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, (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.

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