Autodir demands some extra requirements from backup program being used. The reason for this is that when backup is working on real directory and with corresponding expired virtual directory and that virtual directory is requested again by an application while backup is running, backup is killed. First SIGTERM is sent to gracefully stop it. But if it does not shutdown in time -- one second at this moment; SIGKILL will be sent which is guaranteed to stop the backup.
|When and only when backup stopped, application is given access to the virtual directoryrequested.|
Whatever backup is used, it should be able to recover from this signal gracefully, not causing unrecoverable side effects.
One more important issue is that the environment under which it is run. All backup programs are run as root user. But at the same time all unnecessary root privileges are taken away using POSIX capabilities. In other words these backup programs can read any file or directory that belongs to any user on the system and nothing more than that. Other than that it is like ordinary user level process.