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28 .\" @(#)mount.8 8.8 (Berkeley) 6/16/94
36 .Nd mount file systems
42 .Op Fl t Ar ufs | external_type
49 .Op Fl t Ar ufs | external_type
56 system call to prepare and graft a
58 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 Access Control Lists, or ACLS, which can be customized via the
131 to the file system should be done asynchronously.
134 flag to set, since it does not guarantee that the file system structure
135 on the disk will remain consistent.
138 flag should be used sparingly, and only when some data recovery
139 mechanism is present.
143 flag, this is the same as specifying the options currently in effect for
144 the mounted file system.
148 forces the revocation of write access when trying to downgrade
149 a file system mount status from read-write to read-only.
151 forces the R/W mount of an unclean file system (dangerous; use with caution).
155 flag, this is the same as specifying all the options listed in the
157 file for the file system.
159 This file system should be skipped when
167 Enable multi-label Mandatory Access Control, or MAC, on the specified file
169 If the file system supports multilabel operation, individual labels will
170 be maintained for each object in the file system, rather than using a
171 single label for all objects.
172 An alternative to the
178 for more information, which cause the multilabel mount flag to be set
179 automatically at mount-time.
181 Metadata I/O should be done synchronously, while data I/O should be done
185 Do not update the file access time when reading from a file.
187 is useful on file systems where there are large numbers of files and
188 performance is more critical than updating the file access time (which is
189 rarely ever important).
190 This option is currently only supported on local file systems.
192 This file system should be skipped when
198 Disable read clustering.
200 Disable write clustering.
202 Do not allow execution of any binaries on the mounted file system.
203 This option is useful for a server that has file systems containing
204 binaries for architectures other than its own.
205 Note: This option was not designed as a security feature and no
206 guarantee is made that it will prevent malicious code execution; for
207 example, it is still possible to execute scripts which reside on a
211 Do not allow set-user-identifier or set-group-identifier bits to take effect.
212 Note: this option is worthless if a public available suid or sgid
215 is installed on your system.
216 It is set automatically when the user does not have super-user privileges.
218 Do not follow symlinks
219 on the mounted file system.
223 mount the file system read-only (even the super-user may not write it).
227 to the file system should be done synchronously.
229 This option allows a snapshot of the specified file system to be taken.
232 flag is required with this option.
233 Note that snapshot files must be created in the file system that is being
235 You may create up to 20 snapshots per file system.
236 Active snapshots are recorded in the superblock, so they persist across unmount
237 and remount operations and across system reboots.
238 When you are done with a snapshot, it can be removed with the
241 Snapshots may be removed in any order, however you may not get back all the
242 space contained in the snapshot as another snapshot may claim some of the blocks
243 that it is releasing.
244 Note that the schg flag is set on snapshots to ensure that not even the root
245 user can write to them.
246 The unlink command makes an exception for snapshot files in that it allows them
247 to be removed even though they have the schg flag set, so it is not necessary to
248 clear the schg flag before removing a snapshot file.
250 Once you have taken a snapshot, there are three interesting things that you can
257 on the snapshot file.
258 Assuming that the file system was clean when it was mounted, you should always
259 get a clean (and unchanging) result from running fsck on the snapshot.
260 This is essentially what the background fsck process does.
266 You will get a dump that is consistent with the file system as of the timestamp
270 Mount the snapshot as a frozen image of the file system.
271 To mount the snapshot
272 .Pa /var/snapshot/snap1 :
274 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
275 mount -r /dev/md4 /mnt
278 You can now cruise around your frozen
282 Everything will be in the same state that it was at the time the snapshot was
284 The one exception is that any earlier snapshots will appear as zero length
286 When you are done with the mounted snapshot:
292 Further details can be found in the file at
293 .Pa /usr/src/sys/ufs/ffs/README.snapshot .
296 A directory on the mounted file system will respond to the SUID bit
297 being set, by setting the owner of any new files to be the same
298 as the owner of the directory.
299 New directories will inherit the bit from their parents.
300 Execute bits are removed from
301 the file, and it will not be given to root.
303 This feature is designed for use on fileservers serving PC users via
304 ftp, SAMBA, or netatalk.
305 It provides security holes for shell users and as
306 such should not be used on shell machines, especially on home directories.
307 This option requires the SUIDDIR
308 option in the kernel to work.
309 Only UFS file systems support this option.
312 for more information.
316 indicate that the status of an already mounted file system should be changed.
318 Causes the namespace at the mount point to appear as the union
319 of the mounted file system root and the existing directory.
320 Lookups will be done in the mounted file system first.
321 If those operations fail due to a non-existent file the underlying
322 directory is then accessed.
323 All creates are done in the mounted file system.
326 Any additional options specific to a file system type that is not
327 one of the internally known types (see the
329 option) may be passed as a comma separated list; these options are
330 distinguished by a leading
333 Options that take a value are specified using the syntax -option=value.
337 .Bd -literal -offset indent
338 mount -t unionfs -o -b /sys $HOME/sys
343 to execute the equivalent of:
344 .Bd -literal -offset indent
345 /sbin/mount_unionfs -b /sys $HOME/sys
348 Additional options specific to file system types
349 which are not internally known
350 (see the description of the
353 may be described in the manual pages for the associated
354 .Pa /sbin/mount_ Ns Sy XXX
357 Print mount information in
364 The file system is to be mounted read-only.
365 Mount the file system read-only (even the super-user may not write it).
371 .It Fl t Ar ufs | external_type
372 The argument following the
374 is used to indicate the file system type.
381 to indicate that the actions should only be taken on
382 file systems of the specified type.
383 More than one type may be specified in a comma separated list.
384 The list of file system types can be prefixed with
386 to specify the file system types for which action should
392 .Bd -literal -offset indent
393 mount -a -t nonfs,nullfs
396 mounts all file systems except those of type
401 The default behavior of
405 option directly to the
411 However, for the following file system types:
429 directly and will instead attempt to execute a program in
430 .Pa /sbin/mount_ Ns Sy XXX
433 is replaced by the file system type name.
434 For example, nfs file systems are mounted by the program
435 .Pa /sbin/mount_nfs .
437 Most file systems will be dynamically loaded by the kernel
438 if not already present, and if the kernel module is available.
442 flag indicates that the status of an already mounted file
443 system should be changed.
444 Any of the options discussed above (the
448 also a file system can be changed from read-only to read-write
450 An attempt to change from read-write to read-only will fail if any
451 files on the file system are currently open for writing unless the
453 flag is also specified.
454 The set of options is determined by applying the options specified
457 and finally applying the
465 The file system object is to be read and write.
468 .Bl -tag -width ".Ev PATH_FSTAB"
470 If the environment variable
472 is set, all operations are performed against the specified file.
474 will not be honored if the process environment or memory address space is
479 for more information.)
482 .Bl -tag -width /etc/fstab -compact
487 Various, most of them are self-explanatory.
489 .Dl XXXXX file system is not available
491 The kernel does not support the respective file system type.
493 support for a particular file system might be provided either on a static
494 (kernel compile-time), or dynamic basis (loaded as a kernel module by
507 .Xr mount_msdosfs 8 ,
512 .Xr mount_portalfs 8 ,
517 .Xr mount_unionfs 8 ,
522 the permissions on the original mount point determine if
524 is accessible from the mounted file system.
525 The minimum permissions for
526 the mount point for traversal across the mount point in both
527 directions to be possible for all users is 0111 (execute for all).
534 It is possible for a corrupted file system to cause a crash.