589 lines
21 KiB
TeX
589 lines
21 KiB
TeX
\section{\module{posix} ---
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The most common \POSIX{} system calls.}
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\declaremodule{builtin}{posix}
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\modulesynopsis{The most common \POSIX{} system calls (normally used
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via module \module{os}).}
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This module provides access to operating system functionality that is
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standardized by the \C{} Standard and the \POSIX{} standard (a thinly
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disguised \UNIX{} interface).
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\strong{Do not import this module directly.} Instead, import the
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module \module{os}, which provides a \emph{portable} version of this
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interface. On \UNIX{}, the \module{os} module provides a superset of
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the \module{posix} interface. On non-\UNIX{} operating systems the
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\module{posix} module is not available, but a subset is always
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available through the \module{os} interface. Once \module{os} is
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imported, there is \emph{no} performance penalty in using it instead
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of \module{posix}. In addition, \module{os}\refstmodindex{os}
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provides some additional functionality, such as automatically calling
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\function{putenv()} when an entry in \code{os.environ} is changed.
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The descriptions below are very terse; refer to the corresponding
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\UNIX{} manual (or \POSIX{} documentation) entry for more information.
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Arguments called \var{path} refer to a pathname given as a string.
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Errors are reported as exceptions; the usual exceptions are given for
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type errors, while errors reported by the system calls raise
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\exception{error} (a synonym for the standard exception
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\exception{OSError}), described below.
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\subsection{Large File Support \label{posix-large-files}}
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\index{large files}
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\index{file!large files}
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\sectionauthor{Steve Clift}{clift@mail.anacapa.net}
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Several operating systems (including AIX, HPUX, Irix and Solaris)
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provide support for files that are larger than 2 Gb from a \C{}
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programming model where \ctype{int} and \ctype{long} are 32-bit
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values. This is typically accomplished by defining the relevant size
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and offset types as 64-bit values. Such files are sometimes referred
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to as \dfn{large files}.
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Large file support is enabled in Python when the size of an
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\ctype{off_t} is larger than a \ctype{long} and the \ctype{long long}
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type is available and is at least as large as an \ctype{off_t}. Python
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longs are then used to represent file sizes, offsets and other values
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that can exceed the range of a Python int. It may be necessary to
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configure and compile Python with certain compiler flags to enable
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this mode. For example, it is enabled by default with recent versions
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of Irix, but with Solaris 2.6 and 2.7 you need to do something like:
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\begin{verbatim}
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CFLAGS="-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64" OPT="-g -O2 $CFLAGS" \
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configure
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\end{verbatim} % $ <-- bow to font-lock
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\subsection{\module{posix} Module Contents \label{posix-contents}}
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Module \module{posix} defines the following data items:
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\begin{datadesc}{environ}
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A dictionary or dictionary look-alike representing the string
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environment at the time the interpreter was started. For example,
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\code{posix.environ['HOME']} is the pathname of your home directory,
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equivalent to \code{getenv("HOME")} in \C{}.
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Modifying this dictionary does not affect the string environment
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passed on by \function{execv()}, \function{popen()} or
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\function{system()}; if you need to change the environment, pass
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\code{environ} to \function{execve()} or add variable assignments and
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export statements to the command string for \function{system()} or
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\function{popen()}.
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\emph{However:} If you are using this module via the \module{os}
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module (as you should -- see the introduction above), \code{environ}
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is a a mapping object that behaves almost like a dictionary but
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invokes \function{putenv()} automatically whenever an item is changed.
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\end{datadesc}
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\begin{excdesc}{error}
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This exception is raised when a \POSIX{} function returns a
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\POSIX{}-related error (e.g., not for illegal argument types). The
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accompanying value is a pair containing the numeric error code from
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\cdata{errno} and the corresponding string, as would be printed by the
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\C{} function \cfunction{perror()}. See the module
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\module{errno}\refbimodindex{errno}, which contains names for the
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error codes defined by the underlying operating system.
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When exceptions are classes, this exception carries two attributes,
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\member{errno} and \member{strerror}. The first holds the value of
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the \C{} \cdata{errno} variable, and the latter holds the
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corresponding error message from \cfunction{strerror()}. For
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exceptions that involve a file system path (e.g. \code{chdir} or
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\code{unlink}), the exception instance will contain a third attribute
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\member{filename} which is the file name passed to the
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function.
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When exceptions are strings, the string for the exception is
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\code{'OSError'}.
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\end{excdesc}
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It defines the following functions and constants when the operating
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system provides them directly or provides the means to emulate them:
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\begin{funcdesc}{access}{path, mode}
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Check read/write/execute permissions for this process or extance of file
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\var{path}. Return \code{1} if access is granted, \code{0} if not.
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See the \UNIX{} manual for the semantics.
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\end{funcdesc}
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\begin{funcdesc}{chdir}{path}
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Change the current working directory to \var{path}.
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\end{funcdesc}
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\begin{funcdesc}{chmod}{path, mode}
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Change the mode of \var{path} to the numeric \var{mode}.
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\end{funcdesc}
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\begin{funcdesc}{chown}{path, uid, gid}
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Change the owner and group id of \var{path} to the numeric \var{uid}
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and \var{gid}.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{close}{fd}
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Close file descriptor \var{fd}.
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Note: this function is intended for low-level I/O and must be applied
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to a file descriptor as returned by \function{open()} or
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\function{pipe()}. To close a ``file object'' returned by the
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built-in function \function{open()} or by \function{popen()} or
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\function{fdopen()}, use its \method{close()} method.
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\end{funcdesc}
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\begin{funcdesc}{dup}{fd}
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Return a duplicate of file descriptor \var{fd}.
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\end{funcdesc}
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\begin{funcdesc}{dup2}{fd, fd2}
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Duplicate file descriptor \var{fd} to \var{fd2}, closing the latter
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first if necessary.
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\end{funcdesc}
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\begin{funcdesc}{execv}{path, args}
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Execute the executable \var{path} with argument list \var{args},
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replacing the current process (i.e., the Python interpreter).
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The argument list may be a tuple or list of strings.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{execve}{path, args, env}
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Execute the executable \var{path} with argument list \var{args},
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and environment \var{env},
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replacing the current process (i.e., the Python interpreter).
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The argument list may be a tuple or list of strings.
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The environment must be a dictionary mapping strings to strings.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{_exit}{n}
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Exit to the system with status \var{n}, without calling cleanup
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handlers, flushing stdio buffers, etc.
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(Not on MS-DOS.)
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Note: the standard way to exit is \code{sys.exit(\var{n})}.
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\function{_exit()} should normally only be used in the child process
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after a \function{fork()}.
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\end{funcdesc}
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\begin{funcdesc}{fdopen}{fd\optional{, mode\optional{, bufsize}}}
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Return an open file object connected to the file descriptor \var{fd}.
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The \var{mode} and \var{bufsize} arguments have the same meaning as
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the corresponding arguments to the built-in \function{open()} function.
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\end{funcdesc}
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\begin{funcdesc}{fork}{}
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Fork a child process. Return \code{0} in the child, the child's
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process id in the parent.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{fstat}{fd}
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Return status for file descriptor \var{fd}, like \function{stat()}.
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\end{funcdesc}
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\begin{funcdesc}{fstatvfs}{fd}
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Return information about the filesystem containing the file associated
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with file descriptor \var{fd}, like \function{statvfs()}.
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\end{funcdesc}
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\begin{funcdesc}{ftruncate}{fd, length}
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Truncate the file corresponding to file descriptor \var{fd},
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so that it is at most \var{length} bytes in size.
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\end{funcdesc}
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\begin{funcdesc}{getcwd}{}
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Return a string representing the current working directory.
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\end{funcdesc}
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\begin{funcdesc}{getegid}{}
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Return the current process' effective group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{geteuid}{}
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Return the current process' effective user id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getgid}{}
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Return the current process' group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getpgrp}{}
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\index{process!group}
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Return the current process group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getpid}{}
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\index{process!id}
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Return the current process id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getppid}{}
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\index{process!id of parent}
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Return the parent's process id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getuid}{}
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\index{user id}
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Return the current process' user id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{kill}{pid, sig}
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\index{process!killing}
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\index{process!signalling}
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Kill the process \var{pid} with signal \var{sig}.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{link}{src, dst}
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Create a hard link pointing to \var{src} named \var{dst}.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{listdir}{path}
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Return a list containing the names of the entries in the directory.
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The list is in arbitrary order. It does not include the special
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entries \code{'.'} and \code{'..'} even if they are present in the
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directory.
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\end{funcdesc}
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\begin{funcdesc}{lseek}{fd, pos, how}
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Set the current position of file descriptor \var{fd} to position
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\var{pos}, modified by \var{how}: \code{0} to set the position
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relative to the beginning of the file; \code{1} to set it relative to
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the current position; \code{2} to set it relative to the end of the
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file.
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\end{funcdesc}
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\begin{funcdesc}{lstat}{path}
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Like \function{stat()}, but do not follow symbolic links. (On systems
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without symbolic links, this is identical to \function{stat()}.)
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\end{funcdesc}
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\begin{funcdesc}{mkfifo}{path\optional{, mode}}
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Create a FIFO (a \POSIX{} named pipe) named \var{path} with numeric mode
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\var{mode}. The default \var{mode} is \code{0666} (octal). The current
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umask value is first masked out from the mode.
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(Not on MS-DOS.)
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FIFOs are pipes that can be accessed like regular files. FIFOs exist
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until they are deleted (for example with \function{os.unlink()}).
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Generally, FIFOs are used as rendezvous between ``client'' and
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``server'' type processes: the server opens the FIFO for reading, and
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the client opens it for writing. Note that \function{mkfifo()}
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doesn't open the FIFO --- it just creates the rendezvous point.
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\end{funcdesc}
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\begin{funcdesc}{mkdir}{path\optional{, mode}}
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Create a directory named \var{path} with numeric mode \var{mode}.
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The default \var{mode} is \code{0777} (octal). On some systems,
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\var{mode} is ignored. Where it is used, the current umask value is
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first masked out.
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\end{funcdesc}
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\begin{funcdesc}{nice}{increment}
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Add \var{increment} to the process' ``niceness''. Return the new
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niceness. (Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{open}{file, flags\optional{, mode}}
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Open the file \var{file} and set various flags according to
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\var{flags} and possibly its mode according to \var{mode}.
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The default \var{mode} is \code{0777} (octal), and the current umask
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value is first masked out. Return the file descriptor for the newly
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opened file.
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For a description of the flag and mode values, see the \UNIX{} or \C{}
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run-time documentation; flag constants (like \constant{O_RDONLY} and
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\constant{O_WRONLY}) are defined in this module too (see below).
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Note: this function is intended for low-level I/O. For normal usage,
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use the built-in function \function{open()}, which returns a ``file
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object'' with \method{read()} and \method{write()} methods (and many
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more).
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\end{funcdesc}
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\begin{funcdesc}{pipe}{}
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Create a pipe. Return a pair of file descriptors \code{(\var{r},
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\var{w})} usable for reading and writing, respectively.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{plock}{op}
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Lock program segments into memory. The value of \var{op}
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(defined in \code{<sys/lock.h>}) determines which segments are locked.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{popen}{command\optional{, mode\optional{, bufsize}}}
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Open a pipe to or from \var{command}. The return value is an open
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file object connected to the pipe, which can be read or written
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depending on whether \var{mode} is \code{'r'} (default) or \code{'w'}.
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The \var{bufsize} argument has the same meaning as the corresponding
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argument to the built-in \function{open()} function. The exit status of
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the command (encoded in the format specified for \function{wait()}) is
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available as the return value of the \method{close()} method of the file
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object, except that when the exit status is zero (termination without
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errors), \code{None} is returned.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{putenv}{varname, value}
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\index{environment variables!setting}
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Set the environment variable named \var{varname} to the string
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\var{value}. Such changes to the environment affect subprocesses
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started with \function{os.system()}, \function{os.popen()} or
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\function{os.fork()} and \function{os.execv()}. (Not on all systems.)
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When \function{putenv()} is
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supported, assignments to items in \code{os.environ} are automatically
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translated into corresponding calls to \function{putenv()}; however,
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calls to \function{putenv()} don't update \code{os.environ}, so it is
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actually preferable to assign to items of \code{os.environ}.
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\end{funcdesc}
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\begin{funcdesc}{strerror}{code}
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Return the error message corresponding to the error code in \var{code}.
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\end{funcdesc}
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\begin{funcdesc}{ttyname}{fd}
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Return a string which specifies the terminal device associated with
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file-descriptor \var{fd}. If \var{fd} is not associated with a terminal
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device, an exception is raised.
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\end{funcdesc}
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\begin{funcdesc}{read}{fd, n}
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Read at most \var{n} bytes from file descriptor \var{fd}.
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Return a string containing the bytes read.
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Note: this function is intended for low-level I/O and must be applied
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to a file descriptor as returned by \function{open()} or
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\function{pipe()}. To read a ``file object'' returned by the
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built-in function \function{open()} or by \function{popen()} or
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\function{fdopen()}, or \code{sys.stdin}, use its
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\method{read()} or \method{readline()} methods.
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\end{funcdesc}
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\begin{funcdesc}{readlink}{path}
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Return a string representing the path to which the symbolic link
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points. (On systems without symbolic links, this always raises
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\exception{error}.)
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\end{funcdesc}
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\begin{funcdesc}{remove}{path}
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Remove the file \var{path}. See \function{rmdir()} below to remove a
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directory. This is identical to the \function{unlink()} function
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documented below.
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\end{funcdesc}
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\begin{funcdesc}{rename}{src, dst}
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Rename the file or directory \var{src} to \var{dst}.
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\end{funcdesc}
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\begin{funcdesc}{rmdir}{path}
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Remove the directory \var{path}.
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\end{funcdesc}
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\begin{funcdesc}{setgid}{gid}
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Set the current process' group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setpgrp}{}
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Calls the system call \cfunction{setpgrp()} or \cfunction{setpgrp(0,
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0)} depending on which version is implemented (if any). See the
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\UNIX{} manual for the semantics.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setpgid}{pid, pgrp}
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Calls the system call \cfunction{setpgid()}. See the \UNIX{} manual
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for the semantics.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setsid}{}
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Calls the system call \cfunction{setsid()}. See the \UNIX{} manual
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for the semantics.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setuid}{uid}
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Set the current process' user id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{stat}{path}
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Perform a \cfunction{stat()} system call on the given path. The
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return value is a tuple of at least 10 integers giving the most
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important (and portable) members of the \emph{stat} structure, in the
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order
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\code{st_mode},
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\code{st_ino},
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\code{st_dev},
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\code{st_nlink},
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\code{st_uid},
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\code{st_gid},
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\code{st_size},
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\code{st_atime},
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\code{st_mtime},
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\code{st_ctime}.
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More items may be added at the end by some implementations.
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(On MS-DOS, some items are filled with dummy values.)
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Note: The standard module \module{stat}\refstmodindex{stat} defines
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functions and constants that are useful for extracting information
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from a \ctype{stat} structure.
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\end{funcdesc}
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\begin{funcdesc}{statvfs}{path}
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Perform a \cfunction{statvfs()} system call on the given path. The
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return value is a tuple of 11 integers giving the most common
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members of the \ctype{statvfs} structure, in the order
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\code{f_bsize},
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\code{f_frsize},
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\code{f_blocks},
|
|
\code{f_bfree},
|
|
\code{f_bavail},
|
|
\code{f_files},
|
|
\code{f_ffree},
|
|
\code{f_favail},
|
|
\code{f_fsid},
|
|
\code{f_flag},
|
|
\code{f_namemax}.
|
|
|
|
Note: The standard module \module{statvfs}\refstmodindex{statvfs}
|
|
defines constants that are useful for extracting information
|
|
from a \ctype{statvfs} structure.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{symlink}{src, dst}
|
|
Create a symbolic link pointing to \var{src} named \var{dst}. (On
|
|
systems without symbolic links, this always raises \exception{error}.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{system}{command}
|
|
Execute the command (a string) in a subshell. This is implemented by
|
|
calling the Standard \C{} function \cfunction{system()}, and has the
|
|
same limitations. Changes to \code{posix.environ}, \code{sys.stdin}
|
|
etc.\ are not reflected in the environment of the executed command.
|
|
The return value is the exit status of the process encoded in the
|
|
format specified for \function{wait()}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{tcgetpgrp}{fd}
|
|
Return the process group associated with the terminal given by
|
|
\var{fd} (an open file descriptor as returned by \function{open()}).
|
|
(Not on MS-DOS.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{tcsetpgrp}{fd, pg}
|
|
Set the process group associated with the terminal given by
|
|
\var{fd} (an open file descriptor as returned by \function{open()})
|
|
to \var{pg}.
|
|
(Not on MS-DOS.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{times}{}
|
|
Return a 5-tuple of floating point numbers indicating accumulated (CPU
|
|
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}. (Not on MS-DOS.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{umask}{mask}
|
|
Set the current numeric umask and returns the previous umask.
|
|
(Not on MS-DOS.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{uname}{}
|
|
Return a 5-tuple containing information identifying the current
|
|
operating system. The tuple contains 5 strings:
|
|
\code{(\var{sysname}, \var{nodename}, \var{release}, \var{version},
|
|
\var{machine})}. Some systems truncate the nodename to 8
|
|
characters or to the leading component; a better way to get the
|
|
hostname is \function{socket.gethostname()}%
|
|
\withsubitem{(in module socket)}{\ttindex{gethostname()}}
|
|
or even
|
|
\code{socket.gethostbyaddr(socket.gethostname())}%
|
|
\withsubitem{(in module socket)}{\ttindex{gethostbyaddr()}}.
|
|
(Not on MS-DOS, nor on older \UNIX{} systems.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{unlink}{path}
|
|
Remove the file \var{path}. This is the same function as \code{remove};
|
|
the \code{unlink} name is its traditional \UNIX{} name.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{utime}{path, (atime, mtime)}
|
|
Set the access and modified time of the file to the given values.
|
|
(The second argument is a tuple of two items.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{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. (Not on MS-DOS.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{waitpid}{pid, options}
|
|
Wait for completion of a child process given by proces id, and return
|
|
a tuple containing its pid and exit status indication (encoded as for
|
|
\function{wait()}). The semantics of the call are affected by the
|
|
value of the integer \var{options}, which should be \code{0} for
|
|
normal operation. (If the system does not support
|
|
\function{waitpid()}, this always raises \exception{error}. Not on
|
|
MS-DOS.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{write}{fd, str}
|
|
Write the string \var{str} to file descriptor \var{fd}.
|
|
Return the number of bytes actually written.
|
|
|
|
Note: this function is intended for low-level I/O and must be applied
|
|
to a file descriptor as returned by \function{open()} or
|
|
\function{pipe()}. To write a ``file object'' returned by the
|
|
built-in function \function{open()} or by \function{popen()} or
|
|
\function{fdopen()}, or \code{sys.stdout} or \code{sys.stderr}, use
|
|
its \method{write()} method.
|
|
\end{funcdesc}
|
|
|
|
\begin{datadesc}{WNOHANG}
|
|
The option for \function{waitpid()} to avoid hanging if no child
|
|
process status is available immediately.
|
|
\end{datadesc}
|
|
|
|
|
|
\begin{datadesc}{O_RDONLY}
|
|
\dataline{O_WRONLY}
|
|
\dataline{O_RDWR}
|
|
\dataline{O_NDELAY}
|
|
\dataline{O_NONBLOCK}
|
|
\dataline{O_APPEND}
|
|
\dataline{O_DSYNC}
|
|
\dataline{O_RSYNC}
|
|
\dataline{O_SYNC}
|
|
\dataline{O_NOCTTY}
|
|
\dataline{O_CREAT}
|
|
\dataline{O_EXCL}
|
|
\dataline{O_TRUNC}
|
|
Options for the \code{flag} argument to the \function{open()} function.
|
|
These can be bit-wise OR'd together.
|
|
\end{datadesc}
|