The Lino Daemon¶

This document explains why and how to use linod.

A Lino application can declare background tasks. Such tasks run in the background, i.e. as a service in another process than the web server. That other process runs a Lino specific admin command called linod.

linod¶

Starts a long-running process that runs scheduled background tasks.

On a development machine you simply run this in a separate terminal. On a production server we recommend to run this as a daemon via Supervisor as described below.

This feature requires Dan Bader’s schedule package, which will get installed automatically if you run install.

As an application developer you define background tasks using dd.schedule_often and dd.schedule_daily. For example the send_pending_emails_often and clear_seen_messages of the lino.modlib.notify plugin.

use_linod

To enable this feature, you must set use_linod to True. This is usually done by the application developer, but this decision can be overridden by a system admin in a local settings.py file. The linod command will simply do nothing when this setting is False.

Additionally to having use_linod set to True, you must also start the linod service in order to actually execute the scheduled tasks. The getlino configure --linod option specifies that every new Lino site will automatically have a linod.sh file in its project directory and a supervisor job that runs the linod.sh script as a service.

Activating the feature¶

>>> from atelier.sheller import Sheller
>>> shell = Sheller("lino_book/projects/roger")
>>> shell("python manage.py linod --list")
This site does not use linod.

As a site maintainer you can check whether your application has scheduled background jobs by issuing the following command in your project directory:

$ python manage.py linod --list

For example in the noi1e demo project there are 6 jobs:

>>> shell = Sheller("lino_book/projects/noi1e")
>>> shell("python manage.py linod --list")
... 
6 scheduled jobs:
[1] Every 1 day at 20:00:00 do checksummaries() (last run: [never], next run: ...)
[2] Every 1 day at 20:00:00 do checkdata() (last run: [never], next run: ...)
[3] Every 10 seconds do send_pending_emails_often() (last run: [never], next run: ...)
[4] Every 1 day at 20:00:00 do send_pending_emails_daily() (last run: [never], next run: ...)
[5] Every 1 day at 20:00:00 do clear_seen_messages() (last run: [never], next run: ...)
[6] Every 3600 seconds do update_all_repos() (last run: [never], next run: ...)

Installation instructions¶

This section has become useless because these things are now done automatically by getlino.

Install the Supervisor package:
```
$ sudo apt install supervisor
```
The supervisor package is being installed system-wide, it is not related to any specific project.
Create a shell script linod.sh in your project directory:
```
#!/bin/bash
set -e  # exit on error
cd /path/to/myprj
. env/bin/activate
exec python manage.py linod
```
Note: the exec command is needed here in order to avoid #1086. Thanks to Paul Lockaby

Create a file linod_myprj.conf in /etc/supervisor/conf.d/ with this content:

[program:linod_myprj]
command = /path/to/myprj/linod.sh
username = www-data
umask = 002

Restart supervisord:
```
$ sudo service supervisor restart
```
Have a look at the log files in /var/log/supervisor.