uos – 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 uos module contains functions for filesystem access and mounting, terminal redirection and duplication, and the uname and urandom functions.

General functions

uos.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)
uos.urandom(n)

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

Filesystem access

uos.chdir(path)

Change current directory.

uos.getcwd()

Get the current directory.

uos.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.
uos.listdir([dir])

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

uos.mkdir(path)

Create a new directory.

uos.remove(path)

Remove a file.

uos.rmdir(path)

Remove a directory.

uos.rename(old_path, new_path)

Rename a file.

uos.stat(path)

Get the status of a file or directory.

uos.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.

uos.sync()

Sync all filesystems.

Terminal redirection and duplication

uos.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 uio.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.

uos.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.

uos.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 uos.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.

Block devices

A block device is an object which implements the block protocol, which is a set of methods described below by the AbstractBlockDev class. A concrete implementation of this class will usually allow access to the memory-like functionality a piece of hardware (like flash memory). A block device can be used by a particular filesystem driver to store the data for its filesystem.

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.

class uos.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

By way of example, the following class will implement a block device that stores its data in RAM using a bytearray:

class RAMBlockDev:
    def __init__(self, block_size, num_blocks):
        self.block_size = block_size
        self.data = bytearray(block_size * num_blocks)

    def readblocks(self, block_num, buf):
        for i in range(len(buf)):
            buf[i] = self.data[block_num * self.block_size + i]

    def writeblocks(self, block_num, buf):
        for i in range(len(buf)):
            self.data[block_num * self.block_size + i] = buf[i]

    def ioctl(self, op, arg):
        if op == 4: # get number of blocks
            return len(self.data) // self.block_size
        if op == 5: # get block size
            return self.block_size

It can be used as follows:

import uos

bdev = RAMBlockDev(512, 50)
uos.VfsFat.mkfs(bdev)
vfs = uos.VfsFat(bdev)
uos.mount(vfs, '/ramdisk')

An example of a block device that supports both signatures and behaviours of the readblocks() and writeblocks() methods is:

class RAMBlockDev:
    def __init__(self, block_size, num_blocks):
        self.block_size = block_size
        self.data = bytearray(block_size * num_blocks)

    def readblocks(self, block, buf, offset=0):
        addr = block_num * self.block_size + offset
        for i in range(len(buf)):
            buf[i] = self.data[addr + i]

    def writeblocks(self, block_num, buf, offset=None):
        if offset is None:
            # do erase, then write
            for i in range(len(buf) // self.block_size):
                self.ioctl(6, block_num + i)
            offset = 0
        addr = block_num * self.block_size + offset
        for i in range(len(buf)):
            self.data[addr + i] = buf[i]

    def ioctl(self, op, arg):
        if op == 4: # block count
            return len(self.data) // self.block_size
        if op == 5: # block size
            return self.block_size
        if op == 6: # block erase
            return 0