PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

FPATHCONF(3P)             POSIX Programmer's Manual            FPATHCONF(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       fpathconf, pathconf — get configurable pathname variables

SYNOPSIS         top

       #include <unistd.h>

       long fpathconf(int fildes, int name);
       long pathconf(const char *path, int name);

DESCRIPTION         top

       The fpathconf() and pathconf() functions shall determine the current
       value of a configurable limit or option (variable) that is associated
       with a file or directory.

       For pathconf(), the path argument points to the pathname of a file or
       directory.

       For fpathconf(), the fildes argument is an open file descriptor.

       The name argument represents the variable to be queried relative to
       that file or directory. Implementations shall support all of the
       variables listed in the following table and may support others. The
       variables in the following table come from <limits.h> or <unistd.h>
       and the symbolic constants, defined in <unistd.h>, are the
       corresponding values used for name.

      ┌────────────────────────────┬──────────────────────────┬──────────────┐
      │         Variable           Value of nameRequirements │
      ├────────────────────────────┼──────────────────────────┼──────────────┤
      │{FILESIZEBITS}              │ _PC_FILESIZEBITS         │ 4,7          │
      │{LINK_MAX}                  │ _PC_LINK_MAX             │ 1            │
      │{MAX_CANON}                 │ _PC_MAX_CANON            │ 2            │
      │{MAX_INPUT}                 │ _PC_MAX_INPUT            │ 2            │
      │{NAME_MAX}                  │ _PC_NAME_MAX             │ 3,4          │
      │{PATH_MAX}                  │ _PC_PATH_MAX             │ 4,5          │
      │{PIPE_BUF}                  │ _PC_PIPE_BUF             │ 6            │
      │{POSIX2_SYMLINKS}           │ _PC_2_SYMLINKS           │ 4            │
      │{POSIX_ALLOC_SIZE_MIN}      │ _PC_ALLOC_SIZE_MIN       │ 10           │
      │{POSIX_REC_INCR_XFER_SIZE}  │ _PC_REC_INCR_XFER_SIZE   │ 10           │
      │{POSIX_REC_MAX_XFER_SIZE}   │ _PC_REC_MAX_XFER_SIZE    │ 10           │
      │{POSIX_REC_MIN_XFER_SIZE}   │ _PC_REC_MIN_XFER_SIZE    │ 10           │
      │{POSIX_REC_XFER_ALIGN}      │ _PC_REC_XFER_ALIGN       │ 10           │
      │{SYMLINK_MAX}               │ _PC_SYMLINK_MAX          │ 4,9          │
      │_POSIX_CHOWN_RESTRICTED     │ _PC_CHOWN_RESTRICTED     │ 7            │
      │_POSIX_NO_TRUNC             │ _PC_NO_TRUNC             │ 3,4          │
      │_POSIX_VDISABLE             │ _PC_VDISABLE             │ 2            │
      │_POSIX_ASYNC_IO             │ _PC_ASYNC_IO             │ 8            │
      │_POSIX_PRIO_IO              │ _PC_PRIO_IO              │ 8            │
      │_POSIX_SYNC_IO              │ _PC_SYNC_IO              │ 8            │
      │_POSIX_TIMESTAMP_RESOLUTION │ _PC_TIMESTAMP_RESOLUTION │ 1            │
      └────────────────────────────┴──────────────────────────┴──────────────┘
   Requirements
        1. If path or fildes refers to a directory, the value returned shall
           apply to the directory itself.

        2. If path or fildes does not refer to a terminal file, it is
           unspecified whether an implementation supports an association of
           the variable name with the specified file.

        3. If path or fildes refers to a directory, the value returned shall
           apply to filenames within the directory.

        4. If path or fildes does not refer to a directory, it is
           unspecified whether an implementation supports an association of
           the variable name with the specified file.

        5. If path or fildes refers to a directory, the value returned shall
           be the maximum length of a relative pathname that would not cross
           any mount points when the specified directory is the working
           directory.

        6. If path refers to a FIFO, or fildes refers to a pipe or FIFO, the
           value returned shall apply to the referenced object. If path or
           fildes refers to a directory, the value returned shall apply to
           any FIFO that exists or can be created within the directory. If
           path or fildes refers to any other type of file, it is
           unspecified whether an implementation supports an association of
           the variable name with the specified file.

        7. If path or fildes refers to a directory, the value returned shall
           apply to any files, other than directories, that exist or can be
           created within the directory.

        8. If path or fildes refers to a directory, it is unspecified
           whether an implementation supports an association of the variable
           name with the specified file.

        9. If path or fildes refers to a directory, the value returned shall
           be the maximum length of the string that a symbolic link in that
           directory can contain.

       10. If path or fildes des does not refer to a regular file, it is
           unspecified whether an implementation supports an association of
           the variable name with the specified file. If an implementation
           supports such an association for other than a regular file, the
           value returned is unspecified.

RETURN VALUE         top

       If name is an invalid value, both pathconf() and fpathconf() shall
       return −1 and set errno to indicate the error.

       If the variable corresponding to name is described in <limits.h> as a
       maximum or minimum value and the variable has no limit for the path
       or file descriptor, both pathconf() and fpathconf() shall return −1
       without changing errno.  Note that indefinite limits do not imply
       infinite limits; see <limits.h>.

       If the implementation needs to use path to determine the value of
       name and the implementation does not support the association of name
       with the file specified by path, or if the process did not have
       appropriate privileges to query the file specified by path, or path
       does not exist, pathconf() shall return −1 and set errno to indicate
       the error.

       If the implementation needs to use fildes to determine the value of
       name and the implementation does not support the association of name
       with the file specified by fildes, or if fildes is an invalid file
       descriptor, fpathconf() shall return −1 and set errno to indicate the
       error.

       Otherwise, pathconf() or fpathconf() shall return the current
       variable value for the file or directory without changing errno.  The
       value returned shall not be more restrictive than the corresponding
       value available to the application when it was compiled with the
       implementation's <limits.h> or <unistd.h>.

       If the variable corresponding to name is dependent on an unsupported
       option, the results are unspecified.

ERRORS         top

       The pathconf() function shall fail if:

       EINVAL The value of name is not valid.

       ELOOP  A loop exists in symbolic links encountered during resolution
              of the path argument.

       EOVERFLOW
              The value of name is _PC_TIMESTAMP_RESOLUTION and the
              resolution is larger than {LONG_MAX}.

       The pathconf() function may fail if:

       EACCES Search permission is denied for a component of the path
              prefix.

       EINVAL The implementation does not support an association of the
              variable name with the specified file.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during
              resolution of the path argument.

       ENAMETOOLONG
              The length of a component of a pathname is longer than
              {NAME_MAX}.

       ENAMETOOLONG
              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate result
              with a length that exceeds {PATH_MAX}.

       ENOENT A component of path does not name an existing file or path is
              an empty string.

       ENOTDIR
              A component of the path prefix names an existing file that is
              neither a directory nor a symbolic link to a directory, or the
              path argument contains at least one non-<slash> character and
              ends with one or more trailing <slash> characters and the last
              pathname component names an existing file that is neither a
              directory nor a symbolic link to a directory.

       The fpathconf() function shall fail if:

       EINVAL The value of name is not valid.

       EOVERFLOW
              The value of name is _PC_TIMESTAMP_RESOLUTION and the
              resolution is larger than {LONG_MAX}.

       The fpathconf() function may fail if:

       EBADF  The fildes argument is not a valid file descriptor.

       EINVAL The implementation does not support an association of the
              variable name with the specified file.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       Application developers should check whether an option, such as
       _POSIX_ADVISORY_INFO, is supported prior to obtaining and using
       values for related variables such as {POSIX_ALLOC_SIZE_MIN}.

RATIONALE         top

       The pathconf() function was proposed immediately after the sysconf()
       function when it was realized that some configurable values may
       differ across file system, directory, or device boundaries.

       For example, {NAME_MAX} frequently changes between System V and BSD-
       based file systems; System V uses a maximum of 14, BSD 255. On an
       implementation that provides both types of file systems, an
       application would be forced to limit all pathname components to 14
       bytes, as this would be the value specified in <limits.h> on such a
       system.

       Therefore, various useful values can be queried on any pathname or
       file descriptor, assuming that appropriate privileges are in place.

       The value returned for the variable {PATH_MAX} indicates the longest
       relative pathname that could be given if the specified directory is
       the current working directory of the process. A process may not
       always be able to generate a name that long and use it if a
       subdirectory in the pathname crosses into a more restrictive file
       system. Note that implementations are allowed to accept pathnames
       longer than {PATH_MAX} bytes long, but are not allowed to return
       pathnames longer than this unless the user specifies a larger buffer
       using a function that provides a buffer size argument.

       The value returned for the variable _POSIX_CHOWN_RESTRICTED also
       applies to directories that do not have file systems mounted on them.
       The value may change when crossing a mount point, so applications
       that need to know should check for each directory. (An even easier
       check is to try the chown() function and look for an error in case it
       happens.)

       Unlike the values returned by sysconf(), the pathname-oriented
       variables are potentially more volatile and are not guaranteed to
       remain constant throughout the lifetime of the process.  For example,
       in between two calls to pathconf(), the file system in question may
       have been unmounted and remounted with different characteristics.

       Also note that most of the errors are optional. If one of the
       variables always has the same value on an implementation, the
       implementation need not look at path or fildes to return that value
       and is, therefore, not required to detect any of the errors except
       the meaning of [EINVAL] that indicates that the value of name is not
       valid for that variable.

       If the value of any of the limits is unspecified (logically
       infinite), they will not be defined in <limits.h> and the pathconf()
       and fpathconf() functions return −1 without changing errno.  This can
       be distinguished from the case of giving an unrecognized name
       argument because errno is set to [EINVAL] in this case.

       Since −1 is a valid return value for the pathconf() and fpathconf()
       functions, applications should set errno to zero before calling them
       and check errno only if the return value is −1.

       For the case of {SYMLINK_MAX}, since both pathconf() and open()
       follow symbolic links, there is no way that path or fildes could
       refer to a symbolic link.

       It was the intention of IEEE Std 1003.1d‐1999 that the following
       variables:

              {POSIX_ALLOC_SIZE_MIN} {POSIX_REC_INCR_XFER_SIZE}
              {POSIX_REC_MAX_XFER_SIZE} {POSIX_REC_MIN_XFER_SIZE}
              {POSIX_REC_XFER_ALIGN}

       only applied to regular files, but Note 10 also permits
       implementation of the advisory semantics on other file types unique
       to an implementation (for example, a character special device).

       The [EOVERFLOW] error for _PC_TIMESTAMP_RESOLUTION cannot occur on
       POSIX-compliant file systems because POSIX requires a timestamp
       resolution no larger than one second. Even on 32-bit systems, this
       can be represented without overflow.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       chown(3p), confstr(3p), sysconf(3p)

       The Base Definitions volume of POSIX.1‐2008, limits.h(0p),
       unistd.h(0p)

       The Shell and Utilities volume of POSIX.1‐2008, getconf(1p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                       FPATHCONF(3P)

Pages that refer to this page: limits.h(0p)unistd.h(0p)getconf(1p)chown(3p)confstr(3p)pathconf(3p)realpath(3p)sysconf(3p)