84d9c625bf
- Fix for possible unset uid/gid in toproto
- Fix for default mtree style
- Update libelf
- Importing libexecinfo
- Resynchronize GCC, mpc, gmp, mpfr
- build.sh: Replace params with show-params.
This has been done as the make target has been renamed in the same
way, while a new target named params has been added. This new
target generates a file containing all the parameters, instead of
printing it on the console.
- Update test48 with new etc/services (Fix by Ben Gras <ben@minix3.org)
get getservbyport() out of the inner loop
Change-Id: Ie6ad5226fa2621ff9f0dee8782ea48f9443d2091
292 lines
8.3 KiB
Groff
292 lines
8.3 KiB
Groff
.\" $NetBSD: access.2,v 1.32 2013/01/13 08:15:02 dholland Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)access.2 8.2 (Berkeley) 4/1/94
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.\"
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.Dd January 12, 2013
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.Dt ACCESS 2
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.Os
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.Sh NAME
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.Nm access ,
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.Nm faccessat
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.Nd check access permissions of a file or pathname
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn access "const char *path" "int mode"
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.In fcntl.h
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.Ft int
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.Fn faccessat "int fd" "const char *path" "int mode" "int flags"
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.Sh DESCRIPTION
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The
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.Fn access
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function checks the accessibility of the
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file named by
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.Fa path .
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The
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.Fn faccessat
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function checks the accessibility of the file named by
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.Fa path
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using
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.Fa fd
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as the starting point for relative pathnames.
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If
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.Fa fd
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is
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.Dv AT_FDCWD
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the current directory is used.
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Calling
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.Fn access
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is equivalent to calling
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.Fn faccessat
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with
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.Fa fd
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set to
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.Dv AT_FDCWD
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and
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.Fa flags
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set to 0.
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.Pp
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The form of access to check is specified by the bitwise or of the
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following values for
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.Fa mode :
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.Bl -tag -width W_OK
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.It Dv R_OK
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Check for read permission.
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.It Dv W_OK
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Check for write permission.
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.It Dv X_OK
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Check for execute/search permission.
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.It Dv F_OK
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Check only for existence.
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.El
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.Pp
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All components of the pathname
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.Fa path
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are checked for access permissions as well.
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.Pp
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.\" Maybe this paragraph should be removed...
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The owner of a file has permission checked with respect to the
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.Dq owner
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read, write, and execute mode bits, members of the file's group
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other than the owner have permission checked with respect to the
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.Dq group
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mode bits, and all others have permissions checked with respect to
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the
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.Dq other
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mode bits.
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.Pp
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The file descriptor
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.Fa fd
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must name a directory.
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Search permission is required on this directory.
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.\" (These alternatives await a decision about the semantics of O_SEARCH)
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.\" Search permission is required on this directory, except if
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.\" .Fa fd
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.\" was opened with the
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.\" .Dv O_SEARCH
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.\" flag.
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.\" - or -
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.\" The directory referred to by
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.\" .Fa fd
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.\" must have been opened with the
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.\" .Dv O_SEARCH
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.\" flag.
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.\" - or -
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.\" The directory referred to by
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.\" .Fa fd
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.\" must have been opened with the
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.\" .Dv O_SEARCH
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.\" flag or must be searchable by the current process at the time the
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.\" call is made.
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.Pp
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The
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.Fa flags
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argument to
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.Fn faccessat
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can specify the following optional behavior:
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.Bl -tag -width AT_SYMLINK_NOFOLLOW
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.It AT_EACCESS
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Use the effective user and group IDs instead of the real user and
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group IDs for checking permission.
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See discussion below.
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.It AT_SYMLINK_NOFOLLOW
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Do not follow a symbolic link encountered as the last component in
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.Fa path .
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.El
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.Pp
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For
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.Fn access ,
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and
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.Fn faccessat
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when the
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.Dv AT_EACCESS
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flag is not passed, the real user ID and the real group ID are used
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for checking permission in place of the effective user ID and
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effective group ID.
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This affects only set-user-ID and set-group-ID programs, which should
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not use these functions.
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(For other programs, the real and effective IDs are the same.)
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.Pp
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For processes running with super-user privileges, these functions may
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return success for read and write checks regardless of whether read
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and write permission bits are actually set.
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This reflects the fact that the super-user may read and write all
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files regardless of permission settings.
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However, even for the super-user, an execute check using
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.Dv X_OK
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will succeed only if the target object has at least one of its
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execute permission bits set.
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.\" XXX: Is this true of search permission and directories? (I believe so.)
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(This does not guarantee that the target object can necessarily be
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successfully executed.
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See
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.Xr execve 2 . )
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.Sh RETURN VALUES
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The
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.Fn access
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and
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.Fn faccessat
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functions succeed and return 0 if, at some point in the recent past,
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the target object named by
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.Fa path
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existed and its permission settings allowed the requested access as
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described above.
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If the requested access would not have been granted, the object did
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not exist, or the path lookup failed, the value \-1 is returned
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and the value of
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.Va errno
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is set to reflect what went wrong.
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.Sh ERRORS
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These functions fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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Search permission is denied for
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.Fa fd ,
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or for the current directory, or for a directory in the prefix of
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.Fa path ;
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or the permission bits on the target file system object do not permit
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the requested access.
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.It Bq Er EBADF
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The file descriptor
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.Fa fd
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is not open and is not
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.Dv AT_FDCWD .
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.\" (possibly -- future)
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.\" or was not opened for searching with
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.\" .Dv O_SEARCH .
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.It Bq Er EFAULT
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.Fa path
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points outside the process's allocated address space.
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.It Bq Er EINVAL
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The
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.Fa mode
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or
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.Fa flags
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argument contained an invalid value.
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.It Bq Er EIO
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An I/O error occurred while reading from or writing to the file system.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded
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.Brq Dv NAME_MAX
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characters, or an entire path name exceeded
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.Brq Dv PATH_MAX
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characters.
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.It Bq Er ENOENT
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The named file does not exist.
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.It Bq Er ENOTDIR
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The file descriptor
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.Fa fd
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does not name a directory, or a component of the path prefix is not a
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directory.
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.It Bq Er EROFS
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Write access is requested for a file on a read-only file system.
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.It Bq Er ETXTBSY
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Write access is requested for a pure procedure (shared text)
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file presently being executed.
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.El
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.Sh SEE ALSO
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.Xr chmod 2 ,
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.Xr execve 2 ,
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.Xr stat 2 ,
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.Xr secure_path 3
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.Sh STANDARDS
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The
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.Fn access
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function conforms to
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.St -p1003.1-90 .
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.Fn faccessat
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function conforms to
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.St -p1003.1-2008 .
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.\" This paragraph could be moved to the end of DESCRIPTION if people
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.\" don't like having it here.
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.Pp
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Note that
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.Fn faccessat
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violates the historic convention that system calls whose names begin
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with `f' operate on file handles rather than paths.
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There is no equivalent to
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.Fn access
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for checking access properties of an already-opened file.
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.Sh SECURITY CONSIDERATIONS
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Because the results of these calls reflect the state of the file
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system at the time they ran, and the file system can potentially be
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modified between that time and the time the caller attempts to act on
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the results, they should
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.Em never
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be used for security enforcement.
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.Pp
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Privileged programs that need to restrict their actions to files or
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directories properly accessible to unprivileged users
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.Em must
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do this by assuming or restoring an unprivileged state (see
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.Xr seteuid 2 )
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when performing the pertinent actions.
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Checking in advance (with
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.Fn access
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or any other method) and performing such actions while privileged
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introduces a race condition that in most cases is easily exploitable
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by even a naive adversary.
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.Pp
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Even for non-privileged programs, the opportunity for the world to
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change after the call runs makes
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.Fn access
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and
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.Fn faccessat
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not very useful.
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In general only
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.Dv F_OK
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should be used, and that sparingly.
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The other checks may occasionally be useful for user interface or
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diagnostic purposes.
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