|ACCESS(2)||System Calls Manual||ACCESS(2)|
LIBRARY¶Standard C Library (libc, -lc)
char *path, int
char *path, int
fd, const char
*path, int mode,
eaccess() system calls check the accessibility of the file named by the path argument for the access permissions indicated by the mode argument. The value of mode is either the bitwise-inclusive OR of the access permissions to be checked (
R_OKfor read permission,
W_OKfor write permission, and
X_OKfor execute/search permission), or the existence test (
eaccess() system call uses the
effective user ID and the group access list to authorize the request; the
access() system call uses the real user ID in place
of the effective user ID, the real group ID in place of the effective group
ID, and the rest of the group access list.
faccessat() system call is equivalent
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
Values for flag are constructed by a bitwise-inclusive
OR of flags from the following list, defined in
- 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
Even if a process's real or effective user has appropriate
privileges and indicates success for
X_OK, the file
may not actually have execute permission bits set. Likewise for
RETURN VALUES¶Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
faccessat() will fail if:
- The value of the mode argument is invalid.
- A component of the path prefix is not a directory.
- A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
- The named file does not exist.
- Too many symbolic links were encountered in translating the pathname.
- Write access is requested for a file on a read-only file system.
- Write access is requested for a pure procedure (shared text) file presently being executed.
- 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 path argument points outside the process's allocated address space.
- An I/O error occurred while reading from or writing to the file system.
faccessat() system call may fail
- The path argument does not specify an absolute path
and the fd argument is neither
AT_FDCWDnor a valid file descriptor.
- The value of the flag argument is not valid.
- The path argument is not an absolute path and
fd is neither
AT_FDCWDnor a file descriptor associated with a directory.
SEE ALSO¶chmod(2), intro(2), stat(2)
access() system call is expected to conform to IEEE Std 1003.1-1990 (“POSIX.1”). The
faccessat() system call follows The Open Group Extended API Set 2 specification.
access() function appeared in Version 7 AT&T UNIX. The
faccessat() system call appeared in FreeBSD 8.0.
access() system call is a potential security hole due to race conditions and should never be used. Set-user-ID and set-group-ID applications should restore the effective user or group ID, and perform actions directly rather than use
access() to simulate access checks for the real user or group ID. The
eaccess() system call likewise may be subject to races if used inappropriately.
access() remains useful for providing
clues to users as to whether operations make sense for particular filesystem
objects (e.g. 'delete' menu item only highlighted in a writable folder ...
avoiding interpretation of the st_mode bits that the application might not
understand -- e.g. in the case of AFS). It also allows a cheaper file
existence test than stat(2).
|September 15, 2014||Linux 4.9.0-9-amd64|