pathconf

PATHCONF(2)                  BSD System Calls Manual                 PATHCONF(2)

NAME
     pathconf, lpathconf, fpathconf — get configurable pathname variables

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

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

     long
     lpathconf(const char *path, int name);

     long
     fpathconf(int fd, int name);

DESCRIPTION
     The pathconf(), lpathconf() and fpathconf() system calls provide a method
     for applications to determine the current value of a configurable system
     limit or option variable associated with a pathname or file descriptor.

     For pathconf() and lpathconf(), the path argument is the name of a file or
     directory.  For fpathconf(), the fd argument is an open file descriptor.
     The name argument specifies the system variable to be queried.  Symbolic
     constants for each name value are found in the include file <unistd.h>.

     The lpathconf() system call is like pathconf() except in the case where the
     named file is a symbolic link, in which case lpathconf() returns
     information about the link, while pathconf() returns information about the
     file the link references.

     The available values are as follows:

     _PC_LINK_MAX
             The maximum file link count.

     _PC_MAX_CANON
             The maximum number of bytes in terminal canonical input line.

     _PC_MAX_INPUT
             The minimum maximum number of bytes for which space is available in
             a terminal input queue.

     _PC_NAME_MAX
             The maximum number of bytes in a file name.

     _PC_PATH_MAX
             The maximum number of bytes in a pathname.

     _PC_PIPE_BUF
             The maximum number of bytes which will be written atomically to a
             pipe.

     _PC_CHOWN_RESTRICTED
             Return 1 if appropriate privilege is required for the chown(2)
             system call, otherwise 0.  IEEE Std 1003.1-2001 (“POSIX.1”)
             requires appropriate privilege in all cases, but this behavior was
             optional in prior editions of the standard.

     _PC_NO_TRUNC
             Return greater than zero if attempts to use pathname components
             longer than {NAME_MAX} will result in an [ENAMETOOLONG] error;
             otherwise, such components will be truncated to {NAME_MAX}.  IEEE
             Std 1003.1-2001 (“POSIX.1”) requires the error in all cases, but
             this behavior was optional in prior editions of the standard, and
             some non-POSIX-compliant file systems do not support this behavior.

     _PC_VDISABLE
             Returns the terminal character disabling value.

     _PC_ASYNC_IO
             Return 1 if asynchronous I/O is supported, otherwise 0.

     _PC_PRIO_IO
             Returns 1 if prioritised I/O is supported for this file, otherwise
             0.

     _PC_SYNC_IO
             Returns 1 if synchronised I/O is supported for this file, otherwise
             0.

     _PC_ALLOC_SIZE_MIN
             Minimum number of bytes of storage allocated for any portion of a
             file.

     _PC_FILESIZEBITS
             Number of bits needed to represent the maximum file size.

     _PC_REC_INCR_XFER_SIZE
             Recommended increment for file transfer sizes between
             _PC_REC_MIN_XFER_SIZE and _PC_REC_MAX_XFER_SIZE.

     _PC_REC_MAX_XFER_SIZE
             Maximum recommended file transfer size.

     _PC_REC_MIN_XFER_SIZE
             Minimum recommended file transfer size.

     _PC_REC_XFER_ALIGN
             Recommended file transfer buffer alignment.

     _PC_SYMLINK_MAX
             Maximum number of bytes in a symbolic link.

     _PC_ACL_EXTENDED
             Returns 1 if an Access Control List (ACL) can be set on the
             specified file, otherwise 0.

     _PC_ACL_NFS4
             Returns 1 if an NFSv4 ACLs can be set on the specified file,
             otherwise 0.

     _PC_ACL_PATH_MAX
             Maximum number of ACL entries per file.

     _PC_CAP_PRESENT
             Returns 1 if a capability state can be set on the specified file,
             otherwise 0.

     _PC_INF_PRESENT
             Returns 1 if an information label can be set on the specified file,
             otherwise 0.

     _PC_MAC_PRESENT
             Returns 1 if a Mandatory Access Control (MAC) label can be set on
             the specified file, otherwise 0.

     _PC_MIN_HOLE_SIZE
             If a file system supports the reporting of holes (see lseek(2)),
             pathconf() and fpathconf() return a positive number that represents
             the minimum hole size returned in bytes.  The offsets of holes
             returned will be aligned to this same value.  A special value of 1
             is returned if the file system does not specify the minimum hole
             size but still reports holes.

RETURN VALUES
     If the call to pathconf() or fpathconf() is not successful, -1 is returned
     and errno is set appropriately.  Otherwise, if the variable is associated
     with functionality that does not have a limit in the system, -1 is returned
     and errno is not modified.  Otherwise, the current variable value is
     returned.

ERRORS
     If any of the following conditions occur, the pathconf() and fpathconf()
     system calls shall return -1 and set errno to the corresponding value.

     [EINVAL]           The value of the name argument is invalid.

     [EINVAL]           The implementation does not support an association of
                        the variable name with the associated file.

     The pathconf() system call will fail if:

     [ENOTDIR]          A component of the path prefix is not a directory.

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX} characters
                        (but see _PC_NO_TRUNC above), or an entire path name
                        exceeded {PATH_MAX} characters.

     [ENOENT]           The named file does not exist.

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

     [ELOOP]            Too many symbolic links were encountered in translating
                        the pathname.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system.

     The fpathconf() system call will fail if:

     [EBADF]            The fd argument is not a valid open file descriptor.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system.

SEE ALSO
     lseek(2), sysctl(3)

HISTORY
     The pathconf() and fpathconf() system calls first appeared in 4.4BSD.  The
     lpathconf() system call first appeared in FreeBSD 8.0.

BSD                               July 7, 2009                               BSD