MOUNT
Section: System Administration (8)
Updated: July 2014
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NAME
mount - mount a filesystem
SYNOPSIS
mount
[
-lhV]
mount -a
[-fFnrsvw]
[-t
vfstype]
[-O
optlist]
mount
[-fnrsvw]
[-o
option[,option]...]
device|dir
mount
[-fnrsvw]
[-t
vfstype]
[-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 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 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 listing.
-
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.
The device indication.
-
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 special device using its filesystem label
or UUID (see the -L and -U options below), or its partition label
or UUID. (Partition identifiers are supported for example for GUID Partition
Tables (GPT).)
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. LABEL=label) 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 command 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 busy' from
umount
can be confusing.)
The /etc/fstab, /etc/mtab and /proc/mounts files.
-
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 list of currently mounted filesystems in the file
/etc/mtab.
The mtab file is still supported, but it's recommended to use a symlink to
the file
/proc/mounts
rather than the regular mtab file on the current Linux systems.
The mtab file maintained in userspace cannot reliably work with namespaces, containers
and another advanced Linux features.
If no arguments are given to
mount,
this list 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.
The usual behavior is that the last option wins if there are conflicting
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
The 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 /dev/cdrom
or
-
mount /cd
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 special file.
The bind mounts.
-
Since Linux 2.4.0 it is possible to 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.
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 regular
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 submounts is attached
a second place by using:
-
mount --rbind
olddir newdir
Note that the filesystem mount options will remain the same as those
on the original mount point, and cannot be changed by passing the
-o
option along with
--bind/--rbind.
The mount options can be
changed by a separate remount command, for example:
-
mount --bind
olddir newdir
mount -o remount,ro
newdir
Note that the behavior of the remount operation depends on the /etc/mtab file.
The first command stores the 'bind' flag in the /etc/mtab file and the second
command reads the flag from the file. If you have a system without the
/etc/mtab file or if you explicitly define source and target for the remount
command (then mount(8) does not read /etc/mtab), then you have to use
the bind flag (or option) for the remount command too. For example:
-
mount --bind
olddir newdir
mount -o remount,ro,bind
olddir newdir
Note that
remount,ro,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.
The move operation.
-
Since Linux 2.5.1 it is possible to atomically move a
mounted tree
to another place. The call is:
-
mount --move
olddir newdir
This will cause the contents which previously appeared under
olddir
to now be accessible under
newdir.
The physical location of the files is not changed.
Note that
olddir
has to be a mountpoint.
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.
The shared subtree operations.
-
Since Linux 2.6.15 it is possible to mark a mount and its submounts 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 abilities. An
unbindable mount is a private mount which cannot be cloned through a bind
operation. The detailed semantics are documented 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 propagation flags
with a single
mount(2)
syscall, and the flags cannot be mixed with other mount options.
Since util-linux 2.23 the mount command allows to use several propagation flags
together and also together with other mount operations. This feature is EXPERIMENTAL.
The propagation flags are applied by additional mount(2) syscalls when the
preceeding 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,
runbindable).
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 filesystem 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:
- -V, --version
-
Display version information and exit.
- -h, --help
-
Display help text and exit.
- -v, --verbose
-
Verbose mode.
- -a, --all
-
Mount all filesystems (of the given types) mentioned in
fstab
(except for those whose line contains the
noauto
keyword). The filesystems are mounted following their order in
fstab.
- -F, --fork
-
(Used in conjunction with
-a.)
Fork off a new incarnation of mount for each device.
This will do the mounts on different 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, --show-labels
-
Add the labels in the mount output. mount must have
permission to read the disk device (e.g. be suid 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).
- -n, --no-mtab
-
Mount without writing in
/etc/mtab.
This is necessary for example when
/etc
is on a read-only filesystem.
- -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 recommended 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.
- -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 dev
-
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 dir
-
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.
- -r, --read-only
-
Mount the filesystem read-only. A synonym is
-o ro.
Note that, depending on the filesystem type, state and kernel 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.
- -w, --rw, --read-write
-
Mount the filesystem read/write. This is the default. A synonym is
-o rw.
- -L, --label label
-
Mount the partition that has the specified
label.
- -U, --uuid uuid
-
Mount the partition that has the specified
uuid.
These two options require the file
/proc/partitions
(present since Linux 2.1.116) to exist.
- -T, --fstab path
-
Specifies an alternative fstab file. If path is a directory then the files
in the directory are sorted by
strverscmp(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 vfstype
-
The argument following the
-t
is used to indicate the filesystem type. The filesystem types which are
currently supported include:
adfs,
affs,
autofs,
btrfs,
cifs,
coda,
coherent,
cramfs,
debugfs,
devpts,
efs,
ext,
ext2,
ext3,
ext4,
hfs,
hfsplus,
hpfs,
iso9660,
jfs,
minix,
msdos,
ncpfs,
nfs,
nfs4,
ntfs,
proc,
qnx4,
ramfs,
reiserfs,
romfs,
squashfs,
smbfs,
sysv,
tmpfs,
ubifs,
udf,
ufs,
umsdos,
usbfs,
vfat,
xenix,
xfs,
xiafs.
Note that coherent, sysv and xenix are equivalent and that
xenix
and
coherent
will be removed at some point in the future - use
sysv
instead. Since kernel version 2.1.21 the types
ext
and
xiafs
do not exist anymore. Earlier,
usbfs
was known as
usbdevfs.
Note, the real list of all supported filesystems depends on your
kernel.
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).
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
necessary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems
have a separate mount program. In order to make it possible 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.
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. The list of filesystem types can be prefixed with
no
to specify the filesystem types on which no action should be taken.
(This can be meaningful with the
-a
option.) For example, the command
-
-
mount -a -t nomsdos,ext
mounts all filesystems except those of type
msdos
and
ext.
- -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.
- -B, --bind
-
Remount a subtree somewhere else (so that its contents are available
in both places). See above.
- -R, --rbind
-
Remount a subtree and all possible submounts somewhere else (so that its
contents are available in both places). See above.
- -M, --move
-
Move a subtree to some other place. See above.
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, fat, vfat and ufs):
- 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
strictatime
and
relatime
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).
- 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 formatted
disk from a non-SELinux workstation. You can also use
context=
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 context.
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 context. This filesystem label is separate from the
individual labels on the files. It represents the entire filesystem 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 context option actually sets the aggregate context that
fscontext 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.
- nodiratime
-
Do not update directory inode access times on this filesystem.
- 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.
(Until recently it was possible to run binaries anyway using a command like
/lib/ld*.so /mnt/binary. This trick fails since Linux 2.4.25 / 2.6.0.)
- group
-
Allow an ordinary (i.e., non-root) user to mount the filesystem if one
of his groups matches the group of the device.
This option implies the options
nosuid and nodev
(unless overridden 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.
- suid
-
Allow set-user-identifier or set-group-identifier bits to take
effect.
- nosuid
-
Do not allow set-user-identifier or set-group-identifier bits to take
effect.
- silent
-
Turn on the silent flag.
- loud
-
Turn off the silent flag.
- owner
-
Allow an ordinary (i.e., non-root) user to mount the filesystem if he
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 functionality follows the standard way the mount command works
with options from fstab. This means that the mount command only doesn't
read fstab (or mtab) when both the
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 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 (or mtab) and merges these options with
the options from the command line (-o).
- 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 shortening.
- user
-
Allow an ordinary user to mount the filesystem.
The name of the mounting user is written to mtab (or to the private libmount
file in /run/mount on system without regular mtab) so that he 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 (i.e., non-root) user to mount the filesystem.
This is the default; it does not imply any other options.
- users
-
Allow every user to mount and unmount the filesystem.
This option implies the options
noexec, nosuid, and nodev
(unless overridden by subsequent options, as in the option line
users,exec,dev,suid).
- x-*
-
All options prefixed with "x-" are interpreted as comments or userspace
application-specific options. These options are not stored in the mtab file,
nor sent to the mount.<type> helpers nor the
mount(2)
system call. The suggested format is x-<appname>.<option> (e.g. x-systemd.automount).
- x-mount.mkdir[=mode]
-
Allow to make a target directory (mountpoint). 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.
FILESYSTEM-SPECIFIC MOUNT OPTIONS
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
Documentation/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/Documentation/filesystems/adfs.txt.
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 following 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 btrfs
Btrfs is a copy-on-write filesystem for Linux aimed at
implementing advanced features while focusing on fault tolerance,
repair, and easy administration.
- alloc_start=bytes
-
Debugging option to force all block allocations above a certain
byte threshold on each block device. The value is specified in
bytes, optionally with a K, M, or G suffix, case insensitive.
Default is 1MB.
- autodefrag
-
Disable/enable auto defragmentation.
Auto defragmentation detects small random writes into files and queues
them up for the defrag process. Works best for small files;
not well-suited for large database workloads.
- check_int|check_int_data|check_int_print_mask=value
-
These debugging options control the behavior of the integrity checking
module(the BTRFS_FS_CHECK_INTEGRITY config option required).
check_int
enables the integrity checker module, which examines all
block-write requests to ensure on-disk consistency, at a large
memory and CPU cost.
check_int_data
includes extent data in the integrity checks, and
implies the check_int option.
check_int_print_mask
takes a bitmask of BTRFSIC_PRINT_MASK_* values
as defined in fs/btrfs/check-integrity.c, to control the integrity
checker module behavior.
See comments at the top of
fs/btrfs/check-integrity.c
for more info.
- commit=seconds
-
Set the interval of periodic commit, 30 seconds by default. Higher
values defer data being synced to permanent storage, with obvious
consequences when the system crashes. The upper bound is not forced,
but a warning is printed if it's more than 300 seconds (5 minutes).
- compress|compress=type|compress-force|compress-force=type
-
Control BTRFS file data compression. Type may be specified as "zlib"
"lzo" or "no" (for no compression, used for remounting). If no type
is specified, zlib is used. If compress-force is specified,
all files will be compressed, whether or not they compress well.
If compression is enabled, nodatacow and nodatasum are disabled.
- degraded
-
Allow mounts to continue with missing devices. A read-write mount may
fail with too many devices missing, for example if a stripe member
is completely missing.
- device=devicepath
-
Specify a device during mount so that ioctls on the control device
can be avoided. Especially useful when trying to mount a multi-device
setup as root. May be specified multiple times for multiple devices.
- discard
-
Disable/enable the discard mount option.
The discard function issues frequent commands to let the block device
reclaim space freed by the filesystem.
This is useful for SSD devices, thinly provisioned
LUNs and virtual machine images, but may have a significant
performance impact. (The fstrim command is also available to
initiate batch trims from userspace.)
- enospc_debug
-
Disable/enable debugging option to be more verbose in some ENOSPC conditions.
- fatal_errors=action
-
Action to take when encountering a fatal error:
"bug" - BUG() on a fatal error. This is the default.
"panic" - panic() on a fatal error.
- flushoncommit
-
The
flushoncommit
mount option forces any data dirtied by a write in a
prior transaction to commit as part of the current commit. This makes
the committed state a fully consistent view of the filesystem from the
application's perspective (i.e., it includes all completed filesystem
operations). This was previously the behavior only when a snapshot is
created.
- inode_cache
-
Enable free inode number caching. Defaults to off due to an overflow
problem when the free space CRCs don't fit inside a single page.
- max_inline=bytes
-
Specify the maximum amount of space, in bytes, that can be inlined in
a metadata B-tree leaf. The value is specified in bytes, optionally
with a K, M, or G suffix, case insensitive. In practice, this value
is limited by the root sector size, with some space unavailable due
to leaf headers. For a 4k sectorsize, max inline data is ~3900 bytes.
- metadata_ratio=value
-
Specify that 1 metadata chunk should be allocated after every
value
data chunks. Off by default.
- noacl
-
Enable/disable support for Posix Access Control Lists (ACLs). See the
acl(5)
manual page for more information about ACLs.
- nobarrier
-
Enable/disable the use of block-layer write barriers. Write barriers
ensure that certain IOs make it through the device cache and are on
persistent storage. If disabled on a device with a volatile
(non-battery-backed) write-back cache, the nobarrier option will
lead to filesystem corruption on a system crash or power loss.
- nodatacow
-
Enable/disable data copy-on-write for newly created files.
This option implies nodatasum, and disables all compression.
- nodatasum
-
Enable/disable data checksumming for newly created files.
This option implies datacow.
- notreelog
-
Enable/disable the tree logging used for fsync and O_SYNC writes.
- recovery
-
Enable autorecovery attempts if a bad tree root is found at mount time.
Currently this scans a list of several previous tree roots and tries to
use the first readable.
- rescan_uuid_tree
-
Force check and rebuild procedure of the UUID tree. This should not
normally be needed.
- skip_balance
-
Skip automatic resume of an interrupted balance operation after mount.
May be resumed with "btrfs balance resume."
- nospace_cache
-
Disable freespace cache loading without clearing the cache.
- clear_cache
-
Force clearing and rebuilding of the disk space cache if something
has gone wrong.
- ssd|nossd|ssd_spread
-
Options to control ssd allocation schemes. By default, BTRFS will
enable or disable ssd allocation heuristics depending on whether a
rotational or nonrotational disk is in use. The ssd and
nossd options can override this autodetection.
The ssd_spread mount option attempts to allocate into big chunks
of unused space, and may perform better on low-end ssds. ssd_spread
implies ssd, enabling all other ssd heuristics as well.
- subvol=path
-
Mount subvolume at
path
rather than the root subvolume. The
path
is relative to the top level subvolume.
- subvolid=ID
-
Mount subvolume specified by an ID number rather than the root subvolume.
This allows mounting of subvolumes which are not in the root of the mounted
filesystem.
You can use "btrfs subvolume list" to see subvolume ID numbers.
- subvolrootid=objectid (deprecated)
-
Mount subvolume specified by
objectid
rather than the root subvolume.
This allows mounting of subvolumes which are not in the root of the mounted
filesystem.
You can use "btrfs subvolume show " to see the object ID for a subvolume.
- thread_pool=number
-
The number of worker threads to allocate. The default number is equal
to the number of CPUs + 2, or 8, whichever is smaller.
- user_subvol_rm_allowed
-
Allow subvolumes to be deleted by a non-root user. Use with caution.
Mount options for cifs
See the options section of the
mount.cifs(8)
man page (cifs-utils package must be installed).
Mount options for coherent
None.
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
independent 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 symbolic link to
pts/ptmx.
See
Documentation/filesystems/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 specified.
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 kernel
configuration.
Mount options for ext
None.
Note that the `ext' filesystem is obsolete. Don't use it.
Since Linux version 2.1.21 extfs is no longer part of the kernel source.
Mount options for ext2
The `ext2' filesystem is the standard Linux filesystem.
Since Linux 2.5.46, for most mount options the default
is determined by the filesystem superblock. Set them with
tune2fs(8).
- acl|noacl
-
Support POSIX Access Control Lists (or not).
- bsddf|minixdf
-
Set the behavior for the
statfs
system call. The
minixdf
behavior is to return in the
f_blocks
field the total number of blocks of the filesystem, while the
bsddf
behavior (which is the default) is to subtract the overhead blocks
used by the ext2 filesystem and not available for file storage. Thus
% mount /k -o minixdf; df /k; umount /k
Filesystem | 1024-blocks | Used | Available | Capacity | Mounted on
|
/dev/sda6 | 2630655 | 86954 | 2412169 | 3% | /k
|
% mount /k -o bsddf; df /k; umount /k
Filesystem | 1024-blocks | Used | Available | Capacity | Mounted on
|
/dev/sda6 | 2543714 | 13 | 2412169 | 0% | /k
|
(Note that this example shows that one can add command-line options
to the options given in
/etc/fstab.)
- check=none or nocheck
-
No checking is done at mount time. This is the default. This is fast.
It is wise to invoke
e2fsck(8)
every now and then, e.g. at boot time. The non-default behavior is unsupported
(check=normal and check=strict options have been removed). Note that these mount options
don't have to be supported if ext4 kernel driver is used for ext2 and ext3 filesystems.
- debug
-
Print debugging info upon each (re)mount.
- 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.)
The default is set in the filesystem superblock, and can be
changed using
tune2fs(8).
- grpid|bsdgroups and nogrpid|sysvgroups
-
These options define what group id a newly created file gets.
When
grpid
is set, it takes the group id of the directory in which it is created;
otherwise (the default) it takes the fsgid of the current process, unless
the directory has the setgid bit set, in which case it takes the gid
from the parent directory, and also gets the setgid bit set
if it is a directory itself.
- grpquota|noquota|quota|usrquota
-
The usrquota (same as quota) mount option enables user quota support on the
filesystem. grpquota enables group quotas support. You need the quota utilities
to actually enable and manage the quota system.
- nouid32
-
Disables 32-bit UIDs and GIDs. This is for interoperability with older
kernels which only store and expect 16-bit values.
- oldalloc or orlov
-
Use old allocator or Orlov allocator for new inodes. Orlov is default.
- resgid=,n and resuid=,n
-
The ext2 filesystem reserves a certain percentage of the available
space (by default 5%, see
mke2fs(8)
and
tune2fs(8)).
These options determine who can use the reserved blocks.
(Roughly: whoever has the specified uid, or belongs to the specified group.)
- sb=n
-
Instead of block 1, use block
n
as superblock. This could be useful when the filesystem has been damaged.
(Earlier, copies of the superblock would be made every 8192 blocks: in
block 1, 8193, 16385, ... (and one got thousands of copies on
a big filesystem). Since version 1.08,
mke2fs
has a -s (sparse superblock) option to reduce the number of backup
superblocks, and since version 1.15 this is the default. Note
that this may mean that ext2 filesystems created by a recent
mke2fs
cannot be mounted r/w under Linux 2.0.*.)
The block number here uses 1 k units. Thus, if you want to use logical
block 32768 on a filesystem with 4 k blocks, use "sb=131072".
- user_xattr|nouser_xattr
-
Support "user." extended attributes (or not).
Mount options for ext3
The ext3 filesystem is a version of the ext2 filesystem which has been
enhanced with journaling. It supports the same options as ext2 as
well as the following additions:
- journal=update
-
Update the ext3 filesystem's journal to the current format.
- journal=inum
-
When a journal already exists, this option is ignored. Otherwise, it
specifies the number of the inode which will represent the ext3 filesystem's
journal file; ext3 will create a new journal, overwriting the old contents
of the file whose inode number is
inum.
- journal_dev=devnum/journal_path=path
-
When the external journal device's major/minor numbers
have changed, these options allow the user to specify
the new journal location. The journal device is
identified either through its new major/minor numbers encoded
in devnum, or via a path to the device.
- norecovery/noload
-
Don't load the journal on mounting. Note that
if the filesystem was not unmounted cleanly,
skipping the journal replay will lead to the
filesystem containing inconsistencies that can
lead to any number of problems.
- data={journal|ordered|writeback}
-
Specifies the journaling mode for file data. Metadata is always journaled.
To use modes other than
ordered
on the root filesystem, pass the mode to the kernel as boot parameter, e.g.
rootflags=data=journal.
-
- journal
-
All data is committed into the journal prior to being written into the
main filesystem.
- ordered
-
This is the default mode. All data is forced directly out to the main file
system prior to its metadata being committed to the journal.
- writeback
-
Data ordering is not preserved - data may be written into the main
filesystem after its metadata has been committed to the journal.
This is rumoured to be the highest-throughput option. It guarantees
internal filesystem integrity, however it can allow old data to appear
in files after a crash and journal recovery.
- data_err=ignore
-
Just print an error message if an error occurs in a file data buffer in
ordered mode.
- data_err=abort
-
Abort the journal if an error occurs in a file data buffer in ordered mode.
- barrier=0 / barrier=1
-
This disables / enables the use of write barriers in the jbd code. barrier=0
disables, barrier=1 enables (default). This also requires an IO stack which can
support barriers, and if jbd gets an error on a barrier write, it will disable
barriers again with a warning. 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 battery-backed in one way or another,
disabling barriers may safely improve performance.
- commit=nrsec
-
Sync all data and metadata every
nrsec
seconds. The default value is 5 seconds. Zero means default.
- user_xattr
-
Enable Extended User Attributes. See the
attr(5)
manual page.
- acl
-
Enable POSIX Access Control Lists. See the
acl(5)
manual page.
- usrjquota=aquota.user|grpjquota=aquota.group|jqfmt=vfsv0
-
Apart from the old quota system (as in ext2, jqfmt=vfsold aka version 1 quota)
ext3 also supports journaled quotas (version 2 quota). jqfmt=vfsv0
enables journaled quotas. For journaled quotas the mount options
usrjquota=aquota.user and grpjquota=aquota.group are required to tell the
quota system which quota database files to use. Journaled quotas have the
advantage that even after a crash no quota check is required.
Mount options for ext4
The ext4 filesystem is an advanced level of the ext3 filesystem which
incorporates scalability and reliability enhancements for supporting large
filesystem.
The options
journal_dev, norecovery, noload, data, commit, orlov, oldalloc, [no]user_xattr
[no]acl, bsddf, minixdf, debug, errors, data_err, grpid, bsdgroups, nogrpid
sysvgroups, resgid, resuid, sb, quota, noquota, grpquota, usrquota
usrjquota, grpjquota and jqfmt
are backwardly compatible with ext3 or ext2.
- journal_checksum
-
Enable checksumming of the journal transactions. This will allow the recovery
code in e2fsck and the kernel to detect corruption in the kernel. It is a
compatible change and will be ignored by older kernels.
- journal_async_commit
-
Commit block can be written to disk without waiting for descriptor blocks.
If enabled, older kernels cannot mount the device.
This will enable 'journal_checksum' internally.
- barrier=0 / barrier=1 / barrier / nobarrier
-
These mount options have the same effect as in ext3. The mount options
"barrier" and "nobarrier" are added for consistency with other ext4 mount
options.
The ext4 filesystem enables write barriers by default.
- inode_readahead_blks=n
-
This tuning parameter controls the maximum number of inode table blocks that
ext4's inode table readahead algorithm will pre-read into the buffer cache.
The value must be a power of 2. The default value is 32 blocks.
- stripe=n
-
Number of filesystem blocks that mballoc will try to use for allocation size
and alignment. For RAID5/6 systems this should be the number of data disks *
RAID chunk size in filesystem blocks.
- delalloc
-
Deferring block allocation until write-out time.
- nodelalloc
-
Disable delayed allocation. Blocks are allocated when data is copied from user
to page cache.
- max_batch_time=usec
-
Maximum amount of time ext4 should wait for additional filesystem operations to
be batch together with a synchronous write operation. Since a synchronous
write operation is going to force a commit and then a wait for the I/O
complete, it doesn't cost much, and can be a huge throughput win, we wait for a
small amount of time to see if any other transactions can piggyback on the
synchronous write. The algorithm used is designed to automatically tune for
the speed of the disk, by measuring the amount of time (on average) that it
takes to finish committing a transaction. Call this time the "commit time".
If the time that the transaction has been running is less than the commit time,
ext4 will try sleeping for the commit time to see if other operations will join
the transaction. The commit time is capped by the max_batch_time, which
defaults to 15000 µs (15 ms). This optimization can be turned off entirely by
setting max_batch_time to 0.
- min_batch_time=usec
-
This parameter sets the commit time (as described above) to be at least
min_batch_time. It defaults to zero microseconds. Increasing this parameter
may improve the throughput of multi-threaded, synchronous workloads on very
fast disks, at the cost of increasing latency.
- journal_ioprio=prio
-
The I/O priority (from 0 to 7, where 0 is the highest priority) which should be
used for I/O operations submitted by kjournald2 during a commit operation.
This defaults to 3, which is a slightly higher priority than the default I/O
priority.
- abort
-
Simulate the effects of calling ext4_abort() for
debugging purposes. This is normally used while
remounting a filesystem which is already mounted.
- auto_da_alloc|noauto_da_alloc
-
Many broken applications don't use fsync() when
replacing existing files via patterns such as
fd = open("foo.new")/write(fd,...)/close(fd)/ rename("foo.new", "foo")
or worse yet
fd = open("foo", O_TRUNC)/write(fd,...)/close(fd).
If auto_da_alloc is enabled, ext4 will detect the replace-via-rename and
replace-via-truncate patterns and force that any delayed allocation blocks are
allocated such that at the next journal commit, in the default data=ordered
mode, the data blocks of the new file are forced to disk before the rename()
operation is committed. This provides roughly the same level of guarantees as
ext3, and avoids the "zero-length" problem that can happen when a system
crashes before the delayed allocation blocks are forced to disk.
- noinit_itable
-
Do not initialize any uninitialized inode table blocks in the background. This
feature may be used by installation CD's so that the install process can
complete as quickly as possible; the inode table initialization process would
then be deferred until the next time the filesystem is mounted.
- init_itable=n
-
The lazy itable init code will wait n times the number of milliseconds it took
to zero out the previous block group's inode table. This minimizes the impact on
system performance while the filesystem's inode table is being initialized.
- discard/nodiscard
-
Controls whether ext4 should issue discard/TRIM commands to the underlying
block device when blocks are freed. This is useful for SSD devices and
sparse/thinly-provisioned LUNs, but it is off by default until sufficient
testing has been done.
- nouid32
-
Disables 32-bit UIDs and GIDs. This is for
interoperability with older kernels which only
store and expect 16-bit values.
- block_validity/noblock_validity
-
This options allows to enables/disables the in-kernel facility for tracking
filesystem metadata blocks within internal data structures. This allows multi-block allocator and other routines to quickly locate extents which might
overlap with filesystem metadata blocks. This option is intended for debugging
purposes and since it negatively affects the performance, it is off by default.
- dioread_lock/dioread_nolock
-
Controls whether or not ext4 should use the DIO read locking. If the
dioread_nolock option is specified ext4 will allocate uninitialized extent
before buffer write and convert the extent to initialized after IO completes.
This approach allows ext4 code to avoid using inode mutex, which improves
scalability on high speed storages. However this does not work with data
journaling and dioread_nolock option will be ignored with kernel warning.
Note that dioread_nolock code path is only used for extent-based files.
Because of the restrictions this options comprises it is off by default
(e.g. dioread_lock).
- max_dir_size_kb=n
-
This limits the size of the directories so that any attempt to expand them
beyond the specified limit in kilobytes will cause an ENOSPC error. This is
useful in memory-constrained environments, where a very large directory can
cause severe performance problems or even provoke the Out Of Memory killer. (For
example, if there is only 512 MB memory available, a 176 MB directory may
seriously cramp the system's style.)
- i_version
-
Enable 64-bit inode version support. This option is off by default.
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.
verylongname.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
-
The
fat
filesystem can perform CRLF<-->NL conversion (MS-DOS text format to UNIX text
format) in the kernel. The following conversion modes are available:
-
- b[inary]
-
No translation is performed. This is the default.
- t[ext]
-
CRLF<-->NL translation is performed on all files.
- a[uto]
-
CRLF<-->NL translation is performed on all files that don't have a
"well-known binary" extension. The list of known extensions can be found at
the beginning of
fs/fat/misc.c
(as of 2.0, the list is: exe, com, bin, app, sys, drv, ovl, ovr, obj,
lib, dll, pif, arc, zip, lha, lzh, zoo, tar, z, arj, tz, taz, tzp, tpz,
gz, tgz, deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk, pxl, dvi).
Programs that do computed lseeks won't like in-kernel text conversion.
Several people have had their data ruined by this translation. Beware!
For filesystems mounted in binary mode, a conversion tool
(fromdos/todos) is available. This option is obsolete.
- 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.
- fat={12|16|32}
-
Specify a 12, 16 or 32 bit fat. This overrides
the automatic FAT type detection routine. Use with caution!
- iocharset=value
-
Character set to use for converting between 8 bit characters
and 16 bit Unicode characters. The default is iso8859-1.
Long filenames are stored on disk in Unicode format.
- nfs
-
If set, enables in-memory indexing of directory inodes to reduce the
frequency of ESTALE errors in NFS client operations. Useful only when
the filesystem is exported via NFS.
- 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 mounting devices (like digital cameras)
that are set to UTC in order to avoid the pitfalls of
local time.
- quiet
-
Turn on the
quiet
flag. Attempts to chown or chmod files do not return errors,
although they fail. Use with caution!
- 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={binary|text|auto}
-
For
conv=text,
delete some random CRs (in particular, all followed by NL)
when reading a file.
For
conv=auto,
choose more or less at random between
conv=binary and conv=text.
For
conv=binary,
just read what is in the file. This is the default.
- 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 a 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 directory 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 available. 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 meaningful 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 converts `;' 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 everybody.)
Since Linux 2.1.37 one no longer needs to specify the mode in
decimal. (Octal is indicated by 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={a[uto]|b[inary]|m[text]|t[ext]}
-
(Default:
conv=binary.)
Since Linux 1.3.54 this option has no effect anymore.
(And non-binary settings used to be very dangerous,
possibly leading to silent data corruption.)
- 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. (Since 2.3.4.)
- sbsector=xxx
-
Session begins from sector xxx. (Since 2.3.4.)
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 characters 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 growing 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 minix
None.
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 nfs and nfs4
See the options section of the
nfs(5)
man page (nfs-utils package must be installed).
The
nfs and nfs4
implementation expects a binary argument (a
struct nfs_mount_data)
to the mount system call. This argument is constructed by
mount.nfs(8)
and the current version of
mount
(2.13) does not know anything about nfs and nfs4.
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 proc
- uid=,value and gid=,value
-
These options are recognized, but have no effect as far as I can see.
Mount options for ramfs
Ramfs is a memory based filesystem. Mount it and you have it. Unmount it
and it is gone. Present since Linux 2.3.99pre4.
There are no mount options.
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 experienced 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 reiserfs's fast recovery from crashes.
Even with this option turned on, reiserfs still performs all journaling
operations, 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
reiserfsck.
- 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(5)
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 warning. 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 battery-backed in
one way or another, disabling barriers may safely improve performance.
Mount options for romfs
None.
Mount options for squashfs
None.
Mount options for smbfs
Just like
nfs, the
smbfs
implementation expects a binary argument (a
struct smb_mount_data)
to the mount system call. This argument is constructed by
smbmount(8)
and the current version of
mount
(2.12) does not know anything about smbfs.
Mount options for sysv
None.
Mount options for tmpfs
- size=nbytes
-
Override default maximum size of the filesystem.
The size is given in bytes, and rounded up to entire pages.
The default is half of the memory. The size parameter also accepts a suffix %
to limit this tmpfs instance to that percentage of your physical RAM:
the default, when neither size nor nr_blocks is specified, is size=50%
- nr_blocks=
-
The same as size, but in blocks of PAGE_CACHE_SIZE
- nr_inodes=
-
The maximum number of inodes for this instance. The default
is half of the number of your physical RAM pages, or (on a
machine with highmem) the number of lowmem RAM pages,
whichever is the lower.
The tmpfs mount options for sizing (size,
nr_blocks,
and
nr_inodes)
accept a suffix
k,
m
or
g
for Ki, Mi, Gi (binary kilo (kibi), binary mega (mebi) and binary giga (gibi)) and can be changed on remount.
- mode=
-
Set initial permissions of the root directory.
- uid=
-
The user id.
- gid=
-
The group id.
- mpol=[default|prefer:Node|bind:NodeList|interleave|interleave:NodeList]
-
Set the NUMA memory allocation policy for all files in that
instance (if the kernel CONFIG_NUMA is enabled) - which can be adjusted on the
fly via 'mount -o remount ...'
-
- default
-
prefers to allocate memory from the local node
- prefer:Node
-
prefers to allocate memory from the given Node
- bind:NodeList
-
allocates memory only from nodes in NodeList
- interleave
-
prefers to allocate from each node in turn
- interleave:NodeList
-
allocates from each node of NodeList in turn.
The NodeList format is a comma-separated list of decimal numbers and ranges, a
range being two "hyphen-minus"-separated decimal numbers, the smallest and largest node
numbers in the range. For example, mpol=bind:0-3,5,7,9-15
Note that trying to mount a tmpfs with an mpol option will fail if the
running kernel does not support NUMA; and will fail if its nodelist
specifies a node which is not online. If your system relies on that
tmpfs being mounted, but from time to time runs a kernel built without
NUMA capability (perhaps a safe recovery kernel), or with fewer nodes
online, then it is advisable to omit the mpol option from automatic
mount options. It can be added later, when the tmpfs is already mounted
on MountPoint, by 'mount -o remount,mpol=Policy:NodeList MountPoint'.
Mount options for ubifs
UBIFS is a flash file system 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 optimization. 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 the Optical
Storage Technology Association, and is often used for DVD-ROM.
See also
iso9660.
- gid=
-
Set the default group.
- umask=
-
Set the default umask.
The value is given in octal.
- uid=
-
Set the default user.
- unhide
-
Show otherwise hidden files.
- undelete
-
Show deleted files in lists.
- nostrict
-
Unset strict conformance.
- iocharset
-
Set the NLS character set.
- bs=
-
Set the block size. (May not work unless 2048.)
- novrs
-
Skip volume sequence recognition.
- session=
-
Set the CDROM session counting from 0. Default: last session.
- anchor=
-
Override standard anchor location. Default: 256.
- volume=
-
Override the VolumeDesc location. (unused)
- partition=
-
Override the PartitionDesc location. (unused)
- lastblock=
-
Set the last block of the filesystem.
- fileset=
-
Override the fileset block location. (unused)
- rootdir=
-
Override the root directory location. (unused)
Mount options for ufs
- ufstype=value
-
UFS is a filesystem widely used in different operating systems.
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 (NetBSD, 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 station) (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
dotsOK
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 filesystem 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.
Mount options for xenix
None.
Mount options for xfs
- allocsize=size
-
Sets the buffered I/O end-of-file preallocation size when
doing delayed allocation writeout. Valid values for this
option are page size (typically 4KiB) through to 1GiB,
inclusive, in power-of-2 increments.
The default behavior is for dynamic end-of-file
preallocation size, which uses a set of heuristics to
optimise the preallocation size based on the current
allocation patterns within the file and the access patterns
to the file. Specifying a fixed allocsize value turns off
the dynamic behavior.
- attr2|noattr2
-
The options enable/disable an "opportunistic" improvement to
be made in the way inline extended attributes are stored
on-disk. When the new form is used for the first time when
attr2 is selected (either when setting or removing extended
attributes) the on-disk superblock feature bit field will be
updated to reflect this format being in use.
The default behavior is determined by the on-disk feature
bit indicating that attr2 behavior is active. If either
mount option it set, then that becomes the new default used
by the filesystem.
CRC enabled filesystems always use the attr2 format, and so
will reject the noattr2 mount option if it is set.
- barrier|nobarrier
-
Enables/disables the use of block layer write barriers for
writes into the journal and for data integrity operations.
This allows for drive level write caching to be enabled, for
devices that support write barriers.
- discard|nodiscard
-
Enable/disable the issuing of commands to let the block
device reclaim space freed by the filesystem. This is
useful for SSD devices, thinly provisioned LUNs and virtual
machine images, but may have a performance impact.
Note: It is currently recommended that you use the fstrim
application to discard unused blocks rather than the discard
mount option because the performance impact of this option
is quite severe.
- grpid|bsdgroups|nogrpid|sysvgroups
-
These options define what group ID a newly created file
gets. When grpid is set, it takes the group ID of the
directory in which it is created; otherwise it takes the
fsgid of the current process, unless the directory has the
setgid bit set, in which case it takes the gid from the
parent directory, and also gets the setgid bit set if it is
a directory itself.
- filestreams
-
Make the data allocator use the filestreams allocation mode
across the entire filesystem rather than just on directories
configured to use it.
- ikeep|noikeep
-
When ikeep is specified, XFS does not delete empty inode
clusters and keeps them around on disk. When noikeep is
specified, empty inode clusters are returned to the free
space pool.
- inode32|inode64
-
When inode32 is specified, it indicates that XFS limits
inode creation to locations which will not result in inode
numbers with more than 32 bits of significance.
When inode64 is specified, it indicates that XFS is allowed
to create inodes at any location in the filesystem,
including those which will result in inode numbers occupying
more than 32 bits of significance.
inode32 is provided for backwards compatibility with older
systems and applications, since 64 bits inode numbers might
cause problems for some applications that cannot handle
large inode numbers. If applications are in use which do
not handle inode numbers bigger than 32 bits, the inode32
option should be specified.
- largeio|nolargeio
-
If "nolargeio" is specified, the optimal I/O reported in
st_blksize by stat(2) will be as small as possible to allow
user applications to avoid inefficient read/modify/write
I/O. This is typically the page size of the machine, as
this is the granularity of the page cache.
If "largeio" specified, a filesystem that was created with a
"swidth" specified will return the "swidth" value (in bytes)
in st_blksize. If the filesystem does not have a "swidth"
specified but does specify an "allocsize" then "allocsize"
(in bytes) will be returned instead. Otherwise the behavior
is the same as if "nolargeio" was specified.
- logbufs=value
-
Set the number of in-memory log buffers. Valid numbers
range from 2-8 inclusive.
The default value is 8 buffers.
If the memory cost of 8 log buffers is too high on small
systems, then it may be reduced at some cost to performance
on metadata intensive workloads. The logbsize option below
controls the size of each buffer and so is also relevant to
this case.
- logbsize=value
-
Set the size of each in-memory log buffer. The size may be
specified in bytes, or in kibibytes (KiB) with a "k" suffix.
Valid sizes for version 1 and version 2 logs are 16384 (value=16k)
and 32768 (value=32k). Valid sizes for version 2 logs also
include 65536 (value=64k), 131072 (value=128k) and 262144 (value=256k).
The logbsize must be an integer multiple of the log
stripe unit configured at mkfs time.
The default value for version 1 logs is 32768, while the
default value for version 2 logs is MAX(32768, log_sunit).
- logdev=device and rtdev=device
-
Use an external log (metadata journal) and/or real-time device.
An XFS filesystem has up to three parts: a data section, a log
section, and a real-time section. The real-time section is
optional, and the log section can be separate from the data
section or contained within it.
- noalign
-
Data allocations will not be aligned at stripe unit
boundaries. This is only relevant to filesystems created
with non-zero data alignment parameters (sunit, swidth) by
mkfs.
- norecovery
-
The filesystem will be mounted without running log recovery.
If the filesystem was not cleanly unmounted, it is likely to
be inconsistent when mounted in "norecovery" mode.
Some files or directories may not be accessible because of this.
Filesystems mounted "norecovery" must be mounted read-only or
the mount will fail.
- nouuid
-
Don't check for double mounted file systems using the file
system uuid. This is useful to mount LVM snapshot volumes,
and often used in combination with "norecovery" for mounting
read-only snapshots.
- noquota
-
Forcibly turns off all quota accounting and enforcement
within the filesystem.
- uquota/usrquota/uqnoenforce/quota
-
User disk quota accounting enabled, and limits (optionally)
enforced. Refer to xfs_quota(8) for further details.
- gquota/grpquota/gqnoenforce
-
Group disk quota accounting enabled and limits (optionally)
enforced. Refer to xfs_quota(8) for further details.
- pquota/prjquota/pqnoenforce
-
Project disk quota accounting enabled and limits (optionally)
enforced. Refer to xfs_quota(8) for further details.
- sunit=value and swidth=value
-
Used to specify the stripe unit and width for a RAID device
or a stripe volume. "value" must be specified in 512-byte
block units. These options are only relevant to filesystems
that were created with non-zero data alignment parameters.
The sunit and swidth parameters specified must be compatible
with the existing filesystem alignment characteristics. In
general, that means the only valid changes to sunit are
increasing it by a power-of-2 multiple. Valid swidth values
are any integer multiple of a valid sunit value.
Typically the only time these mount options are necessary if
after an underlying RAID device has had it's geometry
modified, such as adding a new disk to a RAID5 lun and
reshaping it.
- swalloc
-
Data allocations will be rounded up to stripe width boundaries
when the current end of file is being extended and the file
size is larger than the stripe width size.
- wsync
-
When specified, all filesystem namespace operations are
executed synchronously. This ensures that when the namespace
operation (create, unlink, etc) completes, the change to the
namespace is on stable storage. This is useful in HA setups
where failover must not result in clients seeing
inconsistent namespace presentation during or after a
failover event.
THE LOOP DEVICE
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 regular file if a filesystem type is
not specified or the filesystem is known for libblkid, for example:
-
mount /tmp/disk.img /mnt
mount -t ext3 /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 filesystem 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.
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]
[-o
options]
[-t
type.subtype]
where the suffix is the filesystem type and the -sfnvo 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,
runbindable,
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
- /etc/fstab
-
filesystem table
- /etc/mtab
-
table of mounted filesystems
- /etc/mtab~
-
lock file
- /etc/mtab.tmp
-
temporary file
- /etc/filesystems
-
a list of filesystem types to try
ENVIRONMENT
- LIBMOUNT_FSTAB=<path>
-
overrides the default location of the fstab file
- LIBMOUNT_MTAB=<path>
-
overrides the default location of the mtab file
- LIBMOUNT_DEBUG=0xffff
-
enables debug output
SEE ALSO
mount(2),
umount(2),
fstab(5),
umount(8),
swapon(8),
findmnt(8),
nfs(5),
xfs(5),
e2label(8),
xfs_admin(8),
mountd(8),
nfsd(8),
mke2fs(8),
tune2fs(8),
losetup(8)
BUGS
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don't support
-o sync and -o dirsync
(the ext2, ext3, 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 files
/etc/mtab
and
/proc/mounts
don't match on systems with 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. remote NFS server. In particular case
the mount command may reports unreliable information about a NFS mount point
and the /proc/mounts file usually contains more reliable information.) This is
another reason to replace mtab file with symlink to the
/proc/mounts
file.
Checking files on NFS filesystem referenced by file descriptors (i.e. the
fcntl
and
ioctl
families of functions) may lead to inconsistent result due to the lack of
consistency check in 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 available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- COMMAND-LINE OPTIONS
-
- FILESYSTEM-INDEPENDENT MOUNT OPTIONS
-
- FILESYSTEM-SPECIFIC MOUNT OPTIONS
-
- Mount options for adfs
-
- Mount options for affs
-
- Mount options for btrfs
-
- Mount options for cifs
-
- Mount options for coherent
-
- Mount options for debugfs
-
- Mount options for devpts
-
- Mount options for ext
-
- Mount options for ext2
-
- Mount options for ext3
-
- Mount options for ext4
-
- Mount options for fat
-
- Mount options for hfs
-
- Mount options for hpfs
-
- Mount options for iso9660
-
- Mount options for jfs
-
- Mount options for minix
-
- Mount options for msdos
-
- Mount options for ncpfs
-
- Mount options for nfs and nfs4
-
- Mount options for ntfs
-
- Mount options for proc
-
- Mount options for ramfs
-
- Mount options for reiserfs
-
- Mount options for romfs
-
- Mount options for squashfs
-
- Mount options for smbfs
-
- Mount options for sysv
-
- Mount options for tmpfs
-
- Mount options for ubifs
-
- Mount options for udf
-
- Mount options for ufs
-
- Mount options for umsdos
-
- Mount options for vfat
-
- Mount options for usbfs
-
- Mount options for xenix
-
- Mount options for xfs
-
- THE LOOP DEVICE
-
- RETURN CODES
-
- EXTERNAL HELPERS
-
- FILES
-
- ENVIRONMENT
-
- SEE ALSO
-
- BUGS
-
- HISTORY
-
- AUTHORS
-
- AVAILABILITY
-