Init process in Linux is the first process to start on boot, and it tracks all the system services and Daemons. Various Linux Distros have created different implementations of the standard init systems. Currently, the most popular init system adopted by various Linux distros is systemd.
In Ansible, the systemd processes can be controlled by systemd module. If your target system is not using the systemd init system, then you can use the Ansible service module.
Starting a new service using systemd
As with most of the Ansible modules, we need the name and the state parameters at the minimum. Here you set the service which you need to start, against the name parameter and the state you want, in this case, present, in the state parameter. If the systemd and the service files are not present in the remote system, then the command will throw an error.
The following task is similar to the Linux command ‘systemctl start docker’.
- hosts: loc
tasks:
- name: Ansible systemd service example
systemd:
name: docker
state: started
Note 1: If the process is already started then the state: started does nothing. If your intention is to restart the service – for example, in cases where you made changes in some configuration files- then you can use the ‘state: restarted’. Note that ‘state: restarted’ is not idempotent and it will always restart the service.
- hosts: loc
tasks:
- name: Ansible service restart example
systemd:
name: docker
state: restarted
If you have made any changes to the systemd unit files, and you want it to take effect, then do a daemon reload before restarting. By default, the daemon_reload is set to no.
- hosts: loc
tasks:
- name: Ansible service daemon reload example
systemd:
name: docker
state: restarted
daemon_reload: yes
Error: If the service you are trying to control is not available on the remote server, then you will get an error like below.
fatal: [ansible-control-machine]: FAILED! => {"changed": false, "failed": true, "msg": "Could not find the requested service docker: cannot check nor set state"}
If you need a particular service to be started when the Linux OS boots up, then you will have to enable the service. Systemd module also provides an ‘enabled’ parameter for this.
- hosts: loc
tasks:
- name: Ansible service enable example
systemd:
name: docker
enabled: yes
Stopping a service
You can stop any running services using the ‘stopped’ parameter. This is an idempotent option, so if the service is already stopped, then Ansible won’t throw an error.
- hosts: loc
tasks:
- name: Ansible service stop example
systemd:
name: docker
state: stopped
Starting multiple services using with_items
As with other Ansible modules, you can use the with_items parameter to control multiple services in a single task. Make sure the {{ item }} is within quotes, and the with_items block is intended at the level of module name -here systemd. The following example will restart three tasks docker, Nginx, and NTP. It will do a daemon reload before it restarts the service.
- hosts: loc
tasks:
- name: Ansible service with_items example
systemd:
name: "{{ item }}"
state: restarted
daemon_reload: yes
with_items:
- 'docker'
- 'nginx'
- 'ntp'
Check out the Ansible user module to see how to mange the user accounts in Linux.
