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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.
154 This flag indicates that the file system was mounted by
156 Automounted file systems are automatically unmounted by
159 Mount the file system read-write.
160 If that fails with an error that suggests that the media could be read-only,
161 then automatically try to mount the file system read-only.
165 flag, this is the same as specifying the options currently in effect for
166 the mounted file system.
170 forces the revocation of write access when trying to downgrade
171 a file system mount status from read-write to read-only.
173 forces the R/W mount of an unclean file system (dangerous; use with caution).
177 flag, this is the same as specifying all the options listed in the
179 file for the file system.
181 This file system should be skipped when
188 .It Cm mountprog Ns = Ns Aq Ar program
191 to use the specified program to mount the file system, instead of calling
196 mount -t foofs -o mountprog=/mydir/fooprog /dev/cd0 /mnt
199 Enable multi-label Mandatory Access Control, or MAC, on the specified file
201 If the file system supports multilabel operation, individual labels will
202 be maintained for each object in the file system, rather than using a
203 single label for all objects.
204 An alternative to the
210 for more information, which cause the multilabel mount flag to be set
211 automatically at mount-time.
213 Enable NFSv4 ACLs, which can be customized via the
218 This flag is mutually exclusive with
222 Metadata I/O should be done synchronously, while data I/O should be done
226 Do not update the file access time when reading from a file.
228 is useful on file systems where there are large numbers of files and
229 performance is more critical than updating the file access time (which is
230 rarely ever important).
231 This option is currently only supported on local file systems.
233 This file system should be skipped when
239 Disable read clustering.
241 Disable write clustering.
243 Do not allow execution of any binaries on the mounted file system.
244 This option is useful for a server that has file systems containing
245 binaries for architectures other than its own.
246 Note: This option was not designed as a security feature and no
247 guarantee is made that it will prevent malicious code execution; for
248 example, it is still possible to execute scripts which reside on a
252 Do not allow set-user-identifier or set-group-identifier bits to take effect.
253 Note: this option is worthless if a public available suid or sgid
256 is installed on your system.
257 It is set automatically when the user does not have super-user privileges.
259 Do not follow symlinks
260 on the mounted file system.
264 mount the file system read-only (even the super-user may not write it).
266 This option allows a snapshot of the specified file system to be taken.
269 flag is required with this option.
270 Note that snapshot files must be created in the file system that is being
272 You may create up to 20 snapshots per file system.
273 Active snapshots are recorded in the superblock, so they persist across unmount
274 and remount operations and across system reboots.
275 When you are done with a snapshot, it can be removed with the
278 Snapshots may be removed in any order, however you may not get back all the
279 space contained in the snapshot as another snapshot may claim some of the blocks
280 that it is releasing.
281 Note that the schg flag is set on snapshots to ensure that not even the root
282 user can write to them.
283 The unlink command makes an exception for snapshot files in that it allows them
284 to be removed even though they have the schg flag set, so it is not necessary to
285 clear the schg flag before removing a snapshot file.
287 Once you have taken a snapshot, there are three interesting things that you can
294 on the snapshot file.
295 Assuming that the file system was clean when it was mounted, you should always
296 get a clean (and unchanging) result from running fsck on the snapshot.
297 This is essentially what the background fsck process does.
303 You will get a dump that is consistent with the file system as of the timestamp
307 Mount the snapshot as a frozen image of the file system.
308 To mount the snapshot
309 .Pa /var/snapshot/snap1 :
311 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
312 mount -r /dev/md4 /mnt
315 You can now cruise around your frozen
319 Everything will be in the same state that it was at the time the snapshot was
321 The one exception is that any earlier snapshots will appear as zero length
323 When you are done with the mounted snapshot:
330 A directory on the mounted file system will respond to the SUID bit
331 being set, by setting the owner of any new files to be the same
332 as the owner of the directory.
333 New directories will inherit the bit from their parents.
334 Execute bits are removed from
335 the file, and it will not be given to root.
337 This feature is designed for use on fileservers serving PC users via
338 ftp, SAMBA, or netatalk.
339 It provides security holes for shell users and as
340 such should not be used on shell machines, especially on home directories.
341 This option requires the SUIDDIR
342 option in the kernel to work.
343 Only UFS file systems support this option.
346 for more information.
350 to the file system should be done synchronously.
354 indicate that the status of an already mounted file system should be changed.
356 Causes the namespace at the mount point to appear as the union
357 of the mounted file system root and the existing directory.
358 Lookups will be done in the mounted file system first.
359 If those operations fail due to a non-existent file the underlying
360 directory is then accessed.
361 All creates are done in the mounted file system.
364 Any additional options specific to a file system type that is not
365 one of the internally known types (see the
367 option) may be passed as a comma separated list; these options are
368 distinguished by a leading
374 .Bd -literal -offset indent
375 mount -t cd9660 -o -e /dev/cd0 /cdrom
380 to execute the equivalent of:
381 .Bd -literal -offset indent
382 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
385 Options that take a value are specified using the -option=value syntax:
386 .Bd -literal -offset indent
387 mount -t msdosfs -o -u=fred,-g=wheel /dev/da0s1 /mnt
391 .Bd -literal -offset indent
392 /sbin/mount_msdosfs -u fred -g wheel /dev/da0s1 /mnt
395 Additional options specific to file system types
396 which are not internally known
397 (see the description of the
400 may be described in the manual pages for the associated
401 .Pa /sbin/mount_ Ns Sy XXX
404 Print mount information in
411 The file system is to be mounted read-only.
412 Mount the file system read-only (even the super-user may not write it).
418 .It Fl t Cm ufs | Ar external_type
419 The argument following the
421 is used to indicate the file system type.
428 to indicate that the actions should only be taken on
429 file systems of the specified type.
430 More than one type may be specified in a comma separated list.
431 The list of file system types can be prefixed with
433 to specify the file system types for which action should
439 .Bd -literal -offset indent
440 mount -a -t nonfs,nullfs
443 mounts all file systems except those of type
448 The default behavior of
452 option directly to the
458 However, for the following file system types:
472 directly and will instead attempt to execute a program in
473 .Pa /sbin/mount_ Ns Sy XXX
476 is replaced by the file system type name.
477 For example, nfs file systems are mounted by the program
478 .Pa /sbin/mount_nfs .
480 Most file systems will be dynamically loaded by the kernel
481 if not already present, and if the kernel module is available.
485 flag indicates that the status of an already mounted file
486 system should be changed.
487 Any of the options discussed above (the
491 also a file system can be changed from read-only to read-write
493 An attempt to change from read-write to read-only will fail if any
494 files on the file system are currently open for writing unless the
496 flag is also specified.
497 The set of options is determined by applying the options specified
500 and finally applying the
509 is used alone, show all file systems, including those that were mounted with the
511 flag and show additional information about each file system (including fsid
514 The file system object is to be read and write.
517 .Bl -tag -width ".Ev PATH_FSTAB"
519 If the environment variable
521 is set, all operations are performed against the specified file.
523 will not be honored if the process environment or memory address space is
528 for more information.)
531 .Bl -tag -width /etc/fstab -compact
536 Various, most of them are self-explanatory.
538 .Dl XXXXX file system is not available
540 The kernel does not support the respective file system type.
542 support for a particular file system might be provided either on a static
543 (kernel compile-time), or dynamic basis (loaded as a kernel module by
560 .Xr mount_msdosfs 8 ,
565 .Xr mount_unionfs 8 ,
578 the permissions on the original mount point determine if
580 is accessible from the mounted file system.
581 The minimum permissions for
582 the mount point for traversal across the mount point in both
583 directions to be possible for all users is 0111 (execute for all).
587 is preferred over the use of the file system specific
594 signal (that causes an update of the export list)
595 only when the file system is mounted via
598 It is possible for a corrupted file system to cause a crash.