man-pages/man2/faccessat.2

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.TH FACCESSAT 2 2007-02-28 "Linux" "Linux Programmer's Manual"
.SH NAME
faccessat \- check user's permissions of a file relative to a \
directory file descriptor
.SH SYNOPSIS
.nf
.B #define _ATFILE_SOURCE
.B #include <fcntl.h>
.B #include <unistd.h>
.sp
.BI "int faccessat(int " dirfd ", const char *" pathname ", int " \
mode ", int " flags );
.fi
.SH DESCRIPTION
The
.BR faccessat ()
system call operates in exactly the same way as
.BR access (2),
except for the differences described in this manual page.

If the pathname given in
.I pathname
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.I dirfd
(rather than relative to the current working directory of
the calling process, as is done by
.BR access (2)
for a relative pathname).

If
.I pathname
is relative and
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I pathname
is interpreted relative to the current working
directory of the calling process (like
.BR access (2)).

If
.I pathname
is absolute, then
.I dirfd
is ignored.

.I flags
is constructed by ORing together zero or more of the following values:
.TP
.B AT_EACCESS
Perform access checks using the effective user and group IDs.
By default,
.BR faccessat ()
uses the real IDs (like
.BR access (2)).
.TP
.B AT_SYMLINK_NOFOLLOW
If
.I pathname
is a symbolic link, do not dereference it:
instead return information about the link itself.
.SH "RETURN VALUE"
On success, (all requested permissions granted)
.BR faccessat ()
returns 0.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
The same errors that occur for
.BR access (2)
can also occur for
.BR faccessat ().
The following additional errors can occur for
.BR faccessat ():
.TP
.B EBADF
.I dirfd
is not a valid file descriptor.
.TP
.B EINVAL
Invalid flag specified in
.IR flags .
.TP
.B ENOTDIR
.I pathname
is relative and
.I dirfd
is a file descriptor referring to a file other than a directory.
.SH VERSIONS
.BR faccessat ()
was added to Linux in kernel 2.6.16.
.SH "CONFORMING TO"
This system call is non-standard but is proposed
for inclusion in a future revision of POSIX.1.
.SH NOTES
See
.BR openat (2)
for an explanation of the need for
.BR faccessat ().
.SS Glibc Notes
The
.B AT_EACCESS
and
.B AT_SYMLINK_NOFOLLOW
flags are actually implemented within the glibc wrapper function for
.BR faccessat ().
If either of these flags are specified, then the wrapper function employs
.BR fstatat (2)
to determine access permissions.
.SH "SEE ALSO"
.BR access (2),
.BR openat (2),
.BR euidaccess (3),
.BR credentials (7),
.BR path_resolution (7)