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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.
166 Require that the mount point directory be empty.
170 forces the revocation of write access when trying to downgrade
171 a file system mount status from read-write to read-only.
173 forces the R/W mount of an unclean file system (dangerous; use with caution).
177 flag, this is the same as specifying all the options listed in the
179 file for the file system.
181 This file system should be skipped when
188 .It Cm mountprog Ns = Ns Aq Ar program
191 to use the specified program to mount the file system, instead of calling
196 mount -t foofs -o mountprog=/mydir/fooprog /dev/cd0 /mnt
199 Enable multi-label Mandatory Access Control, or MAC, on the specified file
201 If the file system supports multilabel operation, individual labels will
202 be maintained for each object in the file system, rather than using a
203 single label for all objects.
204 An alternative to the
210 for more information, which cause the multilabel mount flag to be set
211 automatically at mount-time.
213 Enable NFSv4 ACLs, which can be customized via the
218 This flag is mutually exclusive with
222 Metadata I/O should be done synchronously, while data I/O should be done
226 Do not update the file access time when reading from a file.
228 is useful on file systems where there are large numbers of files and
229 performance is more critical than updating the file access time (which is
230 rarely ever important).
231 This option is currently only supported on local file systems.
233 This file system should be skipped when
239 Disable read clustering.
241 Disable write clustering.
243 Do not mount if the requested mount point is already
244 the root of a mount point.
246 Do not allow execution of any binaries on the mounted file system.
247 This option is useful for a server that has file systems containing
248 binaries for architectures other than its own.
249 Note: This option was not designed as a security feature and no
250 guarantee is made that it will prevent malicious code execution; for
251 example, it is still possible to execute scripts which reside on a
255 Do not allow set-user-identifier or set-group-identifier bits to take effect.
256 Note: this option is worthless if a public available suid or sgid
259 is installed on your system.
260 It is set automatically when the user does not have super-user privileges.
262 Do not follow symlinks
263 on the mounted file system.
267 mount the file system read-only (even the super-user may not write it).
269 This option allows a snapshot of the specified file system to be taken.
272 flag is required with this option.
273 Note that snapshot files must be created in the file system that is being
275 You may create up to 20 snapshots per file system.
276 Active snapshots are recorded in the superblock, so they persist across unmount
277 and remount operations and across system reboots.
278 When you are done with a snapshot, it can be removed with the
281 Snapshots may be removed in any order, however you may not get back all the
282 space contained in the snapshot as another snapshot may claim some of the blocks
283 that it is releasing.
284 Note that the schg flag is set on snapshots to ensure that not even the root
285 user can write to them.
286 The unlink command makes an exception for snapshot files in that it allows them
287 to be removed even though they have the schg flag set, so it is not necessary to
288 clear the schg flag before removing a snapshot file.
290 Once you have taken a snapshot, there are three interesting things that you can
297 on the snapshot file.
298 Assuming that the file system was clean when it was mounted, you should always
299 get a clean (and unchanging) result from running fsck on the snapshot.
300 This is essentially what the background fsck process does.
306 You will get a dump that is consistent with the file system as of the timestamp
310 Mount the snapshot as a frozen image of the file system.
311 To mount the snapshot
312 .Pa /var/snapshot/snap1 :
314 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
315 mount -r /dev/md4 /mnt
318 You can now cruise around your frozen
322 Everything will be in the same state that it was at the time the snapshot was
324 The one exception is that any earlier snapshots will appear as zero length
326 When you are done with the mounted snapshot:
333 A directory on the mounted file system will respond to the SUID bit
334 being set, by setting the owner of any new files to be the same
335 as the owner of the directory.
336 New directories will inherit the bit from their parents.
337 Execute bits are removed from
338 the file, and it will not be given to root.
340 This feature is designed for use on fileservers serving PC users via
341 ftp, SAMBA, or netatalk.
342 It provides security holes for shell users and as
343 such should not be used on shell machines, especially on home directories.
344 This option requires the SUIDDIR
345 option in the kernel to work.
346 Only UFS file systems support this option.
349 for more information.
351 All I/O to the file system should be done synchronously.
355 indicate that the status of an already mounted file system should be changed.
357 Causes the namespace at the mount point to appear as the union
358 of the mounted file system root and the existing directory.
359 Lookups will be done in the mounted file system first.
360 If those operations fail due to a non-existent file the underlying
361 directory is then accessed.
362 All creates are done in the mounted file system.
364 The file system is untrusted and the kernel should use more
365 extensive checks on the file-system's metadata before using it.
366 This option is intended to be used when mounting file systems
367 from untrusted media such as USB memory sticks or other
368 externally-provided media.
371 Any additional options specific to a file system type that is not
372 one of the internally known types (see the
374 option) may be passed as a comma separated list; these options are
375 distinguished by a leading
381 .Bd -literal -offset indent
382 mount -t cd9660 -o -e /dev/cd0 /cdrom
387 to execute the equivalent of:
388 .Bd -literal -offset indent
389 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
392 Options that take a value are specified using the -option=value syntax:
393 .Bd -literal -offset indent
394 mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
398 .Bd -literal -offset indent
399 /sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
402 Additional options specific to file system types
403 which are not internally known
404 (see the description of the
407 may be described in the manual pages for the associated
408 .Pa /sbin/mount_ Ns Sy XXX
411 Print mount information in
418 The file system is to be mounted read-only.
419 Mount the file system read-only (even the super-user may not write it).
425 .It Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
426 The argument following the
428 is used to indicate the file system type.
435 to indicate that the actions should only be taken on
436 file systems of the specified type.
437 More than one type may be specified in a comma separated list.
438 The list of file system types can be prefixed with
440 to specify the file system types for which action should
446 .Bd -literal -offset indent
447 mount -a -t nonfs,nullfs
450 mounts all file systems except those of type NFS and NULLFS.
452 The default behavior of
456 option directly to the
462 However, for the following file system types:
475 directly and will instead attempt to execute a program in
476 .Pa /sbin/mount_ Ns Ar type
479 is replaced by the file system type name.
482 file systems are mounted by the program
483 .Pa /sbin/mount_nfs .
485 Most file systems will be dynamically loaded by the kernel
486 if not already present, and if the kernel module is available.
490 flag indicates that the status of an already mounted file
491 system should be changed.
492 Any of the options discussed above (the
496 also a file system can be changed from read-only to read-write
498 An attempt to change from read-write to read-only will fail if any
499 files on the file system are currently open for writing unless the
501 flag is also specified.
502 The set of options is determined by applying the options specified
505 and finally applying the
514 is used alone, show all file systems, including those that were mounted with the
516 flag and show additional information about each file system (including fsid
519 The file system object is to be read and write.
522 .Bl -tag -width ".Ev PATH_FSTAB"
524 If the environment variable
526 is set, all operations are performed against the specified file.
528 will not be honored if the process environment or memory address space is
533 for more information.)
536 .Bl -tag -width /etc/fstab -compact
541 Various, most of them are self-explanatory.
543 .Dl XXXXX file system is not available
545 The kernel does not support the respective file system type.
547 support for a particular file system might be provided either on a static
548 (kernel compile-time), or dynamic basis (loaded as a kernel module by
566 .Xr mount_msdosfs 8 ,
571 .Xr mount_unionfs 8 ,
583 the permissions on the original mount point determine if
585 is accessible from the mounted file system.
586 The minimum permissions for
587 the mount point for traversal across the mount point in both
588 directions to be possible for all users is 0111 (execute for all).
592 is preferred over the use of the file system specific
599 signal (that causes an update of the export list)
600 only when the file system is mounted via
603 It is possible for a corrupted file system to cause a crash.