|ACCESS(2)||System Calls Manual||ACCESS(2)|
faccessat — check
accessibility of a file
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_OK for read
W_OK for write permission, and
X_OK for execute/search permission), or the
existence test (
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.
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
access(). 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
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.
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.
- Corrupted data was detected while reading from 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.
access() system call is expected to
conform to IEEE Std 1003.1-1990
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
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).
|March 30, 2020||Debian|