xref: /freebsd/sbin/mount/mount.8 (revision acd3428b7d3e94cef0e1881c868cb4b131d4ff41)
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28.\"     @(#)mount.8	8.8 (Berkeley) 6/16/94
29.\" $FreeBSD$
30.\"
31.Dd July 12, 2006
32.Dt MOUNT 8
33.Os
34.Sh NAME
35.Nm mount
36.Nd mount file systems
37.Sh SYNOPSIS
38.Nm
39.Op Fl adflpruvw
40.Op Fl F Ar fstab
41.Op Fl o Ar options
42.Op Fl t Cm ufs | Ar external_type
43.Nm
44.Op Fl dfpruvw
45.Ar special | node
46.Nm
47.Op Fl dfpruvw
48.Op Fl o Ar options
49.Op Fl t Cm ufs | Ar external_type
50.Ar special node
51.Sh DESCRIPTION
52The
53.Nm
54utility calls the
55.Xr nmount 2
56system call to prepare and graft a
57.Ar special
58device or the remote node (rhost:path) on to the file system tree at the point
59.Ar node .
60If either
61.Ar special
62or
63.Ar node
64are not provided, the appropriate information is taken from the
65.Xr fstab 5
66file.
67.Pp
68The system maintains a list of currently mounted file systems.
69If no arguments are given to
70.Nm ,
71this list is printed.
72.Pp
73The options are as follows:
74.Bl -tag -width indent
75.It Fl a
76All the file systems described in
77.Xr fstab 5
78are mounted.
79Exceptions are those marked as
80.Dq Li noauto ,
81those marked as
82.Dq Li late
83(unless the
84.Fl l
85option was specified),
86those excluded by the
87.Fl t
88flag (see below), or if they are already mounted (except the
89root file system which is always remounted to preserve
90traditional single user mode behavior).
91.It Fl d
92Causes everything to be done except for the actual system call.
93This option is useful in conjunction with the
94.Fl v
95flag to
96determine what the
97.Nm
98command is trying to do.
99.It Fl F Ar fstab
100Specify the
101.Pa fstab
102file to use.
103.It Fl f
104Forces the revocation of write access when trying to downgrade
105a file system mount status from read-write to read-only.
106Also
107forces the R/W mount of an unclean file system (dangerous; use with
108caution).
109.It Fl l
110When used in conjunction with the
111.Fl a
112option, also mount those file systems which are marked as
113.Dq Li late .
114.It Fl o
115Options are specified with a
116.Fl o
117flag followed by a comma separated string of options.
118In case of conflicting options being specified, the rightmost option
119takes effect.
120The following options are available:
121.Bl -tag -width indent
122.It Cm acls
123Enable Access Control Lists, or ACLS, which can be customized via the
124.Xr setfacl 1
125and
126.Xr getfacl 1
127commands.
128.It Cm async
129All
130.Tn I/O
131to the file system should be done asynchronously.
132This is a
133.Em dangerous
134flag to set, since it does not guarantee that the file system structure
135on the disk will remain consistent.
136For this reason, the
137.Cm async
138flag should be used sparingly, and only when some data recovery
139mechanism is present.
140.It Cm current
141When used with the
142.Fl u
143flag, this is the same as specifying the options currently in effect for
144the mounted file system.
145.It Cm force
146The same as
147.Fl f ;
148forces the revocation of write access when trying to downgrade
149a file system mount status from read-write to read-only.
150Also
151forces the R/W mount of an unclean file system (dangerous; use with caution).
152.It Cm fstab
153When used with the
154.Fl u
155flag, this is the same as specifying all the options listed in the
156.Xr fstab 5
157file for the file system.
158.It Cm late
159This file system should be skipped when
160.Nm
161is run with the
162.Fl a
163flag but without the
164.Fl l
165flag.
166.It Cm multilabel
167Enable multi-label Mandatory Access Control, or MAC, on the specified file
168system.
169If the file system supports multilabel operation, individual labels will
170be maintained for each object in the file system, rather than using a
171single label for all objects.
172An alternative to the
173.Fl l
174flag in
175.Xr tunefs 8 .
176See
177.Xr mac 4
178for more information, which cause the multilabel mount flag to be set
179automatically at mount-time.
180.It Cm noasync
181Metadata I/O should be done synchronously, while data I/O should be done
182asynchronously.
183This is the default.
184.It Cm noatime
185Do not update the file access time when reading from a file.
186This option
187is useful on file systems where there are large numbers of files and
188performance is more critical than updating the file access time (which is
189rarely ever important).
190This option is currently only supported on local file systems.
191.It Cm noauto
192This file system should be skipped when
193.Nm
194is run with the
195.Fl a
196flag.
197.It Cm noclusterr
198Disable read clustering.
199.It Cm noclusterw
200Disable write clustering.
201.It Cm noexec
202Do not allow execution of any binaries on the mounted file system.
203This option is useful for a server that has file systems containing
204binaries for architectures other than its own.
205Note: This option was not designed as a security feature and no
206guarantee is made that it will prevent malicious code execution; for
207example, it is still possible to execute scripts which reside on a
208.Cm noexec
209mounted partition.
210.It Cm nosuid
211Do not allow set-user-identifier or set-group-identifier bits to take effect.
212Note: this option is worthless if a public available suid or sgid
213wrapper like
214.Xr suidperl 1
215is installed on your system.
216It is set automatically when the user does not have super-user privileges.
217.It Cm nosymfollow
218Do not follow symlinks
219on the mounted file system.
220.It Cm ro
221The same as
222.Fl r ;
223mount the file system read-only (even the super-user may not write it).
224.It Cm sync
225All
226.Tn I/O
227to the file system should be done synchronously.
228.It Cm snapshot
229This option allows a snapshot of the specified file system to be taken.
230The
231.Fl u
232flag is required with this option.
233Note that snapshot files must be created in the file system that is being
234snapshotted.
235You may create up to 20 snapshots per file system.
236Active snapshots are recorded in the superblock, so they persist across unmount
237and remount operations and across system reboots.
238When you are done with a snapshot, it can be removed with the
239.Xr rm 1
240command.
241Snapshots may be removed in any order, however you may not get back all the
242space contained in the snapshot as another snapshot may claim some of the blocks
243that it is releasing.
244Note that the schg flag is set on snapshots to ensure that not even the root
245user can write to them.
246The unlink command makes an exception for snapshot files in that it allows them
247to be removed even though they have the schg flag set, so it is not necessary to
248clear the schg flag before removing a snapshot file.
249.Pp
250Once you have taken a snapshot, there are three interesting things that you can
251do with it:
252.Pp
253.Bl -enum -compact
254.It
255Run
256.Xr fsck 8
257on the snapshot file.
258Assuming that the file system was clean when it was mounted, you should always
259get a clean (and unchanging) result from running fsck on the snapshot.
260This is essentially what the background fsck process does.
261.Pp
262.It
263Run
264.Xr dump 8
265on the snapshot.
266You will get a dump that is consistent with the file system as of the timestamp
267of the snapshot.
268.Pp
269.It
270Mount the snapshot as a frozen image of the file system.
271To mount the snapshot
272.Pa /var/snapshot/snap1 :
273.Bd -literal
274mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
275mount -r /dev/md4 /mnt
276.Ed
277.Pp
278You can now cruise around your frozen
279.Pa /var
280file system at
281.Pa /mnt .
282Everything will be in the same state that it was at the time the snapshot was
283taken.
284The one exception is that any earlier snapshots will appear as zero length
285files.
286When you are done with the mounted snapshot:
287.Bd -literal
288umount /mnt
289mdconfig -d -u 4
290.Ed
291.Pp
292Further details can be found in the file at
293.Pa /usr/src/sys/ufs/ffs/README.snapshot .
294.El
295.It Cm suiddir
296A directory on the mounted file system will respond to the SUID bit
297being set, by setting the owner of any new files to be the same
298as the owner of the directory.
299New directories will inherit the bit from their parents.
300Execute bits are removed from
301the file, and it will not be given to root.
302.Pp
303This feature is designed for use on fileservers serving PC users via
304ftp, SAMBA, or netatalk.
305It provides security holes for shell users and as
306such should not be used on shell machines, especially on home directories.
307This option requires the SUIDDIR
308option in the kernel to work.
309Only UFS file systems support this option.
310See
311.Xr chmod 2
312for more information.
313.It Cm update
314The same as
315.Fl u ;
316indicate that the status of an already mounted file system should be changed.
317.It Cm union
318Causes the namespace at the mount point to appear as the union
319of the mounted file system root and the existing directory.
320Lookups will be done in the mounted file system first.
321If those operations fail due to a non-existent file the underlying
322directory is then accessed.
323All creates are done in the mounted file system.
324.El
325.Pp
326Any additional options specific to a file system type that is not
327one of the internally known types (see the
328.Fl t
329option) may be passed as a comma separated list; these options are
330distinguished by a leading
331.Dq \&-
332(dash).
333Options that take a value are specified using the syntax -option=value.
334For example, the
335.Nm
336command:
337.Bd -literal -offset indent
338mount -t unionfs -o -b /sys $HOME/sys
339.Ed
340.Pp
341causes
342.Nm
343to execute the equivalent of:
344.Bd -literal -offset indent
345/sbin/mount_unionfs -b /sys $HOME/sys
346.Ed
347.Pp
348Additional options specific to file system types
349which are not internally known
350(see the description of the
351.Fl t
352option below)
353may be described in the manual pages for the associated
354.Pa /sbin/mount_ Ns Sy XXX
355utilities.
356.It Fl p
357Print mount information in
358.Xr fstab 5
359format.
360Implies also the
361.Fl v
362option.
363.It Fl r
364The file system is to be mounted read-only.
365Mount the file system read-only (even the super-user may not write it).
366The same as the
367.Cm ro
368argument to the
369.Fl o
370option.
371.It Fl t Cm ufs | Ar external_type
372The argument following the
373.Fl t
374is used to indicate the file system type.
375The type
376.Cm ufs
377is the default.
378The
379.Fl t
380option can be used
381to indicate that the actions should only be taken on
382file systems of the specified type.
383More than one type may be specified in a comma separated list.
384The list of file system types can be prefixed with
385.Dq Li no
386to specify the file system types for which action should
387.Em not
388be taken.
389For example, the
390.Nm
391command:
392.Bd -literal -offset indent
393mount -a -t nonfs,nullfs
394.Ed
395.Pp
396mounts all file systems except those of type
397.Tn NFS
398and
399.Tn NULLFS .
400.Pp
401The default behavior of
402.Nm
403is to pass the
404.Fl t
405option directly to the
406.Xr nmount 2
407system call in the
408.Li fstype
409option.
410.Pp
411However, for the following file system types:
412.Cm cd9660 ,
413.Cm mfs ,
414.Cm msdosfs ,
415.Cm nfs ,
416.Cm nfs4 ,
417.Cm ntfs ,
418.Cm nwfs ,
419.Cm nullfs ,
420.Cm portalfs ,
421.Cm smbfs ,
422.Cm udf ,
423.Cm umapfs ,
424and
425.Cm unionfs ,
426.Nm
427will not call
428.Xr nmount 2
429directly and will instead attempt to execute a program in
430.Pa /sbin/mount_ Ns Sy XXX
431where
432.Sy XXX
433is replaced by the file system type name.
434For example, nfs file systems are mounted by the program
435.Pa /sbin/mount_nfs .
436.Pp
437Most file systems will be dynamically loaded by the kernel
438if not already present, and if the kernel module is available.
439.It Fl u
440The
441.Fl u
442flag indicates that the status of an already mounted file
443system should be changed.
444Any of the options discussed above (the
445.Fl o
446option)
447may be changed;
448also a file system can be changed from read-only to read-write
449or vice versa.
450An attempt to change from read-write to read-only will fail if any
451files on the file system are currently open for writing unless the
452.Fl f
453flag is also specified.
454The set of options is determined by applying the options specified
455in the argument to
456.Fl o
457and finally applying the
458.Fl r
459or
460.Fl w
461option.
462.It Fl v
463Verbose mode.
464.It Fl w
465The file system object is to be read and write.
466.El
467.Sh ENVIRONMENT
468.Bl -tag -width ".Ev PATH_FSTAB"
469.It Ev PATH_FSTAB
470If the environment variable
471.Ev PATH_FSTAB
472is set, all operations are performed against the specified file.
473.Ev PATH_FSTAB
474will not be honored if the process environment or memory address space is
475considered
476.Dq tainted .
477(See
478.Xr issetugid 2
479for more information.)
480.El
481.Sh FILES
482.Bl -tag -width /etc/fstab -compact
483.It Pa /etc/fstab
484file system table
485.El
486.Sh DIAGNOSTICS
487Various, most of them are self-explanatory.
488.Pp
489.Dl XXXXX file system is not available
490.Pp
491The kernel does not support the respective file system type.
492Note that
493support for a particular file system might be provided either on a static
494(kernel compile-time), or dynamic basis (loaded as a kernel module by
495.Xr kldload 8 ) .
496.Sh SEE ALSO
497.Xr getfacl 1 ,
498.Xr setfacl 1 ,
499.Xr nmount 2 ,
500.Xr acl 3 ,
501.Xr mac 4 ,
502.Xr ext2fs 5 ,
503.Xr fstab 5 ,
504.Xr procfs 5 ,
505.Xr kldload 8 ,
506.Xr mount_cd9660 8 ,
507.Xr mount_msdosfs 8 ,
508.Xr mount_nfs 8 ,
509.Xr mount_ntfs 8 ,
510.Xr mount_nullfs 8 ,
511.Xr mount_nwfs 8 ,
512.Xr mount_portalfs 8 ,
513.Xr mount_smbfs 8 ,
514.Xr mount_std 8 ,
515.Xr mount_udf 8 ,
516.Xr mount_umapfs 8 ,
517.Xr mount_unionfs 8 ,
518.Xr umount 8
519.Sh CAVEATS
520After a successful
521.Nm ,
522the permissions on the original mount point determine if
523.Pa ..\&
524is accessible from the mounted file system.
525The minimum permissions for
526the mount point for traversal across the mount point in both
527directions to be possible for all users is 0111 (execute for all).
528.Sh HISTORY
529A
530.Nm
531utility appeared in
532.At v1 .
533.Sh BUGS
534It is possible for a corrupted file system to cause a crash.
535