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Manual Pages  — PATHCONF

NAME

pathconf, lpathconf, fpathconf – get configurable pathname variables

CONTENTS

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 BSD 4.4 . The lpathconf() system call first appeared in FreeBSD 8.0 .

PATHCONF (2) July 7, 2009

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One of the advantages of using UNIX to teach an operating systems course is the sources and documentation will easily fit into a student's briefcase.
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