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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
267 wrapper is installed on your system.
268 It is set automatically when the user does not have super-user privileges.
270 Do not follow symlinks
271 on the mounted file system.
275 mount the file system read-only (even the super-user may not write it).
277 Take a snapshot of the specified filesystem.
278 When this option is used, all other options are ignored.
281 flag is required with this option.
283 Snapshot files must be created in the file system that is being
285 You may create up to 20 snapshots per file system.
286 Active snapshots are recorded in the superblock, so they persist across unmount
287 and remount operations and across system reboots.
288 When you are done with a snapshot, it can be removed with the
291 Snapshots may be removed in any order, however you may not get back all the
292 space contained in the snapshot as another snapshot may claim some of the blocks
293 that it is releasing.
294 Note that the schg flag is set on snapshots to ensure that not even the root
295 user can write to them.
296 The unlink command makes an exception for snapshot files in that it allows them
297 to be removed even though they have the schg flag set, so it is not necessary to
298 clear the schg flag before removing a snapshot file.
300 Once you have taken a snapshot, there are three interesting things that you can
307 on the snapshot file.
308 Assuming that the file system was clean when it was mounted, you should always
309 get a clean (and unchanging) result from running fsck on the snapshot.
310 This is essentially what the background fsck process does.
316 You will get a dump that is consistent with the file system as of the timestamp
320 Mount the snapshot as a frozen image of the file system.
321 To mount the snapshot
322 .Pa /var/snapshot/snap1 :
324 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
325 mount -r /dev/md4 /mnt
328 You can now cruise around your frozen
332 Everything will be in the same state that it was at the time the snapshot was
334 The one exception is that any earlier snapshots will appear as zero length
336 When you are done with the mounted snapshot:
343 A directory on the mounted file system will respond to the SUID bit
344 being set, by setting the owner of any new files to be the same
345 as the owner of the directory.
346 New directories will inherit the bit from their parents.
347 Execute bits are removed from
348 the file, and it will not be given to root.
350 This feature is designed for use on fileservers serving PC users via
351 ftp, SAMBA, or netatalk.
352 It provides security holes for shell users and as
353 such should not be used on shell machines, especially on home directories.
354 This option requires the SUIDDIR
355 option in the kernel to work.
356 Only UFS file systems support this option.
359 for more information.
361 All I/O to the file system should be done synchronously.
365 indicate that the status of an already mounted file system should be changed.
367 Causes the namespace at the mount point to appear as the union
368 of the mounted file system root and the existing directory.
369 Lookups will be done in the mounted file system first.
370 If those operations fail due to a non-existent file the underlying
371 directory is then accessed.
372 All creates are done in the mounted file system.
374 The file system is untrusted and the kernel should use more
375 extensive checks on the file-system's metadata before using it.
376 This option is intended to be used when mounting file systems
377 from untrusted media such as USB memory sticks or other
378 externally-provided media.
381 Any additional options specific to a file system type that is not
382 one of the internally known types (see the
384 option) may be passed as a comma separated list; these options are
385 distinguished by a leading
391 .Bd -literal -offset indent
392 mount -t cd9660 -o -e /dev/cd0 /cdrom
397 to execute the equivalent of:
398 .Bd -literal -offset indent
399 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
402 Options that take a value are specified using the -option=value syntax:
403 .Bd -literal -offset indent
404 mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
408 .Bd -literal -offset indent
409 /sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
412 Additional options specific to file system types
413 which are not internally known
414 (see the description of the
417 may be described in the manual pages for the associated
418 .Pa /sbin/mount_ Ns Sy XXX
421 Print mount information in
428 The file system is to be mounted read-only.
429 Mount the file system read-only (even the super-user may not write it).
435 .It Fl t Oo Cm no Oc Ns Cm Ar type Ns Op Cm , Ns Ar type ...
436 The argument following the
438 is used to indicate the file system type.
445 to indicate that the actions should only be taken on
446 file systems of the specified type.
447 More than one type may be specified in a comma separated list.
448 The list of file system types can be prefixed with
450 to specify the file system types for which action should
456 .Bd -literal -offset indent
457 mount -a -t nonfs,nullfs
460 mounts all file systems except those of type NFS and NULLFS.
462 The default behavior of
466 option directly to the
472 However, for the following file system types:
485 directly and will instead attempt to execute a program in
486 .Pa /sbin/mount_ Ns Ar type
489 is replaced by the file system type name.
492 file systems are mounted by the program
493 .Pa /sbin/mount_nfs .
495 Most file systems will be dynamically loaded by the kernel
496 if not already present, and if the kernel module is available.
500 flag indicates that the status of an already mounted file
501 system should be changed.
502 Any of the options discussed above (the
506 also a file system can be changed from read-only to read-write
508 An attempt to change from read-write to read-only will fail if any
509 files on the file system are currently open for writing unless the
511 flag is also specified.
512 The set of options is determined by applying the options specified
515 and finally applying the
524 is used alone, show all file systems, including those that were mounted with the
526 flag and show additional information about each file system (including fsid
529 The file system object is to be read and write.
532 .Bl -tag -width ".Ev PATH_FSTAB"
534 If the environment variable
536 is set, all operations are performed against the specified file.
538 will not be honored if the process environment or memory address space is
543 for more information.)
546 .Bl -tag -width /etc/fstab -compact
551 Various, most of them are self-explanatory.
553 .Dl XXXXX file system is not available
555 The kernel does not support the respective file system type.
557 support for a particular file system might be provided either on a static
558 (kernel compile-time), or dynamic basis (loaded as a kernel module by
566 .Xr xo_parse_args 3 ,
578 .Xr mount_msdosfs 8 ,
583 .Xr mount_unionfs 8 ,
595 the permissions on the original mount point determine if
597 is accessible from the mounted file system.
598 The minimum permissions for
599 the mount point for traversal across the mount point in both
600 directions to be possible for all users is 0111 (execute for all).
604 is preferred over the use of the file system specific
611 signal (that causes an update of the export list)
612 only when the file system is mounted via
615 It is possible for a corrupted file system to cause a crash.