chmod/chmod.1

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  35 .\"     @(#)chmod.1     8.4 (Berkeley) 3/31/94
  36 .\" $FreeBSD: src/bin/chmod/chmod.1,v 1.33 2002/10/01 20:32:59 trhodes Exp $
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  38 .Dd July 08, 2004
  39 .Dt CHMOD 1
  40 .Os
  41 .Sh NAME
  42 .Nm chmod
  43 .Nd change file modes or Access Control Lists
  44 .Sh SYNOPSIS
  45 .Nm chmod
  46 .Op Fl fv
  47 .Op Fl R Op Fl H | L | P
  48 .Ar mode
  49 .Ar
  50 .Nm chmod
  51 .Op Fl fv
  52 .Op Fl R Op Fl H | L | P
  53 .Op -a | +a | =a
  54 .Ar ACE
  55 .Ar
  56 .Nm chmod
  57 .Op Fl fhv
  58 .Op Fl R Op Fl H | L | P
  59 .Op Fl E
  60 .Ar
  61 .Nm chmod
  62 .Op Fl fhv
  63 .Op Fl R Op Fl H | L | P
  64 .Op Fl C
  65 .Ar
  66 .Nm chmod
  67 .Op Fl fhv
  68 .Op Fl R Op Fl H | L | P
  69 .Op Fl N
  70 .Ar
  71 .Sh DESCRIPTION
  72 The
  73 .Nm chmod
  74 utility modifies the file mode bits of the listed files
  75 as specified by the
  76 .Ar mode
  77 operand. It may also be used to modify the Access Control
  78 Lists (ACLs) associated with the listed files.
  79 .Pp
  80 The generic options are as follows:
  81 .Bl -tag -width Ds
  82 .It Fl f
  83 Do not display a diagnostic message if
  84 .Nm chmod
  85 could not modify the mode for
  86 .Va file .
  87 .It Fl H
  88 If the
  89 .Fl R
  90 option is specified, symbolic links on the command line are followed.
  91 (Symbolic links encountered in the tree traversal are not followed by
  92 default.)
  93 .It Fl h
  94 If the file is a symbolic link, change the mode of the link itself
  95 rather than the file that the link points to.
  96 .It Fl L
  97 If the
  98 .Fl R
  99 option is specified, all symbolic links are followed.
 100 .It Fl P
 101 If the
 102 .Fl R
 103 option is specified, no symbolic links are followed.
 104 This is the default.
 105 .It Fl R
 106 Change the modes of the file hierarchies rooted in the files
 107 instead of just the files themselves.
 108 .It Fl v
 109 Cause
 110 .Nm chmod
 111 to be verbose, showing filenames as the mode is modified.
 112 If the
 113 .Fl v
 114 flag is specified more than once, the old and new modes of the file
 115 will also be printed, in both octal and symbolic notation.
 116 .El
 117 .Pp
 118 The
 119 .Fl H ,
 120 .Fl L
 121 and
 122 .Fl P
 123 options are ignored unless the
 124 .Fl R
 125 option is specified.
 126 In addition, these options override each other and the
 127 command's actions are determined by the last one specified.
 128 .Pp
 129 Only the owner of a file or the super-user is permitted to change
 130 the mode of a file.
 131 .Sh DIAGNOSTICS
 132 .Ex -std
 133 .Sh MODES
 134 Modes may be absolute or symbolic.
 135 An absolute mode is an octal number constructed from the sum of
 136 one or more of the following values:
 137 .Pp
 138 .Bl -tag -width 6n -compact -offset indent
 139 .It Li 4000
 140 (the set-user-ID-on-execution bit) Executable files with this bit set
 141 will run with effective uid set to the uid of the file owner.
 142 Directories with the set-user-id bit set will force all files and
 143 sub-directories created in them to be owned by the directory owner
 144 and not by the uid of the creating process, if the underlying file
 145 system supports this feature: see
 146 .Xr chmod 2
 147 and the
 148 .Ar suiddir
 149 option to
 150 .Xr mount 8 .
 151 .It Li 2000
 152 (the set-group-ID-on-execution bit) Executable files with this bit set
 153 will run with effective gid set to the gid of the file owner.
 154 .It Li 1000
 155 (the sticky bit)
 156 See
 157 .Xr chmod 2
 158 and
 159 .Xr sticky 8 .
 160 .It Li 0400
 161 Allow read by owner.
 162 .It Li 0200
 163 Allow write by owner.
 164 .It Li 0100
 165 For files, allow execution by owner.
 166 For directories, allow the owner to
 167 search in the directory.
 168 .It Li 0040
 169 Allow read by group members.
 170 .It Li 0020
 171 Allow write by group members.
 172 .It Li 0010
 173 For files, allow execution by group members.
 174 For directories, allow
 175 group members to search in the directory.
 176 .It Li 0004
 177 Allow read by others.
 178 .It Li 0002
 179 Allow write by others.
 180 .It Li 0001
 181 For files, allow execution by others.
 182 For directories allow others to
 183 search in the directory.
 184 .El
 185 .Pp
 186 For example, the absolute mode that permits read, write and execute by
 187 the owner, read and execute by group members, read and execute by
 188 others, and no set-uid or set-gid behaviour is 755
 189 (400+200+100+040+010+004+001).
 190 .Pp
 191 The symbolic mode is described by the following grammar:
 192 .Bd -literal -offset indent
 193 mode         ::= clause [, clause ...]
 194 clause       ::= [who ...] [action ...] action
 195 action       ::= op [perm ...]
 196 who          ::= a | u | g | o
 197 op           ::= + | \- | =
 198 perm         ::= r | s | t | w | x | X | u | g | o
 199 .Ed
 200 .Pp
 201 The
 202 .Ar who
 203 symbols ``u'', ``g'', and ``o'' specify the user, group, and other parts
 204 of the mode bits, respectively.
 205 The
 206 .Ar who
 207 symbol ``a'' is equivalent to ``ugo''.
 208 .Pp
 209 The
 210 .Ar perm
 211 symbols represent the portions of the mode bits as follows:
 212 .Pp
 213 .Bl -tag -width Ds -compact -offset indent
 214 .It r
 215 The read bits.
 216 .It s
 217 The set-user-ID-on-execution and set-group-ID-on-execution bits.
 218 .It t
 219 The sticky bit.
 220 .It w
 221 The write bits.
 222 .It x
 223 The execute/search bits.
 224 .It X
 225 The execute/search bits if the file is a directory or any of the
 226 execute/search bits are set in the original (unmodified) mode.
 227 Operations with the
 228 .Ar perm
 229 symbol ``X'' are only meaningful in conjunction with the
 230 .Ar op
 231 symbol ``+'', and are ignored in all other cases.
 232 .It u
 233 The user permission bits in the original mode of the file.
 234 .It g
 235 The group permission bits in the original mode of the file.
 236 .It o
 237 The other permission bits in the original mode of the file.
 238 .El
 239 .Pp
 240 The
 241 .Ar op
 242 symbols represent the operation performed, as follows:
 243 .Bl -tag -width 4n
 244 .It +
 245 If no value is supplied for
 246 .Ar perm ,
 247 the ``+'' operation has no effect.
 248 If no value is supplied for
 249 .Ar who ,
 250 each permission bit specified in
 251 .Ar perm ,
 252 for which the corresponding bit in the file mode creation mask
 253 is clear, is set.
 254 Otherwise, the mode bits represented by the specified
 255 .Ar who
 256 and
 257 .Ar perm
 258 values are set.
 259 .It \&\-
 260 If no value is supplied for
 261 .Ar perm ,
 262 the ``\-'' operation has no effect.
 263 If no value is supplied for
 264 .Ar who ,
 265 each permission bit specified in
 266 .Ar perm ,
 267 for which the corresponding bit in the file mode creation mask
 268 is clear, is cleared.
 269 Otherwise, the mode bits represented by the specified
 270 .Ar who
 271 and
 272 .Ar perm
 273 values are cleared.
 274 .It =
 275 The mode bits specified by the
 276 .Ar who
 277 value are cleared, or, if no who value is specified, the owner, group
 278 and other mode bits are cleared.
 279 Then, if no value is supplied for
 280 .Ar who ,
 281 each permission bit specified in
 282 .Ar perm ,
 283 for which the corresponding bit in the file mode creation mask
 284 is clear, is set.
 285 Otherwise, the mode bits represented by the specified
 286 .Ar who
 287 and
 288 .Ar perm
 289 values are set.
 290 .El
 291 .Pp
 292 Each
 293 .Ar clause
 294 specifies one or more operations to be performed on the mode
 295 bits, and each operation is applied to the mode bits in the
 296 order specified.
 297 .Pp
 298 Operations upon the other permissions only (specified by the symbol
 299 ``o'' by itself), in combination with the
 300 .Ar perm
 301 symbols ``s'' or ``t'', are ignored.
 302 .Sh EXAMPLES OF VALID MODES
 303 .Bl -tag -width "u=rwx,go=u-w" -compact
 304 .It Li 644
 305 make a file readable by anyone and writable by the owner only.
 306 .Pp
 307 .It Li go-w
 308 deny write permission to group and others.
 309 .Pp
 310 .It Li =rw,+X
 311 set the read and write permissions to the usual defaults, but
 312 retain any execute permissions that are currently set.
 313 .Pp
 314 .It Li +X
 315 make a directory or file searchable/executable by everyone if it is
 316 already searchable/executable by anyone.
 317 .Pp
 318 .It Li 755
 319 .It Li u=rwx,go=rx
 320 .It Li u=rwx,go=u-w
 321 make a file readable/executable by everyone and writable by the owner only.
 322 .Pp
 323 .It Li go=
 324 clear all mode bits for group and others.
 325 .Pp
 326 .It Li g=u-w
 327 set the group bits equal to the user bits, but clear the group write bit.
 328 .El
 329 .Sh ACL MANIPULATION OPTIONS
 330 ACLs are manipulated using extensions to the symbolic mode
 331 grammar.  Each file has one ACL, containing an ordered list of entries.
 332 Each entry refers to a user or group, and grants or denies a set of
 333 permissions.
 334 In cases where a user and a group exist with the same name, the
 335 user/group name can be prefixed with "user:" or "group:" in order to
 336 specify the type of name.
 337 .Pp
 338 The following permissions are applicable to all filesystem objects:
 339 .Bl -tag -width 6n -compact -offset indent
 340 .It delete
 341 Delete the item.  Deletion may be granted by either this permission
 342 on an object or the delete_child right on the containing directory.
 343 .It readattr
 344 Read an objects basic attributes.  This is implicitly granted if
 345 the object can be looked up and not explicitly denied.
 346 .It writeattr
 347 Write an object's basic attributes.
 348 .It readextattr
 349 Read extended attributes.
 350 .It writeextattr
 351 Write extended attributes.
 352 .It readsecurity
 353 Read an object's extended security information (ACL).
 354 .It writesecurity
 355 Write an object's security information (ownership, mode, ACL).
 356 .It chown
 357 Change an object's ownership.
 358 .El
 359 .Pp
 360 The following permissions are applicable to directories:
 361 .Bl -tag -width 6n -compact -offset indent
 362 .It list
 363 List entries.
 364 .It search
 365 Look up files by name.
 366 .It add_file
 367 Add a file.
 368 .It add_subdirectory
 369 Add a subdirectory.
 370 .It delete_child
 371 Delete a contained object.  See the file delete permission above.
 372 .El
 373 .Pp
 374 The following permissions are applicable to non-directory filesystem objects:
 375 .Bl -tag -width 6n -compact -offset indent
 376 .It read
 377 Open for reading.
 378 .It write
 379 Open for writing.
 380 .It append
 381 Open for writing, but in a fashion that only allows writes into areas of
 382 the file not previously written.
 383 .It execute
 384 Execute the file as a script or program.
 385 .El
 386 .Pp
 387 ACL inheritance is controlled with the following permissions words, which
 388 may only be applied to directories:
 389 .Bl -tag -width 6n -compact -offset indent
 390 .It file_inherit
 391 Inherit to files.
 392 .It directory_inherit
 393 Inherit to directories.
 394 .It limit_inherit
 395 This flag is only relevant to entries inherited by subdirectories; it
 396 causes the directory_inherit flag to be cleared in the entry that is
 397 inherited, preventing further nested subdirectories from also
 398 inheriting the entry.
 399 .It only_inherit
 400 The entry is inherited by created items but not considered when processing
 401 the ACL.
 402 .El
 403 .Pp
 404 The ACL manipulation options are as follows:
 405 .Bl -tag -width Ds
 406 .It \fB+a\fR
 407 The +a mode parses a new ACL entry from the next argument on
 408 the commandline and inserts it into the canonical location in the
 409 ACL. If the supplied entry refers to an identity already listed, the
 410 two entries are combined.
 411 .Pp
 412 \fBExamples\fR
 413  # ls -le
 414  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 415  # chmod +a "admin allow write" file1
 416  # ls -le
 417  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 418    owner: juser
 419    1: admin allow write
 420  # chmod +a "guest deny read" file1
 421  # ls -le
 422  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 423    owner: juser
 424    1: guest deny read
 425    2: admin allow write
 426  # chmod +a "admin allow delete" file1
 427  # ls -le
 428  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 429    owner: juser
 430    1: guest deny read
 431    2: admin allow write,delete
 432 .Pp
 433 The +a mode strives to maintain correct canonical form for the ACL.
 434                  local deny
 435                  local allow
 436                  inherited deny
 437                  inherited allow
 438 .Pp
 439 By default, chmod adds entries to the top of the local deny and local
 440 allow lists. Inherited entries are added by using the +ai mode.
 441 .Pp
 442 \fBExamples\fR
 443  # ls -le
 444  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 445    owner: juser
 446    1: guest deny read
 447    2: admin allow write,delete
 448    3: juser inherited deny delete
 449    4: admin inherited allow delete
 450    5: backup inherited deny read
 451    6: admin inherited allow write-security
 452  # chmod +ai "others allow read" file1
 453  # ls -le
 454  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 455    owner: juser
 456    1: guest deny read
 457    2: admin allow write,delete
 458    3: juser inherited deny delete
 459    4: others inherited allow read
 460    5: admin inherited allow delete
 461    6: backup inherited deny read
 462    7: admin inherited allow write-security
 463 .It \fB+a#\fR
 464 When a specific ordering is required, the exact location at which an
 465 entry will be inserted is specified with the +a# mode.
 466 .Pp
 467 \fBExamples\fR
 468  # ls -le
 469  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 470    owner: juser
 471    1: guest deny read
 472    2: admin allow write
 473  # chmod +a# 2 "others deny read" file1
 474  # ls -le
 475  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 476    owner: juser
 477    1: guest deny read
 478    2: others deny read
 479    3: admin allow write
 480 .Pp
 481 The +ai# mode may be used to insert inherited entries at a specific
 482 location. Note that these modes allow non-canonical ACL ordering to
 483 be constructed.
 484 .It Fl a
 485 The -a mode is used to delete ACL entries. All entries exactly
 486 matching the supplied entry will be deleted. If the entry lists a
 487 subset of rights granted by an entry, only the rights listed are
 488 removed. Entries may also be deleted by index using the -a# mode.
 489 .Pp
 490 \fBExamples\fR
 491  # ls -le
 492  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 493    owner: juser
 494    1: guest deny read
 495    2: admin allow write,delete
 496  # chmod -a# 1 file1
 497  # ls -le
 498  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 499    owner: juser
 500    1: admin allow write,delete
 501  # chmod -a "admin allow write" file1
 502  # ls -le
 503  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 504    owner: juser
 505    1: admin allow delete
 506 .Pp
 507 Inheritance is not considered when processing the -a mode; rights and
 508 entries will be removed regardless of their inherited state.
 509 .It \fB=a#\fR
 510 Individual entries are rewritten using the =a# mode.
 511 .Pp
 512 \fBExamples\fR
 513  # ls -le
 514  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 515    owner: juser
 516    1: admin allow delete
 517  # chmod =a# 1 "admin allow write,chown"
 518  # ls -le
 519  -rw-r--r--+ 1 juser  wheel  0 Apr 28 14:06 file1
 520    owner: juser
 521    1: admin allow write,chown
 522 .Pp
 523 This mode may not be used to add new entries.
 524 .It Fl E
 525 Reads the ACL information from stdin, as a sequential list
 526 of ACEs, separated by newlines.  If the information parses correctly,
 527 the existing information is replaced.
 528 .It Fl C
 529 Returns false if any of the named files have ACLs in non-canonical order.
 530 .It Fl i
 531 Removes the 'inherited' bit from all entries in the named file(s) ACLs.
 532 .It Fl I
 533 Removes all inherited entries from the named file(s) ACL(s).
 534 .It Fl N
 535 Removes the ACL from the named file(s).
 536 .El
 537 .Sh COMPATIBILITY
 538 The
 539 .Fl v
 540 option is non-standard and its use in scripts is not recommended.
 541 .Sh SEE ALSO
 542 .Xr chflags 1 ,
 543 .Xr fsaclctl 1 ,
 544 .Xr install 1 ,
 545 .Xr chmod 2 ,
 546 .Xr stat 2 ,
 547 .Xr umask 2 ,
 548 .Xr fts 3 ,
 549 .Xr setmode 3 ,
 550 .Xr symlink 7 ,
 551 .Xr chown 8 ,
 552 .Xr mount 8 ,
 553 .Xr sticky 8
 554 .Sh STANDARDS
 555 The
 556 .Nm chmod
 557 utility is expected to be
 558 .St -p1003.2
 559 compatible with the exception of the
 560 .Ar perm
 561 symbol
 562 .Dq t
 563 which is not included in that standard.
 564 .Sh HISTORY
 565 A
 566 .Nm chmod
 567 command appeared in
 568 .At v1 .