ACCESS(2)

NAME
access, faccessat - check access permissions of a file or pathname

SYNOPSIS
#include <unistd.h>
int
access(const char *path, int amode);
int
faccessat(int fd, const char *path, int mode, int flag);

DESCRIPTION
The access() function checks the accessibility of the file named by path for the access permissions indicated by amode. The value of amode 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 the existence test, F_OK. All components of the pathname path are checked for access permissions (including F_OK).

The real user ID is used in place of the effective user ID and the real group access list (including the real group ID) are used in place of the effective ID for verifying permission.

The faccessat() system call is equivalent to access() except in the case where path specifies a relative path. In this case the file whose accessibility is to be determined is located relative to the directory associated with the file descriptor fd instead of the current working directory. If faccessat() is passed the special value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to a call to access(). Values for flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:

AT_EACCESS
    The checks for accessibility are performed using the effective user and group IDs instead of the real user and group ID as required in a call to access().

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

RETURN VALUES
If path cannot be found or if any of the desired access modes would not be granted, then a -1 value is returned and the global integer variable errno is set to indicate the error. Otherwise, a 0 value is returned.

ERRORS
Access to the file is denied if:

[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 permission checked with respect to the ``owner'' read, write, and execute mode bits, members of the file's group other than the owner have permission 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.

[EINVAL]
    An invalid value was specified for amode.

[EIO]
    An I/O error occurred while reading from or writing to the file system.

[ELOOP]
    Too many symbolic links were encountered in translating the pathname.

[ENAMETOOLONG]
    A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.

[ENOENT]
    The named file does not exist.

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

[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 that is presently being executed.

Also, the faccessat() system call may fail if:

[EBADF]
    The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor.

[EINVAL]
    The value of the flag argument is not valid.

[ENOTDIR]
    The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.

SEE ALSO
chmod(2), stat(2)

STANDARDS
The access() function conforms to p1003.1-90. The faccessat() system call is expected to conform to POSIX.1-2008 .

CAVEAT
access() is a potential security hole and should never be used.