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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 Access Control Lists, or ACLS, which can be customized via the
131 to the file system should be done asynchronously.
134 flag to set, since it does not guarantee that the file system structure
135 on the disk will remain consistent.
138 flag should be used sparingly, and only when some data recovery
139 mechanism is present.
143 flag, this is the same as specifying the options currently in effect for
144 the mounted file system.
148 forces the revocation of write access when trying to downgrade
149 a file system mount status from read-write to read-only.
151 forces the R/W mount of an unclean file system (dangerous; use with caution).
155 flag, this is the same as specifying all the options listed in the
157 file for the file system.
159 This file system should be skipped when
166 .It Cm mountprog Ns = Ns Aq Ar program
169 to use the specified program to mount the file system, instead of calling
171 directly. For example:
173 mount -t foofs -o mountprog=/mydir/fooprog /dev/acd0 /mnt
176 Enable multi-label Mandatory Access Control, or MAC, on the specified file
178 If the file system supports multilabel operation, individual labels will
179 be maintained for each object in the file system, rather than using a
180 single label for all objects.
181 An alternative to the
187 for more information, which cause the multilabel mount flag to be set
188 automatically at mount-time.
190 Metadata I/O should be done synchronously, while data I/O should be done
194 Do not update the file access time when reading from a file.
196 is useful on file systems where there are large numbers of files and
197 performance is more critical than updating the file access time (which is
198 rarely ever important).
199 This option is currently only supported on local file systems.
201 This file system should be skipped when
207 Disable read clustering.
209 Disable write clustering.
211 Do not allow execution of any binaries on the mounted file system.
212 This option is useful for a server that has file systems containing
213 binaries for architectures other than its own.
214 Note: This option was not designed as a security feature and no
215 guarantee is made that it will prevent malicious code execution; for
216 example, it is still possible to execute scripts which reside on a
220 Do not allow set-user-identifier or set-group-identifier bits to take effect.
221 Note: this option is worthless if a public available suid or sgid
224 is installed on your system.
225 It is set automatically when the user does not have super-user privileges.
227 Do not follow symlinks
228 on the mounted file system.
232 mount the file system read-only (even the super-user may not write it).
234 This option allows a snapshot of the specified file system to be taken.
237 flag is required with this option.
238 Note that snapshot files must be created in the file system that is being
240 You may create up to 20 snapshots per file system.
241 Active snapshots are recorded in the superblock, so they persist across unmount
242 and remount operations and across system reboots.
243 When you are done with a snapshot, it can be removed with the
246 Snapshots may be removed in any order, however you may not get back all the
247 space contained in the snapshot as another snapshot may claim some of the blocks
248 that it is releasing.
249 Note that the schg flag is set on snapshots to ensure that not even the root
250 user can write to them.
251 The unlink command makes an exception for snapshot files in that it allows them
252 to be removed even though they have the schg flag set, so it is not necessary to
253 clear the schg flag before removing a snapshot file.
255 Once you have taken a snapshot, there are three interesting things that you can
262 on the snapshot file.
263 Assuming that the file system was clean when it was mounted, you should always
264 get a clean (and unchanging) result from running fsck on the snapshot.
265 This is essentially what the background fsck process does.
271 You will get a dump that is consistent with the file system as of the timestamp
275 Mount the snapshot as a frozen image of the file system.
276 To mount the snapshot
277 .Pa /var/snapshot/snap1 :
279 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
280 mount -r /dev/md4 /mnt
283 You can now cruise around your frozen
287 Everything will be in the same state that it was at the time the snapshot was
289 The one exception is that any earlier snapshots will appear as zero length
291 When you are done with the mounted snapshot:
297 Further details can be found in the file at
298 .Pa /usr/src/sys/ufs/ffs/README.snapshot .
301 A directory on the mounted file system will respond to the SUID bit
302 being set, by setting the owner of any new files to be the same
303 as the owner of the directory.
304 New directories will inherit the bit from their parents.
305 Execute bits are removed from
306 the file, and it will not be given to root.
308 This feature is designed for use on fileservers serving PC users via
309 ftp, SAMBA, or netatalk.
310 It provides security holes for shell users and as
311 such should not be used on shell machines, especially on home directories.
312 This option requires the SUIDDIR
313 option in the kernel to work.
314 Only UFS file systems support this option.
317 for more information.
321 to the file system should be done synchronously.
325 indicate that the status of an already mounted file system should be changed.
327 Causes the namespace at the mount point to appear as the union
328 of the mounted file system root and the existing directory.
329 Lookups will be done in the mounted file system first.
330 If those operations fail due to a non-existent file the underlying
331 directory is then accessed.
332 All creates are done in the mounted file system.
335 Any additional options specific to a file system type that is not
336 one of the internally known types (see the
338 option) may be passed as a comma separated list; these options are
339 distinguished by a leading
342 Options that take a value are specified using the syntax -option=value.
346 .Bd -literal -offset indent
347 mount -t cd9660 -o -e /dev/cd0 /cdrom
352 to execute the equivalent of:
353 .Bd -literal -offset indent
354 /sbin/mount_cd9660 -e /dev/cd0 /cdrom
357 Additional options specific to file system types
358 which are not internally known
359 (see the description of the
362 may be described in the manual pages for the associated
363 .Pa /sbin/mount_ Ns Sy XXX
366 Print mount information in
373 The file system is to be mounted read-only.
374 Mount the file system read-only (even the super-user may not write it).
380 .It Fl t Cm ufs | Ar external_type
381 The argument following the
383 is used to indicate the file system type.
390 to indicate that the actions should only be taken on
391 file systems of the specified type.
392 More than one type may be specified in a comma separated list.
393 The list of file system types can be prefixed with
395 to specify the file system types for which action should
401 .Bd -literal -offset indent
402 mount -a -t nonfs,nullfs
405 mounts all file systems except those of type
410 The default behavior of
414 option directly to the
420 However, for the following file system types:
437 directly and will instead attempt to execute a program in
438 .Pa /sbin/mount_ Ns Sy XXX
441 is replaced by the file system type name.
442 For example, nfs file systems are mounted by the program
443 .Pa /sbin/mount_nfs .
445 Most file systems will be dynamically loaded by the kernel
446 if not already present, and if the kernel module is available.
450 flag indicates that the status of an already mounted file
451 system should be changed.
452 Any of the options discussed above (the
456 also a file system can be changed from read-only to read-write
458 An attempt to change from read-write to read-only will fail if any
459 files on the file system are currently open for writing unless the
461 flag is also specified.
462 The set of options is determined by applying the options specified
465 and finally applying the
473 The file system object is to be read and write.
476 .Bl -tag -width ".Ev PATH_FSTAB"
478 If the environment variable
480 is set, all operations are performed against the specified file.
482 will not be honored if the process environment or memory address space is
487 for more information.)
490 .Bl -tag -width /etc/fstab -compact
495 Various, most of them are self-explanatory.
497 .Dl XXXXX file system is not available
499 The kernel does not support the respective file system type.
501 support for a particular file system might be provided either on a static
502 (kernel compile-time), or dynamic basis (loaded as a kernel module by
515 .Xr mount_msdosfs 8 ,
520 .Xr mount_portalfs 8 ,
523 .Xr mount_unionfs 8 ,
528 the permissions on the original mount point determine if
530 is accessible from the mounted file system.
531 The minimum permissions for
532 the mount point for traversal across the mount point in both
533 directions to be possible for all users is 0111 (execute for all).
537 is preferred over the use of the file system specific
544 signal (that causes an update of the export list)
545 only when the file system is mounted via
553 It is possible for a corrupted file system to cause a crash.