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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
174 directly. For example:
176 mount -t foofs -o mountprog=/mydir/fooprog /dev/acd0 /mnt
179 Enable multi-label Mandatory Access Control, or MAC, on the specified file
181 If the file system supports multilabel operation, individual labels will
182 be maintained for each object in the file system, rather than using a
183 single label for all objects.
184 An alternative to the
190 for more information, which cause the multilabel mount flag to be set
191 automatically at mount-time.
193 Enable NFSv4 ACLs, which can be customized via the
198 This flag is mutually exclusive with
202 Metadata I/O should be done synchronously, while data I/O should be done
206 Do not update the file access time when reading from a file.
208 is useful on file systems where there are large numbers of files and
209 performance is more critical than updating the file access time (which is
210 rarely ever important).
211 This option is currently only supported on local file systems.
213 This file system should be skipped when
219 Disable read clustering.
221 Disable write clustering.
223 Do not allow execution of any binaries on the mounted file system.
224 This option is useful for a server that has file systems containing
225 binaries for architectures other than its own.
226 Note: This option was not designed as a security feature and no
227 guarantee is made that it will prevent malicious code execution; for
228 example, it is still possible to execute scripts which reside on a
232 Do not allow set-user-identifier or set-group-identifier bits to take effect.
233 Note: this option is worthless if a public available suid or sgid
236 is installed on your system.
237 It is set automatically when the user does not have super-user privileges.
239 Do not follow symlinks
240 on the mounted file system.
244 mount the file system read-only (even the super-user may not write it).
246 This option allows a snapshot of the specified file system to be taken.
249 flag is required with this option.
250 Note that snapshot files must be created in the file system that is being
252 You may create up to 20 snapshots per file system.
253 Active snapshots are recorded in the superblock, so they persist across unmount
254 and remount operations and across system reboots.
255 When you are done with a snapshot, it can be removed with the
258 Snapshots may be removed in any order, however you may not get back all the
259 space contained in the snapshot as another snapshot may claim some of the blocks
260 that it is releasing.
261 Note that the schg flag is set on snapshots to ensure that not even the root
262 user can write to them.
263 The unlink command makes an exception for snapshot files in that it allows them
264 to be removed even though they have the schg flag set, so it is not necessary to
265 clear the schg flag before removing a snapshot file.
267 Once you have taken a snapshot, there are three interesting things that you can
274 on the snapshot file.
275 Assuming that the file system was clean when it was mounted, you should always
276 get a clean (and unchanging) result from running fsck on the snapshot.
277 This is essentially what the background fsck process does.
283 You will get a dump that is consistent with the file system as of the timestamp
287 Mount the snapshot as a frozen image of the file system.
288 To mount the snapshot
289 .Pa /var/snapshot/snap1 :
291 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
292 mount -r /dev/md4 /mnt
295 You can now cruise around your frozen
299 Everything will be in the same state that it was at the time the snapshot was
301 The one exception is that any earlier snapshots will appear as zero length
303 When you are done with the mounted snapshot:
310 A directory on the mounted file system will respond to the SUID bit
311 being set, by setting the owner of any new files to be the same
312 as the owner of the directory.
313 New directories will inherit the bit from their parents.
314 Execute bits are removed from
315 the file, and it will not be given to root.
317 This feature is designed for use on fileservers serving PC users via
318 ftp, SAMBA, or netatalk.
319 It provides security holes for shell users and as
320 such should not be used on shell machines, especially on home directories.
321 This option requires the SUIDDIR
322 option in the kernel to work.
323 Only UFS file systems support this option.
326 for more information.
330 to the file system should be done synchronously.
334 indicate that the status of an already mounted file system should be changed.
336 Causes the namespace at the mount point to appear as the union
337 of the mounted file system root and the existing directory.
338 Lookups will be done in the mounted file system first.
339 If those operations fail due to a non-existent file the underlying
340 directory is then accessed.
341 All creates are done in the mounted file system.
344 Any additional options specific to a file system type that is not
345 one of the internally known types (see the
347 option) may be passed as a comma separated list; these options are
348 distinguished by a leading
351 Options that take a value are specified using the syntax -option=value.
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 Additional options specific to file system types
367 which are not internally known
368 (see the description of the
371 may be described in the manual pages for the associated
372 .Pa /sbin/mount_ Ns Sy XXX
375 Print mount information in
382 The file system is to be mounted read-only.
383 Mount the file system read-only (even the super-user may not write it).
389 .It Fl t Cm ufs | Ar external_type
390 The argument following the
392 is used to indicate the file system type.
399 to indicate that the actions should only be taken on
400 file systems of the specified type.
401 More than one type may be specified in a comma separated list.
402 The list of file system types can be prefixed with
404 to specify the file system types for which action should
410 .Bd -literal -offset indent
411 mount -a -t nonfs,nullfs
414 mounts all file systems except those of type
419 The default behavior of
423 option directly to the
429 However, for the following file system types:
446 directly and will instead attempt to execute a program in
447 .Pa /sbin/mount_ Ns Sy XXX
450 is replaced by the file system type name.
451 For example, nfs file systems are mounted by the program
452 .Pa /sbin/mount_nfs .
454 Most file systems will be dynamically loaded by the kernel
455 if not already present, and if the kernel module is available.
459 flag indicates that the status of an already mounted file
460 system should be changed.
461 Any of the options discussed above (the
465 also a file system can be changed from read-only to read-write
467 An attempt to change from read-write to read-only will fail if any
468 files on the file system are currently open for writing unless the
470 flag is also specified.
471 The set of options is determined by applying the options specified
474 and finally applying the
483 is used alone, show all file systems, including those that were mounted with the
485 flag and show additional information about each file system (including fsid
488 The file system object is to be read and write.
491 .Bl -tag -width ".Ev PATH_FSTAB"
493 If the environment variable
495 is set, all operations are performed against the specified file.
497 will not be honored if the process environment or memory address space is
502 for more information.)
505 .Bl -tag -width /etc/fstab -compact
510 Various, most of them are self-explanatory.
512 .Dl XXXXX file system is not available
514 The kernel does not support the respective file system type.
516 support for a particular file system might be provided either on a static
517 (kernel compile-time), or dynamic basis (loaded as a kernel module by
531 .Xr mount_msdosfs 8 ,
536 .Xr mount_portalfs 8 ,
539 .Xr mount_unionfs 8 ,
546 the permissions on the original mount point determine if
548 is accessible from the mounted file system.
549 The minimum permissions for
550 the mount point for traversal across the mount point in both
551 directions to be possible for all users is 0111 (execute for all).
555 is preferred over the use of the file system specific
562 signal (that causes an update of the export list)
563 only when the file system is mounted via
571 It is possible for a corrupted file system to cause a crash.