bsd/man/man2/chmod.2

   1 .\"     $NetBSD: chmod.2,v 1.7 1995/02/27 12:32:06 cgd Exp $
   2 .\"
   3 .\" Copyright (c) 1980, 1991, 1993
   4 .\"     The Regents of the University of California.  All rights reserved.
   5 .\"
   6 .\" Redistribution and use in source and binary forms, with or without
   7 .\" modification, are permitted provided that the following conditions
   8 .\" are met:
   9 .\" 1. Redistributions of source code must retain the above copyright
  10 .\"    notice, this list of conditions and the following disclaimer.
  11 .\" 2. Redistributions in binary form must reproduce the above copyright
  12 .\"    notice, this list of conditions and the following disclaimer in the
  13 .\"    documentation and/or other materials provided with the distribution.
  14 .\" 3. All advertising materials mentioning features or use of this software
  15 .\"    must display the following acknowledgement:
  16 .\"     This product includes software developed by the University of
  17 .\"     California, Berkeley and its contributors.
  18 .\" 4. Neither the name of the University nor the names of its contributors
  19 .\"    may be used to endorse or promote products derived from this software
  20 .\"    without specific prior written permission.
  21 .\"
  22 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32 .\" SUCH DAMAGE.
  33 .\"
  34 .\"     @(#)chmod.2     8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt CHMOD 2
  38 .Os BSD 4
  39 .Sh NAME
  40 .Nm chmod ,
  41 .Nm fchmod ,
  42 .Nm fchmodat
  43 .Nd change mode of file
  44 .Sh SYNOPSIS
  45 .Fd #include <sys/types.h>
  46 .Fd #include <sys/stat.h>
  47 .Ft int
  48 .Fo chmod
  49 .Fa "const char *path"
  50 .Fa "mode_t mode"
  51 .Fc
  52 .Ft int
  53 .Fo fchmod
  54 .Fa "int fildes"
  55 .Fa "mode_t mode"
  56 .Fc
  57 .Ft int
  58 .Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag"
  59 .Sh DESCRIPTION
  60 The function
  61 .Fn chmod
  62 sets the file permission bits
  63 of the file
  64 specified by the pathname
  65 .Fa path
  66 to
  67 .Fa mode .
  68 .Fn fchmod
  69 sets the permission bits of the specified
  70 file descriptor
  71 .Fa fildes .
  72 .Fn chmod
  73 verifies that the process owner (user) either owns
  74 the file specified by
  75 .Fa path
  76 (or
  77 .Fa fildes ) ,
  78 or
  79 is the super-user.
  80 .Pp
  81 The
  82 .Fn fchmodat
  83 is equivalent to
  84 .Fn chmod
  85 except in the case where
  86 .Fa path
  87 specifies a relative path.
  88 In this case the file to be changed is determined relative to the directory
  89 associated with the file descriptor
  90 .Fa fd
  91 instead of the current working directory.
  92 The values for the
  93 .Fa flag
  94 are constructed by a bitwise-inclusive OR of flags from the following list, defined
  95 in
  96 .In fcntl.h :
  97 .Bl -tag -width indent
  98 .It Dv AT_SYMLINK_NOFOLLOW
  99 If
 100 .Fa path
 101 names a symbolic link, then the mode of the symbolic link is changed.
 102 .El
 103 .Pp
 104 If
 105 .Fn fchmodat
 106 is passed the special value
 107 .Dv AT_FDCWD
 108 in the
 109 .Fa fd
 110 parameter, the current working directory is used.
 111 If also
 112 .Fa flag
 113 is zero, the behavior is identical to a call to
 114 .Fn chmod .
 115 A mode is created from
 116 .Em or'd
 117 permission bit masks
 118 defined in
 119 .Aq Pa sys/stat.h :
 120 .Bd -literal -offset indent -compact
 121 #define S_IRWXU 0000700    /* RWX mask for owner */
 122 #define S_IRUSR 0000400    /* R for owner */
 123 #define S_IWUSR 0000200    /* W for owner */
 124 #define S_IXUSR 0000100    /* X for owner */
 125
 126 #define S_IRWXG 0000070    /* RWX mask for group */
 127 #define S_IRGRP 0000040    /* R for group */
 128 #define S_IWGRP 0000020    /* W for group */
 129 #define S_IXGRP 0000010    /* X for group */
 130
 131 #define S_IRWXO 0000007    /* RWX mask for other */
 132 #define S_IROTH 0000004    /* R for other */
 133 #define S_IWOTH 0000002    /* W for other */
 134 #define S_IXOTH 0000001    /* X for other */
 135
 136 #define S_ISUID 0004000    /* set user id on execution */
 137 #define S_ISGID 0002000    /* set group id on execution */
 138 #define S_ISVTX 0001000    /* save swapped text even after use */
 139 .Ed
 140 .Pp
 141 The
 142 .Dv ISVTX
 143 (the
 144 .Em sticky bit )
 145 indicates to the system which executable files are shareable (the
 146 default) and the system maintains the program text of the files
 147 in the swap area. The sticky bit may only be set by the super user
 148 on shareable executable files.
 149 .Pp
 150 If mode
 151 .Dv ISVTX
 152 (the `sticky bit') is set on a directory,
 153 an unprivileged user may not delete or rename
 154 files of other users in that directory. The sticky bit may be
 155 set by any user on a directory which the user owns or has appropriate
 156 permissions.
 157 For more details of the properties of the sticky bit, see
 158 .Xr sticky 8 .
 159 .Pp
 160 Writing or changing the owner of a file
 161 turns off the set-user-id and set-group-id bits
 162 unless the user is the super-user.
 163 This makes the system somewhat more secure
 164 by protecting set-user-id (set-group-id) files
 165 from remaining set-user-id (set-group-id) if they are modified,
 166 at the expense of a degree of compatibility.
 167 .Sh RETURN VALUES
 168 Upon successful completion, a value of 0 is returned.
 169 Otherwise, a value of -1 is returned and
 170 .Va errno
 171 is set to indicate the error.
 172 .Sh ERRORS
 173 The
 174 .Fn chmod
 175 system call will fail and the file mode will be unchanged if:
 176 .Bl -tag -width Er
 177 .\" ==========
 178 .It Bq Er EACCES
 179 Search permission is denied for a component of the path prefix.
 180 .\" ==========
 181 .It Bq Er EFAULT
 182 .Fa Path
 183 points outside the process's allocated address space.
 184 .\" ==========
 185 .It Bq Er EINTR
 186 Its execution was interrupted by a signal.
 187 .\" ==========
 188 .It Bq Er EIO
 189 An I/O error occurred while reading from or writing to the file system.
 190 .\" ==========
 191 .It Bq Er ELOOP
 192 Too many symbolic links were encountered in translating the pathname.
 193 This is taken to be indicative of a looping symbolic link.
 194 .\" ==========
 195 .It Bq Er ENAMETOOLONG
 196 A component of a pathname exceeded
 197 .Dv {NAME_MAX}
 198 characters, or an entire path name exceeded
 199 .Dv {PATH_MAX}
 200 characters.
 201 .\" ==========
 202 .It Bq Er ENOENT
 203 The named file does not exist.
 204 .\" ==========
 205 .It Bq Er ENOTDIR
 206 A component of the path prefix is not a directory.
 207 .\" ==========
 208 .It Bq Er EPERM
 209 The effective user ID does not match the owner of the file and
 210 the effective user ID is not the super-user.
 211 .\" ==========
 212 .It Bq Er EROFS
 213 The named file resides on a read-only file system.
 214 .El
 215 .Pp
 216 .Fn fchmod
 217 will fail if:
 218 .Bl -tag -width Er
 219 .\" ==========
 220 .It Bq Er EBADF
 221 .Fa fildes
 222 is not a valid file descriptor.
 223 .\" ==========
 224 .It Bq Er EINVAL
 225 .Fa fildes
 226 refers to a socket, not to a file.
 227 .\" ==========
 228 .It Bq Er EINVAL
 229 .Fa mode
 230 is not a valid file mode.
 231 .\" ==========
 232 .It Bq Er EINTR
 233 Its execution was interrupted by a signal.
 234 .\" ==========
 235 .It Bq Er EIO
 236 An I/O error occurred while reading from or writing to the file system.
 237 .\" ==========
 238 .It Bq Er EPERM
 239 The effective user ID does not match the owner of the file and
 240 the effective user ID is not the super-user.
 241 .\" ==========
 242 .It Bq Er EROFS
 243 The file resides on a read-only file system.
 244 .El
 245 .Pp
 246 In addition to the
 247 .Fn chmod
 248 errors,
 249 .Fn fchmodat
 250 fails if:
 251 .Bl -tag -width Er
 252 .It Bq Er EBADF
 253 The
 254 .Fa path
 255 argument does not specify an absolute path and the
 256 .Fa fd
 257 argument is neither
 258 .Fa AT_FDCWD
 259 nor a valid file descriptor open for searching.
 260 .It Bq Er EINVAL
 261 The value of the
 262 .Fa flag
 263 argument is not valid.
 264 .It Bq Er ENOTDIR
 265 The
 266 .Fa path
 267 argument is not an absolute path and
 268 .Fa fd
 269 is neither
 270 .Dv AT_FDCWD
 271 nor a file descriptor associated with a directory.
 272 .El
 273 .Sh LEGACY SYNOPSIS
 274 .Fd #include <sys/types.h>
 275 .Fd #include <sys/stat.h>
 276 .Pp
 277 The include file
 278 .In sys/types.h
 279 is necessary.
 280 .Sh SEE ALSO
 281 .Xr chmod 1 ,
 282 .Xr chown 2 ,
 283 .Xr open 2 ,
 284 .Xr stat 2 ,
 285 .Xr compat 5 ,
 286 .Xr sticky 8
 287 .Sh STANDARDS
 288 The
 289 .Fn chmod
 290 function is expected to conform to
 291 .St -p1003.1-88 .
 292 The
 293 .Fn fchmodat
 294 function is expected to conform to POSIX.1-2008 .
 295 .Sh HISTORY
 296 The
 297 .Fn fchmod
 298 function call
 299 appeared in
 300 .Bx 4.2 .
 301 The
 302 .Fn fchmodat
 303 system call appeared in OS X 10.10