# Managing Services with Systemd

Hiera can also be used to manage services and to automate reoccuring tasks with timers.

## Enabling/Starting a Service

If the software already comes with an systemd unit file, then it is sufficient to just enable it in Hiera by using the `base::services` key:

```
base::services:
    netdata:
        enable: true
```
The key inside is the `systemd` service name without the `.service` suffix.

## Disabling/Stopping a Service

To stop and disable an already running service, disable it in the `base::services` Hiera key with `enable: false`:
```
base::services:
    netdata:
        enable: false
```

## Systemd Timers
To have custom executables run regulary on given time/interval, you may use the `base::timers` Hiera key:

```
base::timers:
    'timer_test':
        description: 'test timers'
        command: '/usr/bin/logger foo'
        on_calendar: '*:*:10'
        persistence:  false
```

For each timer following keys are mandatory

- `description` for a short explaination what it is about
- `command` for the command to run
- `on_calendar` defining when it should run using the [`systemd` calendar event format](https://www.freedesktop.org/software/systemd/man/systemd.time.html#Calendar%20Events), (alternatively see also chapter "CALENDAR EVENTS" of `man systemd.date`)

Optional is
- `persistence` which signals if the timer should run immediately after boot when the node was switched of on the last scheduled run time (default is `false`)

## Manage Services with Custom Unit Files

It is also possible to provide a full systemd unit file if there is none already. For this define the different secions and their content with subkeys below the `options` key as in below example:

```
# The following service stops users from accessing the node
# before the home directory is mounted
base::services:
    'wait_for_home':
        enable: true
        options:
            Unit:
                Before: 'systemd-user-sessions.service'
            Install:
                WantedBy: 'multi-user.target'
                RequiredBy: 'multi-user.target'
            Service:
                Type: 'oneshot'
                ExecStart: '/opt/pli/libexec/waitformount -m /das/home'
                RemainAfterExit: 'true'
```

If you need to set multiple values, then put the values into an list:
```
Service:
    Environment:
        - "FOO=bar"
        - "BIZ=buz"
```

## Enhance a Service with a Dropin Unit File
It is possible to fine-tune already existing `systemd` unit files with dropins. These are placed as `.conf` files in `/etc/systemd/system/$SERVICE.service.d/`.

With the `dropin: true` setting the content of the `options` parameter is written into the according dropin directory:
```
base::services:
    'name_of_enhanced_service':
        enable: true
        dropin: true
    options:
        ...
```
Often this is done to start the service with different options, then you need to reset the orginal value with an emty entry: 

```
base::services:
    'name_of_enhanced_service':
        enable: true
        dropin: true
        options:
            Service:
                ExecStart:
                    - ''
                    - '/usr/sbin/my_service --verbose'
```

If there are multiple dropins, you might also name them individually with the `dropin_name` parameter.