Writable directories

App confinement is part of the Ubuntu Touch security concept. Data can be exchanged between apps only according to the AppArmor policies, mainly using the ContentHub. This being said, apps can only read and write files that are located in one of three app specific directories explained in this guide.

Standard Paths

Besides the write access to the app directories explained below, the app can write debug messages into the app log file located at /home/phablet/.cache/upstart/application-click-<fullappname>_<appname>_<version>.log. To append messages to the log file, use the Qt debug functions.

Config

Path: /home/phablet/.config/<fullappname>/

This is the place to store configurations files to. The music app for example stores its configuration to /home/phablet/.config/com.ubuntu.music/com.ubuntu.music.conf.

Cache

Path: /home/phablet/.cache/<fullappname>/

This is the place to cache data for later use. The cache is also used by the Content Hub. Files that have been shared with the music app for example can be found in /home/phablet/.cache/com.ubuntu.music/HubIncoming/.

App data

Path: /home/phablet/.local/share/<fullappname>/

This is where your app stores any data. The music app for example stores its data bases to /home/phablet/.local/share/com.ubuntu.music/Databases/.

Using Standard Paths in C++

The Qt header QStandardPaths provides the app’s writable locations in C++:

#include <QStandardPaths>
...
QString configPath = QStandardPaths::writableLocation(QStandardPaths::AppConfigLocation);
QString cachePath = QStandardPaths::writableLocation(QStandardPaths::CacheLocation);
QString appDataPath = QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
...

Using Standard Paths in QML

The Qt module Qt.labs.platform provides the app’s writable locations in QML:

import Qt.labs.platform 1.0
...
Label
{
    text: StandardPaths.writableLocation(StandardPaths.AppConfigLocation)
}
Label
{
    text: StandardPaths.writableLocation(StandardPaths.CacheLocation)
}
Label
{
    text: StandardPaths.writableLocation(StandardPaths.AppDataLocation)
}
...