FCL/sf/adapt/qemu: comparison symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/os.rst

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+:mod:`os` --- Miscellaneous operating system interfaces
+=======================================================
+.. module:: os
+:synopsis: Miscellaneous operating system interfaces.
+This module provides a portable way of using operating system dependent
+functionality.  If you just want to read or write a file see :func:`open`, if
+you want to manipulate paths, see the :mod:`os.path` module, and if you want to
+read all the lines in all the files on the command line see the :mod:`fileinput`
+module.  For creating temporary files and directories see the :mod:`tempfile`
+module, and for high-level file and directory handling see the :mod:`shutil`
+module.
+The design of all built-in operating system dependent modules of Python is such
+that as long as the same functionality is available, it uses the same interface;
+for example, the function ``os.stat(path)`` returns stat information about
+*path* in the same format (which happens to have originated with the POSIX
+interface).
+Extensions peculiar to a particular operating system are also available through
+the :mod:`os` module, but using them is of course a threat to portability!
+.. note::
+If not separately noted, all functions that claim "Availability: Unix" are
+supported on Mac OS X, which builds on a Unix core.
+.. note::
+All functions in this module raise :exc:`OSError` in the case of invalid or
+inaccessible file names and paths, or other arguments that have the correct
+type, but are not accepted by the operating system.
+.. exception:: error
+An alias for the built-in :exc:`OSError` exception.
+.. data:: name
+The name of the operating system dependent module imported.  The following names
+have currently been registered: ``'posix'``, ``'nt'``, ``'mac'``, ``'os2'``,
+``'ce'``, ``'java'``, ``'riscos'``.
+.. data:: path
+The corresponding operating system dependent standard module for pathname
+operations, such as :mod:`posixpath` or :mod:`ntpath`.  Thus, given the proper
+imports, ``os.path.split(file)`` is equivalent to but more portable than
+``posixpath.split(file)``.  Note that this is also an importable module: it may
+be imported directly as :mod:`os.path`.
+.. _os-procinfo:
+Process Parameters
+------------------
+These functions and data items provide information and operate on the current
+process and user.
+.. data:: environ
+A mapping object representing the string environment. For example,
+``environ['HOME']`` is the pathname of your home directory (on some platforms),
+and is equivalent to ``getenv("HOME")`` in C.
+This mapping is captured the first time the :mod:`os` module is imported,
+typically during Python startup as part of processing :file:`site.py`.  Changes
+to the environment made after this time are not reflected in ``os.environ``,
+except for changes made by modifying ``os.environ`` directly.
+If the platform supports the :func:`putenv` function, this mapping may be used
+to modify the environment as well as query the environment.  :func:`putenv` will
+be called automatically when the mapping is modified.
+.. note::
+Calling :func:`putenv` directly does not change ``os.environ``, so it's better
+to modify ``os.environ``.
+.. note::
+On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may
+cause memory leaks.  Refer to the system documentation for
+:cfunc:`putenv`.
+If :func:`putenv` is not provided, a modified copy of this mapping  may be
+passed to the appropriate process-creation functions to cause  child processes
+to use a modified environment.
+If the platform supports the :func:`unsetenv` function, you can delete items in
+this mapping to unset environment variables. :func:`unsetenv` will be called
+automatically when an item is deleted from ``os.environ``, and when
+one of the :meth:`pop` or :meth:`clear` methods is called.
+.. versionchanged:: 2.6
+Also unset environment variables when calling :meth:`os.environ.clear`
+and :meth:`os.environ.pop`.
+.. function:: chdir(path)
+fchdir(fd)
+getcwd()
+:noindex:
+These functions are described in :ref:`os-file-dir`.
+.. function:: ctermid()
+Return the filename corresponding to the controlling terminal of the process.
+Availability: Unix.
+.. function:: getegid()
+Return the effective group id of the current process.  This corresponds to the
+"set id" bit on the file being executed in the current process. Availability:
+Unix.
+.. function:: geteuid()
+.. index:: single: user; effective id
+Return the current process's effective user id. Availability: Unix.
+.. function:: getgid()
+.. index:: single: process; group
+Return the real group id of the current process. Availability: Unix.
+.. function:: getgroups()
+Return list of supplemental group ids associated with the current process.
+Availability: Unix.
+.. function:: getlogin()
+Return the name of the user logged in on the controlling terminal of the
+process.  For most purposes, it is more useful to use the environment variable
+:envvar:`LOGNAME` to find out who the user is, or
+``pwd.getpwuid(os.getuid())[0]`` to get the login name of the currently
+effective user id. Availability: Unix.
+.. function:: getpgid(pid)
+Return the process group id of the process with process id *pid*. If *pid* is 0,
+the process group id of the current process is returned. Availability: Unix.
+.. versionadded:: 2.3
+.. function:: getpgrp()
+.. index:: single: process; group
+Return the id of the current process group. Availability: Unix.
+.. function:: getpid()
+.. index:: single: process; id
+Return the current process id. Availability: Unix, Windows.
+.. function:: getppid()
+.. index:: single: process; id of parent
+Return the parent's process id. Availability: Unix.
+.. function:: getuid()
+.. index:: single: user; id
+Return the current process's user id. Availability: Unix.
+.. function:: getenv(varname[, value])
+Return the value of the environment variable *varname* if it exists, or *value*
+if it doesn't.  *value* defaults to ``None``. Availability: most flavors of
+Unix, Windows.
+.. function:: putenv(varname, value)
+.. index:: single: environment variables; setting
+Set the environment variable named *varname* to the string *value*.  Such
+changes to the environment affect subprocesses started with :func:`os.system`,
+:func:`popen` or :func:`fork` and :func:`execv`. Availability: most flavors of
+Unix, Windows.
+.. note::
+On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may
+cause memory leaks. Refer to the system documentation for putenv.
+When :func:`putenv` is supported, assignments to items in ``os.environ`` are
+automatically translated into corresponding calls to :func:`putenv`; however,
+calls to :func:`putenv` don't update ``os.environ``, so it is actually
+preferable to assign to items of ``os.environ``.
+.. function:: setegid(egid)
+Set the current process's effective group id. Availability: Unix.
+.. function:: seteuid(euid)
+Set the current process's effective user id. Availability: Unix.
+.. function:: setgid(gid)
+Set the current process' group id. Availability: Unix.
+.. function:: setgroups(groups)
+Set the list of supplemental group ids associated with the current process to
+*groups*. *groups* must be a sequence, and each element must be an integer
+identifying a group. This operation is typically available only to the superuser.
+Availability: Unix.
+.. versionadded:: 2.2
+.. function:: setpgrp()
+Call the system call :cfunc:`setpgrp` or :cfunc:`setpgrp(0, 0)` depending on
+which version is implemented (if any).  See the Unix manual for the semantics.
+Availability: Unix.
+.. function:: setpgid(pid, pgrp)
+Call the system call :cfunc:`setpgid` to set the process group id of the
+process with id *pid* to the process group with id *pgrp*.  See the Unix manual
+for the semantics. Availability: Unix.
+.. function:: setreuid(ruid, euid)
+Set the current process's real and effective user ids. Availability: Unix.
+.. function:: setregid(rgid, egid)
+Set the current process's real and effective group ids. Availability: Unix.
+.. function:: getsid(pid)
+Call the system call :cfunc:`getsid`.  See the Unix manual for the semantics.
+Availability: Unix.
+.. versionadded:: 2.4
+.. function:: setsid()
+Call the system call :cfunc:`setsid`.  See the Unix manual for the semantics.
+Availability: Unix.
+.. function:: setuid(uid)
+.. index:: single: user; id, setting
+Set the current process's user id. Availability: Unix.
+.. placed in this section since it relates to errno.... a little weak
+.. function:: strerror(code)
+Return the error message corresponding to the error code in *code*.
+On platforms where :cfunc:`strerror` returns ``NULL`` when given an unknown
+error number, :exc:`ValueError` is raised.  Availability: Unix, Windows.
+.. function:: umask(mask)
+Set the current numeric umask and return the previous umask. Availability:
+Unix, Windows.
+.. function:: uname()
+.. index::
+single: gethostname() (in module socket)
+single: gethostbyaddr() (in module socket)
+Return a 5-tuple containing information identifying the current operating
+system.  The tuple contains 5 strings: ``(sysname, nodename, release, version,
+machine)``.  Some systems truncate the nodename to 8 characters or to the
+leading component; a better way to get the hostname is
+:func:`socket.gethostname`  or even
+``socket.gethostbyaddr(socket.gethostname())``. Availability: recent flavors of
+Unix.
+.. function:: unsetenv(varname)
+.. index:: single: environment variables; deleting
+Unset (delete) the environment variable named *varname*. Such changes to the
+environment affect subprocesses started with :func:`os.system`, :func:`popen` or
+:func:`fork` and :func:`execv`. Availability: most flavors of Unix, Windows.
+When :func:`unsetenv` is supported, deletion of items in ``os.environ`` is
+automatically translated into a corresponding call to :func:`unsetenv`; however,
+calls to :func:`unsetenv` don't update ``os.environ``, so it is actually
+preferable to delete items of ``os.environ``.
+.. _os-newstreams:
+File Object Creation
+--------------------
+These functions create new file objects. (See also :func:`open`.)
+.. function:: fdopen(fd[, mode[, bufsize]])
+.. index:: single: I/O control; buffering
+Return an open file object connected to the file descriptor *fd*.  The *mode*
+and *bufsize* arguments have the same meaning as the corresponding arguments to
+the built-in :func:`open` function. Availability: Unix, Windows.
+.. versionchanged:: 2.3
+When specified, the *mode* argument must now start with one of the letters
+``'r'``, ``'w'``, or ``'a'``, otherwise a :exc:`ValueError` is raised.
+.. versionchanged:: 2.5
+On Unix, when the *mode* argument starts with ``'a'``, the *O_APPEND* flag is
+set on the file descriptor (which the :cfunc:`fdopen` implementation already
+does on most platforms).
+.. function:: popen(command[, mode[, bufsize]])
+Open a pipe to or from *command*.  The return value is an open file object
+connected to the pipe, which can be read or written depending on whether *mode*
+is ``'r'`` (default) or ``'w'``. The *bufsize* argument has the same meaning as
+the corresponding argument to the built-in :func:`open` function.  The exit
+status of the command (encoded in the format specified for :func:`wait`) is
+available as the return value of the :meth:`close` method of the file object,
+except that when the exit status is zero (termination without errors), ``None``
+is returned. Availability: Unix, Windows.
+.. deprecated:: 2.6
+This function is obsolete.  Use the :mod:`subprocess` module.  Check
+especially the :ref:`subprocess-replacements` section.
+.. versionchanged:: 2.0
+This function worked unreliably under Windows in earlier versions of Python.
+This was due to the use of the :cfunc:`_popen` function from the libraries
+provided with Windows.  Newer versions of Python do not use the broken
+implementation from the Windows libraries.
+.. function:: tmpfile()
+Return a new file object opened in update mode (``w+b``).  The file has no
+directory entries associated with it and will be automatically deleted once
+there are no file descriptors for the file. Availability: Unix,
+Windows.
+There are a number of different :func:`popen\*` functions that provide slightly
+different ways to create subprocesses.
+.. deprecated:: 2.6
+All of the :func:`popen\*` functions are obsolete. Use the :mod:`subprocess`
+module.
+For each of the :func:`popen\*` variants, if *bufsize* is specified, it
+specifies the buffer size for the I/O pipes. *mode*, if provided, should be the
+string ``'b'`` or ``'t'``; on Windows this is needed to determine whether the
+file objects should be opened in binary or text mode.  The default value for
+*mode* is ``'t'``.
+Also, for each of these variants, on Unix, *cmd* may be a sequence, in which
+case arguments will be passed directly to the program without shell intervention
+(as with :func:`os.spawnv`). If *cmd* is a string it will be passed to the shell
+(as with :func:`os.system`).
+These methods do not make it possible to retrieve the exit status from the child
+processes.  The only way to control the input and output streams and also
+retrieve the return codes is to use the :mod:`subprocess` module; these are only
+available on Unix.
+For a discussion of possible deadlock conditions related to the use of these
+functions, see :ref:`popen2-flow-control`.
+.. function:: popen2(cmd[, mode[, bufsize]])
+Execute *cmd* as a sub-process and return the file objects ``(child_stdin,
+child_stdout)``.
+.. deprecated:: 2.6
+This function is obsolete.  Use the :mod:`subprocess` module.  Check
+especially the :ref:`subprocess-replacements` section.
+Availability: Unix, Windows.
+.. versionadded:: 2.0
+.. function:: popen3(cmd[, mode[, bufsize]])
+Execute *cmd* as a sub-process and return the file objects ``(child_stdin,
+child_stdout, child_stderr)``.
+.. deprecated:: 2.6
+This function is obsolete.  Use the :mod:`subprocess` module.  Check
+especially the :ref:`subprocess-replacements` section.
+Availability: Unix, Windows.
+.. versionadded:: 2.0
+.. function:: popen4(cmd[, mode[, bufsize]])
+Execute *cmd* as a sub-process and return the file objects ``(child_stdin,
+child_stdout_and_stderr)``.
+.. deprecated:: 2.6
+This function is obsolete.  Use the :mod:`subprocess` module.  Check
+especially the :ref:`subprocess-replacements` section.
+Availability: Unix, Windows.
+.. versionadded:: 2.0
+(Note that ``child_stdin, child_stdout, and child_stderr`` are named from the
+point of view of the child process, so *child_stdin* is the child's standard
+input.)
+This functionality is also available in the :mod:`popen2` module using functions
+of the same names, but the return values of those functions have a different
+order.
+.. _os-fd-ops:
+File Descriptor Operations
+--------------------------
+These functions operate on I/O streams referenced using file descriptors.
+File descriptors are small integers corresponding to a file that has been opened
+by the current process.  For example, standard input is usually file descriptor
+0, standard output is 1, and standard error is 2.  Further files opened by a
+process will then be assigned 3, 4, 5, and so forth.  The name "file descriptor"
+is slightly deceptive; on Unix platforms, sockets and pipes are also referenced
+by file descriptors.
+.. function:: close(fd)
+Close file descriptor *fd*. Availability: Unix, Windows.
+.. note::
+This function is intended for low-level I/O and must be applied to a file
+descriptor as returned by :func:`open` or :func:`pipe`.  To close a "file
+object" returned by the built-in function :func:`open` or by :func:`popen` or
+:func:`fdopen`, use its :meth:`close` method.
+.. function:: closerange(fd_low, fd_high)
+Close all file descriptors from *fd_low* (inclusive) to *fd_high* (exclusive),
+ignoring errors. Availability: Unix, Windows. Equivalent to::
+for fd in xrange(fd_low, fd_high):
+try:
+os.close(fd)
+except OSError:
+pass
+.. versionadded:: 2.6
+.. function:: dup(fd)
+Return a duplicate of file descriptor *fd*. Availability: Unix,
+Windows.
+.. function:: dup2(fd, fd2)
+Duplicate file descriptor *fd* to *fd2*, closing the latter first if necessary.
+Availability: Unix, Windows.
+.. function:: fchmod(fd, mode)
+Change the mode of the file given by *fd* to the numeric *mode*.  See the docs
+for :func:`chmod` for possible values of *mode*.  Availability: Unix.
+.. versionadded:: 2.6
+.. function:: fchown(fd, uid, gid)
+Change the owner and group id of the file given by *fd* to the numeric *uid*
+and *gid*.  To leave one of the ids unchanged, set it to -1.
+Availability: Unix.
+.. versionadded:: 2.6
+.. function:: fdatasync(fd)
+Force write of file with filedescriptor *fd* to disk. Does not force update of
+metadata. Availability: Unix.
+.. function:: fpathconf(fd, name)
+Return system configuration information relevant to an open file. *name*
+specifies the configuration value to retrieve; it may be a string which is the
+name of a defined system value; these names are specified in a number of
+standards (POSIX.1, Unix 95, Unix 98, and others).  Some platforms define
+additional names as well.  The names known to the host operating system are
+given in the ``pathconf_names`` dictionary.  For configuration variables not
+included in that mapping, passing an integer for *name* is also accepted.
+Availability: Unix.
+If *name* is a string and is not known, :exc:`ValueError` is raised.  If a
+specific value for *name* is not supported by the host system, even if it is
+included in ``pathconf_names``, an :exc:`OSError` is raised with
+:const:`errno.EINVAL` for the error number.
+.. function:: fstat(fd)
+Return status for file descriptor *fd*, like :func:`stat`. Availability:
+Unix, Windows.
+.. function:: fstatvfs(fd)
+Return information about the filesystem containing the file associated with file
+descriptor *fd*, like :func:`statvfs`. Availability: Unix.
+.. function:: fsync(fd)
+Force write of file with filedescriptor *fd* to disk.  On Unix, this calls the
+native :cfunc:`fsync` function; on Windows, the MS :cfunc:`_commit` function.
+If you're starting with a Python file object *f*, first do ``f.flush()``, and
+then do ``os.fsync(f.fileno())``, to ensure that all internal buffers associated
+with *f* are written to disk. Availability: Unix, and Windows
+starting in 2.2.3.
+.. function:: ftruncate(fd, length)
+Truncate the file corresponding to file descriptor *fd*, so that it is at most
+*length* bytes in size. Availability: Unix.
+.. function:: isatty(fd)
+Return ``True`` if the file descriptor *fd* is open and connected to a
+tty(-like) device, else ``False``. Availability: Unix.
+.. function:: lseek(fd, pos, how)
+Set the current position of file descriptor *fd* to position *pos*, modified
+by *how*: :const:`SEEK_SET` or ``0`` to set the position relative to the
+beginning of the file; :const:`SEEK_CUR` or ``1`` to set it relative to the
+current position; :const:`os.SEEK_END` or ``2`` to set it relative to the end of
+the file. Availability: Unix, Windows.
+.. function:: open(file, flags[, mode])
+Open the file *file* and set various flags according to *flags* and possibly its
+mode according to *mode*. The default *mode* is ``0777`` (octal), and the
+current umask value is first masked out.  Return the file descriptor for the
+newly opened file. Availability: Unix, Windows.
+For a description of the flag and mode values, see the C run-time documentation;
+flag constants (like :const:`O_RDONLY` and :const:`O_WRONLY`) are defined in
+this module too (see below).
+.. note::
+This function is intended for low-level I/O.  For normal usage, use the built-in
+function :func:`open`, which returns a "file object" with :meth:`read` and
+:meth:`write` methods (and many more).  To wrap a file descriptor in a "file
+object", use :func:`fdopen`.
+.. function:: openpty()
+.. index:: module: pty
+Open a new pseudo-terminal pair. Return a pair of file descriptors ``(master,
+slave)`` for the pty and the tty, respectively. For a (slightly) more portable
+approach, use the :mod:`pty` module. Availability: some flavors of
+Unix.
+.. function:: pipe()
+Create a pipe.  Return a pair of file descriptors ``(r, w)`` usable for reading
+and writing, respectively. Availability: Unix, Windows.
+.. function:: read(fd, n)
+Read at most *n* bytes from file descriptor *fd*. Return a string containing the
+bytes read.  If the end of the file referred to by *fd* has been reached, an
+empty string is returned. Availability: Unix, Windows.
+.. note::
+This function is intended for low-level I/O and must be applied to a file
+descriptor as returned by :func:`open` or :func:`pipe`.  To read a "file object"
+returned by the built-in function :func:`open` or by :func:`popen` or
+:func:`fdopen`, or :data:`sys.stdin`, use its :meth:`read` or :meth:`readline`
+methods.
+.. function:: tcgetpgrp(fd)
+Return the process group associated with the terminal given by *fd* (an open
+file descriptor as returned by :func:`open`). Availability: Unix.
+.. function:: tcsetpgrp(fd, pg)
+Set the process group associated with the terminal given by *fd* (an open file
+descriptor as returned by :func:`open`) to *pg*. Availability: Unix.
+.. function:: ttyname(fd)
+Return a string which specifies the terminal device associated with
+file descriptor *fd*.  If *fd* is not associated with a terminal device, an
+exception is raised. Availability: Unix.
+.. function:: write(fd, str)
+Write the string *str* to file descriptor *fd*. Return the number of bytes
+actually written. Availability: Unix, Windows.
+.. note::
+This function is intended for low-level I/O and must be applied to a file
+descriptor as returned by :func:`open` or :func:`pipe`.  To write a "file
+object" returned by the built-in function :func:`open` or by :func:`popen` or
+:func:`fdopen`, or :data:`sys.stdout` or :data:`sys.stderr`, use its :meth:`write`
+method.
+The following data items are available for use in constructing the *flags*
+parameter to the :func:`open` function.  Some items will not be available on all
+platforms.  For descriptions of their availability and use, consult
+:manpage:`open(2)`.
+.. data:: O_RDONLY
+O_WRONLY
+O_RDWR
+O_APPEND
+O_CREAT
+O_EXCL
+O_TRUNC
+Options for the *flag* argument to the :func:`open` function. These can be
+combined using the bitwise OR operator ``|``. Availability: Unix, Windows.
+.. data:: O_DSYNC
+O_RSYNC
+O_SYNC
+O_NDELAY
+O_NONBLOCK
+O_NOCTTY
+O_SHLOCK
+O_EXLOCK
+More options for the *flag* argument to the :func:`open` function. Availability:
+Unix.
+.. data:: O_BINARY
+O_NOINHERIT
+O_SHORT_LIVED
+O_TEMPORARY
+O_RANDOM
+O_SEQUENTIAL
+O_TEXT
+Options for the *flag* argument to the :func:`open` function. These can be
+combined using the bitwise OR operator ``|``. Availability: Windows.
+.. data:: O_ASYNC
+O_DIRECT
+O_DIRECTORY
+O_NOFOLLOW
+O_NOATIME
+Options for the *flag* argument to the :func:`open` function. These are
+GNU extensions and not present if they are not defined by the C library.
+.. data:: SEEK_SET
+SEEK_CUR
+SEEK_END
+Parameters to the :func:`lseek` function. Their values are 0, 1, and 2,
+respectively. Availability: Windows, Unix.
+.. versionadded:: 2.5
+.. _os-file-dir:
+Files and Directories
+---------------------
+.. function:: access(path, mode)
+Use the real uid/gid to test for access to *path*.  Note that most operations
+will use the effective uid/gid, therefore this routine can be used in a
+suid/sgid environment to test if the invoking user has the specified access to
+*path*.  *mode* should be :const:`F_OK` to test the existence of *path*, or it
+can be the inclusive OR of one or more of :const:`R_OK`, :const:`W_OK`, and
+:const:`X_OK` to test permissions.  Return :const:`True` if access is allowed,
+:const:`False` if not. See the Unix man page :manpage:`access(2)` for more
+information. Availability: Unix, Windows.
+.. note::
+Using :func:`access` to check if a user is authorized to e.g. open a file before
+actually doing so using :func:`open` creates a  security hole, because the user
+might exploit the short time interval  between checking and opening the file to
+manipulate it.
+.. note::
+I/O operations may fail even when :func:`access` indicates that they would
+succeed, particularly for operations on network filesystems which may have
+permissions semantics beyond the usual POSIX permission-bit model.
+.. data:: F_OK
+Value to pass as the *mode* parameter of :func:`access` to test the existence of
+*path*.
+.. data:: R_OK
+Value to include in the *mode* parameter of :func:`access` to test the
+readability of *path*.
+.. data:: W_OK
+Value to include in the *mode* parameter of :func:`access` to test the
+writability of *path*.
+.. data:: X_OK
+Value to include in the *mode* parameter of :func:`access` to determine if
+*path* can be executed.
+.. function:: chdir(path)
+.. index:: single: directory; changing
+Change the current working directory to *path*. Availability: Unix,
+Windows.
+.. function:: fchdir(fd)
+Change the current working directory to the directory represented by the file
+descriptor *fd*.  The descriptor must refer to an opened directory, not an open
+file. Availability: Unix.
+.. versionadded:: 2.3
+.. function:: getcwd()
+Return a string representing the current working directory. Availability:
+Unix, Windows.
+.. function:: getcwdu()
+Return a Unicode object representing the current working directory.
+Availability: Unix, Windows.
+.. versionadded:: 2.3
+.. function:: chflags(path, flags)
+Set the flags of *path* to the numeric *flags*. *flags* may take a combination
+(bitwise OR) of the following values (as defined in the :mod:`stat` module):
+* ``UF_NODUMP``
+* ``UF_IMMUTABLE``
+* ``UF_APPEND``
+* ``UF_OPAQUE``
+* ``UF_NOUNLINK``
+* ``SF_ARCHIVED``
+* ``SF_IMMUTABLE``
+* ``SF_APPEND``
+* ``SF_NOUNLINK``
+* ``SF_SNAPSHOT``
+Availability: Unix.
+.. versionadded:: 2.6
+.. function:: chroot(path)
+Change the root directory of the current process to *path*. Availability:
+Unix.
+.. versionadded:: 2.2
+.. function:: chmod(path, mode)
+Change the mode of *path* to the numeric *mode*. *mode* may take one of the
+following values (as defined in the :mod:`stat` module) or bitwise ORed
+combinations of them:
+* ``stat.S_ISUID``
+* ``stat.S_ISGID``
+* ``stat.S_ENFMT``
+* ``stat.S_ISVTX``
+* ``stat.S_IREAD``
+* ``stat.S_IWRITE``
+* ``stat.S_IEXEC``
+* ``stat.S_IRWXU``
+* ``stat.S_IRUSR``
+* ``stat.S_IWUSR``
+* ``stat.S_IXUSR``
+* ``stat.S_IRWXG``
+* ``stat.S_IRGRP``
+* ``stat.S_IWGRP``
+* ``stat.S_IXGRP``
+* ``stat.S_IRWXO``
+* ``stat.S_IROTH``
+* ``stat.S_IWOTH``
+* ``stat.S_IXOTH``
+Availability: Unix, Windows.
+.. note::
+Although Windows supports :func:`chmod`, you can only  set the file's read-only
+flag with it (via the ``stat.S_IWRITE``  and ``stat.S_IREAD``
+constants or a corresponding integer value).  All other bits are
+ignored.
+.. function:: chown(path, uid, gid)
+Change the owner and group id of *path* to the numeric *uid* and *gid*. To leave
+one of the ids unchanged, set it to -1. Availability: Unix.
+.. function:: lchflags(path, flags)
+Set the flags of *path* to the numeric *flags*, like :func:`chflags`, but do not
+follow symbolic links. Availability: Unix.
+.. versionadded:: 2.6
+.. function:: lchmod(path, mode)
+Change the mode of *path* to the numeric *mode*. If path is a symlink, this
+affects the symlink rather than the target. See the docs for :func:`chmod`
+for possible values of *mode*.  Availability: Unix.
+.. versionadded:: 2.6
+.. function:: lchown(path, uid, gid)
+Change the owner and group id of *path* to the numeric *uid* and *gid*. This
+function will not follow symbolic links. Availability: Unix.
+.. versionadded:: 2.3
+.. function:: link(src, dst)
+Create a hard link pointing to *src* named *dst*. Availability: Unix.
+.. function:: listdir(path)
+Return a list containing the names of the entries in the directory. The list is
+in arbitrary order.  It does not include the special entries ``'.'`` and
+``'..'`` even if they are present in the directory. Availability:
+Unix, Windows.
+.. versionchanged:: 2.3
+On Windows NT/2k/XP and Unix, if *path* is a Unicode object, the result will be
+a list of Unicode objects.
+.. function:: lstat(path)
+Like :func:`stat`, but do not follow symbolic links.  This is an alias for
+:func:`stat` on platforms that do not support symbolic links, such as
+Windows.
+.. function:: mkfifo(path[, mode])
+Create a FIFO (a named pipe) named *path* with numeric mode *mode*.  The default
+*mode* is ``0666`` (octal).  The current umask value is first masked out from
+the mode. Availability: Unix.
+FIFOs are pipes that can be accessed like regular files.  FIFOs exist until they
+are deleted (for example with :func:`os.unlink`). Generally, FIFOs are used as
+rendezvous between "client" and "server" type processes: the server opens the
+FIFO for reading, and the client opens it for writing.  Note that :func:`mkfifo`
+doesn't open the FIFO --- it just creates the rendezvous point.
+.. function:: mknod(filename[, mode=0600, device])
+Create a filesystem node (file, device special file or named pipe) named
+*filename*. *mode* specifies both the permissions to use and the type of node to
+be created, being combined (bitwise OR) with one of ``stat.S_IFREG``,
+``stat.S_IFCHR``, ``stat.S_IFBLK``,
+and ``stat.S_IFIFO`` (those constants are available in :mod:`stat`).
+For ``stat.S_IFCHR`` and
+``stat.S_IFBLK``, *device* defines the newly created device special file (probably using
+:func:`os.makedev`), otherwise it is ignored.
+.. versionadded:: 2.3
+.. function:: major(device)
+Extract the device major number from a raw device number (usually the
+:attr:`st_dev` or :attr:`st_rdev` field from :ctype:`stat`).
+.. versionadded:: 2.3
+.. function:: minor(device)
+Extract the device minor number from a raw device number (usually the
+:attr:`st_dev` or :attr:`st_rdev` field from :ctype:`stat`).
+.. versionadded:: 2.3
+.. function:: makedev(major, minor)
+Compose a raw device number from the major and minor device numbers.
+.. versionadded:: 2.3
+.. function:: mkdir(path[, mode])
+Create a directory named *path* with numeric mode *mode*. The default *mode* is
+``0777`` (octal).  On some systems, *mode* is ignored.  Where it is used, the
+current umask value is first masked out. Availability: Unix, Windows.
+It is also possible to create temporary directories; see the
+:mod:`tempfile` module's :func:`tempfile.mkdtemp` function.
+.. function:: makedirs(path[, mode])
+.. index::
+single: directory; creating
+single: UNC paths; and os.makedirs()
+Recursive directory creation function.  Like :func:`mkdir`, but makes all
+intermediate-level directories needed to contain the leaf directory.  Throws an
+:exc:`error` exception if the leaf directory already exists or cannot be
+created.  The default *mode* is ``0777`` (octal).  On some systems, *mode* is
+ignored. Where it is used, the current umask value is first masked out.
+.. note::
+:func:`makedirs` will become confused if the path elements to create include
+:data:`os.pardir`.
+.. versionadded:: 1.5.2
+.. versionchanged:: 2.3
+This function now handles UNC paths correctly.
+.. function:: pathconf(path, name)
+Return system configuration information relevant to a named file. *name*
+specifies the configuration value to retrieve; it may be a string which is the
+name of a defined system value; these names are specified in a number of
+standards (POSIX.1, Unix 95, Unix 98, and others).  Some platforms define
+additional names as well.  The names known to the host operating system are
+given in the ``pathconf_names`` dictionary.  For configuration variables not
+included in that mapping, passing an integer for *name* is also accepted.
+Availability: Unix.
+If *name* is a string and is not known, :exc:`ValueError` is raised.  If a
+specific value for *name* is not supported by the host system, even if it is
+included in ``pathconf_names``, an :exc:`OSError` is raised with
+:const:`errno.EINVAL` for the error number.
+.. data:: pathconf_names
+Dictionary mapping names accepted by :func:`pathconf` and :func:`fpathconf` to
+the integer values defined for those names by the host operating system.  This
+can be used to determine the set of names known to the system. Availability:
+Unix.
+.. function:: readlink(path)
+Return a string representing the path to which the symbolic link points.  The
+result may be either an absolute or relative pathname; if it is relative, it may
+be converted to an absolute pathname using ``os.path.join(os.path.dirname(path),
+result)``.
+.. versionchanged:: 2.6
+If the *path* is a Unicode object the result will also be a Unicode object.
+Availability: Unix.
+.. function:: remove(path)
+Remove the file *path*.  If *path* is a directory, :exc:`OSError` is raised; see
+:func:`rmdir` below to remove a directory.  This is identical to the
+:func:`unlink` function documented below.  On Windows, attempting to remove a
+file that is in use causes an exception to be raised; on Unix, the directory
+entry is removed but the storage allocated to the file is not made available
+until the original file is no longer in use. Availability: Unix,
+Windows.
+.. function:: removedirs(path)
+.. index:: single: directory; deleting
+Remove directories recursively.  Works like :func:`rmdir` except that, if the
+leaf directory is successfully removed, :func:`removedirs`  tries to
+successively remove every parent directory mentioned in  *path* until an error
+is raised (which is ignored, because it generally means that a parent directory
+is not empty). For example, ``os.removedirs('foo/bar/baz')`` will first remove
+the directory ``'foo/bar/baz'``, and then remove ``'foo/bar'`` and ``'foo'`` if
+they are empty. Raises :exc:`OSError` if the leaf directory could not be
+successfully removed.
+.. versionadded:: 1.5.2
+.. function:: rename(src, dst)
+Rename the file or directory *src* to *dst*.  If *dst* is a directory,
+:exc:`OSError` will be raised.  On Unix, if *dst* exists and is a file, it will
+be replaced silently if the user has permission.  The operation may fail on some
+Unix flavors if *src* and *dst* are on different filesystems.  If successful,
+the renaming will be an atomic operation (this is a POSIX requirement).  On
+Windows, if *dst* already exists, :exc:`OSError` will be raised even if it is a
+file; there may be no way to implement an atomic rename when *dst* names an
+existing file. Availability: Unix, Windows.
+.. function:: renames(old, new)
+Recursive directory or file renaming function. Works like :func:`rename`, except
+creation of any intermediate directories needed to make the new pathname good is
+attempted first. After the rename, directories corresponding to rightmost path
+segments of the old name will be pruned away using :func:`removedirs`.
+.. versionadded:: 1.5.2
+.. note::
+This function can fail with the new directory structure made if you lack
+permissions needed to remove the leaf directory or file.
+.. function:: rmdir(path)
+Remove the directory *path*. Availability: Unix, Windows.
+.. function:: stat(path)
+Perform a :cfunc:`stat` system call on the given path.  The return value is an
+object whose attributes correspond to the members of the :ctype:`stat`
+structure, namely: :attr:`st_mode` (protection bits), :attr:`st_ino` (inode
+number), :attr:`st_dev` (device), :attr:`st_nlink` (number of hard links),
+:attr:`st_uid` (user id of owner), :attr:`st_gid` (group id of owner),
+:attr:`st_size` (size of file, in bytes), :attr:`st_atime` (time of most recent
+access), :attr:`st_mtime` (time of most recent content modification),
+:attr:`st_ctime` (platform dependent; time of most recent metadata change on
+Unix, or the time of creation on Windows)::
+>>> import os
+>>> statinfo = os.stat('somefile.txt')
+>>> statinfo
+(33188, 422511L, 769L, 1, 1032, 100, 926L, 1105022698,1105022732, 1105022732)
+>>> statinfo.st_size
+926L
+>>>
+.. versionchanged:: 2.3
+If :func:`stat_float_times` returns ``True``, the time values are floats, measuring
+seconds. Fractions of a second may be reported if the system supports that. On
+Mac OS, the times are always floats. See :func:`stat_float_times` for further
+discussion.
+On some Unix systems (such as Linux), the following attributes may also be
+available: :attr:`st_blocks` (number of blocks allocated for file),
+:attr:`st_blksize` (filesystem blocksize), :attr:`st_rdev` (type of device if an
+inode device). :attr:`st_flags` (user defined flags for file).
+On other Unix systems (such as FreeBSD), the following attributes may be
+available (but may be only filled out if root tries to use them): :attr:`st_gen`
+(file generation number), :attr:`st_birthtime` (time of file creation).
+On Mac OS systems, the following attributes may also be available:
+:attr:`st_rsize`, :attr:`st_creator`, :attr:`st_type`.
+On RISCOS systems, the following attributes are also available: :attr:`st_ftype`
+(file type), :attr:`st_attrs` (attributes), :attr:`st_obtype` (object type).
+.. index:: module: stat
+For backward compatibility, the return value of :func:`stat` is also accessible
+as a tuple of at least 10 integers giving the most important (and portable)
+members of the :ctype:`stat` structure, in the order :attr:`st_mode`,
+:attr:`st_ino`, :attr:`st_dev`, :attr:`st_nlink`, :attr:`st_uid`,
+:attr:`st_gid`, :attr:`st_size`, :attr:`st_atime`, :attr:`st_mtime`,
+:attr:`st_ctime`. More items may be added at the end by some implementations.
+The standard module :mod:`stat` defines functions and constants that are useful
+for extracting information from a :ctype:`stat` structure. (On Windows, some
+items are filled with dummy values.)
+.. note::
+The exact meaning and resolution of the :attr:`st_atime`, :attr:`st_mtime`, and
+:attr:`st_ctime` members depends on the operating system and the file system.
+For example, on Windows systems using the FAT or FAT32 file systems,
+:attr:`st_mtime` has 2-second resolution, and :attr:`st_atime` has only 1-day
+resolution.  See your operating system documentation for details.
+Availability: Unix, Windows.
+.. versionchanged:: 2.2
+Added access to values as attributes of the returned object.
+.. versionchanged:: 2.5
+Added :attr:`st_gen` and :attr:`st_birthtime`.
+.. function:: stat_float_times([newvalue])
+Determine whether :class:`stat_result` represents time stamps as float objects.
+If *newvalue* is ``True``, future calls to :func:`stat` return floats, if it is
+``False``, future calls return ints. If *newvalue* is omitted, return the
+current setting.
+For compatibility with older Python versions, accessing :class:`stat_result` as
+a tuple always returns integers.
+.. versionchanged:: 2.5
+Python now returns float values by default. Applications which do not work
+correctly with floating point time stamps can use this function to restore the
+old behaviour.
+The resolution of the timestamps (that is the smallest possible fraction)
+depends on the system. Some systems only support second resolution; on these
+systems, the fraction will always be zero.
+It is recommended that this setting is only changed at program startup time in
+the *__main__* module; libraries should never change this setting. If an
+application uses a library that works incorrectly if floating point time stamps
+are processed, this application should turn the feature off until the library
+has been corrected.
+.. function:: statvfs(path)
+Perform a :cfunc:`statvfs` system call on the given path.  The return value is
+an object whose attributes describe the filesystem on the given path, and
+correspond to the members of the :ctype:`statvfs` structure, namely:
+:attr:`f_bsize`, :attr:`f_frsize`, :attr:`f_blocks`, :attr:`f_bfree`,
+:attr:`f_bavail`, :attr:`f_files`, :attr:`f_ffree`, :attr:`f_favail`,
+:attr:`f_flag`, :attr:`f_namemax`. Availability: Unix.
+.. index:: module: statvfs
+For backward compatibility, the return value is also accessible as a tuple whose
+values correspond to the attributes, in the order given above. The standard
+module :mod:`statvfs` defines constants that are useful for extracting
+information from a :ctype:`statvfs` structure when accessing it as a sequence;
+this remains useful when writing code that needs to work with versions of Python
+that don't support accessing the fields as attributes.
+.. versionchanged:: 2.2
+Added access to values as attributes of the returned object.
+.. function:: symlink(src, dst)
+Create a symbolic link pointing to *src* named *dst*. Availability: Unix.
+.. function:: tempnam([dir[, prefix]])
+Return a unique path name that is reasonable for creating a temporary file.
+This will be an absolute path that names a potential directory entry in the
+directory *dir* or a common location for temporary files if *dir* is omitted or
+``None``.  If given and not ``None``, *prefix* is used to provide a short prefix
+to the filename.  Applications are responsible for properly creating and
+managing files created using paths returned by :func:`tempnam`; no automatic
+cleanup is provided. On Unix, the environment variable :envvar:`TMPDIR`
+overrides *dir*, while on Windows :envvar:`TMP` is used.  The specific
+behavior of this function depends on the C library implementation; some aspects
+are underspecified in system documentation.
+.. warning::
+Use of :func:`tempnam` is vulnerable to symlink attacks; consider using
+:func:`tmpfile` (section :ref:`os-newstreams`) instead.
+Availability: Unix, Windows.
+.. function:: tmpnam()
+Return a unique path name that is reasonable for creating a temporary file.
+This will be an absolute path that names a potential directory entry in a common
+location for temporary files.  Applications are responsible for properly
+creating and managing files created using paths returned by :func:`tmpnam`; no
+automatic cleanup is provided.
+.. warning::
+Use of :func:`tmpnam` is vulnerable to symlink attacks; consider using
+:func:`tmpfile` (section :ref:`os-newstreams`) instead.
+Availability: Unix, Windows.  This function probably shouldn't be used on
+Windows, though: Microsoft's implementation of :func:`tmpnam` always creates a
+name in the root directory of the current drive, and that's generally a poor
+location for a temp file (depending on privileges, you may not even be able to
+open a file using this name).
+.. data:: TMP_MAX
+The maximum number of unique names that :func:`tmpnam` will generate before
+reusing names.
+.. function:: unlink(path)
+Remove the file *path*.  This is the same function as :func:`remove`; the
+:func:`unlink` name is its traditional Unix name. Availability: Unix,
+Windows.
+.. function:: utime(path, times)
+Set the access and modified times of the file specified by *path*. If *times*
+is ``None``, then the file's access and modified times are set to the current
+time. (The effect is similar to running the Unix program :program:`touch` on
+the path.)  Otherwise, *times* must be a 2-tuple of numbers, of the form
+``(atime, mtime)`` which is used to set the access and modified times,
+respectively. Whether a directory can be given for *path* depends on whether
+the operating system implements directories as files (for example, Windows
+does not).  Note that the exact times you set here may not be returned by a
+subsequent :func:`stat` call, depending on the resolution with which your
+operating system records access and modification times; see :func:`stat`.
+.. versionchanged:: 2.0
+Added support for ``None`` for *times*.
+Availability: Unix, Windows.
+.. function:: walk(top[, topdown=True [, onerror=None[, followlinks=False]]])
+.. index::
+single: directory; walking
+single: directory; traversal
+Generate the file names in a directory tree by walking the tree
+either top-down or bottom-up. For each directory in the tree rooted at directory
+*top* (including *top* itself), it yields a 3-tuple ``(dirpath, dirnames,
+filenames)``.
+*dirpath* is a string, the path to the directory.  *dirnames* is a list of the
+names of the subdirectories in *dirpath* (excluding ``'.'`` and ``'..'``).
+*filenames* is a list of the names of the non-directory files in *dirpath*.
+Note that the names in the lists contain no path components.  To get a full path
+(which begins with *top*) to a file or directory in *dirpath*, do
+``os.path.join(dirpath, name)``.
+If optional argument *topdown* is ``True`` or not specified, the triple for a
+directory is generated before the triples for any of its subdirectories
+(directories are generated top-down).  If *topdown* is ``False``, the triple for a
+directory is generated after the triples for all of its subdirectories
+(directories are generated bottom-up).
+When *topdown* is ``True``, the caller can modify the *dirnames* list in-place
+(perhaps using :keyword:`del` or slice assignment), and :func:`walk` will only
+recurse into the subdirectories whose names remain in *dirnames*; this can be
+used to prune the search, impose a specific order of visiting, or even to inform
+:func:`walk` about directories the caller creates or renames before it resumes
+:func:`walk` again.  Modifying *dirnames* when *topdown* is ``False`` is
+ineffective, because in bottom-up mode the directories in *dirnames* are
+generated before *dirpath* itself is generated.
+By default errors from the :func:`listdir` call are ignored.  If optional
+argument *onerror* is specified, it should be a function; it will be called with
+one argument, an :exc:`OSError` instance.  It can report the error to continue
+with the walk, or raise the exception to abort the walk.  Note that the filename
+is available as the ``filename`` attribute of the exception object.
+By default, :func:`walk` will not walk down into symbolic links that resolve to
+directories. Set *followlinks* to ``True`` to visit directories pointed to by
+symlinks, on systems that support them.
+.. versionadded:: 2.6
+The *followlinks* parameter.
+.. note::
+Be aware that setting *followlinks* to ``True`` can lead to infinite recursion if a
+link points to a parent directory of itself. :func:`walk` does not keep track of
+the directories it visited already.
+.. note::
+If you pass a relative pathname, don't change the current working directory
+between resumptions of :func:`walk`.  :func:`walk` never changes the current
+directory, and assumes that its caller doesn't either.
+This example displays the number of bytes taken by non-directory files in each
+directory under the starting directory, except that it doesn't look under any
+CVS subdirectory::
+import os
+from os.path import join, getsize
+for root, dirs, files in os.walk('python/Lib/email'):
+print root, "consumes",
+print sum(getsize(join(root, name)) for name in files),
+print "bytes in", len(files), "non-directory files"
+if 'CVS' in dirs:
+dirs.remove('CVS')  # don't visit CVS directories
+In the next example, walking the tree bottom-up is essential: :func:`rmdir`
+doesn't allow deleting a directory before the directory is empty::
+# Delete everything reachable from the directory named in "top",
+# assuming there are no symbolic links.
+# CAUTION:  This is dangerous!  For example, if top == '/', it
+# could delete all your disk files.
+import os
+for root, dirs, files in os.walk(top, topdown=False):
+for name in files:
+os.remove(os.path.join(root, name))
+for name in dirs:
+os.rmdir(os.path.join(root, name))
+.. versionadded:: 2.3
+.. _os-process:
+Process Management
+------------------
+These functions may be used to create and manage processes.
+The various :func:`exec\*` functions take a list of arguments for the new
+program loaded into the process.  In each case, the first of these arguments is
+passed to the new program as its own name rather than as an argument a user may
+have typed on a command line.  For the C programmer, this is the ``argv[0]``
+passed to a program's :cfunc:`main`.  For example, ``os.execv('/bin/echo',
+['foo', 'bar'])`` will only print ``bar`` on standard output; ``foo`` will seem
+to be ignored.
+.. function:: abort()
+Generate a :const:`SIGABRT` signal to the current process.  On Unix, the default
+behavior is to produce a core dump; on Windows, the process immediately returns
+an exit code of ``3``.  Be aware that programs which use :func:`signal.signal`
+to register a handler for :const:`SIGABRT` will behave differently.
+Availability: Unix, Windows.
+.. function:: execl(path, arg0, arg1, ...)
+execle(path, arg0, arg1, ..., env)
+execlp(file, arg0, arg1, ...)
+execlpe(file, arg0, arg1, ..., env)
+execv(path, args)
+execve(path, args, env)
+execvp(file, args)
+execvpe(file, args, env)
+These functions all execute a new program, replacing the current process; they
+do not return.  On Unix, the new executable is loaded into the current process,
+and will have the same process id as the caller.  Errors will be reported as
+:exc:`OSError` exceptions.
+The current process is replaced immediately. Open file objects and
+descriptors are not flushed, so if there may be data buffered
+on these open files, you should flush them using
+:func:`sys.stdout.flush` or :func:`os.fsync` before calling an
+:func:`exec\*` function.
+The "l" and "v" variants of the :func:`exec\*` functions differ in how
+command-line arguments are passed.  The "l" variants are perhaps the easiest
+to work with if the number of parameters is fixed when the code is written; the
+individual parameters simply become additional parameters to the :func:`execl\*`
+functions.  The "v" variants are good when the number of parameters is
+variable, with the arguments being passed in a list or tuple as the *args*
+parameter.  In either case, the arguments to the child process should start with
+the name of the command being run, but this is not enforced.
+The variants which include a "p" near the end (:func:`execlp`,
+:func:`execlpe`, :func:`execvp`, and :func:`execvpe`) will use the
+:envvar:`PATH` environment variable to locate the program *file*.  When the
+environment is being replaced (using one of the :func:`exec\*e` variants,
+discussed in the next paragraph), the new environment is used as the source of
+the :envvar:`PATH` variable. The other variants, :func:`execl`, :func:`execle`,
+:func:`execv`, and :func:`execve`, will not use the :envvar:`PATH` variable to
+locate the executable; *path* must contain an appropriate absolute or relative
+path.
+For :func:`execle`, :func:`execlpe`, :func:`execve`, and :func:`execvpe` (note
+that these all end in "e"), the *env* parameter must be a mapping which is
+used to define the environment variables for the new process (these are used
+instead of the current process' environment); the functions :func:`execl`,
+:func:`execlp`, :func:`execv`, and :func:`execvp` all cause the new process to
+inherit the environment of the current process.
+Availability: Unix, Windows.
+.. function:: _exit(n)
+Exit to the system with status *n*, without calling cleanup handlers, flushing
+stdio buffers, etc. Availability: Unix, Windows.
+.. note::
+The standard way to exit is ``sys.exit(n)``. :func:`_exit` should normally only
+be used in the child process after a :func:`fork`.
+The following exit codes are defined and can be used with :func:`_exit`,
+although they are not required.  These are typically used for system programs
+written in Python, such as a mail server's external command delivery program.
+.. note::
+Some of these may not be available on all Unix platforms, since there is some
+variation.  These constants are defined where they are defined by the underlying
+platform.
+.. data:: EX_OK
+Exit code that means no error occurred. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_USAGE
+Exit code that means the command was used incorrectly, such as when the wrong
+number of arguments are given. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_DATAERR
+Exit code that means the input data was incorrect. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_NOINPUT
+Exit code that means an input file did not exist or was not readable.
+Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_NOUSER
+Exit code that means a specified user did not exist. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_NOHOST
+Exit code that means a specified host did not exist. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_UNAVAILABLE
+Exit code that means that a required service is unavailable. Availability:
+Unix.
+.. versionadded:: 2.3
+.. data:: EX_SOFTWARE
+Exit code that means an internal software error was detected. Availability:
+Unix.
+.. versionadded:: 2.3
+.. data:: EX_OSERR
+Exit code that means an operating system error was detected, such as the
+inability to fork or create a pipe. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_OSFILE
+Exit code that means some system file did not exist, could not be opened, or had
+some other kind of error. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_CANTCREAT
+Exit code that means a user specified output file could not be created.
+Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_IOERR
+Exit code that means that an error occurred while doing I/O on some file.
+Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_TEMPFAIL
+Exit code that means a temporary failure occurred.  This indicates something
+that may not really be an error, such as a network connection that couldn't be
+made during a retryable operation. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_PROTOCOL
+Exit code that means that a protocol exchange was illegal, invalid, or not
+understood. Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_NOPERM
+Exit code that means that there were insufficient permissions to perform the
+operation (but not intended for file system problems). Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_CONFIG
+Exit code that means that some kind of configuration error occurred.
+Availability: Unix.
+.. versionadded:: 2.3
+.. data:: EX_NOTFOUND
+Exit code that means something like "an entry was not found". Availability:
+Unix.
+.. versionadded:: 2.3
+.. function:: fork()
+Fork a child process.  Return ``0`` in the child and the child's process id in the
+parent.  If an error occurs :exc:`OSError` is raised.
+Note that some platforms including FreeBSD <= 6.3, Cygwin and OS/2 EMX have
+known issues when using fork() from a thread.
+Availability: Unix.
+.. function:: forkpty()
+Fork a child process, using a new pseudo-terminal as the child's controlling
+terminal. Return a pair of ``(pid, fd)``, where *pid* is ``0`` in the child, the
+new child's process id in the parent, and *fd* is the file descriptor of the
+master end of the pseudo-terminal.  For a more portable approach, use the
+:mod:`pty` module.  If an error occurs :exc:`OSError` is raised.
+Availability: some flavors of Unix.
+.. function:: kill(pid, sig)
+.. index::
+single: process; killing
+single: process; signalling
+Send signal *sig* to the process *pid*.  Constants for the specific signals
+available on the host platform are defined in the :mod:`signal` module.
+Availability: Unix.
+.. function:: killpg(pgid, sig)
+.. index::
+single: process; killing
+single: process; signalling
+Send the signal *sig* to the process group *pgid*. Availability: Unix.
+.. versionadded:: 2.3
+.. function:: nice(increment)
+Add *increment* to the process's "niceness".  Return the new niceness.
+Availability: Unix.
+.. function:: plock(op)
+Lock program segments into memory.  The value of *op* (defined in
+``<sys/lock.h>``) determines which segments are locked. Availability: Unix.
+.. function:: popen(...)
+popen2(...)
+popen3(...)
+popen4(...)
+:noindex:
+Run child processes, returning opened pipes for communications.  These functions
+are described in section :ref:`os-newstreams`.
+.. function:: spawnl(mode, path, ...)
+spawnle(mode, path, ..., env)
+spawnlp(mode, file, ...)
+spawnlpe(mode, file, ..., env)
+spawnv(mode, path, args)
+spawnve(mode, path, args, env)
+spawnvp(mode, file, args)
+spawnvpe(mode, file, args, env)
+Execute the program *path* in a new process.
+(Note that the :mod:`subprocess` module provides more powerful facilities for
+spawning new processes and retrieving their results; using that module is
+preferable to using these functions.  Check specially the *Replacing Older
+Functions with the subprocess Module* section in that documentation page.)
+If *mode* is :const:`P_NOWAIT`, this function returns the process id of the new
+process; if *mode* is :const:`P_WAIT`, returns the process's exit code if it
+exits normally, or ``-signal``, where *signal* is the signal that killed the
+process.  On Windows, the process id will actually be the process handle, so can
+be used with the :func:`waitpid` function.
+The "l" and "v" variants of the :func:`spawn\*` functions differ in how
+command-line arguments are passed.  The "l" variants are perhaps the easiest
+to work with if the number of parameters is fixed when the code is written; the
+individual parameters simply become additional parameters to the
+:func:`spawnl\*` functions.  The "v" variants are good when the number of
+parameters is variable, with the arguments being passed in a list or tuple as
+the *args* parameter.  In either case, the arguments to the child process must
+start with the name of the command being run.
+The variants which include a second "p" near the end (:func:`spawnlp`,
+:func:`spawnlpe`, :func:`spawnvp`, and :func:`spawnvpe`) will use the
+:envvar:`PATH` environment variable to locate the program *file*.  When the
+environment is being replaced (using one of the :func:`spawn\*e` variants,
+discussed in the next paragraph), the new environment is used as the source of
+the :envvar:`PATH` variable.  The other variants, :func:`spawnl`,
+:func:`spawnle`, :func:`spawnv`, and :func:`spawnve`, will not use the
+:envvar:`PATH` variable to locate the executable; *path* must contain an
+appropriate absolute or relative path.
+For :func:`spawnle`, :func:`spawnlpe`, :func:`spawnve`, and :func:`spawnvpe`
+(note that these all end in "e"), the *env* parameter must be a mapping
+which is used to define the environment variables for the new process (they are
+used instead of the current process' environment); the functions
+:func:`spawnl`, :func:`spawnlp`, :func:`spawnv`, and :func:`spawnvp` all cause
+the new process to inherit the environment of the current process.
+As an example, the following calls to :func:`spawnlp` and :func:`spawnvpe` are
+equivalent::
+import os
+os.spawnlp(os.P_WAIT, 'cp', 'cp', 'index.html', '/dev/null')
+L = ['cp', 'index.html', '/dev/null']
+os.spawnvpe(os.P_WAIT, 'cp', L, os.environ)
+Availability: Unix, Windows.  :func:`spawnlp`, :func:`spawnlpe`, :func:`spawnvp`
+and :func:`spawnvpe` are not available on Windows.
+.. versionadded:: 1.6
+.. data:: P_NOWAIT
+P_NOWAITO
+Possible values for the *mode* parameter to the :func:`spawn\*` family of
+functions.  If either of these values is given, the :func:`spawn\*` functions
+will return as soon as the new process has been created, with the process id as
+the return value. Availability: Unix, Windows.
+.. versionadded:: 1.6
+.. data:: P_WAIT
+Possible value for the *mode* parameter to the :func:`spawn\*` family of
+functions.  If this is given as *mode*, the :func:`spawn\*` functions will not
+return until the new process has run to completion and will return the exit code
+of the process the run is successful, or ``-signal`` if a signal kills the
+process. Availability: Unix, Windows.
+.. versionadded:: 1.6
+.. data:: P_DETACH
+P_OVERLAY
+Possible values for the *mode* parameter to the :func:`spawn\*` family of
+functions.  These are less portable than those listed above. :const:`P_DETACH`
+is similar to :const:`P_NOWAIT`, but the new process is detached from the
+console of the calling process. If :const:`P_OVERLAY` is used, the current
+process will be replaced; the :func:`spawn\*` function will not return.
+Availability: Windows.
+.. versionadded:: 1.6
+.. function:: startfile(path[, operation])
+Start a file with its associated application.
+When *operation* is not specified or ``'open'``, this acts like double-clicking
+the file in Windows Explorer, or giving the file name as an argument to the
+:program:`start` command from the interactive command shell: the file is opened
+with whatever application (if any) its extension is associated.
+When another *operation* is given, it must be a "command verb" that specifies
+what should be done with the file. Common verbs documented by Microsoft are
+``'print'`` and  ``'edit'`` (to be used on files) as well as ``'explore'`` and
+``'find'`` (to be used on directories).
+:func:`startfile` returns as soon as the associated application is launched.
+There is no option to wait for the application to close, and no way to retrieve
+the application's exit status.  The *path* parameter is relative to the current
+directory.  If you want to use an absolute path, make sure the first character
+is not a slash (``'/'``); the underlying Win32 :cfunc:`ShellExecute` function
+doesn't work if it is.  Use the :func:`os.path.normpath` function to ensure that
+the path is properly encoded for Win32. Availability: Windows.
+.. versionadded:: 2.0
+.. versionadded:: 2.5
+The *operation* parameter.
+.. function:: system(command)
+Execute the command (a string) in a subshell.  This is implemented by calling
+the Standard C function :cfunc:`system`, and has the same limitations.  Changes
+to :data:`os.environ`, :data:`sys.stdin`, etc. are not reflected in the
+environment of the executed command.
+On Unix, the return value is the exit status of the process encoded in the
+format specified for :func:`wait`.  Note that POSIX does not specify the meaning
+of the return value of the C :cfunc:`system` function, so the return value of
+the Python function is system-dependent.
+On Windows, the return value is that returned by the system shell after running
+*command*, given by the Windows environment variable :envvar:`COMSPEC`: on
+:program:`command.com` systems (Windows 95, 98 and ME) this is always ``0``; on
+:program:`cmd.exe` systems (Windows NT, 2000 and XP) this is the exit status of
+the command run; on systems using a non-native shell, consult your shell
+documentation.
+Availability: Unix, Windows.
+The :mod:`subprocess` module provides more powerful facilities for spawning new
+processes and retrieving their results; using that module is preferable to using
+this function.  Use the :mod:`subprocess` module.  Check especially the
+:ref:`subprocess-replacements` section.
+.. function:: times()
+Return a 5-tuple of floating point numbers indicating accumulated (processor or
+other) times, in seconds.  The items are: user time, system time, children's
+user time, children's system time, and elapsed real time since a fixed point in
+the past, in that order.  See the Unix manual page :manpage:`times(2)` or the
+corresponding Windows Platform API documentation. Availability: Unix,
+Windows.  On Windows, only the first two items are filled, the others are zero.
+.. function:: wait()
+Wait for completion of a child process, and return a tuple containing its pid
+and exit status indication: a 16-bit number, whose low byte is the signal number
+that killed the process, and whose high byte is the exit status (if the signal
+number is zero); the high bit of the low byte is set if a core file was
+produced. Availability: Unix.
+.. function:: waitpid(pid, options)
+The details of this function differ on Unix and Windows.
+On Unix: Wait for completion of a child process given by process id *pid*, and
+return a tuple containing its process id and exit status indication (encoded as
+for :func:`wait`).  The semantics of the call are affected by the value of the
+integer *options*, which should be ``0`` for normal operation.
+If *pid* is greater than ``0``, :func:`waitpid` requests status information for
+that specific process.  If *pid* is ``0``, the request is for the status of any
+child in the process group of the current process.  If *pid* is ``-1``, the
+request pertains to any child of the current process.  If *pid* is less than
+``-1``, status is requested for any process in the process group ``-pid`` (the
+absolute value of *pid*).
+An :exc:`OSError` is raised with the value of errno when the syscall
+returns -1.
+On Windows: Wait for completion of a process given by process handle *pid*, and
+return a tuple containing *pid*, and its exit status shifted left by 8 bits
+(shifting makes cross-platform use of the function easier). A *pid* less than or
+equal to ``0`` has no special meaning on Windows, and raises an exception. The
+value of integer *options* has no effect. *pid* can refer to any process whose
+id is known, not necessarily a child process. The :func:`spawn` functions called
+with :const:`P_NOWAIT` return suitable process handles.
+.. function:: wait3([options])
+Similar to :func:`waitpid`, except no process id argument is given and a
+3-element tuple containing the child's process id, exit status indication, and
+resource usage information is returned.  Refer to :mod:`resource`.\
+:func:`getrusage` for details on resource usage information.  The option
+argument is the same as that provided to :func:`waitpid` and :func:`wait4`.
+Availability: Unix.
+.. versionadded:: 2.5
+.. function:: wait4(pid, options)
+Similar to :func:`waitpid`, except a 3-element tuple, containing the child's
+process id, exit status indication, and resource usage information is returned.
+Refer to :mod:`resource`.\ :func:`getrusage` for details on resource usage
+information.  The arguments to :func:`wait4` are the same as those provided to
+:func:`waitpid`. Availability: Unix.
+.. versionadded:: 2.5
+.. data:: WNOHANG
+The option for :func:`waitpid` to return immediately if no child process status
+is available immediately. The function returns ``(0, 0)`` in this case.
+Availability: Unix.
+.. data:: WCONTINUED
+This option causes child processes to be reported if they have been continued
+from a job control stop since their status was last reported. Availability: Some
+Unix systems.
+.. versionadded:: 2.3
+.. data:: WUNTRACED
+This option causes child processes to be reported if they have been stopped but
+their current state has not been reported since they were stopped. Availability:
+Unix.
+.. versionadded:: 2.3
+The following functions take a process status code as returned by
+:func:`system`, :func:`wait`, or :func:`waitpid` as a parameter.  They may be
+used to determine the disposition of a process.
+.. function:: WCOREDUMP(status)
+Return ``True`` if a core dump was generated for the process, otherwise
+return ``False``. Availability: Unix.
+.. versionadded:: 2.3
+.. function:: WIFCONTINUED(status)
+Return ``True`` if the process has been continued from a job control stop,
+otherwise return ``False``. Availability: Unix.
+.. versionadded:: 2.3
+.. function:: WIFSTOPPED(status)
+Return ``True`` if the process has been stopped, otherwise return
+``False``. Availability: Unix.
+.. function:: WIFSIGNALED(status)
+Return ``True`` if the process exited due to a signal, otherwise return
+``False``. Availability: Unix.
+.. function:: WIFEXITED(status)
+Return ``True`` if the process exited using the :manpage:`exit(2)` system call,
+otherwise return ``False``. Availability: Unix.
+.. function:: WEXITSTATUS(status)
+If ``WIFEXITED(status)`` is true, return the integer parameter to the
+:manpage:`exit(2)` system call.  Otherwise, the return value is meaningless.
+Availability: Unix.
+.. function:: WSTOPSIG(status)
+Return the signal which caused the process to stop. Availability: Unix.
+.. function:: WTERMSIG(status)
+Return the signal which caused the process to exit. Availability: Unix.
+.. _os-path:
+Miscellaneous System Information
+--------------------------------
+.. function:: confstr(name)
+Return string-valued system configuration values. *name* specifies the
+configuration value to retrieve; it may be a string which is the name of a
+defined system value; these names are specified in a number of standards (POSIX,
+Unix 95, Unix 98, and others).  Some platforms define additional names as well.
+The names known to the host operating system are given as the keys of the
+``confstr_names`` dictionary.  For configuration variables not included in that
+mapping, passing an integer for *name* is also accepted. Availability:
+Unix.
+If the configuration value specified by *name* isn't defined, ``None`` is
+returned.
+If *name* is a string and is not known, :exc:`ValueError` is raised.  If a
+specific value for *name* is not supported by the host system, even if it is
+included in ``confstr_names``, an :exc:`OSError` is raised with
+:const:`errno.EINVAL` for the error number.
+.. data:: confstr_names
+Dictionary mapping names accepted by :func:`confstr` to the integer values
+defined for those names by the host operating system. This can be used to
+determine the set of names known to the system. Availability: Unix.
+.. function:: getloadavg()
+Return the number of processes in the system run queue averaged over the last
+1, 5, and 15 minutes or raises :exc:`OSError` if the load average was
+unobtainable.  Availability: Unix.
+.. versionadded:: 2.3
+.. function:: sysconf(name)
+Return integer-valued system configuration values. If the configuration value
+specified by *name* isn't defined, ``-1`` is returned.  The comments regarding
+the *name* parameter for :func:`confstr` apply here as well; the dictionary that
+provides information on the known names is given by ``sysconf_names``.
+Availability: Unix.
+.. data:: sysconf_names
+Dictionary mapping names accepted by :func:`sysconf` to the integer values
+defined for those names by the host operating system. This can be used to
+determine the set of names known to the system. Availability: Unix.
+The following data values are used to support path manipulation operations.  These
+are defined for all platforms.
+Higher-level operations on pathnames are defined in the :mod:`os.path` module.
+.. data:: curdir
+The constant string used by the operating system to refer to the current
+directory. This is ``'.'`` for Windows and POSIX. Also available via
+:mod:`os.path`.
+.. data:: pardir
+The constant string used by the operating system to refer to the parent
+directory. This is ``'..'`` for Windows and POSIX. Also available via
+:mod:`os.path`.
+.. data:: sep
+The character used by the operating system to separate pathname components.
+This is ``'/'`` for POSIX and ``'\\'`` for Windows.  Note that knowing this
+is not sufficient to be able to parse or concatenate pathnames --- use
+:func:`os.path.split` and :func:`os.path.join` --- but it is occasionally
+useful. Also available via :mod:`os.path`.
+.. data:: altsep
+An alternative character used by the operating system to separate pathname
+components, or ``None`` if only one separator character exists.  This is set to
+``'/'`` on Windows systems where ``sep`` is a backslash. Also available via
+:mod:`os.path`.
+.. data:: extsep
+The character which separates the base filename from the extension; for example,
+the ``'.'`` in :file:`os.py`. Also available via :mod:`os.path`.
+.. versionadded:: 2.2
+.. data:: pathsep
+The character conventionally used by the operating system to separate search
+path components (as in :envvar:`PATH`), such as ``':'`` for POSIX or ``';'`` for
+Windows. Also available via :mod:`os.path`.
+.. data:: defpath
+The default search path used by :func:`exec\*p\*` and :func:`spawn\*p\*` if the
+environment doesn't have a ``'PATH'`` key. Also available via :mod:`os.path`.
+.. data:: linesep
+The string used to separate (or, rather, terminate) lines on the current
+platform.  This may be a single character, such as ``'\n'`` for POSIX, or
+multiple characters, for example, ``'\r\n'`` for Windows. Do not use
+*os.linesep* as a line terminator when writing files opened in text mode (the
+default); use a single ``'\n'`` instead, on all platforms.
+.. data:: devnull
+The file path of the null device. For example: ``'/dev/null'`` for POSIX.
+Also available via :mod:`os.path`.
+.. versionadded:: 2.4
+.. _os-miscfunc:
+Miscellaneous Functions
+-----------------------
+.. function:: urandom(n)
+Return a string of *n* random bytes suitable for cryptographic use.
+This function returns random bytes from an OS-specific randomness source.  The
+returned data should be unpredictable enough for cryptographic applications,
+though its exact quality depends on the OS implementation.  On a UNIX-like
+system this will query /dev/urandom, and on Windows it will use CryptGenRandom.
+If a randomness source is not found, :exc:`NotImplementedError` will be raised.
+.. versionadded:: 2.4