249 lines
7 KiB
Groff
249 lines
7 KiB
Groff
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.\" $NetBSD: chmod.2,v 1.37 2010/05/31 12:16:20 njoly 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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.\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
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.\"
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.Dd January 4, 2009
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.Dt CHMOD 2
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.Os
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.Sh NAME
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.Nm chmod ,
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.Nm lchmod ,
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.Nm fchmod
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.Nd change mode of file
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/stat.h
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.Ft int
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.Fn chmod "const char *path" "mode_t mode"
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.Ft int
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.Fn lchmod "const char *path" "mode_t mode"
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.Ft int
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.Fn fchmod "int fd" "mode_t mode"
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.Sh DESCRIPTION
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The function
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.Fn chmod
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sets the file permission bits
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of the file
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specified by the pathname
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.Fa path
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to
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.Fa mode .
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.Fn fchmod
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sets the permission bits of the specified
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file descriptor
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.Fa fd .
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.Fn lchmod
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is like
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.Fn chmod
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except in the case where the named file is a symbolic link,
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in which case
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.Fn lchmod
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sets the permission bits of the link,
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while
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.Fn chmod
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sets the bits of the file the link references.
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.Fn chmod
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verifies that the process owner (user) either owns
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the file specified by
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.Fa path
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(or
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.Fa fd ) ,
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or
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is the super-user.
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A mode is created from
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.Em or'd
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permission bit masks
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defined in
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.In sys/stat.h :
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.Bd -literal -offset indent -compact
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#define S_IRWXU 0000700 /* RWX mask for owner */
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#define S_IRUSR 0000400 /* R for owner */
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#define S_IWUSR 0000200 /* W for owner */
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#define S_IXUSR 0000100 /* X for owner */
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#define S_IRWXG 0000070 /* RWX mask for group */
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#define S_IRGRP 0000040 /* R for group */
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#define S_IWGRP 0000020 /* W for group */
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#define S_IXGRP 0000010 /* X for group */
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#define S_IRWXO 0000007 /* RWX mask for other */
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#define S_IROTH 0000004 /* R for other */
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#define S_IWOTH 0000002 /* W for other */
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#define S_IXOTH 0000001 /* X for other */
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#define S_ISUID 0004000 /* set user id on execution */
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#define S_ISGID 0002000 /* set group id on execution */
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#define S_ISVTX 0001000 /* save swapped text even after use */
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.Ed
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.Pp
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If mode
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.Dv ISVTX
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(the
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.Sq sticky bit )
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is set on a regular file, it historically meant that the system should
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save a shareable copy of the program text in the swap area.
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When applied to commonly used programs like the shell or editor, this
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would decrease memory usage and startup time.
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In
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.Nx ,
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the sticky bit may still be set on regular files by the super-user,
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but has no effect.
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The historical meaning became obsolete in the 1980s with the advent of
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memory-mapped executables, and is only documented as a matter of
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historical interest.
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.Pp
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If mode
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.Dv ISVTX
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(the
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.Sq sticky bit )
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is set on a directory,
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an unprivileged user may not delete or rename
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files of other users in that directory.
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The sticky bit may be set by any user on a directory which the user
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owns or has appropriate permissions.
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.Pp
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For more information about the properties of the sticky bit, see
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.Xr sticky 7 .
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.Pp
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Changing the owner of a file
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turns off the set-user-id and set-group-id bits;
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writing to a file
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turns off the set-user-id and set-group-id bits
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unless the user is the super-user.
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This makes the system somewhat more secure
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by protecting set-user-id (set-group-id) files
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from remaining set-user-id (set-group-id) if they are modified,
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at the expense of a degree of compatibility.
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.Sh RETURN VALUES
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Upon successful completion, a value of 0 is returned.
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Otherwise, a value of \-1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn chmod
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and
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.Fn lchmod
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will fail and the file mode will be unchanged if:
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory.
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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 EACCES
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Search permission is denied for a component of the path prefix.
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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 EPERM
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The effective user ID does not match the owner of the file and
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the effective user ID is not the super-user.
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.It Bq Er EPERM
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The mode includes the setgid bit
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.Pq Dv S_ISGID
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but the file's group is neither the effective group ID nor is it in the
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group access list.
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.It Bq Er EROFS
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The named file resides on a read-only file system.
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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 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 EFTYPE
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The effective user ID is not the super-user, the
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.Fa mode
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includes the sticky bit
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.Pq Dv S_ISVTX ,
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and
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.Fa path
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does not refer to a directory.
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.El
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.Pp
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.Fn fchmod
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The descriptor is not valid.
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.It Bq Er EINVAL
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.Fa fd
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refers to a socket, not to a file.
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.It Bq Er EPERM
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The effective user ID does not match the owner of the file and
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the effective user ID is not the super-user.
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.It Bq Er EPERM
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The mode includes the setgid bit
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.Pq Dv S_ISGID
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but the file's group is neither the effective group ID nor is it in the
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group access list.
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.It Bq Er EROFS
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The file resides on a read-only file system.
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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 EFTYPE
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The effective user ID is not the super-user, the
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.Fa mode
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includes the sticky bit
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.Pq Dv S_ISVTX ,
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and
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.Fa fd
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does not refer to a directory.
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.El
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.Sh SEE ALSO
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.Xr chmod 1 ,
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.Xr chflags 2 ,
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.Xr chown 2 ,
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.Xr open 2 ,
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.Xr stat 2 ,
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.Xr getmode 3 ,
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.Xr setmode 3 ,
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.Xr sticky 7 ,
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.Xr symlink 7
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.Sh STANDARDS
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The
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.Fn chmod
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function conforms to
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.St -p1003.1-90 .
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.Sh HISTORY
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The
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.Fn fchmod
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function call
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appeared in
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.Bx 4.2 .
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The
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.Fn lchmod
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function call appeared in
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.Nx 1.3 .
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