config: Set volatile logging by default

This reduces the number of writes to the disk improving disk longevity and IO
performance. Note that systemd-journald is already very reasonable with how
often it writes to the disk. It's flush interval is 5 minutes.

Most users of FreedomBox are not expected to see logs. Those that see the logs
do so for debugging purposes. Debugging can still be done if reboot does not
occur. Users can change the logging mode to 'persistent' before debugging issues
that require reboot. This makes debugging harder for non-reproducible bugs, but
is, at present, considered an acceptable compromise.

Tests:

- On a fresh container, with the patch applied, config page shows 'volatile' as
the logging mode.

- On an container with changes not applied, start freedombox service. Then apply
the patch and restart service. config app setup will be run. Config page shows
'volatile' as the logging mode.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/config/__init__.py

@@ -19,6 +19,8 @@ from plinth.modules.names.components import DomainType
 from plinth.package import Packages
 from plinth.signals import domain_added
 
+from . import privileged
+
 _description = [
     _('Here you can set some general configuration options '
       'like hostname, domain name, webserver home page etc.')
@@ -40,7 +42,7 @@ class ConfigApp(app_module.App):
 
     app_id = 'config'
 
-    _version = 3
+    _version = 4
 
     can_be_disabled = False
 
@@ -195,6 +197,9 @@ def setup(helper, old_version=None):
     app.setup(old_version)
     _migrate_home_page_config()
 
+    if old_version <= 3:
+        privileged.set_logging_mode('volatile')
+
     # systemd-journald is socket activated, it may not be running and it does
     # not support reload.
     actions.superuser_run('service', ['try-restart', 'systemd-journald'])