FPATHCONF

Section: Linux Programmer's Manual (3)
Updated: 2017-07-13
Page Index

NAME

fpathconf, pathconf - get configuration values for files

SYNOPSIS

#include <unistd.h>

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

DESCRIPTION

fpathconf() gets a value for the configuration option name for the open file descriptor fd.

pathconf() gets a value for configuration option name for the filename path.

The corresponding macros defined in <unistd.h> are minimum values; if an application wants to take advantage of values which may change, a call to fpathconf() or pathconf() can be made, which may yield more liberal results.

Setting name equal to one of the following constants returns the following configuration options:

_PC_LINK_MAX: The maximum number of links to the file. If fd or path refer to a directory, then the value applies to the whole directory. The corresponding macro is _POSIX_LINK_MAX.
_PC_MAX_CANON: The maximum length of a formatted input line, where fd or path must refer to a terminal. The corresponding macro is _POSIX_MAX_CANON.
_PC_MAX_INPUT: The maximum length of an input line, where fd or path must refer to a terminal. The corresponding macro is _POSIX_MAX_INPUT.
_PC_NAME_MAX: The maximum length of a filename in the directory path or fd that the process is allowed to create. The corresponding macro is _POSIX_NAME_MAX.
_PC_PATH_MAX: The maximum length of a relative pathname when path or fd is the current working directory. The corresponding macro is _POSIX_PATH_MAX.
_PC_PIPE_BUF: The maximum number of bytes that can be written atomically to a pipe of FIFO. For fpathconf(), fd should refer to a pipe or FIFO. For fpathconf(), path should refer to a FIFO or a directory; in the latter case, the returned value corresponds to FIFOs created in that directory. The corresponding macro is _POSIX_PIPE_BUF.
_PC_CHOWN_RESTRICTED: This returns a positive value if the use of chown(2) and fchown(2) for changing a file's user ID is restricted to a process with appropriate privileges, and changing a file's group ID to a value other than the process's effective group ID or one of its supplementary group IDs is restricted to a process with appropriate privileges. According to POSIX.1, this variable shall always be defined with a value other than -1. The corresponding macro is _POSIX_CHOWN_RESTRICTED.
: If fd or path refers to a directory, then the return value applies to all files in that directory.
_PC_NO_TRUNC: This returns nonzero if accessing filenames longer than _POSIX_NAME_MAX generates an error. The corresponding macro is _POSIX_NO_TRUNC.
_PC_VDISABLE: This returns nonzero if special character processing can be disabled, where fd or path must refer to a terminal.

RETURN VALUE

The return value of these functions is one of the following:

*: On error, -1 is returned and errno is set to indicate the cause of the error (for example, EINVAL, indicating that name is invalid).
*: If name corresponds to a maximum or minimum limit, and that limit is indeterminate, -1 is returned and errno is not changed. (To distinguish an indeterminate limit from an error, set errno to zero before the call, and then check whether errno is nonzero when -1 is returned.)
*: If name corresponds to an option, a positive value is returned if the option is supported, and -1 is returned if the option is not supported.
*: Otherwise, the current value of the option or limit is returned. This value will not be more restrictive than the corresponding value that was described to the application in <unistd.h> or <limits.h> when the application was compiled.

ERRORS

EACCES: (pathconf()) Search permission is denied for one of the directories in the path prefix of path.
EBADF: (fpathconf()) fd is not a valid file descriptor.
EINVAL: name is invalid.
EINVAL: The implementation does not support an association of name with the specified file.
ELOOP: (pathconf()) Too many symbolic links were encountered while resolving path.
ENAMETOOLONG: (pathconf()) path is too long.
ENOENT: (pathconf()) A component of path does not exist, or path is an empty string.
ENOTDIR: (pathconf()) A component used as a directory in path is not in fact a directory.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
fpathconf(), pathconf()	Thread safety	MT-Safe

CONFORMING TO

POSIX.1-2001, POSIX.1-2008.

NOTES

Files with name lengths longer than the value returned for name equal to _PC_NAME_MAX may exist in the given directory.

Some returned values may be huge; they are not suitable for allocating memory.

COLOPHON

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