access, accessx, faccessx, accessxat, or faccessat Subroutine

Purpose

Determines the accessibility of a file.

Library

Standard C Library (libc.a)

Syntax

#include <unistd.h>

int access (PathName,Mode) char *PathName; int Mode; int accessx (PathName, Mode, Who) char *PathName; int Mode, Who; int faccessx (FileDescriptor, Mode, Who) int FileDescriptor; int Mode, Who; int accessxat (DirFileDescriptor, PathName, Mode, Who) int DirFileDescriptor; char *PathName; int Mode, Who; int faccessat (DirFileDescriptor, PathName, Mode, Flag) int DirFileDescriptor; char *PathName; int Mode, Flag;

Description

The access, accessx, accessxat, faccessat and faccessx subroutines determine the accessibility of a file system object. The accessx, accessxat, and faccessx subroutines allow the specification of a class of users or processes for whom access is to be checked.

The caller must have search permission for all components of the PathName parameter.

The accessxat subroutine is equivalent to the accessx subroutine, and the faccessat subroutine is equivalent to the access subroutine if the PathName parameter specifies an absolute path or if the DirFileDescriptor parameter is set to AT_FDCWD. The file accessibility is determined by the relative path to the directory that is associated with the DirFileDescriptor parameter instead of the current working directory. If the directory is accessed without the O_SEARCH open flag, the subroutine checks to determine whether directory searches are permitted by using the current permissions of the directory. If the directory is accessed with the O_SEARCH open flag, the subroutine does not perform the check.

Parameters

Item	Description
PathName	Specifies the path name of the file. If the PathName parameter refers to a symbolic link, the access subroutine returns information about the file pointed to by the symbolic link. If the DirFileDescriptor is specified and PathName is relative, then the DirFileDescriptor specifies the effective current working directory for the PathName.
FileDescriptor	Specifies the file descriptor of an open file.
Mode	Specifies the access modes to be checked. This parameter is a bit mask containing 0 or more of the following values, which are defined in the <sys/access.h> file: R_OK Check read permission. W_OK Check write permission. X_OK Check execute or search permission. F_OK Check the existence of a file. If none of these values are specified, the existence of a file is checked.
Who	Specifies the class of users for whom access is to be checked. This parameter must be one of the following values, which are defined in the <sys/access.h> file: ACC_SELF Determines if access is permitted for the current process. The effective user and group IDs, the concurrent group set and the privilege of the current process are used for the calculation. ACC_INVOKER Determines if access is permitted for the invoker of the current process. The real user and group IDs, the concurrent group set, and the privilege of the invoker are used for the calculation. Note: The expression access (PathName, Mode) is equivalent to accessx (PathName, Mode, ACC_INVOKER). ACC_OTHERS Determines if the specified access is permitted for any user other than the object owner. The Mode parameter must contain only one of the valid modes. Privilege is not considered in the calculation. ACC_ALL Determines if the specified access is permitted for all users. The Mode parameter must contain only one of the valid modes. Privilege is not considered in the calculation . Note: The accessx subroutine shows the same behavior by both the user and root with ACC_ALL.
DirFileDescriptor	Specifies the file descriptor of an open directory, which is used as the effective current working directory for the PathName argument. If the DirFileDescriptor parameter equals AT_FDCWD, the DirFileDescriptor parameter is ignored and the PathName argument specifies the complete file.
Flag	Specifies a bit field argument. If the Flag parameter equals AT_EACCESS, the effective user and group IDs are checked (ACC_SELF). If the Flag parameter is zero, the real IDs are checked (ACC_INVOKER).

Return Values

If the requested access is permitted, the access, accessx, faccessx, accessxat, and faccessat subroutines return a value of 0. If the requested access is not permitted or the function call fails, a value of -1 is returned and the errno global variable is set to indicate the error.

The access subroutine indicates success for X_OK even if none of the execute file permission bits are set.

Error Codes

The access faccessat, accessx, and accessx subroutines fail if one or more of the following are true:

Item	Description
EACCES	Search permission is denied on a component of the PathName prefix.
EFAULT	The PathName parameter points to a location outside the allocated address space of the process.
ELOOP	Too many symbolic links were encountered in translating the PathName parameter.
ENAMETOOLONG	A component of the PathName parameter exceeded 255 characters or the entire PathName parameter exceeded 1022 characters.
ENOENT	A component of the PathName does not exist or the process has the disallow truncation attribute set.
ENOENT	The named file does not exist.
ENOENT	The PathName parameter was null.
ENOENT	A symbolic link was named, but the file to which it refers does not exist.
ENOTDIR	A component of the PathName is not a directory.
ESTALE	The process root or current directory is located in a virtual file system that has been unmounted.

The faccessx subroutine fails if the following is true:

Item	Description
EBADF	The value of the FileDescriptor parameter is not valid.

The access, accessx, and faccessx subroutines fail if one or more of the following is true:

Item	Description
EACCES	The file protection does not allow the requested access.
ENOMEM	Unable to allocate memory.
EIO	An I/O error occurred during the operation.
EROFS	Write access is requested for a file on a read-only file system.

The accessxat and faccessat subroutines fail if one or more of the following settings are true:

Item	Description
EBADF	The PathName parameter does not specify an absolute path and the DirFileDescriptor argument is neither AT_FDCWD nor a valid file descriptor.
EINVAL	The value of the Flag parameter is not valid.
ENOTDIR	The PathName parameter is not an absolute path and DirFileDescriptor is a file descriptor but is not associated with a directory.

If Network File System (NFS) is installed on your system, the accessx, accessxat, and faccessx subroutines can also fail if the following settings are true:

Item	Description
ETIMEDOUT	The connection timed out.
ETXTBSY	Write access is requested for a shared text file that is being executed.
EINVAL	The value of the Mode argument is invalid.