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28 .\" @(#)mount.8 8.8 (Berkeley) 6/16/94
36 .Nd mount file systems
43 .Op Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
52 .Op Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
59 system call to prepare and graft a
61 device or the remote node (rhost:path) on to the file system tree at the point
67 are not provided, the appropriate information is taken from the
71 The system maintains a list of currently mounted file systems.
72 If no arguments are given to
76 The options are as follows:
77 .Bl -tag -width indent
81 in a selection of different human and machine readable formats.
84 for details on command line arguments.
86 All the file systems described in
89 Exceptions are those marked as
95 option was specified),
98 flag (see below), or if they are already mounted (except the
99 root file system which is always remounted to preserve
100 traditional single user mode behavior).
102 Causes everything to be done except for the actual system call.
103 This option is useful in conjunction with the
108 command is trying to do.
114 Forces the revocation of write access when trying to downgrade
115 a file system mount status from read-write to read-only.
117 forces the R/W mount of an unclean file system (dangerous; use with
120 When used in conjunction with the
124 those file systems which are marked as
127 When used in conjunction with the
129 option, also mount those file systems which are marked as
132 For compatibility with some other implementations, this flag is
135 Options are specified with a
137 flag followed by a comma separated string of options.
138 In case of conflicting options being specified, the rightmost option
140 The following options are available:
141 .Bl -tag -width indent
143 Enable POSIX.1e Access Control Lists, or ACLs, which can be customized via the
148 This flag is mutually exclusive with
152 All I/O to the file system should be done asynchronously.
155 flag to set, since it does not guarantee that the file system structure
156 on the disk will remain consistent.
159 flag should be used sparingly, and only when some data recovery
160 mechanism is present.
162 This flag indicates that the file system was mounted by
164 Automounted file systems are automatically unmounted by
167 Mount the file system read-write.
168 If that fails with an error that suggests that the media could be read-only,
169 then automatically try to mount the file system read-only.
173 flag, this is the same as specifying the options currently in effect for
174 the mounted file system.
176 Require that the mount point directory be empty.
180 forces the revocation of write access when trying to downgrade
181 a file system mount status from read-write to read-only.
183 forces the R/W mount of an unclean file system (dangerous; use with caution).
187 flag, this is the same as specifying all the options listed in the
189 file for the file system.
191 This file system should be skipped when
198 .It Cm mountprog Ns = Ns Aq Ar program
201 to use the specified program to mount the file system, instead of calling
206 mount -t foofs -o mountprog=/mydir/fooprog /dev/cd0 /mnt
209 Enable multi-label Mandatory Access Control, or MAC, on the specified file
211 If the file system supports multilabel operation, individual labels will
212 be maintained for each object in the file system, rather than using a
213 single label for all objects.
214 An alternative to the
220 for more information, which cause the multilabel mount flag to be set
221 automatically at mount-time.
223 Enable NFSv4 ACLs, which can be customized via the
228 This flag is mutually exclusive with
232 Metadata I/O should be done synchronously, while data I/O should be done
236 Do not update the file access time when reading from a file.
238 is useful on file systems where there are large numbers of files and
239 performance is more critical than updating the file access time (which is
240 rarely ever important).
241 This option is currently only supported on local file systems.
243 This file system should be skipped when
249 Disable read clustering.
251 Disable write clustering.
253 Do not mount if the requested mount point is already
254 the root of a mount point.
256 Do not allow execution of any binaries on the mounted file system.
257 This option is useful for a server that has file systems containing
258 binaries for architectures other than its own.
259 Note: This option was not designed as a security feature and no
260 guarantee is made that it will prevent malicious code execution; for
261 example, it is still possible to execute scripts which reside on a
265 Do not allow set-user-identifier or set-group-identifier bits to take effect.
266 Note: this option is worthless if a public available suid or sgid
269 is installed on your system.
270 It is set automatically when the user does not have super-user privileges.
272 Do not follow symlinks
273 on the mounted file system.
277 mount the file system read-only (even the super-user may not write it).
279 Take a snapshot of the specified filesystem.
280 When this option is used, all other options are ignored.
283 flag is required with this option.
285 Snapshot files must be created in the file system that is being
287 You may create up to 20 snapshots per file system.
288 Active snapshots are recorded in the superblock, so they persist across unmount
289 and remount operations and across system reboots.
290 When you are done with a snapshot, it can be removed with the
293 Snapshots may be removed in any order, however you may not get back all the
294 space contained in the snapshot as another snapshot may claim some of the blocks
295 that it is releasing.
296 Note that the schg flag is set on snapshots to ensure that not even the root
297 user can write to them.
298 The unlink command makes an exception for snapshot files in that it allows them
299 to be removed even though they have the schg flag set, so it is not necessary to
300 clear the schg flag before removing a snapshot file.
302 Once you have taken a snapshot, there are three interesting things that you can
309 on the snapshot file.
310 Assuming that the file system was clean when it was mounted, you should always
311 get a clean (and unchanging) result from running fsck on the snapshot.
312 This is essentially what the background fsck process does.
318 You will get a dump that is consistent with the file system as of the timestamp
322 Mount the snapshot as a frozen image of the file system.
323 To mount the snapshot
324 .Pa /var/snapshot/snap1 :
326 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
327 mount -r /dev/md4 /mnt
330 You can now cruise around your frozen
334 Everything will be in the same state that it was at the time the snapshot was
336 The one exception is that any earlier snapshots will appear as zero length
338 When you are done with the mounted snapshot:
345 A directory on the mounted file system will respond to the SUID bit
346 being set, by setting the owner of any new files to be the same
347 as the owner of the directory.
348 New directories will inherit the bit from their parents.
349 Execute bits are removed from
350 the file, and it will not be given to root.
352 This feature is designed for use on fileservers serving PC users via
353 ftp, SAMBA, or netatalk.
354 It provides security holes for shell users and as
355 such should not be used on shell machines, especially on home directories.
356 This option requires the SUIDDIR
357 option in the kernel to work.
358 Only UFS file systems support this option.
361 for more information.
363 All I/O to the file system should be done synchronously.
367 indicate that the status of an already mounted file system should be changed.
369 Causes the namespace at the mount point to appear as the union
370 of the mounted file system root and the existing directory.
371 Lookups will be done in the mounted file system first.
372 If those operations fail due to a non-existent file the underlying
373 directory is then accessed.
374 All creates are done in the mounted file system.
376 The file system is untrusted and the kernel should use more
377 extensive checks on the file-system's metadata before using it.
378 This option is intended to be used when mounting file systems
379 from untrusted media such as USB memory sticks or other
380 externally-provided media.
383 Any additional options specific to a file system type that is not
384 one of the internally known types (see the
386 option) may be passed as a comma separated list; these options are
387 distinguished by a leading
393 .Bd -literal -offset indent
394 mount -t cd9660 -o -e /dev/cd0 /cdrom
399 to execute the equivalent of:
400 .Bd -literal -offset indent
401 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
404 Options that take a value are specified using the -option=value syntax:
405 .Bd -literal -offset indent
406 mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
410 .Bd -literal -offset indent
411 /sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
414 Additional options specific to file system types
415 which are not internally known
416 (see the description of the
419 may be described in the manual pages for the associated
420 .Pa /sbin/mount_ Ns Sy XXX
423 Print mount information in
430 The file system is to be mounted read-only.
431 Mount the file system read-only (even the super-user may not write it).
437 .It Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
438 The argument following the
440 is used to indicate the file system type.
447 to indicate that the actions should only be taken on
448 file systems of the specified type.
449 More than one type may be specified in a comma separated list.
450 The list of file system types can be prefixed with
452 to specify the file system types for which action should
458 .Bd -literal -offset indent
459 mount -a -t nonfs,nullfs
462 mounts all file systems except those of type NFS and NULLFS.
464 The default behavior of
468 option directly to the
474 However, for the following file system types:
487 directly and will instead attempt to execute a program in
488 .Pa /sbin/mount_ Ns Ar type
491 is replaced by the file system type name.
494 file systems are mounted by the program
495 .Pa /sbin/mount_nfs .
497 Most file systems will be dynamically loaded by the kernel
498 if not already present, and if the kernel module is available.
502 flag indicates that the status of an already mounted file
503 system should be changed.
504 Any of the options discussed above (the
508 also a file system can be changed from read-only to read-write
510 An attempt to change from read-write to read-only will fail if any
511 files on the file system are currently open for writing unless the
513 flag is also specified.
514 The set of options is determined by applying the options specified
517 and finally applying the
526 is used alone, show all file systems, including those that were mounted with the
528 flag and show additional information about each file system (including fsid
531 The file system object is to be read and write.
534 .Bl -tag -width ".Ev PATH_FSTAB"
536 If the environment variable
538 is set, all operations are performed against the specified file.
540 will not be honored if the process environment or memory address space is
545 for more information.)
548 .Bl -tag -width /etc/fstab -compact
553 Various, most of them are self-explanatory.
555 .Dl XXXXX file system is not available
557 The kernel does not support the respective file system type.
559 support for a particular file system might be provided either on a static
560 (kernel compile-time), or dynamic basis (loaded as a kernel module by
568 .Xr xo_parse_args 3 ,
580 .Xr mount_msdosfs 8 ,
585 .Xr mount_unionfs 8 ,
597 the permissions on the original mount point determine if
599 is accessible from the mounted file system.
600 The minimum permissions for
601 the mount point for traversal across the mount point in both
602 directions to be possible for all users is 0111 (execute for all).
606 is preferred over the use of the file system specific
613 signal (that causes an update of the export list)
614 only when the file system is mounted via
617 It is possible for a corrupted file system to cause a crash.