man pathconf (2): get configurable pathname variables

Other Alias

lpathconf, fpathconf

LIBRARY

Lb libc

SYNOPSIS

In unistd.h Ft long Fn pathconf const char *path int name Ft long Fn lpathconf const char *path int name Ft long Fn fpathconf int fd int name

DESCRIPTION

The Fn pathconf , Fn lpathconf and Fn 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 Fn pathconf and Fn lpathconf , the Fa path argument is the name of a file or directory. For Fn fpathconf , the Fa fd argument is an open file descriptor. The Fa name argument specifies the system variable to be queried. Symbolic constants for each name value are found in the include file <unistd.h>

The Fn lpathconf system call is like Fn pathconf except in the case where the named file is a symbolic link, in which case Fn lpathconf returns information about the link, while Fn 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. St -p1003.1-2001 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 Br q Dv NAME_MAX will result in an Bq Er ENAMETOOLONG error; otherwise, such components will be truncated to Br q Dv NAME_MAX . St -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_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)), Fn pathconf and Fn 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 Fn pathconf or Fn 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 Fn pathconf and Fn fpathconf system calls shall return -1 and set errno to the corresponding value.

Bq Er EINVAL: The value of the Fa name argument is invalid.
Bq Er EINVAL: The implementation does not support an association of the variable name with the associated file.

The Fn pathconf system call will fail if:

Bq Er ENOTDIR: A component of the path prefix is not a directory.
Bq Er ENAMETOOLONG: A component of a pathname exceeded Br q Dv NAME_MAX characters (but see _PC_NO_TRUNC above), or an entire path name exceeded Br q Dv PATH_MAX characters.
Bq Er ENOENT: The named file does not exist.
Bq Er EACCES: Search permission is denied for a component of the path prefix.
Bq Er ELOOP: Too many symbolic links were encountered in translating the pathname.
Bq Er EIO: An I/O error occurred while reading from or writing to the file system.

The Fn fpathconf system call will fail if:

Bq Er EBADF: The Fa fd argument is not a valid open file descriptor.
Bq Er EIO: An I/O error occurred while reading from or writing to the file system.

HISTORY

The Fn pathconf and Fn fpathconf system calls first appeared in BSD 4.4 The Fn lpathconf system call first appeared in Fx 8.0 .