access system call

access system call linux

NAME

access – check access permissions of a file or pathname

SYNOPSIS

#include <unistd.h>

int access(const char *path, int mode);

FEATURES

MSDOSFS, NFS_CLIENT, UFS

DESCRIPTION

The access function checks the accessibility of the file named by path for the access permissions indicated by mode. The value of mode is the bitwise inclusive OR of the access permissions to be checked

R_OK  for read permission,

W_OK  for write permission, and

X_OK  for execute/search permission, or an existence test.

F_OK  All components of the pathname path are checked for access

      permissions (including F_OK).

The real user ID is used instead of the effective user ID, and the real group access list (including the real group ID) are used instead of the effective ID for checking permissions.

Even if a process has appropriate privileges and indicates success for X_OK,R_OK or W_OK, the file may not actually have execute permission bits set.

RETURN VALUES

If path cannot be found or if any of the desired access modes would not be granted, a value of -1 is returned; otherwise a 0 value is returned.

ERRORS

Access to the file is denied if:

[ENOTDIR]       A component of the path prefix is not a directory.

[EINVAL]        The pathname contains a character with the

                high-order bit set.

[ENAMETOOLONG]  A component of a pathname exceeded 255

                characters, or an entire path name exceeded

                1023 characters.

[ENOENT]        The named file does not exist.

[ELOOP]         Too many symbolic links were encountered in

                translating the pathname.

[EROFS]         Write access is requested for a file on a read-only

                file system.

[ETXTBSY]       Write access is requested for a pure procedure

                (shared text) file currently being executed.

[EACCES]        Permission bits of the file mode do not permit the

                requested access, or search permission is denied

                on a component of the path prefix. The owner

                of a file has permissions checked with respect

                to the “owner” read, write, and execute mode

                bits. Members of the file’s group other than the

                owner have permissions checked with respect

                to the “group” mode bits, and all others have

                permissions checked with respect to the “other”

                mode bits.

[EFAULT]        Path points outside the process’s allocated

                address space.

[EIO]           An I/O error occurred while reading from or

                writing to the file system.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving