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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.
135 and should not be used unless you are prepared to recreate the file
136 system should your system crash.
140 flag, this is the same as specifying the options currently in effect for
141 the mounted file system.
145 forces the revocation of write access when trying to downgrade
146 a file system mount status from read-write to read-only.
148 forces the R/W mount of an unclean file system (dangerous; use with caution).
152 flag, this is the same as specifying all the options listed in the
154 file for the file system.
156 This file system should be skipped when
163 Enable multi-label Mandatory Access Control, or MAC, on the specified file
165 If the file system supports multilabel operation, individual labels will
166 be maintained for each object in the file system, rather than using a
167 single label for all objects.
168 An alternative to the
174 for more information, which cause the multilabel mount flag to be set
175 automatically at mount-time.
177 Metadata I/O should be done synchronously, while data I/O should be done
181 Do not update the file access time when reading from a file.
183 is useful on file systems where there are large numbers of files and
184 performance is more critical than updating the file access time (which is
185 rarely ever important).
186 This option is currently only supported on local file systems.
188 This file system should be skipped when
194 Disable read clustering.
196 Disable write clustering.
198 Do not allow execution of any binaries on the mounted file system.
199 This option is useful for a server that has file systems containing
200 binaries for architectures other than its own.
201 Note: This option was not designed as a security feature and no
202 guarantee is made that it will prevent malicious code execution; for
203 example, it is still possible to execute scripts which reside on a
207 Do not allow set-user-identifier or set-group-identifier bits to take effect.
208 Note: this option is worthless if a public available suid or sgid
211 is installed on your system.
212 It is set automatically when the user does not have super-user privileges.
214 Do not follow symlinks
215 on the mounted file system.
219 mount the file system read-only (even the super-user may not write it).
223 to the file system should be done synchronously.
225 This option allows a snapshot of the specified file system to be taken.
228 flag is required with this option.
229 Note that snapshot files must be created in the file system that is being
231 You may create up to 20 snapshots per file system.
232 Active snapshots are recorded in the superblock, so they persist across unmount
233 and remount operations and across system reboots.
234 When you are done with a snapshot, it can be removed with the
237 Snapshots may be removed in any order, however you may not get back all the
238 space contained in the snapshot as another snapshot may claim some of the blocks
239 that it is releasing.
240 Note that the schg flag is set on snapshots to ensure that not even the root
241 user can write to them.
242 The unlink command makes an exception for snapshot files in that it allows them
243 to be removed even though they have the schg flag set, so it is not necessary to
244 clear the schg flag before removing a snapshot file.
246 Once you have taken a snapshot, there are three interesting things that you can
253 on the snapshot file.
254 Assuming that the file system was clean when it was mounted, you should always
255 get a clean (and unchanging) result from running fsck on the snapshot.
256 This is essentially what the background fsck process does.
262 You will get a dump that is consistent with the file system as of the timestamp
266 Mount the snapshot as a frozen image of the file system.
267 To mount the snapshot
268 .Pa /var/snapshot/snap1 :
270 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
271 mount -r /dev/md4 /mnt
274 You can now cruise around your frozen
278 Everything will be in the same state that it was at the time the snapshot was
280 The one exception is that any earlier snapshots will appear as zero length
282 When you are done with the mounted snapshot:
288 Further details can be found in the file at
289 .Pa /usr/src/sys/ufs/ffs/README.snapshot .
292 A directory on the mounted file system will respond to the SUID bit
293 being set, by setting the owner of any new files to be the same
294 as the owner of the directory.
295 New directories will inherit the bit from their parents.
296 Execute bits are removed from
297 the file, and it will not be given to root.
299 This feature is designed for use on fileservers serving PC users via
300 ftp, SAMBA, or netatalk.
301 It provides security holes for shell users and as
302 such should not be used on shell machines, especially on home directories.
303 This option requires the SUIDDIR
304 option in the kernel to work.
305 Only UFS file systems support this option.
308 for more information.
312 indicate that the status of an already mounted file system should be changed.
314 Causes the namespace at the mount point to appear as the union
315 of the mounted file system root and the existing directory.
316 Lookups will be done in the mounted file system first.
317 If those operations fail due to a non-existent file the underlying
318 directory is then accessed.
319 All creates are done in the mounted file system.
322 Any additional options specific to a file system type that is not
323 one of the internally known types (see the
325 option) may be passed as a comma separated list; these options are
326 distinguished by a leading
329 Options that take a value are specified using the syntax -option=value.
333 .Bd -literal -offset indent
334 mount -t unionfs -o -b /sys $HOME/sys
339 to execute the equivalent of:
340 .Bd -literal -offset indent
341 /sbin/mount_unionfs -b /sys $HOME/sys
344 Additional options specific to file system types
345 which are not internally known
346 (see the description of the
349 may be described in the manual pages for the associated
350 .Pa /sbin/mount_ Ns Sy XXX
353 Print mount information in
360 The file system is to be mounted read-only.
361 Mount the file system read-only (even the super-user may not write it).
367 .It Fl t Ar ufs | external_type
368 The argument following the
370 is used to indicate the file system type.
377 to indicate that the actions should only be taken on
378 file systems of the specified type.
379 More than one type may be specified in a comma separated list.
380 The list of file system types can be prefixed with
382 to specify the file system types for which action should
388 .Bd -literal -offset indent
389 mount -a -t nonfs,nullfs
392 mounts all file systems except those of type
397 The default behavior of
401 option directly to the
407 However, for the following file system types:
425 directly and will instead attempt to execute a program in
426 .Pa /sbin/mount_ Ns Sy XXX
429 is replaced by the file system type name.
430 For example, nfs file systems are mounted by the program
431 .Pa /sbin/mount_nfs .
433 Most file systems will be dynamically loaded by the kernel
434 if not already present, and if the kernel module is available.
438 flag indicates that the status of an already mounted file
439 system should be changed.
440 Any of the options discussed above (the
444 also a file system can be changed from read-only to read-write
446 An attempt to change from read-write to read-only will fail if any
447 files on the file system are currently open for writing unless the
449 flag is also specified.
450 The set of options is determined by applying the options specified
453 and finally applying the
461 The file system object is to be read and write.
464 .Bl -tag -width ".Ev PATH_FSTAB"
466 If the environment variable
468 is set, all operations are performed against the specified file.
470 will not be honored if the process environment or memory address space is
475 for more information.)
478 .Bl -tag -width /etc/fstab -compact
483 Various, most of them are self-explanatory.
485 .Dl XXXXX file system is not available
487 The kernel does not support the respective file system type.
489 support for a particular file system might be provided either on a static
490 (kernel compile-time), or dynamic basis (loaded as a kernel module by
503 .Xr mount_msdosfs 8 ,
508 .Xr mount_portalfs 8 ,
513 .Xr mount_unionfs 8 ,
518 the permissions on the original mount point determine if
520 is accessible from the mounted file system.
521 The minimum permissions for
522 the mount point for traversal across the mount point in both
523 directions to be possible for all users is 0111 (execute for all).
530 It is possible for a corrupted file system to cause a crash.