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28 .\" @(#)mount.8 8.8 (Berkeley) 6/16/94
36 .Nd mount file systems
42 .Op Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
49 .Op Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
56 system call to prepare and graft a
58 device or the remote node (rhost:path) on to the file system tree at the point
64 are not provided, the appropriate information is taken from the
68 The system maintains a list of currently mounted file systems.
69 If no arguments are given to
73 The options are as follows:
74 .Bl -tag -width indent
76 All the file systems described in
79 Exceptions are those marked as
85 option was specified),
88 flag (see below), or if they are already mounted (except the
89 root file system which is always remounted to preserve
90 traditional single user mode behavior).
92 Causes everything to be done except for the actual system call.
93 This option is useful in conjunction with the
98 command is trying to do.
104 Forces the revocation of write access when trying to downgrade
105 a file system mount status from read-write to read-only.
107 forces the R/W mount of an unclean file system (dangerous; use with
110 When used in conjunction with the
114 those file systems which are marked as
117 When used in conjunction with the
119 option, also mount those file systems which are marked as
122 For compatibility with some other implementations, this flag is
125 Options are specified with a
127 flag followed by a comma separated string of options.
128 In case of conflicting options being specified, the rightmost option
130 The following options are available:
131 .Bl -tag -width indent
133 Enable POSIX.1e Access Control Lists, or ACLs, which can be customized via the
138 This flag is mutually exclusive with
142 All I/O to the file system should be done asynchronously.
145 flag to set, since it does not guarantee that the file system structure
146 on the disk will remain consistent.
149 flag should be used sparingly, and only when some data recovery
150 mechanism is present.
152 This flag indicates that the file system was mounted by
154 Automounted file systems are automatically unmounted by
157 Mount the file system read-write.
158 If that fails with an error that suggests that the media could be read-only,
159 then automatically try to mount the file system read-only.
163 flag, this is the same as specifying the options currently in effect for
164 the mounted file system.
168 forces the revocation of write access when trying to downgrade
169 a file system mount status from read-write to read-only.
171 forces the R/W mount of an unclean file system (dangerous; use with caution).
175 flag, this is the same as specifying all the options listed in the
177 file for the file system.
179 This file system should be skipped when
186 .It Cm mountprog Ns = Ns Aq Ar program
189 to use the specified program to mount the file system, instead of calling
194 mount -t foofs -o mountprog=/mydir/fooprog /dev/cd0 /mnt
197 Enable multi-label Mandatory Access Control, or MAC, on the specified file
199 If the file system supports multilabel operation, individual labels will
200 be maintained for each object in the file system, rather than using a
201 single label for all objects.
202 An alternative to the
208 for more information, which cause the multilabel mount flag to be set
209 automatically at mount-time.
211 Enable NFSv4 ACLs, which can be customized via the
216 This flag is mutually exclusive with
220 Metadata I/O should be done synchronously, while data I/O should be done
224 Do not update the file access time when reading from a file.
226 is useful on file systems where there are large numbers of files and
227 performance is more critical than updating the file access time (which is
228 rarely ever important).
229 This option is currently only supported on local file systems.
231 This file system should be skipped when
237 Disable read clustering.
239 Disable write clustering.
241 Do not allow execution of any binaries on the mounted file system.
242 This option is useful for a server that has file systems containing
243 binaries for architectures other than its own.
244 Note: This option was not designed as a security feature and no
245 guarantee is made that it will prevent malicious code execution; for
246 example, it is still possible to execute scripts which reside on a
250 Do not allow set-user-identifier or set-group-identifier bits to take effect.
251 Note: this option is worthless if a public available suid or sgid
254 is installed on your system.
255 It is set automatically when the user does not have super-user privileges.
257 Do not follow symlinks
258 on the mounted file system.
262 mount the file system read-only (even the super-user may not write it).
264 This option allows a snapshot of the specified file system to be taken.
267 flag is required with this option.
268 Note that snapshot files must be created in the file system that is being
270 You may create up to 20 snapshots per file system.
271 Active snapshots are recorded in the superblock, so they persist across unmount
272 and remount operations and across system reboots.
273 When you are done with a snapshot, it can be removed with the
276 Snapshots may be removed in any order, however you may not get back all the
277 space contained in the snapshot as another snapshot may claim some of the blocks
278 that it is releasing.
279 Note that the schg flag is set on snapshots to ensure that not even the root
280 user can write to them.
281 The unlink command makes an exception for snapshot files in that it allows them
282 to be removed even though they have the schg flag set, so it is not necessary to
283 clear the schg flag before removing a snapshot file.
285 Once you have taken a snapshot, there are three interesting things that you can
292 on the snapshot file.
293 Assuming that the file system was clean when it was mounted, you should always
294 get a clean (and unchanging) result from running fsck on the snapshot.
295 This is essentially what the background fsck process does.
301 You will get a dump that is consistent with the file system as of the timestamp
305 Mount the snapshot as a frozen image of the file system.
306 To mount the snapshot
307 .Pa /var/snapshot/snap1 :
309 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
310 mount -r /dev/md4 /mnt
313 You can now cruise around your frozen
317 Everything will be in the same state that it was at the time the snapshot was
319 The one exception is that any earlier snapshots will appear as zero length
321 When you are done with the mounted snapshot:
328 A directory on the mounted file system will respond to the SUID bit
329 being set, by setting the owner of any new files to be the same
330 as the owner of the directory.
331 New directories will inherit the bit from their parents.
332 Execute bits are removed from
333 the file, and it will not be given to root.
335 This feature is designed for use on fileservers serving PC users via
336 ftp, SAMBA, or netatalk.
337 It provides security holes for shell users and as
338 such should not be used on shell machines, especially on home directories.
339 This option requires the SUIDDIR
340 option in the kernel to work.
341 Only UFS file systems support this option.
344 for more information.
346 All I/O to the file system should be done synchronously.
350 indicate that the status of an already mounted file system should be changed.
352 Causes the namespace at the mount point to appear as the union
353 of the mounted file system root and the existing directory.
354 Lookups will be done in the mounted file system first.
355 If those operations fail due to a non-existent file the underlying
356 directory is then accessed.
357 All creates are done in the mounted file system.
359 The file system is untrusted and the kernel should use more
360 extensive checks on the file-system's metadata before using it.
361 This option is intended to be used when mounting file systems
362 from untrusted media such as USB memory sticks or other
363 externally-provided media.
366 Any additional options specific to a file system type that is not
367 one of the internally known types (see the
369 option) may be passed as a comma separated list; these options are
370 distinguished by a leading
376 .Bd -literal -offset indent
377 mount -t cd9660 -o -e /dev/cd0 /cdrom
382 to execute the equivalent of:
383 .Bd -literal -offset indent
384 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
387 Options that take a value are specified using the -option=value syntax:
388 .Bd -literal -offset indent
389 mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
393 .Bd -literal -offset indent
394 /sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
397 Additional options specific to file system types
398 which are not internally known
399 (see the description of the
402 may be described in the manual pages for the associated
403 .Pa /sbin/mount_ Ns Sy XXX
406 Print mount information in
413 The file system is to be mounted read-only.
414 Mount the file system read-only (even the super-user may not write it).
420 .It Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
421 The argument following the
423 is used to indicate the file system type.
430 to indicate that the actions should only be taken on
431 file systems of the specified type.
432 More than one type may be specified in a comma separated list.
433 The list of file system types can be prefixed with
435 to specify the file system types for which action should
441 .Bd -literal -offset indent
442 mount -a -t nonfs,nullfs
445 mounts all file systems except those of type NFS and NULLFS.
447 The default behavior of
451 option directly to the
457 However, for the following file system types:
470 directly and will instead attempt to execute a program in
471 .Pa /sbin/mount_ Ns Ar type
474 is replaced by the file system type name.
477 file systems are mounted by the program
478 .Pa /sbin/mount_nfs .
480 Most file systems will be dynamically loaded by the kernel
481 if not already present, and if the kernel module is available.
485 flag indicates that the status of an already mounted file
486 system should be changed.
487 Any of the options discussed above (the
491 also a file system can be changed from read-only to read-write
493 An attempt to change from read-write to read-only will fail if any
494 files on the file system are currently open for writing unless the
496 flag is also specified.
497 The set of options is determined by applying the options specified
500 and finally applying the
509 is used alone, show all file systems, including those that were mounted with the
511 flag and show additional information about each file system (including fsid
514 The file system object is to be read and write.
517 .Bl -tag -width ".Ev PATH_FSTAB"
519 If the environment variable
521 is set, all operations are performed against the specified file.
523 will not be honored if the process environment or memory address space is
528 for more information.)
531 .Bl -tag -width /etc/fstab -compact
536 Various, most of them are self-explanatory.
538 .Dl XXXXX file system is not available
540 The kernel does not support the respective file system type.
542 support for a particular file system might be provided either on a static
543 (kernel compile-time), or dynamic basis (loaded as a kernel module by
561 .Xr mount_msdosfs 8 ,
566 .Xr mount_unionfs 8 ,
578 the permissions on the original mount point determine if
580 is accessible from the mounted file system.
581 The minimum permissions for
582 the mount point for traversal across the mount point in both
583 directions to be possible for all users is 0111 (execute for all).
587 is preferred over the use of the file system specific
594 signal (that causes an update of the export list)
595 only when the file system is mounted via
598 It is possible for a corrupted file system to cause a crash.