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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
112 option, also mount those file systems which are marked as
115 Options are specified with a
117 flag followed by a comma separated string of options.
118 In case of conflicting options being specified, the rightmost option
120 The following options are available:
121 .Bl -tag -width indent
123 Enable POSIX.1e Access Control Lists, or ACLs, which can be customized via the
128 This flag is mutually exclusive with
134 to the file system should be done asynchronously.
137 flag to set, since it does not guarantee that the file system structure
138 on the disk will remain consistent.
141 flag should be used sparingly, and only when some data recovery
142 mechanism is present.
146 flag, this is the same as specifying the options currently in effect for
147 the mounted file system.
151 forces the revocation of write access when trying to downgrade
152 a file system mount status from read-write to read-only.
154 forces the R/W mount of an unclean file system (dangerous; use with caution).
158 flag, this is the same as specifying all the options listed in the
160 file for the file system.
162 This file system should be skipped when
169 .It Cm mountprog Ns = Ns Aq Ar program
172 to use the specified program to mount the file system, instead of calling
177 mount -t foofs -o mountprog=/mydir/fooprog /dev/acd0 /mnt
180 Enable multi-label Mandatory Access Control, or MAC, on the specified file
182 If the file system supports multilabel operation, individual labels will
183 be maintained for each object in the file system, rather than using a
184 single label for all objects.
185 An alternative to the
191 for more information, which cause the multilabel mount flag to be set
192 automatically at mount-time.
194 Enable NFSv4 ACLs, which can be customized via the
199 This flag is mutually exclusive with
203 Metadata I/O should be done synchronously, while data I/O should be done
207 Do not update the file access time when reading from a file.
209 is useful on file systems where there are large numbers of files and
210 performance is more critical than updating the file access time (which is
211 rarely ever important).
212 This option is currently only supported on local file systems.
214 This file system should be skipped when
220 Disable read clustering.
222 Disable write clustering.
224 Do not allow execution of any binaries on the mounted file system.
225 This option is useful for a server that has file systems containing
226 binaries for architectures other than its own.
227 Note: This option was not designed as a security feature and no
228 guarantee is made that it will prevent malicious code execution; for
229 example, it is still possible to execute scripts which reside on a
233 Do not allow set-user-identifier or set-group-identifier bits to take effect.
234 Note: this option is worthless if a public available suid or sgid
237 is installed on your system.
238 It is set automatically when the user does not have super-user privileges.
240 Do not follow symlinks
241 on the mounted file system.
245 mount the file system read-only (even the super-user may not write it).
247 This option allows a snapshot of the specified file system to be taken.
250 flag is required with this option.
251 Note that snapshot files must be created in the file system that is being
253 You may create up to 20 snapshots per file system.
254 Active snapshots are recorded in the superblock, so they persist across unmount
255 and remount operations and across system reboots.
256 When you are done with a snapshot, it can be removed with the
259 Snapshots may be removed in any order, however you may not get back all the
260 space contained in the snapshot as another snapshot may claim some of the blocks
261 that it is releasing.
262 Note that the schg flag is set on snapshots to ensure that not even the root
263 user can write to them.
264 The unlink command makes an exception for snapshot files in that it allows them
265 to be removed even though they have the schg flag set, so it is not necessary to
266 clear the schg flag before removing a snapshot file.
268 Once you have taken a snapshot, there are three interesting things that you can
275 on the snapshot file.
276 Assuming that the file system was clean when it was mounted, you should always
277 get a clean (and unchanging) result from running fsck on the snapshot.
278 This is essentially what the background fsck process does.
284 You will get a dump that is consistent with the file system as of the timestamp
288 Mount the snapshot as a frozen image of the file system.
289 To mount the snapshot
290 .Pa /var/snapshot/snap1 :
292 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
293 mount -r /dev/md4 /mnt
296 You can now cruise around your frozen
300 Everything will be in the same state that it was at the time the snapshot was
302 The one exception is that any earlier snapshots will appear as zero length
304 When you are done with the mounted snapshot:
311 A directory on the mounted file system will respond to the SUID bit
312 being set, by setting the owner of any new files to be the same
313 as the owner of the directory.
314 New directories will inherit the bit from their parents.
315 Execute bits are removed from
316 the file, and it will not be given to root.
318 This feature is designed for use on fileservers serving PC users via
319 ftp, SAMBA, or netatalk.
320 It provides security holes for shell users and as
321 such should not be used on shell machines, especially on home directories.
322 This option requires the SUIDDIR
323 option in the kernel to work.
324 Only UFS file systems support this option.
327 for more information.
331 to the file system should be done synchronously.
335 indicate that the status of an already mounted file system should be changed.
337 Causes the namespace at the mount point to appear as the union
338 of the mounted file system root and the existing directory.
339 Lookups will be done in the mounted file system first.
340 If those operations fail due to a non-existent file the underlying
341 directory is then accessed.
342 All creates are done in the mounted file system.
345 Any additional options specific to a file system type that is not
346 one of the internally known types (see the
348 option) may be passed as a comma separated list; these options are
349 distinguished by a leading
355 .Bd -literal -offset indent
356 mount -t cd9660 -o -e /dev/cd0 /cdrom
361 to execute the equivalent of:
362 .Bd -literal -offset indent
363 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
366 Options that take a value are specified using the -option=value syntax:
367 .Bd -literal -offset indent
368 mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
372 .Bd -literal -offset indent
373 /sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
376 Additional options specific to file system types
377 which are not internally known
378 (see the description of the
381 may be described in the manual pages for the associated
382 .Pa /sbin/mount_ Ns Sy XXX
385 Print mount information in
392 The file system is to be mounted read-only.
393 Mount the file system read-only (even the super-user may not write it).
399 .It Fl t Cm ufs | Ar external_type
400 The argument following the
402 is used to indicate the file system type.
409 to indicate that the actions should only be taken on
410 file systems of the specified type.
411 More than one type may be specified in a comma separated list.
412 The list of file system types can be prefixed with
414 to specify the file system types for which action should
420 .Bd -literal -offset indent
421 mount -a -t nonfs,nullfs
424 mounts all file systems except those of type
429 The default behavior of
433 option directly to the
439 However, for the following file system types:
456 directly and will instead attempt to execute a program in
457 .Pa /sbin/mount_ Ns Sy XXX
460 is replaced by the file system type name.
461 For example, nfs file systems are mounted by the program
462 .Pa /sbin/mount_nfs .
464 Most file systems will be dynamically loaded by the kernel
465 if not already present, and if the kernel module is available.
469 flag indicates that the status of an already mounted file
470 system should be changed.
471 Any of the options discussed above (the
475 also a file system can be changed from read-only to read-write
477 An attempt to change from read-write to read-only will fail if any
478 files on the file system are currently open for writing unless the
480 flag is also specified.
481 The set of options is determined by applying the options specified
484 and finally applying the
493 is used alone, show all file systems, including those that were mounted with the
495 flag and show additional information about each file system (including fsid
498 The file system object is to be read and write.
501 .Bl -tag -width ".Ev PATH_FSTAB"
503 If the environment variable
505 is set, all operations are performed against the specified file.
507 will not be honored if the process environment or memory address space is
512 for more information.)
515 .Bl -tag -width /etc/fstab -compact
520 Various, most of them are self-explanatory.
522 .Dl XXXXX file system is not available
524 The kernel does not support the respective file system type.
526 support for a particular file system might be provided either on a static
527 (kernel compile-time), or dynamic basis (loaded as a kernel module by
541 .Xr mount_msdosfs 8 ,
546 .Xr mount_portalfs 8 ,
549 .Xr mount_unionfs 8 ,
561 the permissions on the original mount point determine if
563 is accessible from the mounted file system.
564 The minimum permissions for
565 the mount point for traversal across the mount point in both
566 directions to be possible for all users is 0111 (execute for all).
570 is preferred over the use of the file system specific
577 signal (that causes an update of the export list)
578 only when the file system is mounted via
581 It is possible for a corrupted file system to cause a crash.