# `os` – basic “operating system” services

This module implements a subset of the corresponding CPython module, as described below. For more information, refer to the original CPython documentation: `os`.

The `os` module contains functions for filesystem access and mounting, terminal redirection and duplication, and the `uname` and `urandom` functions.

## General functions

os.uname()

  Return a tuple (possibly a named tuple) containing information about the underlying machine and/or its operating system. The tuple has five fields in the following order, each of them being a string:

  > - `sysname` – the name of the underlying system

  > - `nodename` – the network name (can be the same as `sysname`)

  > - `release` – the version of the underlying system

  > - `version` – the MicroPython version and build date

  > - `machine` – an identifier for the underlying hardware (eg board, CPU)

os.urandom(n)

  Return a bytes object with n random bytes. Whenever possible, it is generated by the hardware random number generator.

## Filesystem access

os.chdir(path)

  Change current directory.

os.getcwd()

  Get the current directory.

os.ilistdir([dir])

  This function returns an iterator which then yields tuples corresponding to the entries in the directory that it is listing. With no argument it lists the current directory, otherwise it lists the directory given by dir.

  The tuples have the form (name, type, inode[, size]):

  > - name is a string (or bytes if dir is a bytes object) and is the name of the entry;

  > - type is an integer that specifies the type of the entry, with 0x4000 for directories and 0x8000 for regular files;

  > - inode is an integer corresponding to the inode of the file, and may be 0 for filesystems that don’t have such a notion.

  > - Some platforms may return a 4-tuple that includes the entry’s size. For file entries, size is an integer representing the size of the file or -1 if unknown. Its meaning is currently undefined for directory entries.

os.listdir([dir])

  With no argument, list the current directory. Otherwise list the given directory.

os.mkdir(path)

  Create a new directory.

os.remove(path)

  Remove a file.

os.rmdir(path)

  Remove a directory.

os.rename(old_path, new_path)

  Rename a file.

os.stat(path)

  Get the status of a file or directory.

os.statvfs(path)

  Get the status of a fileystem.

  Returns a tuple with the filesystem information in the following order:

  > - `f_bsize` – file system block size

  > - `f_frsize` – fragment size

  > - `f_blocks` – size of fs in f_frsize units

  > - `f_bfree` – number of free blocks

  > - `f_bavail` – number of free blocks for unprivileged users

  > - `f_files` – number of inodes

  > - `f_ffree` – number of free inodes

  > - `f_favail` – number of free inodes for unprivileged users

  > - `f_flag` – mount flags

  > - `f_namemax` – maximum filename length

  Parameters related to inodes: `f_files`, `f_ffree`, `f_avail` and the `f_flags` parameter may return `0` as they can be unavailable in a port-specific implementation.

os.sync()

  Sync all filesystems.

## Terminal redirection and duplication

os.dupterm(stream_object, index=0, /)

  Duplicate or switch the MicroPython terminal (the REPL) on the given stream-like object. The stream_object argument must be a native stream object, or derive from `io.IOBase` and implement the `readinto()` and `write()` methods. The stream should be in non-blocking mode and `readinto()` should return `None` if there is no data available for reading.

  After calling this function all terminal output is repeated on this stream, and any input that is available on the stream is passed on to the terminal input.

  The index parameter should be a non-negative integer and specifies which duplication slot is set. A given port may implement more than one slot (slot 0 will always be available) and in that case terminal input and output is duplicated on all the slots that are set.

  If `None` is passed as the stream_object then duplication is cancelled on the slot given by index.

  The function returns the previous stream-like object in the given slot.

## Filesystem mounting

Some ports provide a Virtual Filesystem (VFS) and the ability to mount multiple “real” filesystems within this VFS. Filesystem objects can be mounted at either the root of the VFS, or at a subdirectory that lives in the root. This allows dynamic and flexible configuration of the filesystem that is seen by Python programs. Ports that have this functionality provide the `mount()` and `umount()` functions, and possibly various filesystem implementations represented by VFS classes.

os.mount(fsobj, mount_point, *, readonly)

  Mount the filesystem object fsobj at the location in the VFS given by the mount_point string. fsobj can be a a VFS object that has a `mount()` method, or a block device. If it’s a block device then the filesystem type is automatically detected (an exception is raised if no filesystem was recognised). mount_point may be `'/'` to mount fsobj at the root, or `'/<name>'` to mount it at a subdirectory under the root.

  If readonly is `True` then the filesystem is mounted read-only.

  During the mount process the method `mount()` is called on the filesystem object.

  Will raise `OSError(EPERM)` if mount_point is already mounted.

os.umount(mount_point)

  Unmount a filesystem. mount_point can be a string naming the mount location, or a previously-mounted filesystem object. During the unmount process the method `umount()` is called on the filesystem object.

  Will raise `OSError(EINVAL)` if mount_point is not found.

class os.VfsFat(block_dev)

  Create a filesystem object that uses the FAT filesystem format. Storage of the FAT filesystem is provided by block_dev. Objects created by this constructor can be mounted using `mount()`.

  static mkfs(block_dev)

    Build a FAT filesystem on block_dev.

class os.VfsLfs1(block_dev, readsize=32, progsize=32, lookahead=32)

  Create a filesystem object that uses the littlefs v1 filesystem format. Storage of the littlefs filesystem is provided by block_dev, which must support the extended interface. Objects created by this constructor can be mounted using `mount()`.

  See Working with filesystems for more information.

  static mkfs(block_dev, readsize=32, progsize=32, lookahead=32)

    Build a Lfs1 filesystem on block_dev.

  Note

  There are reports of littlefs v1 failing in certain situations, for details see littlefs issue 347.

class os.VfsLfs2(block_dev, readsize=32, progsize=32, lookahead=32, mtime=True)

  Create a filesystem object that uses the littlefs v2 filesystem format. Storage of the littlefs filesystem is provided by block_dev, which must support the extended interface. Objects created by this constructor can be mounted using `mount()`.

  The mtime argument enables modification timestamps for files, stored using littlefs attributes. This option can be disabled or enabled differently each mount time and timestamps will only be added or updated if mtime is enabled, otherwise the timestamps will remain untouched. Littlefs v2 filesystems without timestamps will work without reformatting and timestamps will be added transparently to existing files once they are opened for writing. When mtime is enabled `os.stat` on files without timestamps will return 0 for the timestamp.

  See Working with filesystems for more information.

  static mkfs(block_dev, readsize=32, progsize=32, lookahead=32)

    Build a Lfs2 filesystem on block_dev.

  Note

  There are reports of littlefs v2 failing in certain situations, for details see littlefs issue 295.

## Block devices

A block device is an object which implements the block protocol. This enables a device to support MicroPython filesystems. The physical hardware is represented by a user defined class. The `AbstractBlockDev` class is a template for the design of such a class: MicroPython does not actually provide that class, but an actual block device class must implement the methods described below.

A concrete implementation of this class will usually allow access to the memory-like functionality of a piece of hardware (like flash memory). A block device can be formatted to any supported filesystem and mounted using `os` methods.

See Working with filesystems for example implementations of block devices using the two variants of the block protocol described below.

### Simple and extended interface

There are two compatible signatures for the `readblocks` and `writeblocks` methods (see below), in order to support a variety of use cases. A given block device may implement one form or the other, or both at the same time. The second form (with the offset parameter) is referred to as the “extended interface”.

Some filesystems (such as littlefs) that require more control over write operations, for example writing to sub-block regions without erasing, may require that the block device supports the extended interface.

class os.AbstractBlockDev(...)

  Construct a block device object. The parameters to the constructor are dependent on the specific block device.

  readblocks(block_num, buf)
  readblocks(block_num, buf, offset)

    The first form reads aligned, multiples of blocks. Starting at the block given by the index block_num, read blocks from the device into buf (an array of bytes). The number of blocks to read is given by the length of buf, which will be a multiple of the block size.

    The second form allows reading at arbitrary locations within a block, and arbitrary lengths. Starting at block index block_num, and byte offset within that block of offset, read bytes from the device into buf (an array of bytes). The number of bytes to read is given by the length of buf.

  writeblocks(block_num, buf)
  writeblocks(block_num, buf, offset)

    The first form writes aligned, multiples of blocks, and requires that the blocks that are written to be first erased (if necessary) by this method. Starting at the block given by the index block_num, write blocks from buf (an array of bytes) to the device. The number of blocks to write is given by the length of buf, which will be a multiple of the block size.

    The second form allows writing at arbitrary locations within a block, and arbitrary lengths. Only the bytes being written should be changed, and the caller of this method must ensure that the relevant blocks are erased via a prior `ioctl` call. Starting at block index block_num, and byte offset within that block of offset, write bytes from buf (an array of bytes) to the device. The number of bytes to write is given by the length of buf.

    Note that implementations must never implicitly erase blocks if the offset argument is specified, even if it is zero.

  ioctl(op, arg)

    > Control the block device and query its parameters. The operation to perform is given by op which is one of the following integers:

    > > - 1 – initialise the device (arg is unused)

    > > - 2 – shutdown the device (arg is unused)

    > > - 3 – sync the device (arg is unused)

    > > - 4 – get a count of the number of blocks, should return an integer (arg is unused)

    > > - 5 – get the number of bytes in a block, should return an integer, or `None` in which case the default value of 512 is used (arg is unused)

    > > - 6 – erase a block, arg is the block number to erase

    As a minimum `ioctl(4, ...)` must be intercepted; for littlefs `ioctl(6, ...)` must also be intercepted. The need for others is hardware dependent.

    Prior to any call to `writeblocks(block, ...)` littlefs issues `ioctl(6, block)`. This enables a device driver to erase the block prior to a write if the hardware requires it. Alternatively a driver might intercept `ioctl(6, block)` and return 0 (success). In this case the driver assumes responsibility for detecting the need for erasure.

    Unless otherwise stated `ioctl(op, arg)` can return `None`. Consequently an implementation can ignore unused values of `op`. Where `op` is intercepted, the return value for operations 4 and 5 are as detailed above. Other operations should return 0 on success and non-zero for failure, with the value returned being an `OSError` errno code.

Language and External Links

Language
  English
  中文

External links
  openmv.io
  forums.openmv.io
  github.com/openmv/openmv
  micropython.org
  forum.micropython.org
  github.com/micropython/micropython