Draft of DB migration from Postgresql 9.4 to 9.6

locales/en.json

@@ -225,6 +225,7 @@
     "migration_description_0001_change_cert_group_to_sslcert": "Change certificates group permissions from 'metronome' to 'ssl-cert'",
     "migration_description_0002_migrate_to_tsig_sha256": "Improve security of dyndns TSIG by using SHA512 instead of MD5",
     "migration_description_0003_migrate_to_stretch": "Upgrade the system to Debian Stretch and YunoHost 3.0",
+    "migration_description_0005_postgresql_9p4_to_9p6": "Migrate databases from postgresql 9.4 to 9.6",
     "migration_0003_backward_impossible": "The stretch migration cannot be reverted.",
     "migration_0003_start": "Starting migration to Stretch. The logs will be available in {logfile}.",
     "migration_0003_patching_sources_list": "Patching the sources.lists ...",
@@ -237,6 +238,8 @@
     "migration_0003_general_warning": "Please note that this migration is a delicate operation. While the YunoHost team did its best to review and test it, the migration might still break parts of the system or apps.\n\nTherefore, we recommend you to :\n    - Perform a backup of any critical data or app ;\n    - Be patient after launching the migration : depending on your internet connection and hardware, it might take up to a few hours for everything to upgrade.",
     "migration_0003_problematic_apps_warning": "Please note that the following possibly problematic installed apps were detected. It looks like those were not installed from an applist or are not flagged as 'working'. Consequently, we cannot guarantee that they will still work after the upgrade : {problematic_apps}",
     "migration_0003_modified_files": "Please note that the following files were found to be manually modified and might be overwritten at the end of the upgrade : {manually_modified_files}",
+    "migration_0005_postgresql_94_not_installed": "Postgresql was not installed on your system. Nothing to do!",
+    "migration_0005_postgresql_96_not_installed": "Postgresql 9.4 has been found to be installed, but not postgresql 9.6 !? Something weird might have happened on your system :( ...",
     "migrations_backward": "Migrating backward.",
     "migrations_bad_value_for_target": "Invalid number for target argument, available migrations numbers are 0 or {}",
     "migrations_cant_reach_migration_file": "Can't access migrations files at path %s",

src/yunohost/data_migrations/0005_postgresql_9p4_to_9p6.py

@@ -0,0 +1,44 @@
+import subprocess
+
+from moulinette.core import MoulinetteError
+from moulinette.utils.log import getActionLogger
+
+from yunohost.tools import Migration
+from yunohost.service import _run_service_command
+
+logger = getActionLogger('yunohost.migration')
+
+
+class MyMigration(Migration):
+    "Migrate DBs from Postgresql 9.4 to 9.6 after migrating to Stretch"
+
+
+    def migrate(self):
+
+        if not self.package_is_installed("postgresql-9.4"):
+            logger.warning(m18n.n("migration_0005_postgresql_94_not_installed"))
+            return
+
+        if not self.package_is_installed("postgresql-9.6"):
+            raise MoulinetteError(m18n.n("migration_0005_postgresql_96_not_installed"))
+
+        # FIXME / TODO : maybe add checks about the size of
+        #  /var/lib/postgresql/9.4/main/base/ compared to available space ?
+
+        subprocess.check_call("service postgresql stop", shell=True)
+        subprocess.check_call("pg_dropcluster --stop 9.6 main", shell=True)
+        subprocess.check_call("pg_upgradecluster -m upgrade 9.4 main", shell=True)
+        subprocess.check_call("pg_dropcluster --stop 9.4 main", shell=True)
+        subprocess.check_call("service postgresql start", shell=True)
+
+    def backward(self):
+
+        pass
+
+
+    def package_is_installed(self, package_name):
+
+        p = subprocess.Popen("dpkg --list | grep -q -w {}".format(package_name), shell=True)
+        p.communicate()
+        return p.returncode == 0
+