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+:mod:`uos` -- basic "operating system" services
+===============================================
+
+.. module:: uos
+   :synopsis: basic "operating system" services
+
+The ``os`` module contains functions for filesystem access and ``urandom``
+function.
+
+Port specifics
+--------------
+
+The filesystem has ``/`` as the root directory and the
+available physical drives are accessible from here.  They are currently:
+
+    ``/flash``      -- the internal flash filesystem
+
+    ``/sd``         -- the SD card (if it exists)
+
+.. only:: port_pyboard
+
+    On boot up, the current directory is ``/flash`` if no SD card is inserted,
+    otherwise it is ``/sd``.
+
+.. only:: port_wipy
+
+    On boot up, the current directory is ``/flash``.
+
+Functions
+---------
+
+.. function:: chdir(path)
+
+   Change current directory.
+
+.. function:: getcwd()
+
+   Get the current directory.
+
+.. function:: listdir([dir])
+
+   With no argument, list the current directory.  Otherwise list the given directory.
+
+.. function:: mkdir(path)
+
+   Create a new directory.
+
+.. function:: remove(path)
+
+   Remove a file.
+
+.. function:: rmdir(path)
+
+   Remove a directory.
+
+.. function:: rename(old_path, new_path)
+
+   Rename a file.
+
+.. function:: stat(path)
+
+   Get the status of a file or directory.
+
+.. function:: sync()
+
+   Sync all filesystems.
+
+.. function:: urandom(n)
+
+   Return a bytes object with n random bytes, generated by the hardware
+   random number generator.
+
+.. only:: port_wipy
+
+    .. function:: mount(block_device, mount_point, \*, readonly=False)
+
+       Mounts a block device (like an ``SD`` object) in the specified mount
+       point. Example::
+
+          os.mount(sd, '/sd')
+
+    .. function:: unmount(path)
+
+       Unmounts a prevoulsy mounted block device from the given path.
+
+    .. function:: mkfs(block_device or path)
+
+       Formats the specified path, must be either ``/flash`` or ``/sd``.
+       A block device can also be passed like an ``SD`` object before
+       being mounted.
+
+    .. function:: dupterm(stream_object)
+
+       Duplicate the terminal (the REPL) on the passed stream-like object.
+       The given object must at least implement the ``.read()`` and ``.write()`` methods.
+
+Constants
+---------
+
+.. data:: sep
+
+   separation character used in paths