man2/mount.2

   1 .\" Copyright (C) 1993 Rickard E. Faith <faith@cs.unc.edu>
   2 .\" and Copyright (C) 1994 Andries E. Brouwer <aeb@cwi.nl>
   3 .\" and Copyright (C) 2002, 2005, 2016 Michael Kerrisk <mtk.manpages@gmail.com>
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  15 .\" Since the Linux kernel and libraries are constantly changing, this
  16 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
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  20 .\" which is licensed free of charge, as they might when working
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  26 .\"
  27 .\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com>
  28 .\" Modified 2001-10-13 by Michael Kerrisk <mtk.manpages@gmail.com>
  29 .\"     Added note on historical behavior of MS_NOSUID
  30 .\" Modified 2002-05-16 by Michael Kerrisk <mtk.manpages@gmail.com>
  31 .\"     Extensive changes and additions
  32 .\" Modified 2002-05-27 by aeb
  33 .\" Modified 2002-06-11 by Michael Kerrisk <mtk.manpages@gmail.com>
  34 .\"     Enhanced descriptions of MS_MOVE, MS_BIND, and MS_REMOUNT
  35 .\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
  36 .\" 2005-05-18, mtk, Added MNT_EXPIRE, plus a few other tidy-ups.
  37 .\" 2008-10-06, mtk: move umount*() material into separate umount.2 page.
  38 .\" 2008-10-06, mtk: Add discussion of namespaces.
  39 .\"
  40 .TH MOUNT 2 2019-08-02 "Linux" "Linux Programmer's Manual"
  41 .SH NAME
  42 mount \- mount filesystem
  43 .SH SYNOPSIS
  44 .nf
  45 .B "#include <sys/mount.h>"
  46 .PP
  47 .BI "int mount(const char *" source ", const char *" target ,
  48 .BI "          const char *" filesystemtype ", unsigned long " mountflags ,
  49 .BI "          const void *" data );
  50 .fi
  51 .SH DESCRIPTION
  52 .BR mount ()
  53 attaches the filesystem specified by
  54 .I source
  55 (which is often a pathname referring to a device,
  56 but can also be the pathname of a directory or file,
  57 or a dummy string) to the location (a directory or file)
  58 specified by the pathname in
  59 .IR target .
  60 .PP
  61 Appropriate privilege (Linux: the
  62 .B CAP_SYS_ADMIN
  63 capability) is required to mount filesystems.
  64 .PP
  65 Values for the
  66 .I filesystemtype
  67 argument supported by the kernel are listed in
  68 .I /proc/filesystems
  69 (e.g., "btrfs", "ext4", "jfs", "xfs", "vfat", "fuse",
  70 "tmpfs", "cgroup", "proc", "mqueue", "nfs", "cifs", "iso9660").
  71 Further types may become available when the appropriate modules
  72 are loaded.
  73 .PP
  74 The
  75 .I data
  76 argument is interpreted by the different filesystems.
  77 Typically it is a string of comma-separated options
  78 understood by this filesystem.
  79 See
  80 .BR mount (8)
  81 for details of the options available for each filesystem type.
  82 .PP
  83 A call to
  84 .BR mount ()
  85 performs one of a number of general types of operation,
  86 depending on the bits specified in
  87 .IR mountflags .
  88 The choice of which operation to perform is determined by
  89 testing the bits set in
  90 .IR mountflags ,
  91 with the tests being conducted in the order listed here:
  92 .IP * 3
  93 Remount an existing mount:
  94 .IR mountflags
  95 includes
  96 .BR MS_REMOUNT .
  97 .IP *
  98 Create a bind mount:
  99 .IR mountflags
 100 includes
 101 .BR MS_BIND .
 102 .IP *
 103 Change the propagation type of an existing mount:
 104 .IR mountflags
 105 includes one of
 106 .BR MS_SHARED ,
 107 .BR MS_PRIVATE ,
 108 .BR MS_SLAVE ,
 109 or
 110 .BR MS_UNBINDABLE .
 111 .IP *
 112 Move an existing mount to a new location:
 113 .IR mountflags
 114 includes
 115 .BR MS_MOVE .
 116 .IP *
 117 Create a new mount:
 118 .IR mountflags
 119 includes none of the above flags.
 120 .PP
 121 Each of these operations is detailed later in this page.
 122 Further flags may be specified in
 123 .IR mountflags
 124 to modify the behavior of
 125 .BR mount (),
 126 as described below.
 127 .\"
 128 .SS Additional mount flags
 129 The list below describes the additional flags that can be specified in
 130 .IR mountflags .
 131 Note that some operation types ignore some or all of these flags,
 132 as described later in this page.
 133 .\"
 134 .\" FIXME 2.6.25 Added MS_I_VERSION, which needs to be documented.
 135 .\" commit 7a224228ed79d587ece2304869000aad1b8e97dd
 136 .\" (This is a per-superblock flag)
 137 .\"
 138 .TP
 139 .BR MS_DIRSYNC " (since Linux 2.5.19)"
 140 Make directory changes on this filesystem synchronous.
 141 (This property can be obtained for individual directories
 142 or subtrees using
 143 .BR chattr (1).)
 144 .TP
 145 .BR MS_LAZYTIME " (since Linux 4.0)"
 146 .\" commit 0ae45f63d4ef8d8eeec49c7d8b44a1775fff13e8
 147 .\" commit fe032c422c5ba562ba9c2d316f55e258e03259c6
 148 .\" commit a26f49926da938f47561f386be56a83dd37a496d
 149 Reduce on-disk updates of inode timestamps (atime, mtime, ctime)
 150 by maintaining these changes only in memory.
 151 The on-disk timestamps are updated only when:
 152 .RS
 153 .IP (a) 5
 154 the inode needs to be updated for some change unrelated to file timestamps;
 155 .IP (b)
 156 the application employs
 157 .BR fsync (2),
 158 .BR syncfs (2),
 159 or
 160 .BR sync (2);
 161 .IP (c)
 162 an undeleted inode is evicted from memory; or
 163 .IP (d)
 164 more than 24 hours have passed since the inode was written to disk.
 165 .RE
 166 .IP
 167 This mount option significantly reduces writes
 168 needed to update the inode's timestamps, especially mtime and atime.
 169 However, in the event of a system crash, the atime and mtime fields
 170 on disk might be out of date by up to 24 hours.
 171 .IP
 172 Examples of workloads where this option could be of significant benefit
 173 include frequent random writes to preallocated files,
 174 as well as cases where the
 175 .B MS_STRICTATIME
 176 mount option is also enabled.
 177 (The advantage of combining
 178 .BR MS_STRICTATIME
 179 and
 180 .BR MS_LAZYTIME
 181 is that
 182 .BR stat (2)
 183 will return the correctly updated atime, but the atime updates
 184 will be flushed to disk only in the cases listed above.)
 185 .TP
 186 .B MS_MANDLOCK
 187 Permit mandatory locking on files in this filesystem.
 188 (Mandatory locking must still be enabled on a per-file basis,
 189 as described in
 190 .BR fcntl (2).)
 191 Since Linux 4.5,
 192 .\" commit 95ace75414f312f9a7b93d873f386987b92a5301
 193 this mount option requires the
 194 .B CAP_SYS_ADMIN
 195 capability and a kernel configured with the
 196 .B CONFIG_MANDATORY_FILE_LOCKING
 197 option.
 198 .TP
 199 .B MS_NOATIME
 200 Do not update access times for (all types of) files on this filesystem.
 201 .TP
 202 .B MS_NODEV
 203 Do not allow access to devices (special files) on this filesystem.
 204 .TP
 205 .B MS_NODIRATIME
 206 Do not update access times for directories on this filesystem.
 207 This flag provides a subset of the functionality provided by
 208 .BR MS_NOATIME ;
 209 that is,
 210 .BR MS_NOATIME
 211 implies
 212 .BR MS_NODIRATIME .
 213 .TP
 214 .B MS_NOEXEC
 215 Do not allow programs to be executed from this filesystem.
 216 .\" (Possibly useful for a filesystem that contains non-Linux executables.
 217 .\" Often used as a security feature, e.g., to make sure that restricted
 218 .\" users cannot execute files uploaded using ftp or so.)
 219 .TP
 220 .B MS_NOSUID
 221 Do not honor set-user-ID and set-group-ID bits or file capabilities
 222 when executing programs from this filesystem.
 223 .\" (This is a security feature to prevent users executing set-user-ID and
 224 .\" set-group-ID programs from removable disk devices.)
 225 .TP
 226 .B MS_RDONLY
 227 Mount filesystem read-only.
 228 .TP
 229 .BR MS_REC " (since Linux 2.4.11)"
 230 Used in conjunction with
 231 .BR MS_BIND
 232 to create a recursive bind mount,
 233 and in conjunction with the propagation type flags to recursively change
 234 the propagation type of all of the mounts in a subtree.
 235 See below for further details.
 236 .TP
 237 .BR MS_RELATIME " (since Linux 2.6.20)"
 238 When a file on this filesystem is accessed,
 239 update the file's last access time (atime) only if the current value
 240 of atime is less than or equal to the file's last modification time (mtime)
 241 or last status change time (ctime).
 242 This option is useful for programs, such as
 243 .BR mutt (1),
 244 that need to know when a file has been read since it was last modified.
 245 Since Linux 2.6.30, the kernel defaults to the behavior provided
 246 by this flag (unless
 247 .BR MS_NOATIME
 248 was specified), and the
 249 .B MS_STRICTATIME
 250 flag is required to obtain traditional semantics.
 251 In addition, since Linux 2.6.30,
 252 the file's last access time is always updated if it
 253 is more than 1 day old.
 254 .\" Matthew Garrett notes in the patch that added this behavior
 255 .\" that this lets utilities such as tmpreaper (which deletes
 256 .\" files based on last access time) work correctly.
 257 .TP
 258 .BR MS_SILENT " (since Linux 2.6.17)"
 259 Suppress the display of certain
 260 .RI ( printk ())
 261 warning messages in the kernel log.
 262 This flag supersedes the misnamed and obsolete
 263 .BR MS_VERBOSE
 264 flag (available since Linux 2.4.12), which has the same meaning.
 265 .TP
 266 .BR MS_STRICTATIME " (since Linux 2.6.30)"
 267 Always update the last access time (atime) when files on this
 268 filesystem are accessed.
 269 (This was the default behavior before Linux 2.6.30.)
 270 Specifying this flag overrides the effect of setting the
 271 .BR MS_NOATIME
 272 and
 273 .BR MS_RELATIME
 274 flags.
 275 .TP
 276 .B MS_SYNCHRONOUS
 277 Make writes on this filesystem synchronous (as though
 278 the
 279 .B O_SYNC
 280 flag to
 281 .BR open (2)
 282 was specified for all file opens to this filesystem).
 283 .PP
 284 From Linux 2.4 onward, some of the above flags are
 285 settable on a per-mount basis,
 286 while others apply to the superblock of the mounted filesystem,
 287 meaning that all mounts of the same filesystem share those flags.
 288 (Previously, all of the flags were per-superblock.)
 289 .PP
 290 The per-mount-point flags are as follows:
 291 .IP * 3
 292 Since Linux 2.4:
 293 .BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID
 294 flags are settable on a per-mount-point basis.
 295 .IP *
 296 Since Linux 2.6.16:
 297 .B MS_NOATIME
 298 and
 299 .BR MS_NODIRATIME .
 300 .IP *
 301 Since Linux 2.6.20:
 302 .BR MS_RELATIME .
 303 .PP
 304 The following flags are per-superblock:
 305 .BR MS_DIRSYNC ,
 306 .BR MS_LAZYTIME ,
 307 .BR MS_MANDLOCK ,
 308 .BR MS_SILENT ,
 309 and
 310 .BR MS_SYNCHRONOUS .
 311 .\" And MS_I_VERSION?
 312 The initial settings of these flags are determined on the first
 313 mount of the filesystem, and will be shared by all subsequent mounts
 314 of the same filesystem.
 315 Subsequently, the settings of the flags can be changed
 316 via a remount operation (see below).
 317 Such changes will be visible via all mount points associated
 318 with the filesystem.
 319 .PP
 320 Since Linux 2.6.16,
 321 .B MS_RDONLY
 322 can be set or cleared on a per-mount-point basis as well as on
 323 the underlying filesystem superblock.
 324 The mounted filesystem will be writable only if neither the filesystem
 325 nor the mountpoint are flagged as read-only.
 326 .\"
 327 .SS Remounting an existing mount
 328 An existing mount may be remounted by specifying
 329 .B MS_REMOUNT
 330 in
 331 .IR mountflags .
 332 This allows you to change the
 333 .I mountflags
 334 and
 335 .I data
 336 of an existing mount without having to unmount and remount the filesystem.
 337 .I target
 338 should be the same value specified in the initial
 339 .BR mount ()
 340 call.
 341 .PP
 342 The
 343 .I source
 344 and
 345 .I filesystemtype
 346 arguments are ignored.
 347 .PP
 348 The
 349 .I mountflags
 350 and
 351 .I data
 352 arguments should match the values used in the original
 353 .BR mount ()
 354 call, except for those parameters that are being deliberately changed.
 355 .PP
 356 The following
 357 .I mountflags
 358 can be changed:
 359 .BR MS_LAZYTIME ,
 360 .\" FIXME
 361 .\" MS_LAZYTIME seems to be available only on a few filesystems,
 362 .\" and on ext4, it seems (from experiment that this flag
 363 .\" can only be enabled (but not disabled) on a remount.
 364 .\" The following code in ext4_remount() (kernel 4.17) seems to
 365 .\" confirm this:
 366 .\"
 367 .\"        if (*flags & SB_LAZYTIME)
 368 .\"                sb->s_flags |= SB_LAZYTIME;
 369 .BR MS_MANDLOCK ,
 370 .BR MS_NOATIME ,
 371 .BR MS_NODEV ,
 372 .BR MS_NODIRATIME ,
 373 .BR MS_NOEXEC ,
 374 .BR MS_NOSUID ,
 375 .BR MS_RELATIME ,
 376 .BR MS_RDONLY ,
 377 .BR MS_STRICTATIME
 378 (whose effect is to clear the
 379 .BR MS_NOATIME
 380 and
 381 .BR MS_RELATIME
 382 flags),
 383 and
 384 .BR MS_SYNCHRONOUS .
 385 Attempts to change the setting of the
 386 .\" See the definition of MS_RMT_MASK in include/uapi/linux/fs.h,
 387 .\" which excludes MS_DIRSYNC and MS_SILENT, although SB_DIRSYNC
 388 .\" and SB_SILENT are split out as per-superblock flags in do_mount()
 389 .\" (Linux 4.17 source code)
 390 .BR MS_DIRSYNC
 391 and
 392 .BR MS_SILENT
 393 flags during a remount are silently ignored.
 394 Note that changes to per-superblock flags are visible via
 395 all mount points of the associated filesystem
 396 (because the per-superblock flags are shared by all mount points).
 397 .PP
 398 Since Linux 3.17,
 399 .\" commit ffbc6f0ead47fa5a1dc9642b0331cb75c20a640e
 400 if none of
 401 .BR MS_NOATIME ,
 402 .BR MS_NODIRATIME ,
 403 .BR MS_RELATIME ,
 404 or
 405 .BR MS_STRICTATIME
 406 is specified in
 407 .IR mountflags ,
 408 then the remount operation preserves the existing values of these flags
 409 (rather than defaulting to
 410 .BR MS_RELATIME ).
 411 .PP
 412 Since Linux 2.6.26, the
 413 .B MS_REMOUNT
 414 flag can be used with
 415 .B MS_BIND
 416 to modify only the per-mount-point flags.
 417 .\" See https://lwn.net/Articles/281157/
 418 This is particularly useful for setting or clearing the "read-only"
 419 flag on a mount point without changing the underlying filesystem.
 420 Specifying
 421 .IR mountflags
 422 as:
 423 .PP
 424 .in +4n
 425 .EX
 426 MS_REMOUNT | MS_BIND | MS_RDONLY
 427 .EE
 428 .in
 429 .PP
 430 will make access through this mountpoint read-only, without affecting
 431 other mount points.
 432 .\"
 433 .SS Creating a bind mount
 434 If
 435 .I mountflags
 436 includes
 437 .BR MS_BIND
 438 (available since Linux 2.4),
 439 .\" since 2.4.0-test9
 440 then perform a bind mount.
 441 A bind mount makes a file or a directory subtree visible at
 442 another point within the single directory hierarchy.
 443 Bind mounts may cross filesystem boundaries and span
 444 .BR chroot (2)
 445 jails.
 446 .PP
 447 The
 448 .IR filesystemtype
 449 and
 450 .IR data
 451 arguments are ignored.
 452 .PP
 453 The remaining bits (other than
 454 .BR MS_REC ,
 455 described below) in the
 456 .I mountflags
 457 argument are also ignored.
 458 (The bind mount has the same mount options as
 459 the underlying mount point.)
 460 However, see the discussion of remounting above,
 461 for a method of making an existing bind mount read-only.
 462 .PP
 463 By default, when a directory is bind mounted,
 464 only that directory is mounted;
 465 if there are any submounts under the directory tree,
 466 they are not bind mounted.
 467 If the
 468 .BR MS_REC
 469 flag is also specified, then a recursive bind mount operation is performed:
 470 all submounts under the
 471 .I source
 472 subtree (other than unbindable mounts)
 473 are also bind mounted at the corresponding location in the
 474 .I target
 475 subtree.
 476 .\"
 477 .SS Changing the propagation type of an existing mount
 478 If
 479 .IR mountflags
 480 includes one of
 481 .BR MS_SHARED ,
 482 .BR MS_PRIVATE ,
 483 .BR MS_SLAVE ,
 484 or
 485 .BR MS_UNBINDABLE
 486 (all available since Linux 2.6.15),
 487 then the propagation type of an existing mount is changed.
 488 If more than one of these flags is specified, an error results.
 489 .PP
 490 The only other flags that can be specified while changing
 491 the propagation type are
 492 .BR MS_REC
 493 (described below) and
 494 .BR MS_SILENT
 495 (which is ignored).
 496 .PP
 497 The
 498 .IR source ,
 499 .IR filesystemtype ,
 500 and
 501 .IR data
 502 arguments are ignored.
 503 .PP
 504 The meanings of the propagation type flags are as follows:
 505 .TP
 506 .BR MS_SHARED
 507 Make this mount point shared.
 508 Mount and unmount events immediately under this mount point will propagate
 509 to the other mount points that are members of this mount's peer group.
 510 Propagation here means that the same mount or unmount will automatically
 511 occur under all of the other mount points in the peer group.
 512 Conversely, mount and unmount events that take place under
 513 peer mount points will propagate to this mount point.
 514 .TP
 515 .BR MS_PRIVATE
 516 Make this mount point private.
 517 Mount and unmount events do not propagate into or out of this mount point.
 518 .TP
 519 .BR MS_SLAVE
 520 If this is a shared mount point that is a member of a peer group
 521 that contains other members, convert it to a slave mount.
 522 If this is a shared mount point that is a member of a peer group
 523 that contains no other members, convert it to a private mount.
 524 Otherwise, the propagation type of the mount point is left unchanged.
 525 .IP
 526 When a mount point is a slave,
 527 mount and unmount events propagate into this mount point from
 528 the (master) shared peer group of which it was formerly a member.
 529 Mount and unmount events under this mount point do not propagate to any peer.
 530 .IP
 531 A mount point can be the slave of another peer group
 532 while at the same time sharing mount and unmount events
 533 with a peer group of which it is a member.
 534 .TP
 535 .BR MS_UNBINDABLE
 536 Make this mount unbindable.
 537 This is like a private mount,
 538 and in addition this mount can't be bind mounted.
 539 When a recursive bind mount
 540 .RB ( mount ()
 541 with the
 542 .BR MS_BIND
 543 and
 544 .BR MS_REC
 545 flags) is performed on a directory subtree,
 546 any unbindable mounts within the subtree are automatically pruned
 547 (i.e., not replicated)
 548 when replicating that subtree to produce the target subtree.
 549 .PP
 550 By default, changing the propagation type affects only the
 551 .I target
 552 mount point.
 553 If the
 554 .B MS_REC
 555 flag is also specified in
 556 .IR mountflags ,
 557 then the propagation type of all mount points under
 558 .IR target
 559 is also changed.
 560 .PP
 561 For further details regarding mount propagation types
 562 (including the default propagation type assigned to new mounts), see
 563 .BR mount_namespaces (7).
 564 .\"
 565 .SS Moving a mount
 566 If
 567 .I mountflags
 568 contains the flag
 569 .BR MS_MOVE
 570 (available since Linux 2.4.18),
 571 then move a subtree:
 572 .I source
 573 specifies an existing mount point and
 574 .I target
 575 specifies the new location to which that mount point is to be relocated.
 576 The move is atomic: at no point is the subtree unmounted.
 577 .PP
 578 The remaining bits in the
 579 .IR mountflags
 580 argument are ignored, as are the
 581 .IR filesystemtype
 582 and
 583 .IR data
 584 arguments.
 585 .\"
 586 .SS Creating a new mount point
 587 If none of
 588 .BR MS_REMOUNT ,
 589 .BR MS_BIND ,
 590 .BR MS_MOVE ,
 591 .BR MS_SHARED ,
 592 .BR MS_PRIVATE ,
 593 .BR MS_SLAVE ,
 594 or
 595 .BR MS_UNBINDABLE
 596 is specified in
 597 .IR mountflags ,
 598 then
 599 .BR mount ()
 600 performs its default action: creating a new mount point.
 601 .IR source
 602 specifies the source for the new mount point, and
 603 .IR target
 604 specifies the directory at which to create the mount point.
 605 .PP
 606 The
 607 .I filesystemtype
 608 and
 609 .I data
 610 arguments are employed, and further bits may be specified in
 611 .IR mountflags
 612 to modify the behavior of the call.
 613 .\"
 614 .SH RETURN VALUE
 615 On success, zero is returned.
 616 On error, \-1 is returned, and
 617 .I errno
 618 is set appropriately.
 619 .SH ERRORS
 620 The error values given below result from filesystem type independent
 621 errors.
 622 Each filesystem type may have its own special errors and its
 623 own special behavior.
 624 See the Linux kernel source code for details.
 625 .TP
 626 .B EACCES
 627 A component of a path was not searchable.
 628 (See also
 629 .BR path_resolution (7).)
 630 .TP
 631 .B EACCES
 632 Mounting a read-only filesystem was attempted without giving the
 633 .B MS_RDONLY
 634 flag.
 635 .IP
 636 The filesystem may be read-only for various reasons, including:
 637 it resides on a read-only optical disk;
 638 it is resides on a device with a physical switch that has been set to
 639 mark the device read-only;
 640 the filesystem implementation was compiled with read-only support;
 641 or errors were detected when initially mounting the filesystem,
 642 so that it was marked read-only
 643 and can't be remounted as read-write (until the errors are fixed).
 644 .IP
 645 Some filesystems instead return the error
 646 .BR EROFS
 647 on an attempt to mount a read-only filesystem.
 648 .TP
 649 .B EACCES
 650 The block device
 651 .I source
 652 is located on a filesystem mounted with the
 653 .B MS_NODEV
 654 option.
 655 .\" mtk: Probably: write permission is required for MS_BIND, with
 656 .\" the error EPERM if not present; CAP_DAC_OVERRIDE is required.
 657 .TP
 658 .B EBUSY
 659 An attempt was made to stack a new mount directly on
 660 top of an existing mount point that was created in this
 661 mount namespace with the same
 662 .I source
 663 and
 664 .IR target .
 665 .TP
 666 .B EBUSY
 667 .I source
 668 cannot be remounted read-only,
 669 because it still holds files open for writing.
 670 .TP
 671 .B EFAULT
 672 One of the pointer arguments points outside the user address space.
 673 .TP
 674 .B EINVAL
 675 .I source
 676 had an invalid superblock.
 677 .TP
 678 .B EINVAL
 679 A remount operation
 680 .RB ( MS_REMOUNT )
 681 was attempted, but
 682 .I source
 683 was not already mounted on
 684 .IR target .
 685 .TP
 686 .B EINVAL
 687 A move operation
 688 .RB ( MS_MOVE )
 689 was attempted, but the mount tree under
 690 .I source
 691 includes unbindable mounts and
 692 .I target
 693 is a mount point that has propagation type
 694 .BR MS_SHARED .
 695 .TP
 696 .B EINVAL
 697 A move operation
 698 .RB ( MS_MOVE )
 699 was attempted, but the parent mount of
 700 .I source
 701 mount has propagation type
 702 .BR MS_SHARED .
 703 .TP
 704 .B EINVAL
 705 A move operation
 706 .RB ( MS_MOVE )
 707 was attempted, but
 708 .I source
 709 was not a mount point, or was \(aq/\(aq.
 710 .TP
 711 .B EINVAL
 712 .I mountflags
 713 includes more than one of
 714 .BR MS_SHARED ,
 715 .BR MS_PRIVATE ,
 716 .BR MS_SLAVE ,
 717 or
 718 .BR MS_UNBINDABLE .
 719 .TP
 720 .B EINVAL
 721 .I mountflags
 722 includes
 723 .BR MS_SHARED ,
 724 .BR MS_PRIVATE ,
 725 .BR MS_SLAVE ,
 726 or
 727 .BR MS_UNBINDABLE
 728 and also includes a flag other than
 729 .BR MS_REC
 730 or
 731 .BR MS_SILENT .
 732 .TP
 733 .BR EINVAL
 734 An attempt was made to bind mount an unbindable mount.
 735 .TP
 736 .BR EINVAL
 737 In an unprivileged mount namespace
 738 (i.e., a mount namespace owned by a user namespace
 739 that was created by an unprivileged user),
 740 a bind mount operation
 741 .RB ( MS_BIND )
 742 was attempted without specifying
 743 .RB ( MS_REC ),
 744 which would have revealed the filesystem tree underneath one of
 745 the submounts of the directory being bound.
 746 .TP
 747 .B ELOOP
 748 Too many links encountered during pathname resolution.
 749 .TP
 750 .B ELOOP
 751 A move operation was attempted, and
 752 .I target
 753 is a descendant of
 754 .IR source .
 755 .TP
 756 .B EMFILE
 757 (In case no block device is required:)
 758 Table of dummy devices is full.
 759 .TP
 760 .B ENAMETOOLONG
 761 A pathname was longer than
 762 .BR MAXPATHLEN .
 763 .TP
 764 .B ENODEV
 765 .I filesystemtype
 766 not configured in the kernel.
 767 .TP
 768 .B ENOENT
 769 A pathname was empty or had a nonexistent component.
 770 .TP
 771 .B ENOMEM
 772 The kernel could not allocate a free page to copy filenames or data into.
 773 .TP
 774 .B ENOTBLK
 775 .I source
 776 is not a block device (and a device was required).
 777 .TP
 778 .B ENOTDIR
 779 .IR target ,
 780 or a prefix of
 781 .IR source ,
 782 is not a directory.
 783 .TP
 784 .B ENXIO
 785 The major number of the block device
 786 .I source
 787 is out of range.
 788 .TP
 789 .B EPERM
 790 The caller does not have the required privileges.
 791 .TP
 792 .B EROFS
 793 Mounting a read-only filesystem was attempted without giving the
 794 .B MS_RDONLY
 795 flag.
 796 See
 797 .BR EACCES ,
 798 above.
 799 .SH VERSIONS
 800 The definitions of
 801 .BR MS_DIRSYNC ,
 802 .BR MS_MOVE ,
 803 .BR MS_PRIVATE ,
 804 .BR MS_REC ,
 805 .BR MS_RELATIME ,
 806 .BR MS_SHARED ,
 807 .BR MS_SLAVE ,
 808 .BR MS_STRICTATIME ,
 809 and
 810 .BR MS_UNBINDABLE
 811 were added to glibc headers in version 2.12.
 812 .\"
 813 .SH CONFORMING TO
 814 This function is Linux-specific and should not be used in
 815 programs intended to be portable.
 816 .SH NOTES
 817 Since Linux 2.4 a single filesystem can be mounted at
 818 multiple mount points, and multiple mounts can be stacked
 819 on the same mount point.
 820 .\" Multiple mounts on same mount point: since 2.3.99pre7.
 821 .PP
 822 The
 823 .I mountflags
 824 argument may have the magic number 0xC0ED (\fBMS_MGC_VAL\fP)
 825 in the top 16 bits.
 826 (All of the other flags discussed in DESCRIPTION
 827 occupy the low order 16 bits of
 828 .IR mountflags .)
 829 Specifying
 830 .BR MS_MGC_VAL
 831 was required in kernel versions prior to 2.4,
 832 but since Linux 2.4 is no longer required and is ignored if specified.
 833 .PP
 834 The original
 835 .B MS_SYNC
 836 flag was renamed
 837 .B MS_SYNCHRONOUS
 838 in 1.1.69
 839 when a different
 840 .B MS_SYNC
 841 was added to \fI<mman.h>\fP.
 842 .PP
 843 Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program
 844 on a filesystem mounted with
 845 .B MS_NOSUID
 846 would fail with
 847 .BR EPERM .
 848 Since Linux 2.4 the set-user-ID and set-group-ID bits are
 849 just silently ignored in this case.
 850 .\" The change is in patch-2.4.0-prerelease.
 851 .\"
 852 .SS Mount namespaces
 853 Starting with kernel 2.4.19, Linux provides mount namespaces.
 854 A mount namespace is the set of filesystem mounts that
 855 are visible to a process.
 856 Mount namespaces can be (and usually are)
 857 shared between multiple processes,
 858 and changes to the namespace (i.e., mounts and unmounts) by one process
 859 are visible to all other processes sharing the same namespace.
 860 (The pre-2.4.19 Linux situation can be considered as one in which
 861 a single namespace was shared by every process on the system.)
 862 .PP
 863 A child process created by
 864 .BR fork (2)
 865 shares its parent's mount namespace;
 866 the mount namespace is preserved across an
 867 .BR execve (2).
 868 .PP
 869 A process can obtain a private mount namespace if:
 870 it was created using the
 871 .BR clone (2)
 872 .BR CLONE_NEWNS
 873 flag,
 874 in which case its new namespace is initialized to be a
 875 .I copy
 876 of the namespace of the process that called
 877 .BR clone (2);
 878 or it calls
 879 .BR unshare (2)
 880 with the
 881 .BR CLONE_NEWNS
 882 flag,
 883 which causes the caller's mount namespace to obtain a private copy
 884 of the namespace that it was previously sharing with other processes,
 885 so that future mounts and unmounts by the caller are invisible
 886 to other processes (except child processes that the caller
 887 subsequently creates) and vice versa.
 888 .PP
 889 For further details on mount namespaces, see
 890 .BR mount_namespaces (7).
 891 .\"
 892 .SS Parental relationship between mount points
 893 Each mount point has a parent mount point.
 894 The overall parental relationship of all mount points defines
 895 the single directory hierarchy seen by the processes within a mount namespace.
 896 .PP
 897 The parent of a new mount point is defined when the mount point is created.
 898 In the usual case,
 899 the parent of a new mount is the mount point of the filesystem
 900 containing the directory or file at which the new mount is attached.
 901 In the case where a new mount is stacked on top of an existing mount,
 902 the parent of the new mount is the previous mount that was stacked
 903 at that location.
 904 .PP
 905 The parental relationship between mount points can be discovered via the
 906 .I /proc/[pid]/mountinfo
 907 file (see below).
 908 .\"
 909 .SS /proc/[pid]/mounts and /proc/[pid]/mountinfo
 910 The Linux-specific
 911 .I /proc/[pid]/mounts
 912 file exposes the list of mount points in the mount
 913 namespace of the process with the specified ID.
 914 The
 915 .I /proc/[pid]/mountinfo
 916 file exposes even more information about mount points,
 917 including the propagation type and mount ID information that makes it
 918 possible to discover the parental relationship between mount points.
 919 See
 920 .BR proc (5)
 921 and
 922 .BR mount_namespaces (7)
 923 for details of this file.
 924 .SH SEE ALSO
 925 .BR mountpoint (1),
 926 .BR chroot (2),
 927 .BR ioctl_iflags (2),
 928 .BR pivot_root (2),
 929 .BR umount (2),
 930 .BR mount_namespaces (7),
 931 .BR path_resolution (7),
 932 .BR findmnt (8),
 933 .BR lsblk (8),
 934 .BR mount (8),
 935 .BR umount (8)