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Manual page for PATHCONF(2P)

pathconf, fpathconf - (POSIX only) get configurable pathname variables

SYNOPSIS

#include <unistd.h>

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

long fpathconf(int fildes, int name);

DESCRIPTION

The information in this specification applies only to POSIX applications.

The pathconf and fpathconf functions allow an application to query the current value of a configurable limit or option (variable) associated with a file or directory.

The pathconf function takes the name of a file or directory whose pathname is pointed to by the path argument. The fpathconf function, on the other hand, takes an open file descriptor as given by the fildes argument.

The name argument represents the variable to be determined relative to the file. The variables that may be queried by pathconf or fpathconf and the corresponding values for the name argument are listed below:

Variable: name Value Notes
{LINK_MAX}: {_PC_LINK_MAX} (1)
{MAX_CANON}: {_PC_MAX_CANON} (2)
{MAX_INPUT}: {_PC_MAX_INPUT} (2)
{NAME_MAX}: {_PC_NAME_MAX} (3)
{PATH_MAX}: {_PC_PATH_MAX} (4)
{PIPE_BUF}: {_PC_PIPE_BUF} (5)
{_POSIX_CHOWN_RESTRICTED}: {_PC_CHOWN_RESTRICTED} (6)
{_POSIX_NO_TRUNC}: {_PC_NO_TRUNC} (3)
{_POSIX_VDISABLE}: {_PC_VDISABLE} (2)

NOTES:

(1): If path or fildes refers to a directory, the value returned applies to the directory itself.
(2): The value returned only applies to terminal files.
(3): If path or fildes refers to a directory, the value returned applies to the filenames within the directory.
(4): If path or fildes refers to a directory, the value returned is the maximum length of a relative pathname when the specified directory is the current working directory.
(5): If path refers to a FIFO, or fildes refers to a pipe or a FIFO, then the value returned applies to the referenced object itself. If path or fildes refers to a directory, then the value returned applies to any FIFOs that exist or can be created within the specified directory.
(6): If path or fildes refers to a directory, then the value returned applies to terminal files that exist or can be created within the specified directory.

The meaning of each variable is as follows:

Variable: Description
{LINK_MAX}: Maximum value of a file's link count.
{MAX_CANON}: Maximum number of bytes in a terminal canonical input line.
{MAX_INPUT}: Minimum number of bytes for which space will be available in a terminal input queue; therefore, the maximum number of bytes a portable application may require to be typed as input before reading them.
{NAME_MAX}: Maximum number of bytes in a file name, excluding the terminating null.
{PATH_MAX}: Maximum number of bytes in a pathname, excluding the terminating null.
{PIPE_BUF}: Maximum number of bytes that can written atomically when writing to a pipe or FIFO.
{_POSIX_CHOWN_RESTRICTED}: The use of chown is restricted to super-user, and to changing the group ID of a file only to the effective group ID of the process or to one of its supplementary group IDs.
{_POSIX_NO_TRUNC}: Pathname components longer that {NAME_MAX} generate an error.
{_POSIX_VDISABLE}: Terminal special characters can be disabled using this character value, if it is defined. See tcgetattr.2p and tcsetattr.2p

The values for the variables above are given in the header <limits.h>. The symbolic constants used as values for name are given in <unistd.h>.

RETURN VALUE

Upon successful completion, both pathconf and fpathconf return the current variable value for the file or directory without changing errno. If the variable corresponding to name has no limit for the file or directory, then pathconf and fpathconf return -1 without changing errno. Otherwise, if an error condition occurs, then both functions return -1 and change the value of errno to indicate the error.

ERRORS

If any of the following conditions occur, the pathconf and fpathconf functions return -1 and set errno to the corresponding value:

[EINVAL]: The value of name is invalid.