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MOUNT(8) System Administration MOUNT(8)
NAME
mount - mount a filesystem
SYNOPSIS
mount [-l|-h|-V]
mount -a [-fFnrsvw] [-t fstype] [-O optlist]
mount [-fnrsvw] [-o options] device|dir
mount [-fnrsvw] [-t fstype] [-o options] device dir
DESCRIPTION
All files accessible in a Unix system are arranged in one big
tree, the file hierarchy, rooted at /. These files can be spread
out over several devices. The mount command serves to attach the
filesystem found on some device to the big file tree. Conversely,
the umount(8) command will detach it again. The filesystem is
used to control how data is stored on the device or provided in a
virtual way by network or another services.
The standard form of the mount command is:
mount -t type device dir
This tells the kernel to attach the filesystem found on device
(which is of type type) at the directory dir. The option -t type
is optional. The mount command is usually able to detect a
filesystem. The root permissions are necessary to mount a
filesystem by default. See section "Non-superuser mounts" below
for more details. The previous contents (if any) and owner and
mode of dir become invisible, and as long as this filesystem
remains mounted, the pathname dir refers to the root of the
filesystem on device.
If only the directory or the device is given, for example:
mount /dir
then mount looks for a mountpoint (and if not found then for a
device) in the /etc/fstab file. It's possible to use the --target
or --source options to avoid ambivalent interpretation of the
given argument. For example:
mount --target /mountpoint
The same filesystem may be mounted more than once, and in some
cases (e.g., network filesystems) the same filesystem may be
mounted on the same mountpoint more times. The mount command does
not implement any policy to control this behavior. All behavior is
controlled by the kernel and it is usually specific to the
filesystem driver. The exception is --all, in this case already
mounted filesystems are ignored (see --all below for more
details).
Listing the mounts
The listing mode is maintained for backward compatibility only.
For more robust and customizable output use findmnt(8), especially
in your scripts. Note that control characters in the mountpoint
name are replaced with '?'.
The following command lists all mounted filesystems (of type
type):
mount [-l] [-t type]
The option -l adds labels to this listing. See below.
Indicating the device and filesystem
Most devices are indicated by a filename (of a block special
device), like /dev/sda1, but there are other possibilities. For
example, in the case of an NFS mount, device may look like
knuth.cwi.nl:/dir. It is also possible to indicate a block spe‐
cial device using its filesystem label or UUID (see the -L and -U
options below), or its partition label or UUID. Partition identi‐
fiers are supported for example for GUID Partition Tables (GPT).
The device names of disk partitions are unstable; hardware recon‐
figuration, adding or removing a device can cause changes in
names. This is the reason why it's strongly recommended to use
filesystem or partition identifiers like UUID or LABEL.
The command lsblk --fs provides an overview of filesystems, LABELs
and UUIDs on available block devices. The command blkid -p
<device> provides details about a filesystem on the specified
device.
Don't forget that there is no guarantee that UUIDs and labels are
really unique, especially if you move, share or copy the device.
Use lsblk -o +UUID,PARTUUID to verify that the UUIDs are really
unique in your system.
The recommended setup is to use tags (e.g. UUID=uuid) rather than
/dev/disk/by-{label,uuid,partuuid,partlabel} udev symlinks in the
/etc/fstab file. Tags are more readable, robust and portable.
The mount(8) command internally uses udev symlinks, so the use of
symlinks in /etc/fstab has no advantage over tags. For more
details see libblkid(3).
Note that mount(8) uses UUIDs as strings. The UUIDs from the com‐
mand line or from fstab(5) are not converted to internal binary
representation. The string representation of the UUID should be
based on lower case characters.
The proc filesystem is not associated with a special device, and
when mounting it, an arbitrary keyword, such as proc can be used
instead of a device specification. (The customary choice none is
less fortunate: the error message `none already mounted' from
mount can be confusing.)
The files /etc/fstab, /etc/mtab and /proc/mounts
The file /etc/fstab (see fstab(5)), may contain lines describing
what devices are usually mounted where, using which options. The
default location of the fstab(5) file can be overridden with the
--fstab path command-line option (see below for more details).
The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all filesystems mentioned
in fstab (of the proper type and/or having or not having the
proper options) to be mounted as indicated, except for those whose
line contains the noauto keyword. Adding the -F option will make
mount fork, so that the filesystems are mounted simultaneously.
When mounting a filesystem mentioned in fstab or mtab, it suffices
to specify on the command line only the device, or only the mount
point.
The programs mount and umount traditionally maintained a list of
currently mounted filesystems in the file /etc/mtab. The support
for regular classic /etc/mtab is completely disabled in compile
time by default, because on current Linux systems it is better to
make it a symlink to /proc/mounts instead. The regular mtab file
maintained in userspace cannot reliably work with namespaces, con‐
tainers and other advanced Linux features. If the regular mtab
support is enabled than it's possible to use the file as well as
the symlink.
If no arguments are given to mount, the list of mounted filesys‐
tems is printed.
If you want to override mount options from /etc/fstab you have to
use the -o option:
mount device|dir -o options
and then the mount options from the command line will be appended
to the list of options from /etc/fstab. This default behaviour is
possible to change by command line option --options-mode. The
usual behavior is that the last option wins if there are conflict‐
ing ones.
The mount program does not read the /etc/fstab file if both device
(or LABEL, UUID, PARTUUID or PARTLABEL) and dir are specified.
For example, to mount device foo at /dir:
mount /dev/foo /dir
This default behaviour is possible to change by command line
option --options-source-force to always read configuration from
fstab. For non-root users mount always read fstab configuration.
Non-superuser mounts
Normally, only the superuser can mount filesystems. However, when
fstab contains the user option on a line, anybody can mount the
corresponding filesystem.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 filesystem found on an inserted
CDROM using the command:
mount /cd
Note that mount is very strict about non-root users and all paths
specified on command line are verified before fstab is parsed or a
helper program is executed. It's strongly recommended to use a
valid mountpoint to specify filesystem, otherwise mount may fail.
For example it's bad idea to use NFS or CIFS source on command
line.
Since version 2.35 mount command does not exit when user permis‐
sions are inadequate by internal libmount security rules. It
drops suid permissions and continue as regular non-root user. It
allows to support use-cases where root permissions are not neces‐
sary (e.g., fuse filesystems, user namespaces, etc).
For more details, see fstab(5). Only the user that mounted a
filesystem can unmount it again. If any user should be able to
unmount it, then use users instead of user in the fstab line. The
owner option is similar to the user option, with the restriction
that the user must be the owner of the special file. This may be
useful e.g. for /dev/fd if a login script makes the console user
owner of this device. The group option is similar, with the
restriction that the user must be member of the group of the spe‐
cial file.
Bind mount operation
Remount part of the file hierarchy somewhere else. The call is:
mount --bind olddir newdir
or by using this fstab entry:
/olddir /newdir none bind
After this call the same contents are accessible in two places.
It is important to understand that "bind" does not to create any
second-class or special node in the kernel VFS. The "bind" is just
another operation to attach a filesystem. There is nowhere stored
information that the filesystem has been attached by "bind" opera‐
tion. The olddir and newdir are independent and the olddir may be
umounted.
One can also remount a single file (on a single file). It's also
possible to use the bind mount to create a mountpoint from a regu‐
lar directory, for example:
mount --bind foo foo
The bind mount call attaches only (part of) a single filesystem,
not possible submounts. The entire file hierarchy including sub‐
mounts is attached a second place by using:
mount --rbind olddir newdir
Note that the filesystem mount options maintained by kernel will
remain the same as those on the original mount point. The
userspace mount options (e.g., _netdev) will not be copied by
mount(8) and it's necessary explicitly specify the options on
mount command line.
mount(8) since v2.27 allows to change the mount options by passing
the relevant options along with --bind. For example:
mount -o bind,ro foo foo
This feature is not supported by the Linux kernel; it is imple‐
mented in userspace by an additional mount(2) remounting system
call. This solution is not atomic.
The alternative (classic) way to create a read-only bind mount is
to use the remount operation, for example:
mount --bind olddir newdir
mount -o remount,bind,ro olddir newdir
Note that a read-only bind will create a read-only mountpoint (VFS
entry), but the original filesystem superblock will still be
writable, meaning that the olddir will be writable, but the newdir
will be read-only.
It's also possible to change nosuid, nodev, noexec, noatime, nodi‐
ratime and relatime VFS entry flags by "remount,bind" operation.
The another (for example filesystem specific flags) are silently
ignored. It's impossible to change mount options recursively (for
example with -o rbind,ro).
mount(8) since v2.31 ignores the bind flag from /etc/fstab on
remount operation (if "-o remount" specified on command line).
This is necessary to fully control mount options on remount by
command line. In the previous versions the bind flag has been
always applied and it was impossible to re-define mount options
without interaction with the bind semantic. This mount(8) behavior
does not affect situations when "remount,bind" is specified in the
/etc/fstab file.
The move operation
Move a mounted tree to another place (atomically). The call is:
mount --move olddir newdir
This will cause the contents which previously appeared under old‐
dir to now be accessible under newdir. The physical location of
the files is not changed. Note that olddir has to be a mount‐
point.
Note also that moving a mount residing under a shared mount is
invalid and unsupported. Use findmnt -o TARGET,PROPAGATION to see
the current propagation flags.
Shared subtree operations
Since Linux 2.6.15 it is possible to mark a mount and its sub‐
mounts as shared, private, slave or unbindable. A shared mount
provides the ability to create mirrors of that mount such that
mounts and unmounts within any of the mirrors propagate to the
other mirror. A slave mount receives propagation from its master,
but not vice versa. A private mount carries no propagation abili‐
ties. An unbindable mount is a private mount which cannot be
cloned through a bind operation. The detailed semantics are docu‐
mented in Documentation/filesystems/sharedsubtree.txt file in the
kernel source tree.
Supported operations are:
mount --make-shared mountpoint
mount --make-slave mountpoint
mount --make-private mountpoint
mount --make-unbindable mountpoint
The following commands allow one to recursively change the type of
all the mounts under a given mountpoint.
mount --make-rshared mountpoint
mount --make-rslave mountpoint
mount --make-rprivate mountpoint
mount --make-runbindable mountpoint
mount(8) does not read fstab(5) when a --make-* operation is
requested. All necessary information has to be specified on the
command line.
Note that the Linux kernel does not allow to change multiple prop‐
agation flags with a single mount(2) system call, and the flags
cannot be mixed with other mount options and operations.
Since util-linux 2.23 the mount command allows to do more propaga‐
tion (topology) changes by one mount(8) call and do it also
together with other mount operations. This feature is EXPERIMEN‐
TAL. The propagation flags are applied by additional mount(2)
system calls when the preceding mount operations were successful.
Note that this use case is not atomic. It is possible to specify
the propagation flags in fstab(5) as mount options (private,
slave, shared, unbindable, rprivate, rslave, rshared, runbind‐
able).
For example:
mount --make-private --make-unbindable /dev/sda1 /foo
is the same as:
mount /dev/sda1 /foo
mount --make-private /foo
mount --make-unbindable /foo
COMMAND-LINE OPTIONS
The full set of mount options used by an invocation of mount is
determined by first extracting the mount options for the filesys‐
tem from the fstab table, then applying any options specified by
the -o argument, and finally applying a -r or -w option, when
present.
The command mount does not pass all command-line options to the
/sbin/mount.suffix mount helpers. The interface between mount and
the mount helpers is described below in the section EXTERNAL
HELPERS.
Command-line options available for the mount command are:
-a, --all
Mount all filesystems (of the given types) mentioned in
fstab (except for those whose line contains the noauto key‐
word). The filesystems are mounted following their order
in fstab. The mount command compares filesystem source,
target (and fs root for bind mount or btrfs) to detect
already mounted filesystems. The kernel table with already
mounted filesystems is cached during mount --all. It means
that all duplicated fstab entries will be mounted.
The option --all is possible to use for remount operation
too. In this case all filters (-t and -O) are applied to
the table of already mounted filesystems.
Since version 2.35 is possible to use the command line
option -o to alter mount options from fstab (see also
--options-mode).
Note that it is a bad practice to use mount -a for fstab
checking. The recommended solution is findmnt --verify.
-B, --bind
Remount a subtree somewhere else (so that its contents are
available in both places). See above, under Bind mounts.
-c, --no-canonicalize
Don't canonicalize paths. The mount command canonicalizes
all paths (from command line or fstab) by default. This
option can be used together with the -f flag for already
canonicalized absolute paths. The option is designed for
mount helpers which call mount -i. It is strongly recom‐
mended to not use this command-line option for normal mount
operations.
Note that mount(8) does not pass this option to the
/sbin/mount.type helpers.
-F, --fork
(Used in conjunction with -a.) Fork off a new incarnation
of mount for each device. This will do the mounts on dif‐
ferent devices or different NFS servers in parallel. This
has the advantage that it is faster; also NFS timeouts go
in parallel. A disadvantage is that the mounts are done in
undefined order. Thus, you cannot use this option if you
want to mount both /usr and /usr/spool.
-f, --fake
Causes everything to be done except for the actual system
call; if it's not obvious, this ``fakes'' mounting the
filesystem. This option is useful in conjunction with the
-v flag to determine what the mount command is trying to
do. It can also be used to add entries for devices that
were mounted earlier with the -n option. The -f option
checks for an existing record in /etc/mtab and fails when
the record already exists (with a regular non-fake mount,
this check is done by the kernel).
-i, --internal-only
Don't call the /sbin/mount.filesystem helper even if it
exists.
-L, --label label
Mount the partition that has the specified label.
-l, --show-labels
Add the labels in the mount output. mount must have per‐
mission to read the disk device (e.g. be set-user-ID root)
for this to work. One can set such a label for ext2, ext3
or ext4 using the e2label(8) utility, or for XFS using
xfs_admin(8), or for reiserfs using reiserfstune(8).
-M, --move
Move a subtree to some other place. See above, the subsec‐
tion The move operation.
-n, --no-mtab
Mount without writing in /etc/mtab. This is necessary for
example when /etc is on a read-only filesystem.
-N, --namespace ns
Perform mount in namespace specified by ns. ns is either
PID of process running in that namespace or special file
representing that namespace.
mount(8) switches to the namespace when it reads
/etc/fstab, writes /etc/mtab (or writes to /run/mount) and
calls mount(2) system call, otherwise it runs in the origi‐
nal namespace. It means that the target namespace does not
have to contain any libraries or another requirements nec‐
essary to execute mount(2) command.
See namespaces(7) for more information.
-O, --test-opts opts
Limit the set of filesystems to which the -a option
applies. In this regard it is like the -t option except
that -O is useless without -a. For example, the command:
mount -a -O no_netdev
mounts all filesystems except those which have the option
_netdev specified in the options field in the /etc/fstab
file.
It is different from -t in that each option is matched
exactly; a leading no at the beginning of one option does
not negate the rest.
The -t and -O options are cumulative in effect; that is,
the command
mount -a -t ext2 -O _netdev
mounts all ext2 filesystems with the _netdev option, not
all filesystems that are either ext2 or have the _netdev
option specified.
-o, --options opts
Use the specified mount options. The opts argument is a
comma-separated list. For example:
mount LABEL=mydisk -o noatime,nodev,nosuid
For more details, see the FILESYSTEM-INDEPENDENT MOUNT
OPTIONS and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
--options-mode mode
Controls how to combine options from fstab/mtab with
options from command line. mode can be one of ignore,
append, prepend or replace. For example append means that
options from fstab are appended to options from command
line. Default value is prepend -- it means command line
options are evaluated after fstab options. Note that the
last option wins if there are conflicting ones.
--options-source source
Source of default options. source is comma separated list
of fstab, mtab and disable. disable disables fstab and
mtab and disables --options-source-force. Default value is
fstab,mtab.
--options-source-force
Use options from fstab/mtab even if both device and dir are
specified.
-R, --rbind
Remount a subtree and all possible submounts somewhere else
(so that its contents are available in both places). See
above, the subsection Bind mounts.
-r, --read-only
Mount the filesystem read-only. A synonym is -o ro.
Note that, depending on the filesystem type, state and ker‐
nel behavior, the system may still write to the device.
For example, ext3 and ext4 will replay the journal if the
filesystem is dirty. To prevent this kind of write access,
you may want to mount an ext3 or ext4 filesystem with the
ro,noload mount options or set the block device itself to
read-only mode, see the blockdev(8) command.
-s Tolerate sloppy mount options rather than failing. This
will ignore mount options not supported by a filesystem
type. Not all filesystems support this option. Currently
it's supported by the mount.nfs mount helper only.
--source device
If only one argument for the mount command is given then
the argument might be interpreted as target (mountpoint) or
source (device). This option allows to explicitly define
that the argument is the mount source.
--target directory
If only one argument for the mount command is given then
the argument might be interpreted as target (mountpoint) or
source (device). This option allows to explicitly define
that the argument is the mount target.
--target-prefix directory
Prepend specified directory to all mount targets. This
option allows to follow fstab, but mount operations is done
on another place, for example:
mount --all --target-prefix /chroot -o X-mount.mkdir
mounts all from system fstab to /chroot, all missing muont‐
point are created (due to X-mount.mkdir). See also --fstab
to use an alternative fstab.
-T, --fstab path
Specifies an alternative fstab file. If path is a direc‐
tory then the files in the directory are sorted by strver‐
scmp(3); files that start with "." or without an .fstab
extension are ignored. The option can be specified more
than once. This option is mostly designed for initramfs or
chroot scripts where additional configuration is specified
beyond standard system configuration.
Note that mount(8) does not pass the option --fstab to the
/sbin/mount.type helpers, meaning that the alternative
fstab files will be invisible for the helpers. This is no
problem for normal mounts, but user (non-root) mounts
always require fstab to verify the user's rights.
-t, --types fstype
The argument following the -t is used to indicate the
filesystem type. The filesystem types which are currently
supported depend on the running kernel. See /proc/filesys‐
tems and /lib/modules/$(uname -r)/kernel/fs for a complete
list of the filesystems. The most common are ext2, ext3,
ext4, xfs, btrfs, vfat, sysfs, proc, nfs and cifs.
The programs mount and umount support filesystem subtypes.
The subtype is defined by a '.subtype' suffix. For example
'fuse.sshfs'. It's recommended to use subtype notation
rather than add any prefix to the mount source (for example
'sshfs#example.com' is deprecated).
If no -t option is given, or if the auto type is specified,
mount will try to guess the desired type. Mount uses the
blkid library for guessing the filesystem type; if that
does not turn up anything that looks familiar, mount will
try to read the file /etc/filesystems, or, if that does not
exist, /proc/filesystems. All of the filesystem types
listed there will be tried, except for those that are
labeled "nodev" (e.g. devpts, proc and nfs). If
/etc/filesystems ends in a line with a single *, mount will
read /proc/filesystems afterwards. While trying, all
filesystem types will be mounted with the mount option
silent.
The auto type may be useful for user-mounted floppies.
Creating a file /etc/filesystems can be useful to change
the probe order (e.g., to try vfat before msdos or ext3
before ext2) or if you use a kernel module autoloader.
More than one type may be specified in a comma-separated
list, for option -t as well as in an /etc/fstab entry. The
list of filesystem types for option -t can be prefixed with
no to specify the filesystem types on which no action
should be taken. The prefix no has no effect when speci‐
fied in an /etc/fstab entry.
The prefix no can be meaningful with the -a option. For
example, the command
mount -a -t nomsdos,smbfs
mounts all filesystems except those of type msdos and
smbfs.
For most types all the mount program has to do is issue a
simple mount(2) system call, and no detailed knowledge of
the filesystem type is required. For a few types however
(like nfs, nfs4, cifs, smbfs, ncpfs) an ad hoc code is nec‐
essary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems
have a separate mount program. In order to make it possi‐
ble to treat all types in a uniform way, mount will execute
the program /sbin/mount.type (if that exists) when called
with type type. Since different versions of the smbmount
program have different calling conventions,
/sbin/mount.smbfs may have to be a shell script that sets
up the desired call.
-U, --uuid uuid
Mount the partition that has the specified uuid.
-v, --verbose
Verbose mode.
-w, --rw, --read-write
Mount the filesystem read/write. The read-write is kernel
default. A synonym is -o rw.
Note that specify -w on command line forces mount command
to never try read-only mount on write-protected devices.
The default is try read-only if the previous mount syscall
with read-write flags failed.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
FILESYSTEM-INDEPENDENT MOUNT OPTIONS
Some of these options are only useful when they appear in the
/etc/fstab file.
Some of these options could be enabled or disabled by default in
the system kernel. To check the current setting see the options
in /proc/mounts. Note that filesystems also have per-filesystem
specific default mount options (see for example tune2fs -l output
for extN filesystems).
The following options apply to any filesystem that is being
mounted (but not every filesystem actually honors them – e.g., the
sync option today has an effect only for ext2, ext3, ext4, fat,
vfat, ufs and xfs):
async All I/O to the filesystem should be done asynchronously.
(See also the sync option.)
atime Do not use the noatime feature, so the inode access time is
controlled by kernel defaults. See also the descriptions
of the relatime and strictatime mount options.
noatime
Do not update inode access times on this filesystem (e.g.
for faster access on the news spool to speed up news
servers). This works for all inode types (directories
too), so it implies nodiratime.
auto Can be mounted with the -a option.
noauto Can only be mounted explicitly (i.e., the -a option will
not cause the filesystem to be mounted).
context=context, fscontext=context, defcontext=context, and
rootcontext=context
The context= option is useful when mounting filesystems
that do not support extended attributes, such as a floppy
or hard disk formatted with VFAT, or systems that are not
normally running under SELinux, such as an ext3 or ext4
formatted
disk from a non-SELinux workstation. You can also use con‐
text= on filesystems you do not trust, such as a floppy.
It also helps in compatibility with xattr-supporting
filesystems on earlier 2.4.<x> kernel versions. Even where
xattrs are supported, you can save time not having to label
every file by assigning the entire disk one security con‐
text.
A commonly used option for removable media is
context="system_u:object_r:removable_t".
Two other options are fscontext= and defcontext=, both of
which are mutually exclusive of the context option. This
means you can use fscontext and defcontext with each other,
but neither can be used with context.
The fscontext= option works for all filesystems, regardless
of their xattr support. The fscontext option sets the
overarching filesystem label to a specific security con‐
text. This filesystem label is separate from the individ‐
ual labels on the files. It represents the entire filesys‐
tem for certain kinds of permission checks, such as during
mount or file creation. Individual file labels are still
obtained from the xattrs on the files themselves. The con‐
text option actually sets the aggregate context that fscon‐
text provides, in addition to supplying the same label for
individual files.
You can set the default security context for unlabeled
files using defcontext= option. This overrides the value
set for unlabeled files in the policy and requires a
filesystem that supports xattr labeling.
The rootcontext= option allows you to explicitly label the
root inode of a FS being mounted before that FS or inode
becomes visible to userspace. This was found to be useful
for things like stateless linux.
Note that the kernel rejects any remount request that
includes the context option, even when unchanged from the
current context.
Warning: the context value might contain commas, in which
case the value has to be properly quoted, otherwise
mount(8) will interpret the comma as a separator between
mount options. Don't forget that the shell strips off
quotes and thus double quoting is required. For example:
mount -t tmpfs none /mnt -o \
'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'
For more details, see selinux(8).
defaults
Use the default options: rw, suid, dev, exec, auto, nouser,
and async.
Note that the real set of all default mount options depends
on kernel and filesystem type. See the beginning of this
section for more details.
dev Interpret character or block special devices on the
filesystem.
nodev Do not interpret character or block special devices on the
file system.
diratime
Update directory inode access times on this filesystem.
This is the default. (This option is ignored when noatime
is set.)
nodiratime
Do not update directory inode access times on this filesys‐
tem. (This option is implied when noatime is set.)
dirsync
All directory updates within the filesystem should be done
synchronously. This affects the following system calls:
creat, link, unlink, symlink, mkdir, rmdir, mknod and
rename.
exec Permit execution of binaries.
noexec Do not permit direct execution of any binaries on the
mounted filesystem.
group Allow an ordinary user to mount the filesystem if one of
that user's groups matches the group of the device. This
option implies the options nosuid and nodev (unless over‐
ridden by subsequent options, as in the option line
group,dev,suid).
iversion
Every time the inode is modified, the i_version field will
be incremented.
noiversion
Do not increment the i_version inode field.
mand Allow mandatory locks on this filesystem. See fcntl(2).
nomand Do not allow mandatory locks on this filesystem.
_netdev
The filesystem resides on a device that requires network
access (used to prevent the system from attempting to mount
these filesystems until the network has been enabled on the
system).
nofail Do not report errors for this device if it does not exist.
relatime
Update inode access times relative to modify or change
time. Access time is only updated if the previous access
time was earlier than the current modify or change time.
(Similar to noatime, but it doesn't break mutt or other
applications that need to know if a file has been read
since the last time it was modified.)
Since Linux 2.6.30, the kernel defaults to the behavior
provided by this option (unless noatime was specified), and
the strictatime option is required to obtain traditional
semantics. In addition, since Linux 2.6.30, the file's
last access time is always updated if it is more than 1 day
old.
norelatime
Do not use the relatime feature. See also the strictatime
mount option.
strictatime
Allows to explicitly request full atime updates. This
makes it possible for the kernel to default to relatime or
noatime but still allow userspace to override it. For more
details about the default system mount options see
/proc/mounts.
nostrictatime
Use the kernel's default behavior for inode access time
updates.
lazytime
Only update times (atime, mtime, ctime) on the in-memory
version of the file inode.
This mount option significantly reduces writes to the inode
table for workloads that perform frequent random writes to
preallocated files.
The on-disk timestamps are updated only when:
- the inode needs to be updated for some change unrelated
to file timestamps
- the application employs fsync(2), syncfs(2), or sync(2)
- an undeleted inode is evicted from memory
- more than 24 hours have passed since the i-node was writ‐
ten to disk.
nolazytime
Do not use the lazytime feature.
suid Honor set-user-ID and set-group-ID bits or file capabili‐
ties when executing programs from this filesystem.
nosuid Do not honor set-user-ID and set-group-ID bits or file
capabilities when executing programs from this filesystem.
silent Turn on the silent flag.
loud Turn off the silent flag.
owner Allow an ordinary user to mount the filesystem if that user
is the owner of the device. This option implies the
options nosuid and nodev (unless overridden by subsequent
options, as in the option line owner,dev,suid).
remount
Attempt to remount an already-mounted filesystem. This is
commonly used to change the mount flags for a filesystem,
especially to make a readonly filesystem writable. It does
not change device or mount point.
The remount operation together with the bind flag has spe‐
cial semantic. See above, the subsection Bind mounts.
The remount functionality follows the standard way the
mount command works with options from fstab. This means
that mount does not read fstab (or mtab) only when both
device and dir are specified.
mount -o remount,rw /dev/foo /dir
After this call all old mount options are replaced and
arbitrary stuff from fstab (or mtab) is ignored, except the
loop= option which is internally generated and maintained
by the mount command.
mount -o remount,rw /dir
After this call, mount reads fstab and merges these options
with the options from the command line (-o). If no mount‐
point is found in fstab, then a remount with unspecified
source is allowed.
mount(8) allows to use --all to remount all already mounted
filesystems which match a specified filter (-O and -t).
For example:
mount --all -o remount,ro -t vfat
remounts all already mounted vfat filesystems in read-only
mode. The each of the filesystems is remounted by "mount -o
remount,ro /dir" semantic. It means the mount command reads
fstab or mtab and merges these options with the options
from the command line.
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
sync All I/O to the filesystem should be done synchronously. In
the case of media with a limited number of write cycles
(e.g. some flash drives), sync may cause life-cycle short‐
ening.
user Allow an ordinary user to mount the filesystem. The name
of the mounting user is written to the mtab file (or to the
private libmount file in /run/mount on systems without a
regular mtab) so that this same user can unmount the
filesystem again. This option implies the options noexec,
nosuid, and nodev (unless overridden by subsequent options,
as in the option line user,exec,dev,suid).
nouser Forbid an ordinary user to mount the filesystem. This is
the default; it does not imply any other options.
users Allow any user to mount and to unmount the filesystem, even
when some other ordinary user mounted it. This option
implies the options noexec, nosuid, and nodev (unless over‐
ridden by subsequent options, as in the option line
users,exec,dev,suid).
X-* All options prefixed with "X-" are interpreted as comments
or as userspace application-specific options. These
options are not stored in the user space (e.g., mtab file),
nor sent to the mount.type helpers nor to the mount(2) sys‐
tem call. The suggested format is X-appname.option.
x-* The same as X-* options, but stored permanently in the user
space. It means the options are also available for umount
or another operations. Note that maintain mount options in
user space is tricky, because it's necessary use libmount
based tools and there is no guarantee that the options will
be always available (for example after a move mount opera‐
tion or in unshared namespace).
Note that before util-linux v2.30 the x-* options have not
been maintained by libmount and stored in user space (func‐
tionality was the same as have X-* now), but due to growing
number of use-cases (in initrd, systemd etc.) the function‐
ality have been extended to keep existing fstab configura‐
tions usable without a change.
X-mount.mkdir[=mode]
Allow to make a target directory (mountpoint) if it does
not exit yet. The optional argument mode specifies the
filesystem access mode used for mkdir(2) in octal notation.
The default mode is 0755. This functionality is supported
only for root users or when mount executed without suid
permissions. The option is also supported as x-
mount.mkdir, this notation is deprecated since v2.30.
FILESYSTEM-SPECIFIC MOUNT OPTIONS
You should consult the respective man page for the filesystem
first. If you want to know what options the ext4 filesystem sup‐
ports, then check the ext4(5) man page. If that doesn't exist,
you can also check the corresponding mount page like
mount.cifs(8). Note that you might have to install the respective
userland tools.
The following options apply only to certain filesystems. We sort
them by filesystem. They all follow the -o flag.
What options are supported depends a bit on the running kernel.
More info may be found in the kernel source subdirectory Documen‐
tation/filesystems.
Mount options for adfs
uid=value and gid=value
Set the owner and group of the files in the filesystem
(default: uid=gid=0).
ownmask=value and othmask=value
Set the permission mask for ADFS 'owner' permissions and
'other' permissions, respectively (default: 0700 and 0077,
respectively). See also /usr/src/linux/Documenta‐
tion/filesystems/adfs.rst.
Mount options for affs
uid=value and gid=value
Set the owner and group of the root of the filesystem
(default: uid=gid=0, but with option uid or gid without
specified value, the UID and GID of the current process are
taken).
setuid=value and setgid=value
Set the owner and group of all files.
mode=value
Set the mode of all files to value & 0777 disregarding the
original permissions. Add search permission to directories
that have read permission. The value is given in octal.
protect
Do not allow any changes to the protection bits on the
filesystem.
usemp Set UID and GID of the root of the filesystem to the UID
and GID of the mount point upon the first sync or umount,
and then clear this option. Strange...
verbose
Print an informational message for each successful mount.
prefix=string
Prefix used before volume name, when following a link.
volume=string
Prefix (of length at most 30) used before '/' when follow‐
ing a symbolic link.
reserved=value
(Default: 2.) Number of unused blocks at the start of the
device.
root=value
Give explicitly the location of the root block.
bs=value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota|noquota|quota|usrquota
These options are accepted but ignored. (However, quota
utilities may react to such strings in /etc/fstab.)
Mount options for debugfs
The debugfs filesystem is a pseudo filesystem, traditionally
mounted on /sys/kernel/debug. As of kernel version 3.4, debugfs
has the following options:
uid=n, gid=n
Set the owner and group of the mountpoint.
mode=value
Sets the mode of the mountpoint.
Mount options for devpts
The devpts filesystem is a pseudo filesystem, traditionally
mounted on /dev/pts. In order to acquire a pseudo terminal, a
process opens /dev/ptmx; the number of the pseudo terminal is then
made available to the process and the pseudo terminal slave can be
accessed as /dev/pts/<number>.
uid=value and gid=value
This sets the owner or the group of newly created PTYs to
the specified values. When nothing is specified, they will
be set to the UID and GID of the creating process. For
example, if there is a tty group with GID 5, then gid=5
will cause newly created PTYs to belong to the tty group.
mode=value
Set the mode of newly created PTYs to the specified value.
The default is 0600. A value of mode=620 and gid=5 makes
"mesg y" the default on newly created PTYs.
newinstance
Create a private instance of devpts filesystem, such that
indices of ptys allocated in this new instance are indepen‐
dent of indices created in other instances of devpts.
All mounts of devpts without this newinstance option share
the same set of pty indices (i.e., legacy mode). Each
mount of devpts with the newinstance option has a private
set of pty indices.
This option is mainly used to support containers in the
linux kernel. It is implemented in linux kernel versions
starting with 2.6.29. Further, this mount option is valid
only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the
kernel configuration.
To use this option effectively, /dev/ptmx must be a sym‐
bolic link to pts/ptmx. See Documentation/filesys‐
tems/devpts.txt in the linux kernel source tree for
details.
ptmxmode=value
Set the mode for the new ptmx device node in the devpts
filesystem.
With the support for multiple instances of devpts (see
newinstance option above), each instance has a private ptmx
node in the root of the devpts filesystem (typically
/dev/pts/ptmx).
For compatibility with older versions of the kernel, the
default mode of the new ptmx node is 0000. ptmxmode=value
specifies a more useful mode for the ptmx node and is
highly recommended when the newinstance option is speci‐
fied.
This option is only implemented in linux kernel versions
starting with 2.6.29. Further, this option is valid only
if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the ker‐
nel configuration.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the
msdos, umsdos and vfat filesystems.)
blocksize={512|1024|2048}
Set blocksize (default 512). This option is obsolete.
uid=value and gid=value
Set the owner and group of all files. (Default: the UID
and GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process.
The value is given in octal.
dmask=value
Set the umask applied to directories only. The default is
the umask of the current process. The value is given in
octal.
fmask=value
Set the umask applied to regular files only. The default
is the umask of the current process. The value is given in
octal.
allow_utime=value
This option controls the permission check of mtime/atime.
20 If current process is in group of file's group ID,
you can change timestamp.
2 Other users can change timestamp.
The default is set from `dmask' option. (If the directory
is writable, utime(2) is also allowed. I.e. ~dmask & 022)
Normally utime(2) checks current process is owner of the
file, or it has CAP_FOWNER capability. But FAT filesystem
doesn't have UID/GID on disk, so normal check is too
inflexible. With this option you can relax it.
check=value
Three different levels of pickiness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent,
long name parts are truncated (e.g. verylong‐
name.foobar becomes verylong.foo), leading and
embedded spaces are accepted in each name part (name
and extension).
n[ormal]
Like "relaxed", but many special characters (*, ?,
<, spaces, etc.) are rejected. This is the default.
s[trict]
Like "normal", but names that contain long parts or
special characters that are sometimes used on Linux
but are not accepted by MS-DOS (+, =, etc.) are
rejected.
codepage=value
Sets the codepage for converting to shortname characters on
FAT and VFAT filesystems. By default, codepage 437 is
used.
conv=mode
This option is obsolete and may fail or being ignored.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File)
module cvf_module instead of auto-detection. If the kernel
supports kmod, the cvf_format=xxx option also controls on-
demand CVF module loading. This option is obsolete.
cvf_option=option
Option passed to the CVF module. This option is obsolete.
debug Turn on the debug flag. A version string and a list of
filesystem parameters will be printed (these data are also
printed if the parameters appear to be inconsistent).
discard
If set, causes discard/TRIM commands to be issued to the
block device when blocks are freed. This is useful for SSD
devices and sparse/thinly-provisioned LUNs.
dos1xfloppy
If set, use a fallback default BIOS Parameter Block config‐
uration, determined by backing device size. These static
parameters match defaults assumed by DOS 1.x for 160 kiB,
180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
errors={panic|continue|remount-ro}
Specify FAT behavior on critical errors: panic, continue
without doing anything, or remount the partition in read-
only mode (default behavior).
fat={12|16|32}
Specify a 12, 16 or 32 bit fat. This overrides the auto‐
matic FAT type detection routine. Use with caution!
iocharset=value
Character set to use for converting between 8 bit charac‐
ters and 16 bit Unicode characters. The default is
iso8859-1. Long filenames are stored on disk in Unicode
format.
nfs={stale_rw|nostale_ro}
Enable this only if you want to export the FAT filesystem
over NFS.
stale_rw: This option maintains an index (cache) of direc‐
tory inodes which is used by the nfs-related code to
improve look-ups. Full file operations (read/write) over
NFS are supported but with cache eviction at NFS server,
this could result in spurious ESTALE errors.
nostale_ro: This option bases the inode number and file
handle on the on-disk location of a file in the FAT direc‐
tory entry. This ensures that ESTALE will not be returned
after a file is evicted from the inode cache. However, it
means that operations such as rename, create and unlink
could cause file handles that previously pointed at one
file to point at a different file, potentially causing data
corruption. For this reason, this option also mounts the
filesystem readonly.
To maintain backward compatibility, '-o nfs' is also
accepted, defaulting to stale_rw.
tz=UTC This option disables the conversion of timestamps between
local time (as used by Windows on FAT) and UTC (which Linux
uses internally). This is particularly useful when mount‐
ing devices (like digital cameras) that are set to UTC in
order to avoid the pitfalls of local time.
time_offset=minutes
Set offset for conversion of timestamps from local time
used by FAT to UTC. I.e., minutes will be subtracted from
each timestamp to convert it to UTC used internally by
Linux. This is useful when the time zone set in the kernel
via settimeofday(2) is not the time zone used by the
filesystem. Note that this option still does not provide
correct time stamps in all cases in presence of DST - time
stamps in a different DST setting will be off by one hour.
quiet Turn on the quiet flag. Attempts to chown or chmod files
do not return errors, although they fail. Use with cau‐
tion!
rodir FAT has the ATTR_RO (read-only) attribute. On Windows, the
ATTR_RO of the directory will just be ignored, and is used
only by applications as a flag (e.g. it's set for the cus‐
tomized folder).
If you want to use ATTR_RO as read-only flag even for the
directory, set this option.
showexec
If set, the execute permission bits of the file will be
allowed only if the extension part of the name is .EXE,
.COM, or .BAT. Not set by default.
sys_immutable
If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE
flag on Linux. Not set by default.
flush If set, the filesystem will try to flush to disk more early
than normal. Not set by default.
usefree
Use the "free clusters" value stored on FSINFO. It'll be
used to determine number of free clusters without scanning
disk. But it's not used by default, because recent Windows
don't update it correctly in some case. If you are sure
the "free clusters" on FSINFO is correct, by this option
you can avoid scanning disk.
dots, nodots, dotsOK=[yes|no]
Various misguided attempts to force Unix or DOS conventions
onto a FAT filesystem.
Mount options for hfs
creator=cccc, type=cccc
Set the creator/type values as shown by the MacOS finder
used for creating new files. Default values: '????'.
uid=n, gid=n
Set the owner and group of all files. (Default: the UID
and GID of the current process.)
dir_umask=n, file_umask=n, umask=n
Set the umask used for all directories, all regular files,
or all files and directories. Defaults to the umask of the
current process.
session=n
Select the CDROM session to mount. Defaults to leaving
that decision to the CDROM driver. This option will fail
with anything but a CDROM as underlying device.
part=n Select partition number n from the device. Only makes
sense for CDROMs. Defaults to not parsing the partition
table at all.
quiet Don't complain about invalid mount options.
Mount options for hpfs
uid=value and gid=value
Set the owner and group of all files. (Default: the UID and
GID of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process.
The value is given in octal.
case={lower|asis}
Convert all files names to lower case, or leave them.
(Default: case=lower.)
conv=mode
This option is obsolete and may fail or being ignored.
nocheck
Do not abort mounting when certain consistency checks fail.
Mount options for iso9660
ISO 9660 is a standard describing a filesystem structure to be
used on CD-ROMs. (This filesystem type is also seen on some DVDs.
See also the udf filesystem.)
Normal iso9660 filenames appear in an 8.3 format (i.e., DOS-like
restrictions on filename length), and in addition all characters
are in upper case. Also there is no field for file ownership,
protection, number of links, provision for block/character
devices, etc.
Rock Ridge is an extension to iso9660 that provides all of these
UNIX-like features. Basically there are extensions to each direc‐
tory record that supply all of the additional information, and
when Rock Ridge is in use, the filesystem is indistinguishable
from a normal UNIX filesystem (except that it is read-only, of
course).
norock Disable the use of Rock Ridge extensions, even if avail‐
able. Cf. map.
nojoliet
Disable the use of Microsoft Joliet extensions, even if
available. Cf. map.
check={r[elaxed]|s[trict]}
With check=relaxed, a filename is first converted to lower
case before doing the lookup. This is probably only mean‐
ingful together with norock and map=normal. (Default:
check=strict.)
uid=value and gid=value
Give all files in the filesystem the indicated user or
group id, possibly overriding the information found in the
Rock Ridge extensions. (Default: uid=0,gid=0.)
map={n[ormal]|o[ff]|a[corn]}
For non-Rock Ridge volumes, normal name translation maps
upper to lower case ASCII, drops a trailing `;1', and con‐
verts `;' to `.'. With map=off no name translation is
done. See norock. (Default: map=normal.) map=acorn is
like map=normal but also apply Acorn extensions if present.
mode=value
For non-Rock Ridge volumes, give all files the indicated
mode. (Default: read and execute permission for every‐
body.) Octal mode values require a leading 0.
unhide Also show hidden and associated files. (If the ordinary
files and the associated or hidden files have the same
filenames, this may make the ordinary files inaccessible.)
block={512|1024|2048}
Set the block size to the indicated value. (Default:
block=1024.)
conv=mode
This option is obsolete and may fail or being ignored.
cruft If the high byte of the file length contains other garbage,
set this mount option to ignore the high order bits of the
file length. This implies that a file cannot be larger
than 16 MB.
session=x
Select number of session on multisession CD.
sbsector=xxx
Session begins from sector xxx.
The following options are the same as for vfat and specifying them
only makes sense when using discs encoded using Microsoft's Joliet
extensions.
iocharset=value
Character set to use for converting 16 bit Unicode charac‐
ters on CD to 8 bit characters. The default is iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for jfs
iocharset=name
Character set to use for converting from Unicode to ASCII.
The default is to do no conversion. Use iocharset=utf8 for
UTF8 translations. This requires CONFIG_NLS_UTF8 to be set
in the kernel .config file.
resize=value
Resize the volume to value blocks. JFS only supports grow‐
ing a volume, not shrinking it. This option is only valid
during a remount, when the volume is mounted read-write.
The resize keyword with no value will grow the volume to
the full size of the partition.
nointegrity
Do not write to the journal. The primary use of this
option is to allow for higher performance when restoring a
volume from backup media. The integrity of the volume is
not guaranteed if the system abnormally ends.
integrity
Default. Commit metadata changes to the journal. Use this
option to remount a volume where the nointegrity option was
previously specified in order to restore normal behavior.
errors={continue|remount-ro|panic}
Define the behavior when an error is encountered. (Either
ignore errors and just mark the filesystem erroneous and
continue, or remount the filesystem read-only, or panic and
halt the system.)
noquota|quota|usrquota|grpquota
These options are accepted but ignored.
Mount options for msdos
See mount options for fat. If the msdos filesystem detects an
inconsistency, it reports an error and sets the file system read-
only. The filesystem can be made writable again by remounting it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument
(a struct ncp_mount_data) to the mount system call. This argument
is constructed by ncpmount(8) and the current version of mount
(2.12) does not know anything about ncpfs.
Mount options for ntfs
iocharset=name
Character set to use when returning file names. Unlike
VFAT, NTFS suppresses names that contain nonconvertible
characters. Deprecated.
nls=name
New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
uni_xlate={0|1|2}
For 0 (or `no' or `false'), do not use escape sequences for
unknown Unicode characters. For 1 (or `yes' or `true') or
2, use vfat-style 4-byte escape sequences starting with
":". Here 2 give a little-endian encoding and 1 a
byteswapped bigendian encoding.
posix=[0|1]
If enabled (posix=1), the filesystem distinguishes between
upper and lower case. The 8.3 alias names are presented as
hard links instead of being suppressed. This option is
obsolete.
uid=value, gid=value and umask=value
Set the file permission on the filesystem. The umask value
is given in octal. By default, the files are owned by root
and not readable by somebody else.
Mount options for overlay
Since Linux 3.18 the overlay pseudo filesystem implements a union
mount for other filesystems.
An overlay filesystem combines two filesystems - an upper filesys‐
tem and a lower filesystem. When a name exists in both filesys‐
tems, the object in the upper filesystem is visible while the
object in the lower filesystem is either hidden or, in the case of
directories, merged with the upper object.
The lower filesystem can be any filesystem supported by Linux and
does not need to be writable. The lower filesystem can even be
another overlayfs. The upper filesystem will normally be writable
and if it is it must support the creation of trusted.* extended
attributes, and must provide a valid d_type in readdir responses,
so NFS is not suitable.
A read-only overlay of two read-only filesystems may use any
filesystem type. The options lowerdir and upperdir are combined
into a merged directory by using:
mount -t overlay overlay \
-olowerdir=/lower,upperdir=/upper,workdir=/work /merged
lowerdir=directory
Any filesystem, does not need to be on a writable filesys‐
tem.
upperdir=directory
The upperdir is normally on a writable filesystem.
workdir=directory
The workdir needs to be an empty directory on the same
filesystem as upperdir.
Mount options for reiserfs
Reiserfs is a journaling filesystem.
conv Instructs version 3.6 reiserfs software to mount a version
3.5 filesystem, using the 3.6 format for newly created
objects. This filesystem will no longer be compatible with
reiserfs 3.5 tools.
hash={rupasov|tea|r5|detect}
Choose which hash function reiserfs will use to find files
within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast and
preserves locality, mapping lexicographically close
file names to close hash values. This option should
not be used, as it causes a high probability of hash
collisions.
tea A Davis-Meyer function implemented by Jeremy
Fitzhardinge. It uses hash permuting bits in the
name. It gets high randomness and, therefore, low
probability of hash collisions at some CPU cost.
This may be used if EHASHCOLLISION errors are expe‐
rienced with the r5 hash.
r5 A modified version of the rupasov hash. It is used
by default and is the best choice unless the
filesystem has huge directories and unusual file-
name patterns.
detect Instructs mount to detect which hash function is in
use by examining the filesystem being mounted, and
to write this information into the reiserfs
superblock. This is only useful on the first mount
of an old format filesystem.
hashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
noborder
Disable the border allocator algorithm invented by Yury Yu.
Rupasov. This may provide performance improvements in some
situations.
nolog Disable journaling. This will provide slight performance
improvements in some situations at the cost of losing reis‐
erfs's fast recovery from crashes. Even with this option
turned on, reiserfs still performs all journaling opera‐
tions, save for actual writes into its journaling area.
Implementation of nolog is a work in progress.
notail By default, reiserfs stores small files and `file tails'
directly into its tree. This confuses some utilities such
as LILO(8). This option is used to disable packing of
files into the tree.
replayonly
Replay the transactions which are in the journal, but do
not actually mount the filesystem. Mainly used by reiserf‐
sck.
resize=number
A remount option which permits online expansion of reiserfs
partitions. Instructs reiserfs to assume that the device
has number blocks. This option is designed for use with
devices which are under logical volume management (LVM).
There is a special resizer utility which can be obtained
from ftp://ftp.namesys.com/pub/reiserfsprogs.
user_xattr
Enable Extended User Attributes. See the attr(1) manual
page.
acl Enable POSIX Access Control Lists. See the acl(5) manual
page.
barrier=none / barrier=flush
This disables / enables the use of write barriers in the
journaling code. barrier=none disables, barrier=flush
enables (default). This also requires an IO stack which
can support barriers, and if reiserfs gets an error on a
barrier write, it will disable barriers again with a warn‐
ing. Write barriers enforce proper on-disk ordering of
journal commits, making volatile disk write caches safe to
use, at some performance penalty. If your disks are bat‐
tery-backed in one way or another, disabling barriers may
safely improve performance.
Mount options for ubifs
UBIFS is a flash filesystem which works on top of UBI volumes.
Note that atime is not supported and is always turned off.
The device name may be specified as
ubiX_Y UBI device number X, volume number Y
ubiY UBI device number 0, volume number Y
ubiX:NAME
UBI device number X, volume with name NAME
ubi:NAME
UBI device number 0, volume with name NAME
Alternative ! separator may be used instead of :.
The following mount options are available:
bulk_read
Enable bulk-read. VFS read-ahead is disabled because it
slows down the file system. Bulk-Read is an internal opti‐
mization. Some flashes may read faster if the data are
read at one go, rather than at several read requests. For
example, OneNAND can do "read-while-load" if it reads more
than one NAND page.
no_bulk_read
Do not bulk-read. This is the default.
chk_data_crc
Check data CRC-32 checksums. This is the default.
no_chk_data_crc.
Do not check data CRC-32 checksums. With this option, the
filesystem does not check CRC-32 checksum for data, but it
does check it for the internal indexing information. This
option only affects reading, not writing. CRC-32 is always
calculated when writing the data.
compr={none|lzo|zlib}
Select the default compressor which is used when new files
are written. It is still possible to read compressed files
if mounted with the none option.
Mount options for udf
UDF is the "Universal Disk Format" filesystem defined by OSTA, the
Optical Storage Technology Association, and is often used for DVD-
ROM, frequently in the form of a hybrid UDF/ISO-9660 filesystem.
It is, however, perfectly usable by itself on disk drives, flash
drives and other block devices. See also iso9660.
uid= Make all files in the filesystem belong to the given user.
uid=forget can be specified independently of (or usually in
addition to) uid=<user> and results in UDF not storing uids
to the media. In fact the recorded uid is the 32-bit over‐
flow uid -1 as defined by the UDF standard. The value is
given as either <user> which is a valid user name or the
corresponding decimal user id, or the special string "for‐
get".
gid= Make all files in the filesystem belong to the given group.
gid=forget can be specified independently of (or usually in
addition to) gid=<group> and results in UDF not storing
gids to the media. In fact the recorded gid is the 32-bit
overflow gid -1 as defined by the UDF standard. The value
is given as either <group> which is a valid group name or
the corresponding decimal group id, or the special string
"forget".
umask= Mask out the given permissions from all inodes read from
the filesystem. The value is given in octal.
mode= If mode= is set the permissions of all non-directory inodes
read from the filesystem will be set to the given mode. The
value is given in octal.
dmode= If dmode= is set the permissions of all directory inodes
read from the filesystem will be set to the given dmode.
The value is given in octal.
bs= Set the block size. Default value prior to kernel version
2.6.30 was 2048. Since 2.6.30 and prior to 4.11 it was log‐
ical device block size with fallback to 2048. Since 4.11 it
is logical block size with fallback to any valid block size
between logical device block size and 4096.
For other details see the mkudffs(8) 2.0+ manpage, sections
COMPATIBILITY and BLOCK SIZE.
unhide Show otherwise hidden files.
undelete
Show deleted files in lists.
adinicb
Embed data in the inode. (default)
noadinicb
Don't embed data in the inode.
shortad
Use short UDF address descriptors.
longad Use long UDF address descriptors. (default)
nostrict
Unset strict conformance.
iocharset=
Set the NLS character set. This requires kernel compiled
with CONFIG_UDF_NLS option.
utf8 Set the UTF-8 character set.
Mount options for debugging and disaster recovery
novrs Ignore the Volume Recognition Sequence and attempt to mount
anyway.
session=
Select the session number for multi-session recorded opti‐
cal media. (default= last session)
anchor=
Override standard anchor location. (default= 256)
lastblock=
Set the last block of the filesystem.
Unused historical mount options that may be encountered and should be
removed
uid=ignore
Ignored, use uid=<user> instead.
gid=ignore
Ignored, use gid=<group> instead.
volume=
Unimplemented and ignored.
partition=
Unimplemented and ignored.
fileset=
Unimplemented and ignored.
rootdir=
Unimplemented and ignored.
Mount options for ufs
ufstype=value
UFS is a filesystem widely used in different operating sys‐
tems. The problem are differences among implementations.
Features of some implementations are undocumented, so its
hard to recognize the type of ufs automatically. That's
why the user must specify the type of ufs by mount option.
Possible values are:
old Old format of ufs, this is the default, read only.
(Don't forget to give the -r option.)
44bsd For filesystems created by a BSD-like system (Net‐
BSD, FreeBSD, OpenBSD).
ufs2 Used in FreeBSD 5.x supported as read-write.
5xbsd Synonym for ufs2.
sun For filesystems created by SunOS or Solaris on
Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT sta‐
tion) (currently read only).
nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
openstep
For filesystems created by OpenStep (currently read
only). The same filesystem type is also used by Mac
OS X.
onerror=value
Set behavior on error:
panic If an error is encountered, cause a kernel panic.
[lock|umount|repair]
These mount options don't do anything at present;
when an error is encountered only a console message
is printed.
Mount options for umsdos
See mount options for msdos. The dotsOK option is explicitly
killed by umsdos.
Mount options for vfat
First of all, the mount options for fat are recognized. The dot‐
sOK option is explicitly killed by vfat. Furthermore, there are
uni_xlate
Translate unhandled Unicode characters to special escaped
sequences. This lets you backup and restore filenames that
are created with any Unicode characters. Without this
option, a '?' is used when no translation is possible. The
escape character is ':' because it is otherwise invalid on
the vfat filesystem. The escape sequence that gets used,
where u is the Unicode character, is: ':', (u & 0x3f),
((u>>6) & 0x3f), (u>>12).
posix Allow two files with names that only differ in case. This
option is obsolete.
nonumtail
First try to make a short name without sequence number,
before trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that
is used by the console. It can be enabled for the filesys‐
tem with this option or disabled with utf8=0, utf8=no or
utf8=false. If `uni_xlate' gets set, UTF8 gets disabled.
shortname=mode
Defines the behavior for creation and display of filenames
which fit into 8.3 characters. If a long name for a file
exists, it will always be the preferred one for display.
There are four modes:
lower Force the short name to lower case upon display;
store a long name when the short name is not all
upper case.
win95 Force the short name to upper case upon display;
store a long name when the short name is not all
upper case.
winnt Display the short name as is; store a long name when
the short name is not all lower case or all upper
case.
mixed Display the short name as is; store a long name when
the short name is not all upper case. This mode is
the default since Linux 2.6.32.
Mount options for usbfs
devuid=uid and devgid=gid and devmode=mode
Set the owner and group and mode of the device files in the
usbfs filesystem (default: uid=gid=0, mode=0644). The mode
is given in octal.
busuid=uid and busgid=gid and busmode=mode
Set the owner and group and mode of the bus directories in
the usbfs filesystem (default: uid=gid=0, mode=0555). The
mode is given in octal.
listuid=uid and listgid=gid and listmode=mode
Set the owner and group and mode of the file devices
(default: uid=gid=0, mode=0444). The mode is given in
octal.
DM-VERITY SUPPORT (experimental)
The device-mapper verity target provides read-only transparent
integrity checking of block devices using kernel crypto API. The
mount command can open the dm-verity device and do the integrity
verification before on the device filesystem is mounted. Requires
libcryptsetup with in libmount. If libcryptsetup supports
extracting the root hash of an already mounted device, existing
devices will be automatically reused in case of a match. Mount
options for dm-verity:
verity.hashdevice=path
Path to the hash tree device associated with the source
volume to pass to dm-verity.
verity.roothash=hex
Hex-encoded hash of the root of verity.hashdevice Mutually
exclusive with verity.roothashfile.
verity.roothashfile=path
Path to file containing the hex-encoded hash of the root of
verity.hashdevice. Mutually exclusive with ver‐
ity.roothash.
verity.hashoffset=offset
If the hash tree device is embedded in the source volume,
offset (default: 0) is used by dm-verity to get to the
tree.
verity.fecdevice=path
Path to the Forward Error Correction (FEC) device associ‐
ated with the source volume to pass to dm-verity.
Optional. Requires kernel built with CONFIG_DM_VERITY_FEC.
verity.fecoffset=offset
If the FEC device is embedded in the source volume, offset
(default: 0) is used by dm-verity to get to the FEC area.
Optional.
verity.fecroots=value
Parity bytes for FEC (default: 2). Optional.
Supported since util-linux v2.35.
For example commands:
mksquashfs /etc /tmp/etc.squashfs
dd if=/dev/zero of=/tmp/etc.hash bs=1M count=10
veritysetup format /tmp/etc.squashfs /tmp/etc.hash
mount -o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash> /tmp/etc.squashfs /mnt
create squashfs image from /etc directory, verity hash device and
mount verified filesystem image to /mnt.
LOOP-DEVICE SUPPORT
One further possible type is a mount via the loop device. For
example, the command
mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop3
will set up the loop device /dev/loop3 to correspond to the file
/tmp/disk.img, and then mount this device on /mnt.
If no explicit loop device is mentioned (but just an option `-o
loop' is given), then mount will try to find some unused loop
device and use that, for example
mount /tmp/disk.img /mnt -o loop
The mount command automatically creates a loop device from a regu‐
lar file if a filesystem type is not specified or the filesystem
is known for libblkid, for example:
mount /tmp/disk.img /mnt
mount -t ext4 /tmp/disk.img /mnt
This type of mount knows about three options, namely loop, offset
and sizelimit, that are really options to losetup(8). (These
options can be used in addition to those specific to the filesys‐
tem type.)
Since Linux 2.6.25 auto-destruction of loop devices is supported,
meaning that any loop device allocated by mount will be freed by
umount independently of /etc/mtab.
You can also free a loop device by hand, using losetup -d or
umount -d.
Since util-linux v2.29 mount command re-uses the loop device
rather than initialize a new device if the same backing file is
already used for some loop device with the same offset and size‐
limit. This is necessary to avoid a filesystem corruption.
RETURN CODES
mount has the following return codes (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop
devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
The command mount -a returns 0 (all succeeded), 32 (all
failed), or 64 (some failed, some succeeded).
EXTERNAL HELPERS
The syntax of external mount helpers is:
/sbin/mount.suffix spec dir [-sfnv] [-N namespace] [-o
options] [-t type.subtype]
where the suffix is the filesystem type and the -sfnvoN options
have the same meaning as the normal mount options. The -t option
is used for filesystems with subtypes support (for example
/sbin/mount.fuse -t fuse.sshfs).
The command mount does not pass the mount options unbindable, run‐
bindable, private, rprivate, slave, rslave, shared, rshared, auto,
noauto, comment, x-*, loop, offset and sizelimit to the
mount.<suffix> helpers. All other options are used in a comma-
separated list as argument to the -o option.
FILES
See also "The files /etc/fstab, /etc/mtab and /proc/mounts" sec‐
tion above.
/etc/fstab filesystem table
/run/mount libmount private runtime directory
/etc/mtab table of mounted filesystems or symlink to
/proc/mounts
/etc/mtab~ lock file (unused on systems with mtab symlink)
/etc/mtab.tmp temporary file (unused on systems with mtab sym‐
link)
/etc/filesystems a list of filesystem types to try
ENVIRONMENT
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file (ignored
for suid)
LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file (ignored
for suid)
LIBMOUNT_DEBUG=all
enables libmount debug output
LIBBLKID_DEBUG=all
enables libblkid debug output
LOOPDEV_DEBUG=all
enables loop device setup debug output
SEE ALSO
mount(2), umount(2), umount(8), fstab(5), nfs(5), xfs(5),
e2label(8), findmnt(8), losetup(8), mke2fs(8), mountd(8), nfsd(8),
swapon(8), tune2fs(8), xfs_admin(8)
BUGS
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don't support -o sync nor -o dirsync (the
ext2, ext3, ext4, fat and vfat filesystems do support synchronous
updates (a la BSD) when mounted with the sync option).
The -o remount may not be able to change mount parameters (all
ext2fs-specific parameters, except sb, are changeable with a
remount, for example, but you can't change gid or umask for the
fatfs).
It is possible that the files /etc/mtab and /proc/mounts don't
match on systems with a regular mtab file. The first file is
based only on the mount command options, but the content of the
second file also depends on the kernel and others settings (e.g.
on a remote NFS server -- in certain cases the mount command may
report unreliable information about an NFS mount point and the
/proc/mounts file usually contains more reliable information.)
This is another reason to replace the mtab file with a symlink to
the /proc/mounts file.
Checking files on NFS filesystems referenced by file descriptors
(i.e. the fcntl and ioctl families of functions) may lead to
inconsistent results due to the lack of a consistency check in the
kernel even if noac is used.
The loop option with the offset or sizelimit options used may fail
when using older kernels if the mount command can't confirm that
the size of the block device has been configured as requested.
This situation can be worked around by using the losetup command
manually before calling mount with the configured loop device.
HISTORY
A mount command existed in Version 5 AT&T UNIX.
AUTHORS
Karel Zak <kzak@redhat.com>
AVAILABILITY
The mount command is part of the util-linux package and is avail‐
able from https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux August 2015 MOUNT(8)