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access.2: Merge text from faccessat(2)
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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man2/access.2
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man2/access.2
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.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
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.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
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.\" and Copyright (C) 1993 Michael Haardt, Ian Jackson.
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.\" and Copyright (C) 1993 Michael Haardt, Ian Jackson.
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.\" and Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
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.\" and Copyright (C) 2004, 2006, 2007, 2014 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" Permission is granted to make and distribute verbatim copies of this
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@ -40,14 +40,40 @@
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.\" Modified 2004-06-23 by Michael Kerrisk
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.\" Modified 2004-06-23 by Michael Kerrisk
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.\" 2007-06-10, mtk, various parts rewritten, and added BUGS section.
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.\" 2007-06-10, mtk, various parts rewritten, and added BUGS section.
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.\"
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.\"
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.TH ACCESS 2 2013-09-13 "Linux" "Linux Programmer's Manual"
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.TH ACCESS 2 2014-02-21 "Linux" "Linux Programmer's Manual"
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.SH NAME
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.SH NAME
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access \- check real user's permissions for a file
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access, faccessat \- check user's permissions for a file
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.SH SYNOPSIS
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.SH SYNOPSIS
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.nf
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.nf
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.B #include <unistd.h>
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.B #include <unistd.h>
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.sp
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.sp
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.BI "int access(const char *" pathname ", int " mode );
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.BI "int access(const char *" pathname ", int " mode );
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.B #include <fcntl.h> /* Definition of AT_* constants */
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.B #include <unistd.h>
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.sp
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.BI "int faccessat(int " dirfd ", const char *" pathname ", int " \
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mode ", int " flags );
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.fi
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.BR faccessat ():
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.PD 0
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.ad l
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.RS 4
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.TP 4
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Since glibc 2.10:
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_XOPEN_SOURCE\ >=\ 700 || _POSIX_C_SOURCE\ >=\ 200809L
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.TP
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Before glibc 2.10:
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_ATFILE_SOURCE
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.RE
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.ad
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.PD
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.fi
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.fi
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.SH DESCRIPTION
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.SH DESCRIPTION
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.BR access ()
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.BR access ()
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@ -85,6 +111,56 @@ then an
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.B X_OK
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.B X_OK
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check is successful for a regular file if execute permission
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check is successful for a regular file if execute permission
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is enabled for any of the file owner, group, or other.
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is enabled for any of the file owner, group, or other.
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.SS faccessat ()
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The
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.BR faccessat ()
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system call operates in exactly the same way as
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.BR access (2),
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except for the differences described here.
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If the pathname given in
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.I pathname
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is relative, then it is interpreted relative to the directory
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referred to by the file descriptor
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.I dirfd
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(rather than relative to the current working directory of
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the calling process, as is done by
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.BR access (2)
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for a relative pathname).
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If
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.I pathname
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is relative and
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.I dirfd
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is the special value
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.BR AT_FDCWD ,
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then
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.I pathname
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is interpreted relative to the current working
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directory of the calling process (like
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.BR access (2)).
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If
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.I pathname
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is absolute, then
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.I dirfd
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is ignored.
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.I flags
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is constructed by ORing together zero or more of the following values:
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.TP
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.B AT_EACCESS
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Perform access checks using the effective user and group IDs.
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By default,
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.BR faccessat ()
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uses the real IDs (like
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.BR access (2)).
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.TP
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.B AT_SYMLINK_NOFOLLOW
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If
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.I pathname
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is a symbolic link, do not dereference it:
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instead return information about the link itself.
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.SH "RETURN VALUE"
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.SH "RETURN VALUE"
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On success (all requested permissions granted, or
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On success (all requested permissions granted, or
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.I mode
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.I mode
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@ -153,8 +229,33 @@ Insufficient kernel memory was available.
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.B ETXTBSY
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.B ETXTBSY
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Write access was requested to an executable which is being
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Write access was requested to an executable which is being
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executed.
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executed.
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.PP
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The following additional errors can occur for
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.BR faccessat ():
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.TP
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.B EBADF
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.I dirfd
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is not a valid file descriptor.
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.TP
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.B EINVAL
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Invalid flag specified in
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.IR flags .
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.TP
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.B ENOTDIR
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.I pathname
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is relative and
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.I dirfd
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is a file descriptor referring to a file other than a directory.
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.SH VERSIONS
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.BR faccessat ()
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was added to Linux in kernel 2.6.16;
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library support was added to glibc in version 2.4.
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.SH "CONFORMING TO"
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.SH "CONFORMING TO"
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.BR access (2):
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SVr4, 4.3BSD, POSIX.1-2001.
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SVr4, 4.3BSD, POSIX.1-2001.
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.BR faccessat (2):
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POSIX.1-2008.
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.SH NOTES
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.SH NOTES
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.PP
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.PP
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.BR Warning :
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.BR Warning :
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@ -214,6 +315,31 @@ because UID mapping is done on the server and hidden from the client,
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which checks permissions. (NFS versions 3 and higher perform the check on
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which checks permissions. (NFS versions 3 and higher perform the check on
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the server.)
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the server.)
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Similar problems can occur to FUSE mounts.
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Similar problems can occur to FUSE mounts.
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.\"
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.\"
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.SS faccessat ()
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See
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.BR openat (2)
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for an explanation of the need for
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.BR faccessat ().
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.IR Warning :
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.BR faccessat ()
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is subject to the same kinds of races as
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.BR access (2)
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and
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.BR euidaccess (3).
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.SS Glibc notes
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The raw system call takes only the first three arguments.
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The
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.B AT_EACCESS
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and
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.B AT_SYMLINK_NOFOLLOW
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flags are actually implemented within the glibc wrapper function for
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.BR faccessat ().
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If either of these flags is specified, then the wrapper function employs
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.BR fstatat (2)
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to determine access permissions.
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.SH BUGS
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.SH BUGS
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In kernel 2.4 (and earlier) there is some strangeness in the handling of
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In kernel 2.4 (and earlier) there is some strangeness in the handling of
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.B X_OK
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.B X_OK
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@ -251,11 +377,11 @@ honors this flag.
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.SH "SEE ALSO"
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.SH "SEE ALSO"
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.BR chmod (2),
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.BR chmod (2),
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.BR chown (2),
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.BR chown (2),
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.BR faccessat (2),
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.BR open (2),
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.BR open (2),
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.BR setgid (2),
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.BR setgid (2),
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.BR setuid (2),
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.BR setuid (2),
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.BR stat (2),
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.BR stat (2),
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.BR euidaccess (3),
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.BR euidaccess (3),
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.BR credentials (7),
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.BR credentials (7),
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.BR path_resolution (7)
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.BR path_resolution (7),
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.BR symlink (7)
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