NAME

pathconf, pathconfat, fpathconf — get configurable pathname variables

SYNOPSIS

#include <unistd.h>

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

long
fpathconf(int fd, int name);

#include <fcntl.h>

long
pathconfat(int fd, const char *path, int name, int flag);

DESCRIPTION

The pathconf(), pathconfat(), and fpathconf() functions 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(), 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 available values are as follows:

_PC_LINK_MAX: The maximum file link count.
_PC_MAX_CANON: The maximum number of bytes in a terminal canonical input line.
_PC_MAX_INPUT: The 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: Returns 1 if appropriate privileges are 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: Returns 1 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_2_SYMLINKS: Returns 1 if the filesystem supports the creation of symbolic links within the specified directory; the meaning of _PC_2_SYMLINKS is unspecified for non-directory files.
_PC_ALLOC_SIZE_MIN: Minimum number of bytes of storage allocated for any portion of a file.
_PC_ASYNC_IO: Returns 1 if asynchronous I/O is supported, otherwise 0.
_PC_FILESIZEBITS: Number of bits needed to represent the maximum file size.
_PC_PRIO_IO: Returns 1 if prioritized I/O is supported, otherwise 0.
_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_SYNC_IO: Returns 1 if synchronized I/O is supported, otherwise 0.
_PC_TIMESTAMP_RESOLUTION: The resolution in nanoseconds of file timestamps.

The pathconfat() function is equivalent to pathconf() except in the case where path specifies a relative path. In this case the file to be changed is determined relative to the directory associated with the file descriptor fd instead of the current working directory.

If pathconfat() is passed the special value AT_FDCWD (defined in <fcntl.h>) in the fd parameter, the current working directory is used. If flag is also zero, the behavior is identical to a call to pathconf().

The flag argument is the bitwise OR of zero or more of the following values:

AT_SYMLINK_NOFOLLOW: If path names a symbolic link, then the system variable for the symbolic link is queried.

RETURN VALUES

If the call to pathconf(), pathconfat(), 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(), pathconfat(), and fpathconf() functions 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.
[EIO]: An I/O error occurred while reading from the file system.

pathconf() and pathconfat() 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 pathname (including the terminating NUL) exceeded PATH_MAX bytes.
[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.
[EFAULT]: path points outside the process's allocated address space.

Additionally, the pathconfat() function will fail if:

[EINVAL]: The value of the flag argument was neither zero nor AT_SYMLINK_NOFOLLOW.
[EBADF]: The path argument specifies a relative path and the fd argument is neither AT_FDCWD nor a valid file descriptor.
[ENOTDIR]: The path argument specifies a relative path and the fd argument is a valid file descriptor but it does not reference a directory.
[EACCES]: The path argument specifies a relative path but search permission is denied for the directory which the fd file descriptor references.

fpathconf() will fail if:

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

STANDARDS

The pathconf() and fpathconf() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

HISTORY

The pathconf() and fpathconf() functions first appeared in 4.4BSD. The pathconfat() function first appeared in OpenBSD 7.6.