1MOUNT(8) System Administration MOUNT(8)
2
6 mount - mount a filesystem
7
9 mount [-h|-V]
10 mount [-l] [-t fstype]
12 mount -a [-fFnrsvw] [-t fstype] [-O optlist]
14 mount [-fnrsvw] [-o options] device|mountpoint
16 mount [-fnrsvw] [-t fstype] [-o options] device mountpoint
18 mount --bind|--rbind|--move olddir newdir
20 mount
22 --make-[shared|slave|private|unbindable|rshared|rslave|rprivate|runbindable]
23 mountpoint
24
26 All files accessible in a Unix system are arranged in one big tree, the
27 file hierarchy, rooted at /. These files can be spread out over several
28 devices. The mount command serves to attach the filesystem found on
29 some device to the big file tree. Conversely, the umount(8) command
30 will detach it again. The filesystem is used to control how data is
31 stored on the device or provided in a virtual way by network or other
32 services.
33 The standard form of the mount command is:
35 mount -t type device dir
37 This tells the kernel to attach the filesystem found on device (which
39 is of type type) at the directory dir. The option -t type is optional.
40 The mount command is usually able to detect a filesystem. The root
41 permissions are necessary to mount a filesystem by default. See section
42 "Non-superuser mounts" below for more details. The previous contents
43 (if any) and owner and mode of dir become invisible, and as long as
44 this filesystem remains mounted, the pathname dir refers to the root of
45 the filesystem on device.
46 If only the directory or the device is given, for example:
48 mount /dir
50 then mount looks for a mountpoint (and if not found then for a device)
52 in the /etc/fstab file. It’s possible to use the --target or --source
53 options to avoid ambiguous interpretation of the given argument. For
54 example:
55 mount --target /mountpoint
57 The same filesystem may be mounted more than once, and in some cases
59 (e.g., network filesystems) the same filesystem may be mounted on the
60 same mountpoint multiple times. The mount command does not implement
61 any policy to control this behavior. All behavior is controlled by the
62 kernel and it is usually specific to the filesystem driver. The
63 exception is --all, in this case already mounted filesystems are
64 ignored (see --all below for more details).
65 Listing the mounts
67 The listing mode is maintained for backward compatibility only.
68 For more robust and customizable output use findmnt(8), especially in
70 your scripts. Note that control characters in the mountpoint name are
71 replaced with '?'.
72 The following command lists all mounted filesystems (of type type):
74 mount [-l] [-t type]
76 The option -l adds labels to this listing. See below.
78 Indicating the device and filesystem
80 Most devices are indicated by a filename (of a block special device),
81 like /dev/sda1, but there are other possibilities. For example, in the
82 case of an NFS mount, device may look like knuth.cwi.nl:/dir.
83 The device names of disk partitions are unstable; hardware
85 reconfiguration, and adding or removing a device can cause changes in
86 names. This is the reason why it’s strongly recommended to use
87 filesystem or partition identifiers like UUID or LABEL. Currently
88 supported identifiers (tags):
89 LABEL=label
91 Human readable filesystem identifier. See also -L.
92 UUID=uuid
94 Filesystem universally unique identifier. The format of the UUID is
95 usually a series of hex digits separated by hyphens. See also -U.
96 Note that mount uses UUIDs as strings. The UUIDs from the command
98 line or from fstab(5) are not converted to internal binary
99 representation. The string representation of the UUID should be
100 based on lower case characters.
101 PARTLABEL=label
103 Human readable partition identifier. This identifier is independent
104 on filesystem and does not change by mkfs or mkswap operations.
105 It’s supported for example for GUID Partition Tables (GPT).
106 PARTUUID=uuid
108 Partition universally unique identifier. This identifier is
109 independent on filesystem and does not change by mkfs or mkswap
110 operations. It’s supported for example for GUID Partition Tables
111 (GPT).
112 ID=id
114 Hardware block device ID as generated by udevd. This identifier is
115 usually based on WWN (unique storage identifier) and assigned by
116 the hardware manufacturer. See ls /dev/disk/by-id for more details,
117 this directory and running udevd is required. This identifier is
118 not recommended for generic use as the identifier is not strictly
119 defined and it depends on udev, udev rules and hardware.
120 The command lsblk --fs provides an overview of filesystems, LABELs and
122 UUIDs on available block devices. The command blkid -p <device>
123 provides details about a filesystem on the specified device.
124 Don’t forget that there is no guarantee that UUIDs and labels are
126 really unique, especially if you move, share or copy the device. Use
127 lsblk -o +UUID,PARTUUID to verify that the UUIDs are really unique in
128 your system.
129 The recommended setup is to use tags (e.g. UUID=uuid) rather than
131 /dev/disk/by-{label,uuid,id,partuuid,partlabel} udev symlinks in the
132 /etc/fstab file. Tags are more readable, robust and portable. The
133 mount(8) command internally uses udev symlinks, so the use of symlinks
134 in /etc/fstab has no advantage over tags. For more details see
135 libblkid(3).
136 The proc filesystem is not associated with a special device, and when
138 mounting it, an arbitrary keyword - for example, proc - can be used
139 instead of a device specification. (The customary choice none is less
140 fortunate: the error message 'none already mounted' from mount can be
141 confusing.)
142 The files /etc/fstab, /etc/mtab and /proc/mounts
144 The file /etc/fstab (see fstab(5)), may contain lines describing what
145 devices are usually mounted where, using which options. The default
146 location of the fstab(5) file can be overridden with the --fstab path
147 command-line option (see below for more details).
148 The command
150 mount -a [-t type] [-O optlist]
152 (usually given in a bootscript) causes all filesystems mentioned in
154 fstab (of the proper type and/or having or not having the proper
155 options) to be mounted as indicated, except for those whose line
156 contains the noauto keyword. Adding the -F option will make mount fork,
157 so that the filesystems are mounted in parallel.
158 When mounting a filesystem mentioned in fstab or mtab, it suffices to
160 specify on the command line only the device, or only the mount point.
161 The programs mount and umount(8) traditionally maintained a list of
163 currently mounted filesystems in the file /etc/mtab. The support for
164 regular classic /etc/mtab is completely disabled at compile time by
165 default, because on current Linux systems it is better to make
166 /etc/mtab a symlink to /proc/mounts instead. The regular mtab file
167 maintained in userspace cannot reliably work with namespaces,
168 containers and other advanced Linux features. If the regular mtab
169 support is enabled, then it’s possible to use the file as well as the
170 symlink.
171 If no arguments are given to mount, the list of mounted filesystems is
173 printed.
174 If you want to override mount options from /etc/fstab, you have to use
176 the -o option:
177 mount device|dir -o options
179 and then the mount options from the command line will be appended to
181 the list of options from /etc/fstab. This default behaviour can be
182 changed using the --options-mode command-line option. The usual
183 behavior is that the last option wins if there are conflicting ones.
184 The mount program does not read the /etc/fstab file if both device (or
186 LABEL, UUID, ID, PARTUUID or PARTLABEL) and dir are specified. For
187 example, to mount device foo at /dir:
188 mount /dev/foo /dir
190 This default behaviour can be changed by using the
192 --options-source-force command-line option to always read configuration
193 from fstab. For non-root users mount always reads the fstab
194 configuration.
195 Non-superuser mounts
197 Normally, only the superuser can mount filesystems. However, when fstab
198 contains the user option on a line, anybody can mount the corresponding
199 filesystem.
200 Thus, given a line
202 /dev/cdrom /cd iso9660 ro,user,noauto,unhide
204 any user can mount the iso9660 filesystem found on an inserted CDROM
206 using the command:
207 mount /cd
209 Note that mount is very strict about non-root users and all paths
211 specified on command line are verified before fstab is parsed or a
212 helper program is executed. It’s strongly recommended to use a valid
213 mountpoint to specify filesystem, otherwise mount may fail. For example
214 it’s a bad idea to use NFS or CIFS source on command line.
215 Since util-linux 2.35, mount does not exit when user permissions are
217 inadequate according to libmount’s internal security rules. Instead, it
218 drops suid permissions and continues as regular non-root user. This
219 behavior supports use-cases where root permissions are not necessary
220 (e.g., fuse filesystems, user namespaces, etc).
221 For more details, see fstab(5). Only the user that mounted a filesystem
223 can unmount it again. If any user should be able to unmount it, then
224 use users instead of user in the fstab line. The owner option is
225 similar to the user option, with the restriction that the user must be
226 the owner of the special file. This may be useful e.g. for /dev/fd if a
227 login script makes the console user owner of this device. The group
228 option is similar, with the restriction that the user must be a member
229 of the group of the special file.
230 Bind mount operation
232 Remount part of the file hierarchy somewhere else. The call is:
233 mount --bind olddir newdir
235 or by using this fstab entry:
237 /olddir /newdir none bind
239 After this call the same contents are accessible in two places.
241 It is important to understand that "bind" does not create any
243 second-class or special node in the kernel VFS. The "bind" is just
244 another operation to attach a filesystem. There is nowhere stored
245 information that the filesystem has been attached by a "bind"
246 operation. The olddir and newdir are independent and the olddir may be
247 unmounted.
248 One can also remount a single file (on a single file). It’s also
250 possible to use a bind mount to create a mountpoint from a regular
251 directory, for example:
252 mount --bind foo foo
254 The bind mount call attaches only (part of) a single filesystem, not
256 possible submounts. The entire file hierarchy including submounts can
257 be attached a second place by using:
258 mount --rbind olddir newdir
260 Note that the filesystem mount options maintained by the kernel will
262 remain the same as those on the original mount point. The userspace
263 mount options (e.g., _netdev) will not be copied by mount and it’s
264 necessary to explicitly specify the options on the mount command line.
265 Since util-linux 2.27 mount permits changing the mount options by
267 passing the relevant options along with --bind. For example:
268 mount -o bind,ro foo foo
270 This feature is not supported by the Linux kernel; it is implemented in
272 userspace by an additional mount(2) remounting system call. This
273 solution is not atomic.
274 The alternative (classic) way to create a read-only bind mount is to
276 use the remount operation, for example:
277 mount --bind olddir newdir
279 mount -o remount,bind,ro olddir newdir
281 Note that a read-only bind will create a read-only mountpoint (VFS
283 entry), but the original filesystem superblock will still be writable,
284 meaning that the olddir will be writable, but the newdir will be
285 read-only.
286 It’s also possible to change nosuid, nodev, noexec, noatime,
288 nodiratime, relatime and nosymfollow VFS entry flags via a
289 "remount,bind" operation. The other flags (for example
290 filesystem-specific flags) are silently ignored. It’s impossible to
291 change mount options recursively (for example with -o rbind,ro).
292 Since util-linux 2.31, mount ignores the bind flag from /etc/fstab on a
294 remount operation (if -o remount is specified on command line). This is
295 necessary to fully control mount options on remount by command line. In
296 previous versions the bind flag has been always applied and it was
297 impossible to re-define mount options without interaction with the bind
298 semantic. This mount behavior does not affect situations when
299 "remount,bind" is specified in the /etc/fstab file.
300 The move operation
302 Move a mounted tree to another place (atomically). The call is:
303 mount --move olddir newdir
305 This will cause the contents which previously appeared under olddir to
307 now be accessible under newdir. The physical location of the files is
308 not changed. Note that olddir has to be a mountpoint.
309 Note also that moving a mount residing under a shared mount is invalid
311 and unsupported. Use findmnt -o TARGET,PROPAGATION to see the current
312 propagation flags.
313 Shared subtree operations
315 Since Linux 2.6.15 it is possible to mark a mount and its submounts as
316 shared, private, slave or unbindable. A shared mount provides the
317 ability to create mirrors of that mount such that mounts and unmounts
318 within any of the mirrors propagate to the other mirror. A slave mount
319 receives propagation from its master, but not vice versa. A private
320 mount carries no propagation abilities. An unbindable mount is a
321 private mount which cannot be cloned through a bind operation. The
322 detailed semantics are documented in
323 Documentation/filesystems/sharedsubtree.txt file in the kernel source
324 tree; see also mount_namespaces(7).
325 Supported operations are:
327 mount --make-shared mountpoint
329 mount --make-slave mountpoint
330 mount --make-private mountpoint
331 mount --make-unbindable mountpoint
332 The following commands allow one to recursively change the type of all
334 the mounts under a given mountpoint.
335 mount --make-rshared mountpoint
337 mount --make-rslave mountpoint
338 mount --make-rprivate mountpoint
339 mount --make-runbindable mountpoint
340 mount does not read fstab(5) when a --make-* operation is requested.
342 All necessary information has to be specified on the command line.
343 Note that the Linux kernel does not allow changing multiple propagation
345 flags with a single mount(2) system call, and the flags cannot be mixed
346 with other mount options and operations.
347 Since util-linux 2.23 the mount command can be used to do more
349 propagation (topology) changes by one mount(8) call and do it also
350 together with other mount operations. The propagation flags are applied
351 by additional mount(2) system calls when the preceding mount operations
352 were successful. Note that this use case is not atomic. It is possible
353 to specify the propagation flags in fstab(5) as mount options (private,
354 slave, shared, unbindable, rprivate, rslave, rshared, runbindable).
355 For example:
357 mount --make-private --make-unbindable /dev/sda1 /foo
359 is the same as:
361 mount /dev/sda1 /foo
363 mount --make-private /foo
364 mount --make-unbindable /foo
365
367 The full set of mount options used by an invocation of mount is
368 determined by first extracting the mount options for the filesystem
369 from the fstab table, then applying any options specified by the -o
370 argument, and finally applying a -r or -w option, when present.
371 The mount command does not pass all command-line options to the
373 /sbin/mount.suffix mount helpers. The interface between mount and the
374 mount helpers is described below in the EXTERNAL HELPERS section.
375 Command-line options available for the mount command are:
377 -a, --all
379 Mount all filesystems (of the given types) mentioned in fstab
380 (except for those whose line contains the noauto keyword). The
381 filesystems are mounted following their order in fstab. The mount
382 command compares filesystem source, target (and fs root for bind
383 mount or btrfs) to detect already mounted filesystems. The kernel
384 table with already mounted filesystems is cached during mount
385 --all. This means that all duplicated fstab entries will be
386 mounted.
387 The correct functionality depends on /proc (to detect already
389 mounted filesystems) and on /sys (to evaluate filesystem tags like
390 UUID= or LABEL=). It’s strongly recommended to mount /proc and /sys
391 filesystems before mount -a is executed, or keep /proc and /sys at
392 the beginning of fstab.
393 The option --all is possible to use for remount operation too. In
395 this case all filters (-t and -O) are applied to the table of
396 already mounted filesystems.
397 Since version 2.35 it is possible to use the command line option -o
399 to alter mount options from fstab (see also --options-mode).
400 Note that it is a bad practice to use mount -a for fstab checking.
402 The recommended solution is findmnt --verify.
403 -B, --bind
405 Remount a subtree somewhere else (so that its contents are
406 available in both places). See above, under Bind mounts.
407 -c, --no-canonicalize
409 Don’t canonicalize paths. The mount command canonicalizes all paths
410 (from the command line or fstab) by default. This option can be
411 used together with the -f flag for already canonicalized absolute
412 paths. The option is designed for mount helpers which call mount
413 -i. It is strongly recommended to not use this command-line option
414 for normal mount operations.
415 Note that mount does not pass this option to the /sbin/mount.type
417 helpers.
418 -F, --fork
420 (Used in conjunction with -a.) Fork off a new incarnation of mount
421 for each device. This will do the mounts on different devices or
422 different NFS servers in parallel. This has the advantage that it
423 is faster; also NFS timeouts proceed in parallel. A disadvantage is
424 that the order of the mount operations is undefined. Thus, you
425 cannot use this option if you want to mount both /usr and
426 /usr/spool.
427 -f, --fake
429 Causes everything to be done except for the actual system call; if
430 it’s not obvious, this "fakes" mounting the filesystem. This option
431 is useful in conjunction with the -v flag to determine what the
432 mount command is trying to do. It can also be used to add entries
433 for devices that were mounted earlier with the -n option. The -f
434 option checks for an existing record in /etc/mtab and fails when
435 the record already exists (with a regular non-fake mount, this
436 check is done by the kernel).
437 -i, --internal-only
439 Don’t call the /sbin/mount.filesystem helper even if it exists.
440 -L, --label label
442 Mount the partition that has the specified label.
443 -l, --show-labels
445 Add the labels in the mount output. mount must have permission to
446 read the disk device (e.g. be set-user-ID root) for this to work.
447 One can set such a label for ext2, ext3 or ext4 using the
448 e2label(8) utility, or for XFS using xfs_admin(8), or for reiserfs
449 using reiserfstune(8).
450 -M, --move
452 Move a subtree to some other place. See above, the subsection The
453 move operation.
454 -m, --mkdir[=mode]
456 Allow to make a target directory (mountpoint) if it does not exist
457 yet. Alias to "-o X-mount.mkdir[=mode]", the default mode is 0755.
458 For more details see X-mount.mkdir below.
459 -n, --no-mtab
461 Mount without writing in /etc/mtab. This is necessary for example
462 when /etc is on a read-only filesystem.
463 -N, --namespace ns
465 Perform the mount operation in the mount namespace specified by ns.
466 ns is either PID of process running in that namespace or special
467 file representing that namespace.
468 mount switches to the mount namespace when it reads /etc/fstab,
470 writes /etc/mtab: (or writes to _/run/mount) and calls mount(2),
471 otherwise it runs in the original mount namespace. This means that
472 the target namespace does not have to contain any libraries or
473 other requirements necessary to execute the mount(2) call.
474 See mount_namespaces(7) for more information.
476 -O, --test-opts opts
478 Limit the set of filesystems to which the -a option applies. In
479 this regard it is like the -t option except that -O is useless
480 without -a. For example, the command
481 mount -a -O no_netdev
483 mounts all filesystems except those which have the option netdev
485 specified in the options field in the /etc/fstab file.
486 It is different from -t in that each option is matched exactly; a
488 leading no at the beginning of one option does not negate the rest.
489 The -t and -O options are cumulative in effect; that is, the
491 command
492 mount -a -t ext2 -O _netdev
494 mounts all ext2 filesystems with the _netdev option, not all
496 filesystems that are either ext2 or have the _netdev option
497 specified.
498 -o, --options opts
500 Use the specified mount options. The opts argument is a
501 comma-separated list. For example:
502 mount LABEL=mydisk -o noatime,nodev,nosuid
504 For more details, see the FILESYSTEM-INDEPENDENT MOUNT OPTIONS and
506 FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
507 --options-mode mode
509 Controls how to combine options from fstab/mtab with options from
510 the command line. mode can be one of ignore, append, prepend or
511 replace. For example, append means that options from fstab are
512 appended to options from the command line. The default value is
513 prepend — it means command line options are evaluated after fstab
514 options. Note that the last option wins if there are conflicting
515 ones.
516 --options-source source
518 Source of default options. source is a comma-separated list of
519 fstab, mtab and disable. disable disables fstab and mtab and
520 enables --options-source-force. The default value is fstab,mtab.
521 --options-source-force
523 Use options from fstab/mtab even if both device and dir are
524 specified.
525 -R, --rbind
527 Remount a subtree and all possible submounts somewhere else (so
528 that its contents are available in both places). See above, the
529 subsection Bind mounts.
530 -r, --read-only
532 Mount the filesystem read-only. A synonym is -o ro.
533 Note that, depending on the filesystem type, state and kernel
535 behavior, the system may still write to the device. For example,
536 ext3 and ext4 will replay the journal if the filesystem is dirty.
537 To prevent this kind of write access, you may want to mount an ext3
538 or ext4 filesystem with the ro,noload mount options or set the
539 block device itself to read-only mode, see the blockdev(8) command.
540 -s
542 Tolerate sloppy mount options rather than failing. This will ignore
543 mount options not supported by a filesystem type. Not all
544 filesystems support this option. Currently it’s supported by the
545 mount.nfs mount helper only.
546 --source device
548 If only one argument for the mount command is given, then the
549 argument might be interpreted as the target (mountpoint) or source
550 (device). This option allows you to explicitly define that the
551 argument is the mount source.
552 --target directory
554 If only one argument for the mount command is given, then the
555 argument might be interpreted as the target (mountpoint) or source
556 (device). This option allows you to explicitly define that the
557 argument is the mount target.
558 --target-prefix directory
560 Prepend the specified directory to all mount targets. This option
561 can be used to follow fstab, but mount operations are done in
562 another place, for example:
563 mount --all --target-prefix /chroot -o X-mount.mkdir
565 mounts all from system fstab to /chroot, all missing mountpoint are
567 created (due to X-mount.mkdir). See also --fstab to use an
568 alternative fstab.
569 -T, --fstab path
571 Specifies an alternative fstab file. If path is a directory, then
572 the files in the directory are sorted by strverscmp(3); files that
573 start with "." or without an .fstab extension are ignored. The
574 option can be specified more than once. This option is mostly
575 designed for initramfs or chroot scripts where additional
576 configuration is specified beyond standard system configuration.
577 Note that mount does not pass the option --fstab to the
579 /sbin/mount.type helpers, meaning that the alternative fstab files
580 will be invisible for the helpers. This is no problem for normal
581 mounts, but user (non-root) mounts always require fstab to verify
582 the user’s rights.
583 -t, --types fstype
585 The argument following the -t is used to indicate the filesystem
586 type. The filesystem types which are currently supported depend on
587 the running kernel. See /proc/filesystems and /lib/modules/$(uname
588 -r)/kernel/fs for a complete list of the filesystems. The most
589 common are ext2, ext3, ext4, xfs, btrfs, vfat, sysfs, proc, nfs and
590 cifs.
591 The programs mount and umount(8) support filesystem subtypes. The
593 subtype is defined by a '.subtype' suffix. For example
594 'fuse.sshfs'. It’s recommended to use subtype notation rather than
595 add any prefix to the mount source (for example 'sshfs#example.com'
596 is deprecated).
597 If no -t option is given, or if the auto type is specified, mount
599 will try to guess the desired type. mount uses the libblkid(3)
600 library for guessing the filesystem type; if that does not turn up
601 anything that looks familiar, mount will try to read the file
602 /etc/filesystems, or, if that does not exist, /proc/filesystems.
603 All of the filesystem types listed there will be tried, except for
604 those that are labeled "nodev" (e.g. devpts, proc and nfs). If
605 /etc/filesystems ends in a line with a single *, mount will read
606 /proc/filesystems afterwards. While trying, all filesystem types
607 will be mounted with the mount option silent.
608 The auto type may be useful for user-mounted floppies. Creating a
610 file /etc/filesystems can be useful to change the probe order
611 (e.g., to try vfat before msdos or ext3 before ext2) or if you use
612 a kernel module autoloader.
613 More than one type may be specified in a comma-separated list, for
615 the -t option as well as in an /etc/fstab entry. The list of
616 filesystem types for the -t option can be prefixed with no to
617 specify the filesystem types on which no action should be taken.
618 The prefix no has no effect when specified in an /etc/fstab entry.
619 The prefix no can be meaningful with the -a option. For example,
621 the command
622 mount -a -t nomsdos,smbfs
624 mounts all filesystems except those of type msdos and smbfs.
626 For most types all the mount program has to do is issue a simple
628 mount(2) system call, and no detailed knowledge of the filesystem
629 type is required. For a few types however (like nfs, nfs4, cifs,
630 smbfs, ncpfs) an ad hoc code is necessary. The nfs, nfs4, cifs,
631 smbfs, and ncpfs filesystems have a separate mount program. In
632 order to make it possible to treat all types in a uniform way,
633 mount will execute the program /sbin/mount.type (if that exists)
634 when called with type type. Since different versions of the
635 smbmount program have different calling conventions,
636 /sbin/mount.smbfs may have to be a shell script that sets up the
637 desired call.
638 -U, --uuid uuid
640 Mount the partition that has the specified uuid.
641 -v, --verbose
643 Verbose mode.
644 -w, --rw, --read-write
646 Mount the filesystem read/write. Read-write is the kernel default
647 and the mount default is to try read-only if the previous mount(2)
648 syscall with read-write flags on write-protected devices failed.
649 A synonym is -o rw.
651 Note that specifying -w on the command line forces mount to never
653 try read-only mount on write-protected devices or already mounted
654 read-only filesystems.
655 -h, --help
657 Display help text and exit.
658 -V, --version
660 Print version and exit.
661
663 Some of these options are only useful when they appear in the
664 /etc/fstab file.
665 Some of these options could be enabled or disabled by default in the
667 system kernel. To check the current setting see the options in
668 /proc/mounts. Note that filesystems also have per-filesystem specific
669 default mount options (see for example tune2fs -l output for extN
670 filesystems).
671 The following options apply to any filesystem that is being mounted
673 (but not every filesystem actually honors them - e.g., the sync option
674 today has an effect only for ext2, ext3, ext4, fat, vfat, ufs and xfs):
675 async
677 All I/O to the filesystem should be done asynchronously. (See also
678 the sync option.)
679 atime
681 Do not use the noatime feature, so the inode access time is
682 controlled by kernel defaults. See also the descriptions of the
683 relatime and strictatime mount options.
684 noatime
686 Do not update inode access times on this filesystem (e.g. for
687 faster access on the news spool to speed up news servers). This
688 works for all inode types (directories too), so it implies
689 nodiratime.
690 auto
692 Can be mounted with the -a option.
693 noauto
695 Can only be mounted explicitly (i.e., the -a option will not cause
696 the filesystem to be mounted).
697 context=context, fscontext=context, defcontext=context, and
699 rootcontext=context
700 The context= option is useful when mounting filesystems that do not
701 support extended attributes, such as a floppy or hard disk
702 formatted with VFAT, or systems that are not normally running under
703 SELinux, such as an ext3 or ext4 formatted disk from a non-SELinux
704 workstation. You can also use context= on filesystems you do not
705 trust, such as a floppy. It also helps in compatibility with
706 xattr-supporting filesystems on earlier 2.4.<x> kernel versions.
707 Even where xattrs are supported, you can save time not having to
708 label every file by assigning the entire disk one security context.
709 A commonly used option for removable media is
711 context="system_u:object_r:removable_t.
712 The fscontext= option works for all filesystems, regardless of
714 their xattr support. The fscontext option sets the overarching
715 filesystem label to a specific security context. This filesystem
716 label is separate from the individual labels on the files. It
717 represents the entire filesystem for certain kinds of permission
718 checks, such as during mount or file creation. Individual file
719 labels are still obtained from the xattrs on the files themselves.
720 The context option actually sets the aggregate context that
721 fscontext provides, in addition to supplying the same label for
722 individual files.
723 You can set the default security context for unlabeled files using
725 defcontext= option. This overrides the value set for unlabeled
726 files in the policy and requires a filesystem that supports xattr
727 labeling.
728 The rootcontext= option allows you to explicitly label the root
730 inode of a FS being mounted before that FS or inode becomes visible
731 to userspace. This was found to be useful for things like stateless
732 Linux.
733 Note that the kernel rejects any remount request that includes the
735 context option, even when unchanged from the current context.
736 Warning: the context value might contain commas, in which case the
738 value has to be properly quoted, otherwise mount will interpret the
739 comma as a separator between mount options. Don’t forget that the
740 shell strips off quotes and thus double quoting is required. For
741 example:
742 mount -t tmpfs none /mnt -o \
744 'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'
745 For more details, see selinux(8).
747 defaults
749 Use the default options: rw, suid, dev, exec, auto, nouser, and
750 async.
751 Note that the real set of all default mount options depends on the
753 kernel and filesystem type. See the beginning of this section for
754 more details.
755 dev
757 Interpret character or block special devices on the filesystem.
758 nodev
760 Do not interpret character or block special devices on the
761 filesystem.
762 diratime
764 Update directory inode access times on this filesystem. This is the
765 default. (This option is ignored when noatime is set.)
766 nodiratime
768 Do not update directory inode access times on this filesystem.
769 (This option is implied when noatime is set.)
770 dirsync
772 All directory updates within the filesystem should be done
773 synchronously. This affects the following system calls: creat(2),
774 link(2), unlink(2), symlink(2), mkdir(2), rmdir(2), mknod(2) and
775 rename(2).
776 exec
778 Permit execution of binaries and other executable files.
779 noexec
781 Do not permit direct execution of any binaries on the mounted
782 filesystem.
783 group
785 Allow an ordinary user to mount the filesystem if one of that
786 user’s groups matches the group of the device. This option implies
787 the options nosuid and nodev (unless overridden by subsequent
788 options, as in the option line group,dev,suid).
789 iversion
791 Every time the inode is modified, the i_version field will be
792 incremented.
793 noiversion
795 Do not increment the i_version inode field.
796 mand
798 Allow mandatory locks on this filesystem. See fcntl(2). This option
799 was deprecated in Linux 5.15.
800 nomand
802 Do not allow mandatory locks on this filesystem.
803 _netdev
805 The filesystem resides on a device that requires network access
806 (used to prevent the system from attempting to mount these
807 filesystems until the network has been enabled on the system).
808 nofail
810 Do not report errors for this device if it does not exist.
811 relatime
813 Update inode access times relative to modify or change time. Access
814 time is only updated if the previous access time was earlier than
815 the current modify or change time. (Similar to noatime, but it
816 doesn’t break mutt(1) or other applications that need to know if a
817 file has been read since the last time it was modified.)
818 Since Linux 2.6.30, the kernel defaults to the behavior provided by
820 this option (unless noatime was specified), and the strictatime
821 option is required to obtain traditional semantics. In addition,
822 since Linux 2.6.30, the file’s last access time is always updated
823 if it is more than 1 day old.
824 norelatime
826 Do not use the relatime feature. See also the strictatime mount
827 option.
828 strictatime
830 Allows to explicitly request full atime updates. This makes it
831 possible for the kernel to default to relatime or noatime but still
832 allow userspace to override it. For more details about the default
833 system mount options see /proc/mounts.
834 nostrictatime
836 Use the kernel’s default behavior for inode access time updates.
837 lazytime
839 Only update times (atime, mtime, ctime) on the in-memory version of
840 the file inode.
841 This mount option significantly reduces writes to the inode table
843 for workloads that perform frequent random writes to preallocated
844 files.
845 The on-disk timestamps are updated only when:
847 • the inode needs to be updated for some change unrelated to file
849 timestamps
850 • the application employs fsync(2), syncfs(2), or sync(2)
852 • an undeleted inode is evicted from memory
854 • more than 24 hours have passed since the inode was written to
856 disk.
857 nolazytime
859 Do not use the lazytime feature.
860 suid
862 Honor set-user-ID and set-group-ID bits or file capabilities when
863 executing programs from this filesystem.
864 nosuid
866 Do not honor set-user-ID and set-group-ID bits or file capabilities
867 when executing programs from this filesystem. In addition, SELinux
868 domain transitions require permission nosuid_transition, which in
869 turn needs also policy capability nnp_nosuid_transition.
870 silent
872 Turn on the silent flag.
873 loud
875 Turn off the silent flag.
876 owner
878 Allow an ordinary user to mount the filesystem if that user is the
879 owner of the device. This option implies the options nosuid and
880 nodev (unless overridden by subsequent options, as in the option
881 line owner,dev,suid).
882 remount
884 Attempt to remount an already-mounted filesystem. This is commonly
885 used to change the mount flags for a filesystem, especially to make
886 a readonly filesystem writable. It does not change device or mount
887 point.
888 The remount operation together with the bind flag has special
890 semantics. See above, the subsection Bind mounts.
891 The remount functionality follows the standard way the mount
893 command works with options from fstab. This means that mount does
894 not read fstab (or mtab) only when both device and dir are
895 specified.
896 mount -o remount,rw /dev/foo /dir
898 After this call all old mount options are replaced and arbitrary
900 stuff from fstab (or mtab) is ignored, except the loop= option
901 which is internally generated and maintained by the mount command.
902 mount -o remount,rw /dir
904 After this call, mount reads fstab and merges these options with
906 the options from the command line (-o). If no mountpoint is found
907 in fstab, then a remount with unspecified source is allowed.
908 mount allows the use of --all to remount all already mounted
910 filesystems which match a specified filter (-O and -t). For
911 example:
912 mount --all -o remount,ro -t vfat
914 remounts all already mounted vfat filesystems in read-only mode.
916 Each of the filesystems is remounted by mount -o remount,ro /dir
917 semantic. This means the mount command reads fstab or mtab and
918 merges these options with the options from the command line.
919 ro
921 Mount the filesystem read-only.
922 rw
924 Mount the filesystem read-write.
925 sync
927 All I/O to the filesystem should be done synchronously. In the case
928 of media with a limited number of write cycles (e.g. some flash
929 drives), sync may cause life-cycle shortening.
930 user
932 Allow an ordinary user to mount the filesystem. The name of the
933 mounting user is written to the mtab file (or to the private
934 libmount file in /run/mount on systems without a regular mtab) so
935 that this same user can unmount the filesystem again. This option
936 implies the options noexec, nosuid, and nodev (unless overridden by
937 subsequent options, as in the option line user,exec,dev,suid).
938 nouser
940 Forbid an ordinary user to mount the filesystem. This is the
941 default; it does not imply any other options.
942 users
944 Allow any user to mount and to unmount the filesystem, even when
945 some other ordinary user mounted it. This option implies the
946 options noexec, nosuid, and nodev (unless overridden by subsequent
947 options, as in the option line users,exec,dev,suid).
948 X-*
950 All options prefixed with "X-" are interpreted as comments or as
951 userspace application-specific options. These options are not
952 stored in user space (e.g., mtab file), nor sent to the mount.type
953 helpers nor to the mount(2) system call. The suggested format is
954 X-appname.option.
955 x-*
957 The same as X-* options, but stored permanently in user space. This
958 means the options are also available for umount(8) or other
959 operations. Note that maintaining mount options in user space is
960 tricky, because it’s necessary use libmount-based tools and there
961 is no guarantee that the options will be always available (for
962 example after a move mount operation or in unshared namespace).
963 Note that before util-linux v2.30 the x-* options have not been
965 maintained by libmount and stored in user space (functionality was
966 the same as for X-* now), but due to the growing number of
967 use-cases (in initrd, systemd etc.) the functionality has been
968 extended to keep existing fstab configurations usable without a
969 change.
970 X-mount.mkdir[=mode]
972 Allow to make a target directory (mountpoint) if it does not exist
973 yet. The optional argument mode specifies the filesystem access
974 mode used for mkdir(2) in octal notation. The default mode is 0755.
975 This functionality is supported only for root users or when mount
976 is executed without suid permissions. The option is also supported
977 as x-mount.mkdir, but this notation is deprecated since v2.30. See
978 also --mkdir command line option.
979 X-mount.subdir=directory
981 Allow mounting sub-directory from a filesystem instead of the root
982 directory. For now, this feature is implemented by temporary
983 filesystem root directory mount in unshared namespace and then bind
984 the sub-directory to the final mount point and umount the root of
985 the filesystem. The sub-directory mount shows up atomically for the
986 rest of the system although it is implemented by multiple mount(2)
987 syscalls. This feature is EXPERIMENTAL.
988 nosymfollow
990 Do not follow symlinks when resolving paths. Symlinks can still be
991 created, and readlink(1), readlink(2), realpath(1), and realpath(3)
992 all still work properly.
993
995 This section lists options that are specific to particular filesystems.
996 Where possible, you should first consult filesystem-specific manual
997 pages for details. Some of those pages are listed in the following
998 table.
999 ┌─────────────────┬───────────────┐
1001 │ │ │
1002 │Filesystem(s) │ Manual page │
1003 ├─────────────────┼───────────────┤
1004 │ │ │
1005 │btrfs │ btrfs(5) │
1006 ├─────────────────┼───────────────┤
1007 │ │ │
1008 │cifs │ mount.cifs(8) │
1009 ├─────────────────┼───────────────┤
1010 │ │ │
1011 │ext2, ext3, ext4 │ ext4(5) │
1012 ├─────────────────┼───────────────┤
1013 │ │ │
1014 │fuse │ fuse(8) │
1015 ├─────────────────┼───────────────┤
1016 │ │ │
1017 │nfs │ nfs(5) │
1018 ├─────────────────┼───────────────┤
1019 │ │ │
1020 │tmpfs │ tmpfs(5) │
1021 ├─────────────────┼───────────────┤
1022 │ │ │
1023 │xfs │ xfs(5) │
1024 └─────────────────┴───────────────┘
1025 Note that some of the pages listed above might be available only after
1027 you install the respective userland tools.
1028 The following options apply only to certain filesystems. We sort them
1030 by filesystem. All options follow the -o flag.
1031 What options are supported depends a bit on the running kernel. Further
1033 information may be available in filesystem-specific files in the kernel
1034 source subdirectory Documentation/filesystems.
1035 Mount options for adfs
1037 uid=value and gid=value
1038 Set the owner and group of the files in the filesystem (default:
1039 uid=gid=0).
1040 ownmask=value and othmask=value
1042 Set the permission mask for ADFS 'owner' permissions and 'other'
1043 permissions, respectively (default: 0700 and 0077, respectively).
1044 See also /usr/src/linux/Documentation/filesystems/adfs.rst.
1045 Mount options for affs
1047 uid=value and gid=value
1048 Set the owner and group of the root of the filesystem (default:
1049 uid=gid=0, but with option uid or gid without specified value, the
1050 UID and GID of the current process are taken).
1051 setuid=value and setgid=value
1053 Set the owner and group of all files.
1054 mode=value
1056 Set the mode of all files to value & 0777 disregarding the original
1057 permissions. Add search permission to directories that have read
1058 permission. The value is given in octal.
1059 protect
1061 Do not allow any changes to the protection bits on the filesystem.
1062 usemp
1064 Set UID and GID of the root of the filesystem to the UID and GID of
1065 the mount point upon the first sync or umount, and then clear this
1066 option. Strange...
1067 verbose
1069 Print an informational message for each successful mount.
1070 prefix=string
1072 Prefix used before volume name, when following a link.
1073 volume=string
1075 Prefix (of length at most 30) used before '/' when following a
1076 symbolic link.
1077 reserved=value
1079 (Default: 2.) Number of unused blocks at the start of the device.
1080 root=value
1082 Give explicitly the location of the root block.
1083 bs=value
1085 Give blocksize. Allowed values are 512, 1024, 2048, 4096.
1086 grpquota|noquota|quota|usrquota
1088 These options are accepted but ignored. (However, quota utilities
1089 may react to such strings in /etc/fstab.)
1090 Mount options for debugfs
1092 The debugfs filesystem is a pseudo filesystem, traditionally mounted on
1093 /sys/kernel/debug. As of kernel version 3.4, debugfs has the following
1094 options:
1095 uid=n, gid=n
1097 Set the owner and group of the mountpoint.
1098 mode=value
1100 Sets the mode of the mountpoint.
1101 Mount options for devpts
1103 The devpts filesystem is a pseudo filesystem, traditionally mounted on
1104 /dev/pts. In order to acquire a pseudo terminal, a process opens
1105 /dev/ptmx; the number of the pseudo terminal is then made available to
1106 the process and the pseudo terminal slave can be accessed as
1107 /dev/pts/<number>.
1108 uid=value and gid=value
1110 This sets the owner or the group of newly created pseudo terminals
1111 to the specified values. When nothing is specified, they will be
1112 set to the UID and GID of the creating process. For example, if
1113 there is a tty group with GID 5, then gid=5 will cause newly
1114 created pseudo terminals to belong to the tty group.
1115 mode=value
1117 Set the mode of newly created pseudo terminals to the specified
1118 value. The default is 0600. A value of mode=620 and gid=5 makes
1119 "mesg y" the default on newly created pseudo terminals.
1120 newinstance
1122 Create a private instance of the devpts filesystem, such that
1123 indices of pseudo terminals allocated in this new instance are
1124 independent of indices created in other instances of devpts.
1125 All mounts of devpts without this newinstance option share the same
1127 set of pseudo terminal indices (i.e., legacy mode). Each mount of
1128 devpts with the newinstance option has a private set of pseudo
1129 terminal indices.
1130 This option is mainly used to support containers in the Linux
1132 kernel. It is implemented in Linux kernel versions starting with
1133 2.6.29. Further, this mount option is valid only if
1134 CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel
1135 configuration.
1136 To use this option effectively, /dev/ptmx must be a symbolic link
1138 to pts/ptmx. See Documentation/filesystems/devpts.txt in the Linux
1139 kernel source tree for details.
1140 ptmxmode=value
1142 Set the mode for the new ptmx device node in the devpts filesystem.
1143 With the support for multiple instances of devpts (see newinstance
1145 option above), each instance has a private ptmx node in the root of
1146 the devpts filesystem (typically /dev/pts/ptmx).
1147 For compatibility with older versions of the kernel, the default
1149 mode of the new ptmx node is 0000. ptmxmode=value specifies a more
1150 useful mode for the ptmx node and is highly recommended when the
1151 newinstance option is specified.
1152 This option is only implemented in Linux kernel versions starting
1154 with 2.6.29. Further, this option is valid only if
1155 CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel
1156 configuration.
1157 Mount options for fat
1159 (Note: fat is not a separate filesystem, but a common part of the
1160 msdos, umsdos and vfat filesystems.)
1161 blocksize={512|1024|2048}
1163 Set blocksize (default 512). This option is obsolete.
1164 uid=value and gid=value
1166 Set the owner and group of all files. (Default: the UID and GID of
1167 the current process.)
1168 umask=value
1170 Set the umask (the bitmask of the permissions that are not
1171 present). The default is the umask of the current process. The
1172 value is given in octal.
1173 dmask=value
1175 Set the umask applied to directories only. The default is the umask
1176 of the current process. The value is given in octal.
1177 fmask=value
1179 Set the umask applied to regular files only. The default is the
1180 umask of the current process. The value is given in octal.
1181 allow_utime=value
1183 This option controls the permission check of mtime/atime.
1184 20
1186 If current process is in group of file’s group ID, you can
1187 change timestamp.
1188 2
1190 Other users can change timestamp.
1191 The default is set from 'dmask' option. (If the directory is writable,
1193 utime(2) is also allowed. I.e. ~dmask & 022)
1194 Normally utime(2) checks that the current process is owner of the file,
1196 or that it has the CAP_FOWNER capability. But FAT filesystems don’t
1197 have UID/GID on disk, so the normal check is too inflexible. With this
1198 option you can relax it.
1199 check=value
1201 Three different levels of pickiness can be chosen:
1202 r[elaxed]
1204 Upper and lower case are accepted and equivalent, long name
1205 parts are truncated (e.g. verylongname.foobar becomes
1206 verylong.foo), leading and embedded spaces are accepted in each
1207 name part (name and extension).
1208 n[ormal]
1210 Like "relaxed", but many special characters (*, ?, <, spaces,
1211 etc.) are rejected. This is the default.
1212 s[trict]
1214 Like "normal", but names that contain long parts or special
1215 characters that are sometimes used on Linux but are not
1216 accepted by MS-DOS (+, =, etc.) are rejected.
1217 codepage=value
1219 Sets the codepage for converting to shortname characters on FAT and
1220 VFAT filesystems. By default, codepage 437 is used.
1221 conv=mode
1223 This option is obsolete and may fail or be ignored.
1224 cvf_format=module
1226 Forces the driver to use the CVF (Compressed Volume File) module
1227 cvf_module instead of auto-detection. If the kernel supports kmod,
1228 the cvf_format=xxx option also controls on-demand CVF module
1229 loading. This option is obsolete.
1230 cvf_option=option
1232 Option passed to the CVF module. This option is obsolete.
1233 debug
1235 Turn on the debug flag. A version string and a list of filesystem
1236 parameters will be printed (these data are also printed if the
1237 parameters appear to be inconsistent).
1238 discard
1240 If set, causes discard/TRIM commands to be issued to the block
1241 device when blocks are freed. This is useful for SSD devices and
1242 sparse/thinly-provisioned LUNs.
1243 dos1xfloppy
1245 If set, use a fallback default BIOS Parameter Block configuration,
1246 determined by backing device size. These static parameters match
1247 defaults assumed by DOS 1.x for 160 kiB, 180 kiB, 320 kiB, and 360
1248 kiB floppies and floppy images.
1249 errors={panic|continue|remount-ro}
1251 Specify FAT behavior on critical errors: panic, continue without
1252 doing anything, or remount the partition in read-only mode (default
1253 behavior).
1254 fat={12|16|32}
1256 Specify a 12, 16 or 32 bit fat. This overrides the automatic FAT
1257 type detection routine. Use with caution!
1258 iocharset=value
1260 Character set to use for converting between 8 bit characters and 16
1261 bit Unicode characters. The default is iso8859-1. Long filenames
1262 are stored on disk in Unicode format.
1263 nfs={stale_rw|nostale_ro}
1265 Enable this only if you want to export the FAT filesystem over NFS.
1266 stale_rw: This option maintains an index (cache) of directory
1268 inodes which is used by the nfs-related code to improve look-ups.
1269 Full file operations (read/write) over NFS are supported but with
1270 cache eviction at NFS server, this could result in spurious ESTALE
1271 errors.
1272 nostale_ro: This option bases the inode number and file handle on
1274 the on-disk location of a file in the FAT directory entry. This
1275 ensures that ESTALE will not be returned after a file is evicted
1276 from the inode cache. However, it means that operations such as
1277 rename, create and unlink could cause file handles that previously
1278 pointed at one file to point at a different file, potentially
1279 causing data corruption. For this reason, this option also mounts
1280 the filesystem readonly.
1281 To maintain backward compatibility, -o nfs is also accepted,
1283 defaulting to stale_rw.
1284 tz=UTC
1286 This option disables the conversion of timestamps between local
1287 time (as used by Windows on FAT) and UTC (which Linux uses
1288 internally). This is particularly useful when mounting devices
1289 (like digital cameras) that are set to UTC in order to avoid the
1290 pitfalls of local time.
1291 time_offset=minutes
1293 Set offset for conversion of timestamps from local time used by FAT
1294 to UTC. I.e., minutes will be subtracted from each timestamp to
1295 convert it to UTC used internally by Linux. This is useful when the
1296 time zone set in the kernel via settimeofday(2) is not the time
1297 zone used by the filesystem. Note that this option still does not
1298 provide correct time stamps in all cases in presence of DST - time
1299 stamps in a different DST setting will be off by one hour.
1300 quiet
1302 Turn on the quiet flag. Attempts to chown or chmod files do not
1303 return errors, although they fail. Use with caution!
1304 rodir
1306 FAT has the ATTR_RO (read-only) attribute. On Windows, the ATTR_RO
1307 of the directory will just be ignored, and is used only by
1308 applications as a flag (e.g. it’s set for the customized folder).
1309 If you want to use ATTR_RO as read-only flag even for the
1311 directory, set this option.
1312 showexec
1314 If set, the execute permission bits of the file will be allowed
1315 only if the extension part of the name is .EXE, .COM, or .BAT. Not
1316 set by default.
1317 sys_immutable
1319 If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag on
1320 Linux. Not set by default.
1321 flush
1323 If set, the filesystem will try to flush to disk more early than
1324 normal. Not set by default.
1325 usefree
1327 Use the "free clusters" value stored on FSINFO. It’ll be used to
1328 determine number of free clusters without scanning disk. But it’s
1329 not used by default, because recent Windows don’t update it
1330 correctly in some case. If you are sure the "free clusters" on
1331 FSINFO is correct, by this option you can avoid scanning disk.
1332 dots, nodots, dotsOK=[yes|no]
1334 Various misguided attempts to force Unix or DOS conventions onto a
1335 FAT filesystem.
1336 Mount options for hfs
1338 creator=cccc, type=cccc
1339 Set the creator/type values as shown by the MacOS finder used for
1340 creating new files. Default values: '????'.
1341 uid=n, gid=n
1343 Set the owner and group of all files. (Default: the UID and GID of
1344 the current process.)
1345 dir_umask=n, file_umask=n, umask=n
1347 Set the umask used for all directories, all regular files, or all
1348 files and directories. Defaults to the umask of the current
1349 process.
1350 session=n
1352 Select the CDROM session to mount. Defaults to leaving that
1353 decision to the CDROM driver. This option will fail with anything
1354 but a CDROM as underlying device.
1355 part=n
1357 Select partition number n from the device. Only makes sense for
1358 CDROMs. Defaults to not parsing the partition table at all.
1359 quiet
1361 Don’t complain about invalid mount options.
1362 Mount options for hpfs
1364 uid=value and gid=value
1365 Set the owner and group of all files. (Default: the UID and GID of
1366 the current process.)
1367 umask=value
1369 Set the umask (the bitmask of the permissions that are not
1370 present). The default is the umask of the current process. The
1371 value is given in octal.
1372 case={lower|asis}
1374 Convert all files names to lower case, or leave them. (Default:
1375 case=lower.)
1376 conv=mode
1378 This option is obsolete and may fail or being ignored.
1379 nocheck
1381 Do not abort mounting when certain consistency checks fail.
1382 Mount options for iso9660
1384 ISO 9660 is a standard describing a filesystem structure to be used on
1385 CD-ROMs. (This filesystem type is also seen on some DVDs. See also the
1386 udf filesystem.)
1387 Normal iso9660 filenames appear in an 8.3 format (i.e., DOS-like
1389 restrictions on filename length), and in addition all characters are in
1390 upper case. Also there is no field for file ownership, protection,
1391 number of links, provision for block/character devices, etc.
1392 Rock Ridge is an extension to iso9660 that provides all of these
1394 UNIX-like features. Basically there are extensions to each directory
1395 record that supply all of the additional information, and when Rock
1396 Ridge is in use, the filesystem is indistinguishable from a normal UNIX
1397 filesystem (except that it is read-only, of course).
1398 norock
1400 Disable the use of Rock Ridge extensions, even if available. Cf.
1401 map.
1402 nojoliet
1404 Disable the use of Microsoft Joliet extensions, even if available.
1405 Cf. map.
1406 check={r[elaxed]|s[trict]}
1408 With check=relaxed, a filename is first converted to lower case
1409 before doing the lookup. This is probably only meaningful together
1410 with norock and map=normal. (Default: check=strict.)
1411 uid=value and gid=value
1413 Give all files in the filesystem the indicated user or group id,
1414 possibly overriding the information found in the Rock Ridge
1415 extensions. (Default: uid=0,gid=0.)
1416 map={n[ormal]|o[ff]|a[corn]}
1418 For non-Rock Ridge volumes, normal name translation maps upper to
1419 lower case ASCII, drops a trailing ';1', and converts ';' to '.'.
1420 With map=off no name translation is done. See norock. (Default:
1421 map=normal.) map=acorn is like map=normal but also apply Acorn
1422 extensions if present.
1423 mode=value
1425 For non-Rock Ridge volumes, give all files the indicated mode.
1426 (Default: read and execute permission for everybody.) Octal mode
1427 values require a leading 0.
1428 unhide
1430 Also show hidden and associated files. (If the ordinary files and
1431 the associated or hidden files have the same filenames, this may
1432 make the ordinary files inaccessible.)
1433 block={512|1024|2048}
1435 Set the block size to the indicated value. (Default: block=1024.)
1436 conv=mode
1438 This option is obsolete and may fail or being ignored.
1439 cruft
1441 If the high byte of the file length contains other garbage, set
1442 this mount option to ignore the high order bits of the file length.
1443 This implies that a file cannot be larger than 16 MB.
1444 session=x
1446 Select number of session on a multisession CD.
1447 sbsector=xxx
1449 Session begins from sector xxx.
1450 The following options are the same as for vfat and specifying them only
1452 makes sense when using discs encoded using Microsoft’s Joliet
1453 extensions.
1454 iocharset=value
1456 Character set to use for converting 16 bit Unicode characters on CD
1457 to 8 bit characters. The default is iso8859-1.
1458 utf8
1460 Convert 16 bit Unicode characters on CD to UTF-8.
1461 Mount options for jfs
1463 iocharset=name
1464 Character set to use for converting from Unicode to ASCII. The
1465 default is to do no conversion. Use iocharset=utf8 for UTF8
1466 translations. This requires CONFIG_NLS_UTF8 to be set in the kernel
1467 .config file.
1468 resize=value
1470 Resize the volume to value blocks. JFS only supports growing a
1471 volume, not shrinking it. This option is only valid during a
1472 remount, when the volume is mounted read-write. The resize keyword
1473 with no value will grow the volume to the full size of the
1474 partition.
1475 nointegrity
1477 Do not write to the journal. The primary use of this option is to
1478 allow for higher performance when restoring a volume from backup
1479 media. The integrity of the volume is not guaranteed if the system
1480 abnormally ends.
1481 integrity
1483 Default. Commit metadata changes to the journal. Use this option to
1484 remount a volume where the nointegrity option was previously
1485 specified in order to restore normal behavior.
1486 errors={continue|remount-ro|panic}
1488 Define the behavior when an error is encountered. (Either ignore
1489 errors and just mark the filesystem erroneous and continue, or
1490 remount the filesystem read-only, or panic and halt the system.)
1491 noquota|quota|usrquota|grpquota
1493 These options are accepted but ignored.
1494 Mount options for msdos
1496 See mount options for fat. If the msdos filesystem detects an
1497 inconsistency, it reports an error and sets the file system read-only.
1498 The filesystem can be made writable again by remounting it.
1499 Mount options for ncpfs
1501 Just like nfs, the ncpfs implementation expects a binary argument (a
1502 struct ncp_mount_data) to the mount(2) system call. This argument is
1503 constructed by ncpmount(8) and the current version of mount (2.12) does
1504 not know anything about ncpfs.
1505 Mount options for ntfs
1507 iocharset=name
1508 Character set to use when returning file names. Unlike VFAT, NTFS
1509 suppresses names that contain nonconvertible characters.
1510 Deprecated.
1511 nls=name
1513 New name for the option earlier called iocharset.
1514 utf8
1516 Use UTF-8 for converting file names.
1517 uni_xlate={0|1|2}
1519 For 0 (or 'no' or 'false'), do not use escape sequences for unknown
1520 Unicode characters. For 1 (or 'yes' or 'true') or 2, use vfat-style
1521 4-byte escape sequences starting with ":". Here 2 gives a
1522 little-endian encoding and 1 a byteswapped bigendian encoding.
1523 posix=[0|1]
1525 If enabled (posix=1), the filesystem distinguishes between upper
1526 and lower case. The 8.3 alias names are presented as hard links
1527 instead of being suppressed. This option is obsolete.
1528 uid=value, gid=value and umask=value
1530 Set the file permission on the filesystem. The umask value is given
1531 in octal. By default, the files are owned by root and not readable
1532 by somebody else.
1533 Mount options for overlay
1535 Since Linux 3.18 the overlay pseudo filesystem implements a union mount
1536 for other filesystems.
1537 An overlay filesystem combines two filesystems - an upper filesystem
1539 and a lower filesystem. When a name exists in both filesystems, the
1540 object in the upper filesystem is visible while the object in the lower
1541 filesystem is either hidden or, in the case of directories, merged with
1542 the upper object.
1543 The lower filesystem can be any filesystem supported by Linux and does
1545 not need to be writable. The lower filesystem can even be another
1546 overlayfs. The upper filesystem will normally be writable and if it is
1547 it must support the creation of trusted.* extended attributes, and must
1548 provide a valid d_type in readdir responses, so NFS is not suitable.
1549 A read-only overlay of two read-only filesystems may use any filesystem
1551 type. The options lowerdir and upperdir are combined into a merged
1552 directory by using:
1553 mount -t overlay overlay \
1555 -olowerdir=/lower,upperdir=/upper,workdir=/work /merged
1556 lowerdir=directory
1558 Any filesystem, does not need to be on a writable filesystem.
1559 upperdir=directory
1561 The upperdir is normally on a writable filesystem.
1562 workdir=directory
1564 The workdir needs to be an empty directory on the same filesystem
1565 as upperdir.
1566 userxattr
1568 Use the "user.overlay." xattr namespace instead of
1569 "trusted.overlay.". This is useful for unprivileged mounting of
1570 overlayfs.
1571 redirect_dir={on|off|follow|nofollow}
1573 If the redirect_dir feature is enabled, then the directory will be
1574 copied up (but not the contents). Then the
1575 "{trusted|user}.overlay.redirect" extended attribute is set to the
1576 path of the original location from the root of the overlay. Finally
1577 the directory is moved to the new location.
1578 on
1580 Redirects are enabled.
1581 off
1583 Redirects are not created and only followed if
1584 "redirect_always_follow" feature is enabled in the
1585 kernel/module config.
1586 follow
1588 Redirects are not created, but followed.
1589 nofollow
1591 Redirects are not created and not followed (equivalent to
1592 "redirect_dir=off" if "redirect_always_follow" feature is not
1593 enabled).
1594 index={on|off}
1596 Inode index. If this feature is disabled and a file with multiple
1597 hard links is copied up, then this will "break" the link. Changes
1598 will not be propagated to other names referring to the same inode.
1599 uuid={on|off}
1601 Can be used to replace UUID of the underlying filesystem in file
1602 handles with null, and effectively disable UUID checks. This can be
1603 useful in case the underlying disk is copied and the UUID of this
1604 copy is changed. This is only applicable if all lower/upper/work
1605 directories are on the same filesystem, otherwise it will fallback
1606 to normal behaviour.
1607 nfs_export={on|off}
1609 When the underlying filesystems supports NFS export and the
1610 "nfs_export" feature is enabled, an overlay filesystem may be
1611 exported to NFS.
1612 With the "nfs_export" feature, on copy_up of any lower object, an
1614 index entry is created under the index directory. The index entry
1615 name is the hexadecimal representation of the copy up origin file
1616 handle. For a non-directory object, the index entry is a hard link
1617 to the upper inode. For a directory object, the index entry has an
1618 extended attribute "{trusted|user}.overlay.upper" with an encoded
1619 file handle of the upper directory inode.
1620 When encoding a file handle from an overlay filesystem object, the
1622 following rules apply
1623 • For a non-upper object, encode a lower file handle from
1625 lower inode
1626 • For an indexed object, encode a lower file handle from
1628 copy_up origin
1629 • For a pure-upper object and for an existing non-indexed
1631 upper object, encode an upper file handle from upper inode
1632 The encoded overlay file handle includes
1634 • Header including path type information (e.g. lower/upper)
1636 • UUID of the underlying filesystem
1638 • Underlying filesystem encoding of underlying inode
1640 This encoding format is identical to the encoding format of file
1642 handles that are stored in extended attribute
1643 "{trusted|user}.overlay.origin". When decoding an overlay file
1644 handle, the following steps are followed
1645 • Find underlying layer by UUID and path type information.
1647 • Decode the underlying filesystem file handle to underlying
1649 dentry.
1650 • For a lower file handle, lookup the handle in index
1652 directory by name.
1653 • If a whiteout is found in index, return ESTALE. This
1655 represents an overlay object that was deleted after its
1656 file handle was encoded.
1657 • For a non-directory, instantiate a disconnected overlay
1659 dentry from the decoded underlying dentry, the path type
1660 and index inode, if found.
1661 • For a directory, use the connected underlying decoded
1663 dentry, path type and index, to lookup a connected overlay
1664 dentry.
1665 Decoding a non-directory file handle may return a disconnected
1667 dentry. copy_up of that disconnected dentry will create an upper
1668 index entry with no upper alias.
1669 When overlay filesystem has multiple lower layers, a middle layer
1671 directory may have a "redirect" to lower directory. Because middle
1672 layer "redirects" are not indexed, a lower file handle that was
1673 encoded from the "redirect" origin directory, cannot be used to
1674 find the middle or upper layer directory. Similarly, a lower file
1675 handle that was encoded from a descendant of the "redirect" origin
1676 directory, cannot be used to reconstruct a connected overlay path.
1677 To mitigate the cases of directories that cannot be decoded from a
1678 lower file handle, these directories are copied up on encode and
1679 encoded as an upper file handle. On an overlay filesystem with no
1680 upper layer this mitigation cannot be used NFS export in this setup
1681 requires turning off redirect follow (e.g.
1682 "redirect_dir=nofollow").
1683 The overlay filesystem does not support non-directory connectable
1685 file handles, so exporting with the subtree_check exportfs
1686 configuration will cause failures to lookup files over NFS.
1687 When the NFS export feature is enabled, all directory index entries
1689 are verified on mount time to check that upper file handles are not
1690 stale. This verification may cause significant overhead in some
1691 cases.
1692 Note: the mount options index=off,nfs_export=on are conflicting for
1694 a read-write mount and will result in an error.
1695 xino={on|off|auto}
1697 The "xino" feature composes a unique object identifier from the
1698 real object st_ino and an underlying fsid index. The "xino" feature
1699 uses the high inode number bits for fsid, because the underlying
1700 filesystems rarely use the high inode number bits. In case the
1701 underlying inode number does overflow into the high xino bits,
1702 overlay filesystem will fall back to the non xino behavior for that
1703 inode.
1704 For a detailed description of the effect of this option please
1706 refer to
1707 https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html?highlight=overlayfs
1708 metacopy={on|off}
1710 When metadata only copy up feature is enabled, overlayfs will only
1711 copy up metadata (as opposed to whole file), when a metadata
1712 specific operation like chown/chmod is performed. Full file will be
1713 copied up later when file is opened for WRITE operation.
1714 In other words, this is delayed data copy up operation and data is
1716 copied up when there is a need to actually modify data.
1717 volatile
1719 Volatile mounts are not guaranteed to survive a crash. It is
1720 strongly recommended that volatile mounts are only used if data
1721 written to the overlay can be recreated without significant effort.
1722 The advantage of mounting with the "volatile" option is that all
1724 forms of sync calls to the upper filesystem are omitted.
1725 In order to avoid a giving a false sense of safety, the syncfs (and
1727 fsync) semantics of volatile mounts are slightly different than
1728 that of the rest of VFS. If any writeback error occurs on the
1729 upperdir’s filesystem after a volatile mount takes place, all sync
1730 functions will return an error. Once this condition is reached, the
1731 filesystem will not recover, and every subsequent sync call will
1732 return an error, even if the upperdir has not experience a new
1733 error since the last sync call.
1734 When overlay is mounted with "volatile" option, the directory
1736 "$workdir/work/incompat/volatile" is created. During next mount,
1737 overlay checks for this directory and refuses to mount if present.
1738 This is a strong indicator that user should throw away upper and
1739 work directories and create fresh one. In very limited cases where
1740 the user knows that the system has not crashed and contents of
1741 upperdir are intact, The "volatile" directory can be removed.
1742 Mount options for reiserfs
1744 Reiserfs is a journaling filesystem.
1745 conv
1747 Instructs version 3.6 reiserfs software to mount a version 3.5
1748 filesystem, using the 3.6 format for newly created objects. This
1749 filesystem will no longer be compatible with reiserfs 3.5 tools.
1750 hash={rupasov|tea|r5|detect}
1752 Choose which hash function reiserfs will use to find files within
1753 directories.
1754 rupasov
1756 A hash invented by Yury Yu. Rupasov. It is fast and preserves
1757 locality, mapping lexicographically close file names to close
1758 hash values. This option should not be used, as it causes a
1759 high probability of hash collisions.
1760 tea
1762 A Davis-Meyer function implemented by Jeremy Fitzhardinge. It
1763 uses hash permuting bits in the name. It gets high randomness
1764 and, therefore, low probability of hash collisions at some CPU
1765 cost. This may be used if EHASHCOLLISION errors are experienced
1766 with the r5 hash.
1767 r5
1769 A modified version of the rupasov hash. It is used by default
1770 and is the best choice unless the filesystem has huge
1771 directories and unusual file-name patterns.
1772 detect
1774 Instructs mount to detect which hash function is in use by
1775 examining the filesystem being mounted, and to write this
1776 information into the reiserfs superblock. This is only useful
1777 on the first mount of an old format filesystem.
1778 hashed_relocation
1780 Tunes the block allocator. This may provide performance
1781 improvements in some situations.
1782 no_unhashed_relocation
1784 Tunes the block allocator. This may provide performance
1785 improvements in some situations.
1786 noborder
1788 Disable the border allocator algorithm invented by Yury Yu.
1789 Rupasov. This may provide performance improvements in some
1790 situations.
1791 nolog
1793 Disable journaling. This will provide slight performance
1794 improvements in some situations at the cost of losing reiserfs’s
1795 fast recovery from crashes. Even with this option turned on,
1796 reiserfs still performs all journaling operations, save for actual
1797 writes into its journaling area. Implementation of nolog is a work
1798 in progress.
1799 notail
1801 By default, reiserfs stores small files and 'file tails' directly
1802 into its tree. This confuses some utilities such as lilo(8). This
1803 option is used to disable packing of files into the tree.
1804 replayonly
1806 Replay the transactions which are in the journal, but do not
1807 actually mount the filesystem. Mainly used by reiserfsck.
1808 resize=number
1810 A remount option which permits online expansion of reiserfs
1811 partitions. Instructs reiserfs to assume that the device has number
1812 blocks. This option is designed for use with devices which are
1813 under logical volume management (LVM). There is a special resizer
1814 utility which can be obtained from
1815 ftp://ftp.namesys.com/pub/reiserfsprogs.
1816 user_xattr
1818 Enable Extended User Attributes. See the attr(1) manual page.
1819 acl
1821 Enable POSIX Access Control Lists. See the acl(5) manual page.
1822 barrier=none / barrier=flush
1824 This disables / enables the use of write barriers in the journaling
1825 code. barrier=none disables, barrier=flush enables (default). This
1826 also requires an IO stack which can support barriers, and if
1827 reiserfs gets an error on a barrier write, it will disable barriers
1828 again with a warning. Write barriers enforce proper on-disk
1829 ordering of journal commits, making volatile disk write caches safe
1830 to use, at some performance penalty. If your disks are
1831 battery-backed in one way or another, disabling barriers may safely
1832 improve performance.
1833 Mount options for ubifs
1835 UBIFS is a flash filesystem which works on top of UBI volumes. Note
1836 that atime is not supported and is always turned off.
1837 The device name may be specified as
1839 ubiX_Y
1841 UBI device number X, volume number Y
1842 ubiY
1844 UBI device number 0, volume number Y
1845 ubiX:NAME
1847 UBI device number X, volume with name NAME
1848 ubi:NAME
1850 UBI device number 0, volume with name NAME
1851 Alternative ! separator may be used instead of :.
1853 The following mount options are available:
1855 bulk_read
1857 Enable bulk-read. VFS read-ahead is disabled because it slows down
1858 the filesystem. Bulk-Read is an internal optimization. Some flashes
1859 may read faster if the data are read at one go, rather than at
1860 several read requests. For example, OneNAND can do
1861 "read-while-load" if it reads more than one NAND page.
1862 no_bulk_read
1864 Do not bulk-read. This is the default.
1865 chk_data_crc
1867 Check data CRC-32 checksums. This is the default.
1868 no_chk_data_crc
1870 Do not check data CRC-32 checksums. With this option, the
1871 filesystem does not check CRC-32 checksum for data, but it does
1872 check it for the internal indexing information. This option only
1873 affects reading, not writing. CRC-32 is always calculated when
1874 writing the data.
1875 compr={none|lzo|zlib}
1877 Select the default compressor which is used when new files are
1878 written. It is still possible to read compressed files if mounted
1879 with the none option.
1880 Mount options for udf
1882 UDF is the "Universal Disk Format" filesystem defined by OSTA, the
1883 Optical Storage Technology Association, and is often used for DVD-ROM,
1884 frequently in the form of a hybrid UDF/ISO-9660 filesystem. It is,
1885 however, perfectly usable by itself on disk drives, flash drives and
1886 other block devices. See also iso9660.
1887 uid=
1889 Make all files in the filesystem belong to the given user.
1890 uid=forget can be specified independently of (or usually in
1891 addition to) uid=<user> and results in UDF not storing uids to the
1892 media. In fact the recorded uid is the 32-bit overflow uid -1 as
1893 defined by the UDF standard. The value is given as either <user>
1894 which is a valid user name or the corresponding decimal user id, or
1895 the special string "forget".
1896 gid=
1898 Make all files in the filesystem belong to the given group.
1899 gid=forget can be specified independently of (or usually in
1900 addition to) gid=<group> and results in UDF not storing gids to the
1901 media. In fact the recorded gid is the 32-bit overflow gid -1 as
1902 defined by the UDF standard. The value is given as either <group>
1903 which is a valid group name or the corresponding decimal group id,
1904 or the special string "forget".
1905 umask=
1907 Mask out the given permissions from all inodes read from the
1908 filesystem. The value is given in octal.
1909 mode=
1911 If mode= is set the permissions of all non-directory inodes read
1912 from the filesystem will be set to the given mode. The value is
1913 given in octal.
1914 dmode=
1916 If dmode= is set the permissions of all directory inodes read from
1917 the filesystem will be set to the given dmode. The value is given
1918 in octal.
1919 bs=
1921 Set the block size. Default value prior to kernel version 2.6.30
1922 was 2048. Since 2.6.30 and prior to 4.11 it was logical device
1923 block size with fallback to 2048. Since 4.11 it is logical block
1924 size with fallback to any valid block size between logical device
1925 block size and 4096.
1926 For other details see the mkudffs(8) 2.0+ manpage, see the
1928 COMPATIBILITY and BLOCK SIZE sections.
1929 unhide
1931 Show otherwise hidden files.
1932 undelete
1934 Show deleted files in lists.
1935 adinicb
1937 Embed data in the inode. (default)
1938 noadinicb
1940 Don’t embed data in the inode.
1941 shortad
1943 Use short UDF address descriptors.
1944 longad
1946 Use long UDF address descriptors. (default)
1947 nostrict
1949 Unset strict conformance.
1950 iocharset=
1952 Set the NLS character set. This requires kernel compiled with
1953 CONFIG_UDF_NLS option.
1954 utf8
1956 Set the UTF-8 character set.
1957 Mount options for debugging and disaster recovery
1959 novrs
1960 Ignore the Volume Recognition Sequence and attempt to mount anyway.
1961 session=
1963 Select the session number for multi-session recorded optical media.
1964 (default= last session)
1965 anchor=
1967 Override standard anchor location. (default= 256)
1968 lastblock=
1970 Set the last block of the filesystem.
1971 Unused historical mount options that may be encountered and should be
1973 removed
1974 uid=ignore
1975 Ignored, use uid=<user> instead.
1976 gid=ignore
1978 Ignored, use gid=<group> instead.
1979 volume=
1981 Unimplemented and ignored.
1982 partition=
1984 Unimplemented and ignored.
1985 fileset=
1987 Unimplemented and ignored.
1988 rootdir=
1990 Unimplemented and ignored.
1991 Mount options for ufs
1993 ufstype=value
1994 UFS is a filesystem widely used in different operating systems. The
1995 problem are differences among implementations. Features of some
1996 implementations are undocumented, so its hard to recognize the type
1997 of ufs automatically. That’s why the user must specify the type of
1998 ufs by mount option. Possible values are:
1999 old
2001 Old format of ufs, this is the default, read only. (Don’t
2002 forget to give the -r option.)
2003 44bsd
2005 For filesystems created by a BSD-like system (NetBSD, FreeBSD,
2006 OpenBSD).
2007 ufs2
2009 Used in FreeBSD 5.x supported as read-write.
2010 5xbsd
2012 Synonym for ufs2.
2013 sun
2015 For filesystems created by SunOS or Solaris on Sparc.
2016 sunx86
2018 For filesystems created by Solaris on x86.
2019 hp
2021 For filesystems created by HP-UX, read-only.
2022 nextstep
2024 For filesystems created by NeXTStep (on NeXT station)
2025 (currently read only).
2026 nextstep-cd
2028 For NextStep CDROMs (block_size == 2048), read-only.
2029 openstep
2031 For filesystems created by OpenStep (currently read only). The
2032 same filesystem type is also used by macOS.
2033 onerror=value
2035 Set behavior on error:
2036 panic
2038 If an error is encountered, cause a kernel panic.
2039 [lock|umount|repair]
2041 These mount options don’t do anything at present; when an error
2042 is encountered only a console message is printed.
2043 Mount options for umsdos
2045 See mount options for msdos. The dotsOK option is explicitly killed by
2046 umsdos.
2047 Mount options for vfat
2049 First of all, the mount options for fat are recognized. The dotsOK
2050 option is explicitly killed by vfat. Furthermore, there are
2051 uni_xlate
2053 Translate unhandled Unicode characters to special escaped
2054 sequences. This lets you backup and restore filenames that are
2055 created with any Unicode characters. Without this option, a '?' is
2056 used when no translation is possible. The escape character is ':'
2057 because it is otherwise invalid on the vfat filesystem. The escape
2058 sequence that gets used, where u is the Unicode character, is: ':',
2059 (u & 0x3f), ((u>>6) & 0x3f), (u>>12).
2060 posix
2062 Allow two files with names that only differ in case. This option is
2063 obsolete.
2064 nonumtail
2066 First try to make a short name without sequence number, before
2067 trying name~num.ext.
2068 utf8
2070 UTF8 is the filesystem safe 8-bit encoding of Unicode that is used
2071 by the console. It can be enabled for the filesystem with this
2072 option or disabled with utf8=0, utf8=no or utf8=false. If uni_xlate
2073 gets set, UTF8 gets disabled.
2074 shortname=mode
2076 Defines the behavior for creation and display of filenames which
2077 fit into 8.3 characters. If a long name for a file exists, it will
2078 always be the preferred one for display. There are four modes:
2079 lower
2081 Force the short name to lower case upon display; store a long
2082 name when the short name is not all upper case.
2083 win95
2085 Force the short name to upper case upon display; store a long
2086 name when the short name is not all upper case.
2087 winnt
2089 Display the short name as is; store a long name when the short
2090 name is not all lower case or all upper case.
2091 mixed
2093 Display the short name as is; store a long name when the short
2094 name is not all upper case. This mode is the default since
2095 Linux 2.6.32.
2096 Mount options for usbfs
2098 devuid=uid and devgid=gid and devmode=mode
2099 Set the owner and group and mode of the device files in the usbfs
2100 filesystem (default: uid=gid=0, mode=0644). The mode is given in
2101 octal.
2102 busuid=uid and busgid=gid and busmode=mode
2104 Set the owner and group and mode of the bus directories in the
2105 usbfs filesystem (default: uid=gid=0, mode=0555). The mode is given
2106 in octal.
2107 listuid=uid and listgid=gid and listmode=mode
2109 Set the owner and group and mode of the file devices (default:
2110 uid=gid=0, mode=0444). The mode is given in octal.
2111
2113 The device-mapper verity target provides read-only transparent
2114 integrity checking of block devices using kernel crypto API. The mount
2115 command can open the dm-verity device and do the integrity verification
2116 before the device filesystem is mounted. Requires libcryptsetup with in
2117 libmount (optionally via dlopen(3)). If libcryptsetup supports
2118 extracting the root hash of an already mounted device, existing devices
2119 will be automatically reused in case of a match. Mount options for
2120 dm-verity:
2121 verity.hashdevice=path
2123 Path to the hash tree device associated with the source volume to
2124 pass to dm-verity.
2125 verity.roothash=hex
2127 Hex-encoded hash of the root of verity.hashdevice. Mutually
2128 exclusive with verity.roothashfile.
2129 verity.roothashfile=path
2131 Path to file containing the hex-encoded hash of the root of
2132 verity.hashdevice. Mutually exclusive with verity.roothash.
2133 verity.hashoffset=offset
2135 If the hash tree device is embedded in the source volume, offset
2136 (default: 0) is used by dm-verity to get to the tree.
2137 verity.fecdevice=path
2139 Path to the Forward Error Correction (FEC) device associated with
2140 the source volume to pass to dm-verity. Optional. Requires kernel
2141 built with CONFIG_DM_VERITY_FEC.
2142 verity.fecoffset=offset
2144 If the FEC device is embedded in the source volume, offset
2145 (default: 0) is used by dm-verity to get to the FEC area. Optional.
2146 verity.fecroots=value
2148 Parity bytes for FEC (default: 2). Optional.
2149 verity.roothashsig=path
2151 Path to pkcs7(1ssl) signature of root hash hex string. Requires
2152 crypt_activate_by_signed_key() from cryptsetup and kernel built
2153 with CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG. For device reuse,
2154 signatures have to be either used by all mounts of a device or by
2155 none. Optional.
2156 verity.oncorruption=ignore|restart|panic
2158 Instruct the kernel to ignore, reboot or panic when corruption is
2159 detected. By default the I/O operation simply fails. Requires Linux
2160 4.1 or newer, and libcrypsetup 2.3.4 or newer. Optional.
2161 Supported since util-linux v2.35.
2163 For example commands:
2165 mksquashfs /etc /tmp/etc.squashfs
2167 dd if=/dev/zero of=/tmp/etc.hash bs=1M count=10
2168 veritysetup format /tmp/etc.squashfs /tmp/etc.hash
2169 openssl smime -sign -in <hash> -nocerts -inkey private.key \
2170 -signer private.crt -noattr -binary -outform der -out /tmp/etc.roothash.p7s
2171 mount -o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash>,\
2172 verity.roothashsig=/tmp/etc.roothash.p7s /tmp/etc.squashfs /mnt
2173 create squashfs image from /etc directory, verity hash device and mount
2175 verified filesystem image to /mnt. The kernel will verify that the root
2176 hash is signed by a key from the kernel keyring if roothashsig is used.
2177
2179 One further possible type is a mount via the loop device. For example,
2180 the command
2181 mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop3
2183 will set up the loop device /dev/loop3 to correspond to the file
2185 /tmp/disk.img, and then mount this device on /mnt.
2186 If no explicit loop device is mentioned (but just an option '-o loop'
2188 is given), then mount will try to find some unused loop device and use
2189 that, for example
2190 mount /tmp/disk.img /mnt -o loop
2192 The mount command automatically creates a loop device from a regular
2194 file if a filesystem type is not specified or the filesystem is known
2195 for libblkid, for example:
2196 mount /tmp/disk.img /mnt
2198 mount -t ext4 /tmp/disk.img /mnt
2200 This type of mount knows about three options, namely loop, offset and
2202 sizelimit, that are really options to losetup(8). (These options can be
2203 used in addition to those specific to the filesystem type.)
2204 Since Linux 2.6.25 auto-destruction of loop devices is supported,
2206 meaning that any loop device allocated by mount will be freed by umount
2207 independently of /etc/mtab.
2208 You can also free a loop device by hand, using losetup -d or umount -d.
2210 Since util-linux v2.29, mount re-uses the loop device rather than
2212 initializing a new device if the same backing file is already used for
2213 some loop device with the same offset and sizelimit. This is necessary
2214 to avoid a filesystem corruption.
2215
2217 mount has the following exit status values (the bits can be ORed):
2218 0
2220 success
2221 1
2223 incorrect invocation or permissions
2224 2
2226 system error (out of memory, cannot fork, no more loop devices)
2227 4
2229 internal mount bug
2230 8
2232 user interrupt
2233 16
2235 problems writing or locking /etc/mtab
2236 32
2238 mount failure
2239 64
2241 some mount succeeded
2242 The command mount -a returns 0 (all succeeded), 32 (all failed), or
2244 64 (some failed, some succeeded).
2245
2247 The syntax of external mount helpers is:
2248 /sbin/mount.suffix spec dir [-sfnv] [-N namespace] [-o options] [-t
2250 type.subtype]
2251 where the suffix is the filesystem type and the -sfnvoN options have
2253 the same meaning as the normal mount options. The -t option is used for
2254 filesystems with subtypes support (for example /sbin/mount.fuse -t
2255 fuse.sshfs).
2256 The command mount does not pass the mount options unbindable,
2258 runbindable, private, rprivate, slave, rslave, shared, rshared, auto,
2259 noauto, comment, x-*, loop, offset and sizelimit to the mount.<suffix>
2260 helpers. All other options are used in a comma-separated list as an
2261 argument to the -o option.
2262
2264 LIBMOUNT_FSTAB=<path>
2265 overrides the default location of the fstab file (ignored for suid)
2266 LIBMOUNT_MTAB=<path>
2268 overrides the default location of the mtab file (ignored for suid)
2269 LIBMOUNT_DEBUG=all
2271 enables libmount debug output
2272 LIBBLKID_DEBUG=all
2274 enables libblkid debug output
2275 LOOPDEV_DEBUG=all
2277 enables loop device setup debug output
2278
2280 See also "The files /etc/fstab, /etc/mtab and /proc/mounts" section
2281 above.
2282 /etc/fstab
2284 filesystem table
2285 /run/mount
2287 libmount private runtime directory
2288 /etc/mtab
2290 table of mounted filesystems or symlink to /proc/mounts
2291 /etc/mtab~
2293 lock file (unused on systems with mtab symlink)
2294 /etc/mtab.tmp
2296 temporary file (unused on systems with mtab symlink)
2297 /etc/filesystems
2299 a list of filesystem types to try
2300
2302 A mount command existed in Version 5 AT&T UNIX.
2303
2305 It is possible for a corrupted filesystem to cause a crash.
2306 Some Linux filesystems don’t support -o sync and -o dirsync (the ext2,
2308 ext3, ext4, fat and vfat filesystems do support synchronous updates (a
2309 la BSD) when mounted with the sync option).
2310 The -o remount may not be able to change mount parameters (all
2312 ext2fs-specific parameters, except sb, are changeable with a remount,
2313 for example, but you can’t change gid or umask for the fatfs).
2314 It is possible that the files /etc/mtab and /proc/mounts don’t match on
2316 systems with a regular mtab file. The first file is based only on the
2317 mount command options, but the content of the second file also depends
2318 on the kernel and others settings (e.g. on a remote NFS server — in
2319 certain cases the mount command may report unreliable information about
2320 an NFS mount point and the /proc/mount file usually contains more
2321 reliable information.) This is another reason to replace the mtab file
2322 with a symlink to the /proc/mounts file.
2323 Checking files on NFS filesystems referenced by file descriptors (i.e.
2325 the fcntl and ioctl families of functions) may lead to inconsistent
2326 results due to the lack of a consistency check in the kernel even if
2327 the noac mount option is used.
2328 The loop option with the offset or sizelimit options used may fail when
2330 using older kernels if the mount command can’t confirm that the size of
2331 the block device has been configured as requested. This situation can
2332 be worked around by using the losetup(8) command manually before
2333 calling mount with the configured loop device.
2334
2336 Karel Zak <kzak@redhat.com>
2337
2339 mount(2), umount(2), filesystems(5), fstab(5), nfs(5), xfs(5),
2340 mount_namespaces(7), xattr(7), e2label(8), findmnt(8), losetup(8),
2341 lsblk(8), mke2fs(8), mountd(8), nfsd(8), swapon(8), tune2fs(8),
2342 umount(8), xfs_admin(8)
2343
2345 For bug reports, use the issue tracker at
2346 https://github.com/util-linux/util-linux/issues.
2347
2349 The mount command is part of the util-linux package which can be
2350 downloaded from Linux Kernel Archive
2351 <https://www.kernel.org/pub/linux/utils/util-linux/>.
2352util-linux 2.38.1 2022-08-04 MOUNT(8)