these issues. As usual,
I followed the [Arch](https://wiki.archlinux.org/index.php/Systemd/Timers)
[wiki](https://wiki.archlinux.org/index.php/Systemd#Writing_unit_files).

## Preparation

To avoid complications, I prefer having all relevant scripts of all the users
in one place.

### Users and groups

I created a new user and group called `jobs`

    # useradd -m -s /bin/bash -U jobs

Every user `${user}` that needs to perform some task must be added to the
`jobs` group.

    # usermod -aG jobs ${user}

### New directories

Scripts and services are separated into two different directories. We will make
these directories accessible to the `jobs` group only.

    # mkdir -p /home/jobs/{scripts,services}/by-user
    # chmod -R 070 /home/jobs
    # chown -R jobs:jobs /home/jobs

## Example

As an example I will show you the unit files I wrote for one
of my [daily backups]({{ site.baseurl }}/notes/my-backup-system.html).

### Script

Copy the [backup script]({{ site.baseurl }}/notes/my-backup-system.html#incremental-backup-script)
and the [configuration file]({{ site.baseurl }}/notes/my-backup-system.html#configuration-file)
in `/home/jobs/scripts/by-user/root`, and change ownerships and permissions

    # chmod -R 700 /home/jobs/scripts/by-user/root
    # chown -R root:root /home/jobs/scripts/by-user/root

Use the appropriate user and group for the ownership.

### Service unit file

The service file is called `backup-data.service` and needs to be placed in
`/home/jobs/services/by-user/root`

```shell
[Unit]
Description=data backup
Requires=mnt-backup_data.mount
Requires=data.mount
After=mnt-backup_data.mount
After=data.mount

[Service]
Type=simple
ExecStart=-/home/jobs/scripts/by-user/root/backup.sh '/data/*' /mnt/backup_data
User=root
Group=root

[Install]
WantedBy=multi-user.target
```

### Timer unit file

Place the following timer file, called `backup-data.timer`,
under `/home/jobs/services/by-user/root`

```shell
[Unit]
Description=Once a day backup data

[Timer]
OnCalendar=*-*-* 4:00:00
Persistent=true

[Install]
WantedBy=timers.target
```

### Set the permissions and ownership

Since the backup-data files must be run by `root` we must fix the permissions
and ownerships

    # chmod -R 700 /home/jobs/services/by-user/root
    # chown -R root:root /home/jobs/services/by-user/root

Fix the ownerships with the appropriate user depending on the directory. These
steps are useful just to prevent mistakes. All these files
will be loaded by systemd and accessible from other users anyway, for example
via `/etc/systemd/system/backup-data.service`.

## Deployment

To simplify the deployment of the services and timers I wrote this script,
called `deploy.sh`, which needs to be placed in `/home/jobs/services`.

```shell
#!/usr/bin/env bash

set -euo pipefail

SRC_DIR='by-user/'
DST_DIR='/etc/systemd/system'

[ ${UID} -eq 0 ]

find "${SRC_DIR}" \( -name "*.service" -o -name "*.timer" \) \
    -type f -exec cp {} "${DST_DIR}" \;
systemctl daemon-reload
timers=$(find "${SRC_DIR}" -name "*.timer" -type f -printf "%f\n")
systemctl start ${timers}
systemctl enable ${timers}
```

This script will copy the service and timer files in the appropriate directory and
enable the new timers. Before running it, change its permissions and ownership

    # chown root:root /home/jobs/services/deploy.sh
    # chmod 700 /home/jobs/services/deploy.sh

Now, run the previous script and check the status of the systemd timers

    # cd /home/jobs/services
    # ./deploy.sh
    $ systemctl list-timers --all

You should see something like

    NEXT                          LEFT      LAST  PASSED  UNIT                ACTIVATE
    Fri 2019-07-05 04:00:00 CEST  9h left   n/a   n/a     backup-data.timer   backup-data.service

    1 timer listed.

## File and directory structure

Here is a representation of the files and directories mentioned in this post

```
/home/jobs
|-- scripts
|   |-- by-user
|       `-- root
|           |-- backup.conf
|           |-- backup.sh
`-- services
    |-- by-user
    |   `-- root
    |       |-- backup-data.service
    |       |-- backup-data.timer
    `-- deploy.sh
```

~