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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
83 flag (see below), or if they are already mounted (except the
84 root file system which is always remounted to preserve
85 traditional single user mode behavior).
87 Causes everything to be done except for the actual system call.
88 This option is useful in conjunction with the
93 command is trying to do.
99 Forces the revocation of write access when trying to downgrade
100 a file system mount status from read-write to read-only.
102 forces the R/W mount of an unclean file system (dangerous; use with
105 Options are specified with a
107 flag followed by a comma separated string of options.
108 In case of conflicting options being specified, the rightmost option
110 The following options are available:
111 .Bl -tag -width indent
113 Enable Access Control Lists, or ACLS, which can be customized via the
121 to the file system should be done asynchronously.
125 and should not be used unless you are prepared to recreate the file
126 system should your system crash.
130 flag, this is the same as specifying the options currently in effect for
131 the mounted file system.
135 forces the revocation of write access when trying to downgrade
136 a file system mount status from read-write to read-only.
138 forces the R/W mount of an unclean file system (dangerous; use with caution).
142 flag, this is the same as specifying all the options listed in the
144 file for the file system.
146 Enable multi-label Mandatory Access Control, or MAC, on the specified file
148 If the file system supports multilabel operation, individual labels will
149 be maintained for each object in the file system, rather than using a
150 single label for all objects.
151 An alternative to the
157 for more information, which cause the multilabel mount flag to be set
158 automatically at mount-time.
160 Metadata I/O should be done synchronously, while data I/O should be done
164 Do not update the file access time when reading from a file.
166 is useful on file systems where there are large numbers of files and
167 performance is more critical than updating the file access time (which is
168 rarely ever important).
169 This option is currently only supported on local file systems.
171 This file system should be skipped when
177 Disable read clustering.
179 Disable write clustering.
181 Do not allow execution of any binaries on the mounted file system.
182 This option is useful for a server that has file systems containing
183 binaries for architectures other than its own.
184 Note: This option was not designed as a security feature and no
185 guarantee is made that it will prevent malicious code execution; for
186 example, it is still possible to execute scripts which reside on a
190 Do not allow set-user-identifier or set-group-identifier bits to take effect.
191 Note: this option is worthless if a public available suid or sgid
194 is installed on your system.
195 It is set automatically when the user does not have super-user privileges.
197 Do not follow symlinks
198 on the mounted file system.
202 mount the file system read-only (even the super-user may not write it).
206 to the file system should be done synchronously.
208 This option allows a snapshot of the specified file system to be taken.
211 flag is required with this option.
212 Note that snapshot files must be created in the file system that is being
214 You may create up to 20 snapshots per file system.
215 Active snapshots are recorded in the superblock, so they persist across unmount
216 and remount operations and across system reboots.
217 When you are done with a snapshot, it can be removed with the
220 Snapshots may be removed in any order, however you may not get back all the
221 space contained in the snapshot as another snapshot may claim some of the blocks
222 that it is releasing.
223 Note that the schg flag is set on snapshots to ensure that not even the root
224 user can write to them.
225 The unlink command makes an exception for snapshot files in that it allows them
226 to be removed even though they have the schg flag set, so it is not necessary to
227 clear the schg flag before removing a snapshot file.
229 Once you have taken a snapshot, there are three interesting things that you can
236 on the snapshot file.
237 Assuming that the file system was clean when it was mounted, you should always
238 get a clean (and unchanging) result from running fsck on the snapshot.
239 This is essentially what the background fsck process does.
245 You will get a dump that is consistent with the file system as of the timestamp
249 Mount the snapshot as a frozen image of the file system.
250 To mount the snapshot
251 .Pa /var/snapshot/snap1 :
253 mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
254 mount -r /dev/md4 /mnt
257 You can now cruise around your frozen
261 Everything will be in the same state that it was at the time the snapshot was
263 The one exception is that any earlier snapshots will appear as zero length
265 When you are done with the mounted snapshot:
271 Further details can be found in the file at
272 .Pa /usr/src/sys/ufs/ffs/README.snapshot .
275 A directory on the mounted file system will respond to the SUID bit
276 being set, by setting the owner of any new files to be the same
277 as the owner of the directory.
278 New directories will inherit the bit from their parents.
279 Execute bits are removed from
280 the file, and it will not be given to root.
282 This feature is designed for use on fileservers serving PC users via
283 ftp, SAMBA, or netatalk.
284 It provides security holes for shell users and as
285 such should not be used on shell machines, especially on home directories.
286 This option requires the SUIDDIR
287 option in the kernel to work.
288 Only UFS file systems support this option.
291 for more information.
295 indicate that the status of an already mounted file system should be changed.
297 Causes the namespace at the mount point to appear as the union
298 of the mounted file system root and the existing directory.
299 Lookups will be done in the mounted file system first.
300 If those operations fail due to a non-existent file the underlying
301 directory is then accessed.
302 All creates are done in the mounted file system.
305 Any additional options specific to a file system type that is not
306 one of the internally known types (see the
308 option) may be passed as a comma separated list; these options are
309 distinguished by a leading
312 Options that take a value are specified using the syntax -option=value.
316 .Bd -literal -offset indent
317 mount -t unionfs -o -b /sys $HOME/sys
322 to execute the equivalent of:
323 .Bd -literal -offset indent
324 /sbin/mount_unionfs -b /sys $HOME/sys
327 Additional options specific to file system types
328 which are not internally known
329 (see the description of the
332 may be described in the manual pages for the associated
333 .Pa /sbin/mount_ Ns Sy XXX
336 Print mount information in
343 The file system is to be mounted read-only.
344 Mount the file system read-only (even the super-user may not write it).
350 .It Fl t Ar ufs | external_type
351 The argument following the
353 is used to indicate the file system type.
360 to indicate that the actions should only be taken on
361 file systems of the specified type.
362 More than one type may be specified in a comma separated list.
363 The list of file system types can be prefixed with
365 to specify the file system types for which action should
371 .Bd -literal -offset indent
372 mount -a -t nonfs,nullfs
375 mounts all file systems except those of type
380 If the type is not one of the internally known types,
382 will attempt to execute a program in
383 .Pa /sbin/mount_ Ns Sy XXX
386 is replaced by the type name.
387 For example, nfs file systems are mounted by the program
388 .Pa /sbin/mount_nfs .
390 Most file systems will be dynamically loaded by the kernel
391 if not already present, and if the kernel module is available.
395 flag indicates that the status of an already mounted file
396 system should be changed.
397 Any of the options discussed above (the
401 also a file system can be changed from read-only to read-write
403 An attempt to change from read-write to read-only will fail if any
404 files on the file system are currently open for writing unless the
406 flag is also specified.
407 The set of options is determined by applying the options specified
410 and finally applying the
418 The file system object is to be read and write.
421 .Bl -tag -width ".Ev PATH_FSTAB"
423 If the environment variable
425 is set, all operations are performed against the specified file.
427 will not be honored if the process environment or memory address space is
432 for more information.)
435 .Bl -tag -width /etc/fstab -compact
440 Various, most of them are self-explanatory.
442 .Dl XXXXX file system is not available
444 The kernel does not support the respective file system type.
446 support for a particular file system might be provided either on a static
447 (kernel compile-time), or dynamic basis (loaded as a kernel module by
460 .Xr mount_fdescfs 8 ,
461 .Xr mount_linprocfs 8 ,
462 .Xr mount_msdosfs 8 ,
467 .Xr mount_portalfs 8 ,
473 .Xr mount_unionfs 8 ,
478 the permissions on the original mount point determine if
480 is accessible from the mounted file system.
481 The minimum permissions for
482 the mount point for traversal across the mount point in both
483 directions to be possible for all users is 0111 (execute for all).
490 It is possible for a corrupted file system to cause a crash.