|ACCESS(2)||System Calls Manual||ACCESS(2)|
— check access permissions of a file or
char *path, int
fd, const char
*path, int amode,
function checks the accessibility of the file named by
path for the access permissions indicated by
amode. The amode argument is
either the bitwise OR of one or more 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
F_OK. All components of the pathname
path are checked for access permissions (including
The real user ID is used in place of the effective user ID and the real group access list (including the real group ID) is used in place of the effective ID for verifying permission.
If the invoking process has superuser privileges,
will always indicate success for
W_OK, regardless of the actual file permission bits.
X_OK, if the file has any of the
execute bits set and path is not a directory,
access() will indicate success.
function is equivalent to
access() except that where
path specifies a relative path, the file whose
accessibility is checked is determined relative to the directory associated
with file descriptor fd instead of the current working
is passed the special value
AT_FDCWD (defined in
<fcntl.h>) in the
fd parameter, the current working directory is used.
If flag is also zero, the behavior is identical to a
The flag argument is the bitwise OR of zero or more of the following values:
If path cannot be found or if any of the desired access modes would not be granted, then a -1 value is returned; otherwise a 0 value is returned.
Access to the file is denied if:
NAME_MAXcharacters, or an entire pathname (including the terminating NUL) exceeded
faccessat() will fail
AT_FDCWDnor a valid file descriptor.
faccessat() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
access() first appeared as an internal
kernel function in Version 1 AT&T UNIX
and was reimplemented in C before the release of
Version 4 AT&T UNIX. It was first
promoted to a system call in the Programmer's Workbench (PWB/UNIX), which
was later ported to Version 7 AT&T UNIX
faccessat() function appeared in
Ken Thompson first implemented the
access() kernel function in C.
faccessat() should never be used for actual access
control. Doing so can result in a time of check vs. time of use security
|January 19, 2015||OpenBSD-current|