PATHCONF(2)

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. p1003.1-2001 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}. p1003.1-2001 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.

SEE ALSO
sysctl(2), sysconf(3)

STANDARDS
The pathconf() and fpathconf() functions conform to p1003.1-2008.

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