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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 not supported on network file systems when the
213 Support in network files servers on other operating systems
214 with a FreeBSD client is possible,
215 but should be tested before it is relied on.
217 This file system should be skipped when
223 Disable read clustering.
225 Disable write clustering.
227 Do not allow execution of any binaries on the mounted file system.
228 This option is useful for a server that has file systems containing
229 binaries for architectures other than its own.
230 Note: This option was not designed as a security feature and no
231 guarantee is made that it will prevent malicious code execution; for
232 example, it is still possible to execute scripts which reside on a
236 Do not allow set-user-identifier or set-group-identifier bits to take effect.
237 Note: this option is worthless if a public available suid or sgid
240 is installed on your system.
241 It is set automatically when the user does not have super-user privileges.
243 Do not follow symlinks
244 on the mounted file system.
248 mount the file system read-only (even the super-user may not write it).
250 This option allows a snapshot of the specified file system to be taken.
253 flag is required with this option.
254 Note that snapshot files must be created in the file system that is being
256 You may create up to 20 snapshots per file system.
257 Active snapshots are recorded in the superblock, so they persist across unmount
258 and remount operations and across system reboots.
259 When you are done with a snapshot, it can be removed with the
262 Snapshots may be removed in any order, however you may not get back all the
263 space contained in the snapshot as another snapshot may claim some of the blocks
264 that it is releasing.
265 Note that the schg flag is set on snapshots to ensure that not even the root
266 user can write to them.
267 The unlink command makes an exception for snapshot files in that it allows them
268 to be removed even though they have the schg flag set, so it is not necessary to
269 clear the schg flag before removing a snapshot file.
271 Once you have taken a snapshot, there are three interesting things that you can
278 on the snapshot file.
279 Assuming that the file system was clean when it was mounted, you should always
280 get a clean (and unchanging) result from running fsck on the snapshot.
281 This is essentially what the background fsck process does.
287 You will get a dump that is consistent with the file system as of the timestamp
291 Mount the snapshot as a frozen image of the file system.
292 To mount the snapshot
293 .Pa /var/snapshot/snap1 :
295 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
296 mount -r /dev/md4 /mnt
299 You can now cruise around your frozen
303 Everything will be in the same state that it was at the time the snapshot was
305 The one exception is that any earlier snapshots will appear as zero length
307 When you are done with the mounted snapshot:
314 A directory on the mounted file system will respond to the SUID bit
315 being set, by setting the owner of any new files to be the same
316 as the owner of the directory.
317 New directories will inherit the bit from their parents.
318 Execute bits are removed from
319 the file, and it will not be given to root.
321 This feature is designed for use on fileservers serving PC users via
322 ftp, SAMBA, or netatalk.
323 It provides security holes for shell users and as
324 such should not be used on shell machines, especially on home directories.
325 This option requires the SUIDDIR
326 option in the kernel to work.
327 Only UFS file systems support this option.
330 for more information.
334 to the file system should be done synchronously.
338 indicate that the status of an already mounted file system should be changed.
340 Causes the namespace at the mount point to appear as the union
341 of the mounted file system root and the existing directory.
342 Lookups will be done in the mounted file system first.
343 If those operations fail due to a non-existent file the underlying
344 directory is then accessed.
345 All creates are done in the mounted file system.
348 Any additional options specific to a file system type that is not
349 one of the internally known types (see the
351 option) may be passed as a comma separated list; these options are
352 distinguished by a leading
355 Options that take a value are specified using the syntax -option=value.
359 .Bd -literal -offset indent
360 mount -t cd9660 -o -e /dev/cd0 /cdrom
365 to execute the equivalent of:
366 .Bd -literal -offset indent
367 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
370 Additional options specific to file system types
371 which are not internally known
372 (see the description of the
375 may be described in the manual pages for the associated
376 .Pa /sbin/mount_ Ns Sy XXX
379 Print mount information in
386 The file system is to be mounted read-only.
387 Mount the file system read-only (even the super-user may not write it).
393 .It Fl t Cm ufs | Ar external_type
394 The argument following the
396 is used to indicate the file system type.
403 to indicate that the actions should only be taken on
404 file systems of the specified type.
405 More than one type may be specified in a comma separated list.
406 The list of file system types can be prefixed with
408 to specify the file system types for which action should
414 .Bd -literal -offset indent
415 mount -a -t nonfs,nullfs
418 mounts all file systems except those of type
423 The default behavior of
427 option directly to the
433 However, for the following file system types:
450 directly and will instead attempt to execute a program in
451 .Pa /sbin/mount_ Ns Sy XXX
454 is replaced by the file system type name.
455 For example, nfs file systems are mounted by the program
456 .Pa /sbin/mount_nfs .
458 Most file systems will be dynamically loaded by the kernel
459 if not already present, and if the kernel module is available.
463 flag indicates that the status of an already mounted file
464 system should be changed.
465 Any of the options discussed above (the
469 also a file system can be changed from read-only to read-write
471 An attempt to change from read-write to read-only will fail if any
472 files on the file system are currently open for writing unless the
474 flag is also specified.
475 The set of options is determined by applying the options specified
478 and finally applying the
487 is used alone, show all file systems, including those that were mounted with the
489 flag and show additional information about each file system (including fsid
492 The file system object is to be read and write.
495 .Bl -tag -width ".Ev PATH_FSTAB"
497 If the environment variable
499 is set, all operations are performed against the specified file.
501 will not be honored if the process environment or memory address space is
506 for more information.)
509 .Bl -tag -width /etc/fstab -compact
514 Various, most of them are self-explanatory.
516 .Dl XXXXX file system is not available
518 The kernel does not support the respective file system type.
520 support for a particular file system might be provided either on a static
521 (kernel compile-time), or dynamic basis (loaded as a kernel module by
535 .Xr mount_msdosfs 8 ,
540 .Xr mount_portalfs 8 ,
543 .Xr mount_unionfs 8 ,
555 the permissions on the original mount point determine if
557 is accessible from the mounted file system.
558 The minimum permissions for
559 the mount point for traversal across the mount point in both
560 directions to be possible for all users is 0111 (execute for all).
564 is preferred over the use of the file system specific
571 signal (that causes an update of the export list)
572 only when the file system is mounted via
575 It is possible for a corrupted file system to cause a crash.