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faccessat - check user’s permissions of a file relative to a directory
#include <fcntl.h> /* Definition of AT_* constants */
int faccessat(int dirfd, const char *pathname, int mode, int flags);
The faccessat() system call operates in exactly the same way as
access(2), except for the differences described in this manual page.
If the pathname given in pathname is relative, then it is interpreted
relative to the directory referred to by the file descriptor dirfd
(rather than relative to the current working directory of the calling
process, as is done by access(2) for a relative pathname).
If pathname is relative and dirfd is the special value AT_FDCWD, then
pathname is interpreted relative to the current working directory of
the calling process (like access(2)).
If pathname is absolute, then dirfd is ignored.
flags is constructed by ORing together zero or more of the following
Perform access checks using the effective user and group IDs.
By default, faccessat() uses the real IDs (like access(2)).
If pathname is a symbolic link, do not dereference it: instead
return information about the link itself.
On success, (all requested permissions granted) faccessat() returns 0.
On error, -1 is returned and errno is set to indicate the error.
The same errors that occur for access(2) can also occur for
faccessat(). The following additional errors can occur for
EBADF dirfd is not a valid file descriptor.
EINVAL Invalid flag specified in flags.
pathname is relative and dirfd is a file descriptor referring to
a file other than a directory.
faccessat() was added to Linux in kernel 2.6.16.
This system call is non-standard but is proposed for inclusion in a
future revision of POSIX.1.
See openat(2) for an explanation of the need for faccessat().
The AT_EACCESS and AT_SYMLINK_NOFOLLOW flags are actually implemented
within the glibc wrapper function for faccessat(). If either of these
flags are specified, then the wrapper function employs fstatat(2) to
determine access permissions.
access(2), openat(2), euidaccess(3), credentials(7),
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description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.