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28 .\" @(#)mount.8 8.8 (Berkeley) 6/16/94
36 .Nd mount file systems
42 .Op Fl t Cm ufs | Ar external_type
49 .Op Fl t Cm ufs | Ar external_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
144 to the file system should be done asynchronously.
147 flag to set, since it does not guarantee that the file system structure
148 on the disk will remain consistent.
151 flag should be used sparingly, and only when some data recovery
152 mechanism is present.
156 flag, this is the same as specifying the options currently in effect for
157 the mounted file system.
161 forces the revocation of write access when trying to downgrade
162 a file system mount status from read-write to read-only.
164 forces the R/W mount of an unclean file system (dangerous; use with caution).
168 flag, this is the same as specifying all the options listed in the
170 file for the file system.
172 This file system should be skipped when
179 .It Cm mountprog Ns = Ns Aq Ar program
182 to use the specified program to mount the file system, instead of calling
187 mount -t foofs -o mountprog=/mydir/fooprog /dev/acd0 /mnt
190 Enable multi-label Mandatory Access Control, or MAC, on the specified file
192 If the file system supports multilabel operation, individual labels will
193 be maintained for each object in the file system, rather than using a
194 single label for all objects.
195 An alternative to the
201 for more information, which cause the multilabel mount flag to be set
202 automatically at mount-time.
204 Enable NFSv4 ACLs, which can be customized via the
209 This flag is mutually exclusive with
213 Metadata I/O should be done synchronously, while data I/O should be done
217 Do not update the file access time when reading from a file.
219 is useful on file systems where there are large numbers of files and
220 performance is more critical than updating the file access time (which is
221 rarely ever important).
222 This option is currently only supported on local file systems.
224 This file system should be skipped when
230 Disable read clustering.
232 Disable write clustering.
234 Do not allow execution of any binaries on the mounted file system.
235 This option is useful for a server that has file systems containing
236 binaries for architectures other than its own.
237 Note: This option was not designed as a security feature and no
238 guarantee is made that it will prevent malicious code execution; for
239 example, it is still possible to execute scripts which reside on a
243 Do not allow set-user-identifier or set-group-identifier bits to take effect.
244 Note: this option is worthless if a public available suid or sgid
247 is installed on your system.
248 It is set automatically when the user does not have super-user privileges.
250 Do not follow symlinks
251 on the mounted file system.
255 mount the file system read-only (even the super-user may not write it).
257 This option allows a snapshot of the specified file system to be taken.
260 flag is required with this option.
261 Note that snapshot files must be created in the file system that is being
263 You may create up to 20 snapshots per file system.
264 Active snapshots are recorded in the superblock, so they persist across unmount
265 and remount operations and across system reboots.
266 When you are done with a snapshot, it can be removed with the
269 Snapshots may be removed in any order, however you may not get back all the
270 space contained in the snapshot as another snapshot may claim some of the blocks
271 that it is releasing.
272 Note that the schg flag is set on snapshots to ensure that not even the root
273 user can write to them.
274 The unlink command makes an exception for snapshot files in that it allows them
275 to be removed even though they have the schg flag set, so it is not necessary to
276 clear the schg flag before removing a snapshot file.
278 Once you have taken a snapshot, there are three interesting things that you can
285 on the snapshot file.
286 Assuming that the file system was clean when it was mounted, you should always
287 get a clean (and unchanging) result from running fsck on the snapshot.
288 This is essentially what the background fsck process does.
294 You will get a dump that is consistent with the file system as of the timestamp
298 Mount the snapshot as a frozen image of the file system.
299 To mount the snapshot
300 .Pa /var/snapshot/snap1 :
302 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
303 mount -r /dev/md4 /mnt
306 You can now cruise around your frozen
310 Everything will be in the same state that it was at the time the snapshot was
312 The one exception is that any earlier snapshots will appear as zero length
314 When you are done with the mounted snapshot:
321 A directory on the mounted file system will respond to the SUID bit
322 being set, by setting the owner of any new files to be the same
323 as the owner of the directory.
324 New directories will inherit the bit from their parents.
325 Execute bits are removed from
326 the file, and it will not be given to root.
328 This feature is designed for use on fileservers serving PC users via
329 ftp, SAMBA, or netatalk.
330 It provides security holes for shell users and as
331 such should not be used on shell machines, especially on home directories.
332 This option requires the SUIDDIR
333 option in the kernel to work.
334 Only UFS file systems support this option.
337 for more information.
341 to the file system should be done synchronously.
345 indicate that the status of an already mounted file system should be changed.
347 Causes the namespace at the mount point to appear as the union
348 of the mounted file system root and the existing directory.
349 Lookups will be done in the mounted file system first.
350 If those operations fail due to a non-existent file the underlying
351 directory is then accessed.
352 All creates are done in the mounted file system.
355 Any additional options specific to a file system type that is not
356 one of the internally known types (see the
358 option) may be passed as a comma separated list; these options are
359 distinguished by a leading
365 .Bd -literal -offset indent
366 mount -t cd9660 -o -e /dev/cd0 /cdrom
371 to execute the equivalent of:
372 .Bd -literal -offset indent
373 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
376 Options that take a value are specified using the -option=value syntax:
377 .Bd -literal -offset indent
378 mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
382 .Bd -literal -offset indent
383 /sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
386 Additional options specific to file system types
387 which are not internally known
388 (see the description of the
391 may be described in the manual pages for the associated
392 .Pa /sbin/mount_ Ns Sy XXX
395 Print mount information in
402 The file system is to be mounted read-only.
403 Mount the file system read-only (even the super-user may not write it).
409 .It Fl t Cm ufs | Ar external_type
410 The argument following the
412 is used to indicate the file system type.
419 to indicate that the actions should only be taken on
420 file systems of the specified type.
421 More than one type may be specified in a comma separated list.
422 The list of file system types can be prefixed with
424 to specify the file system types for which action should
430 .Bd -literal -offset indent
431 mount -a -t nonfs,nullfs
434 mounts all file systems except those of type
439 The default behavior of
443 option directly to the
449 However, for the following file system types:
463 directly and will instead attempt to execute a program in
464 .Pa /sbin/mount_ Ns Sy XXX
467 is replaced by the file system type name.
468 For example, nfs file systems are mounted by the program
469 .Pa /sbin/mount_nfs .
471 Most file systems will be dynamically loaded by the kernel
472 if not already present, and if the kernel module is available.
476 flag indicates that the status of an already mounted file
477 system should be changed.
478 Any of the options discussed above (the
482 also a file system can be changed from read-only to read-write
484 An attempt to change from read-write to read-only will fail if any
485 files on the file system are currently open for writing unless the
487 flag is also specified.
488 The set of options is determined by applying the options specified
491 and finally applying the
500 is used alone, show all file systems, including those that were mounted with the
502 flag and show additional information about each file system (including fsid
505 The file system object is to be read and write.
508 .Bl -tag -width ".Ev PATH_FSTAB"
510 If the environment variable
512 is set, all operations are performed against the specified file.
514 will not be honored if the process environment or memory address space is
519 for more information.)
522 .Bl -tag -width /etc/fstab -compact
527 Various, most of them are self-explanatory.
529 .Dl XXXXX file system is not available
531 The kernel does not support the respective file system type.
533 support for a particular file system might be provided either on a static
534 (kernel compile-time), or dynamic basis (loaded as a kernel module by
548 .Xr mount_msdosfs 8 ,
553 .Xr mount_unionfs 8 ,
565 the permissions on the original mount point determine if
567 is accessible from the mounted file system.
568 The minimum permissions for
569 the mount point for traversal across the mount point in both
570 directions to be possible for all users is 0111 (execute for all).
574 is preferred over the use of the file system specific
581 signal (that causes an update of the export list)
582 only when the file system is mounted via
585 It is possible for a corrupted file system to cause a crash.