mount(8) - phpMan

MOUNT(8) System Administration MOUNT(8)

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 invis-
ible, and as long as this filesystem remains mounted, the pathname dir refers to the root
of the filesystem on device.

If only directory or 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 --target or --source options to avoid ambivalent interpretation
of the given argument. For example

mount --target /mountpoint

The listing and help.
The listing mode is maintained for backward compatibility only.

For more robust and definable output use findmnt(8), especially in your scripts.
Note that control characters in the mountpoint name are replaced with '?'.

mount [-l] [-t type]
lists all mounted filesystems (of type type). The option -l adds the labels
in this listing. See below.

The device indication.
Most devices are indicated by a file name (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 possible to indicate a block
special device using its filesystem LABEL or UUID (see the -L and -U options below)
and partition PARTUUID or PARTLABEL (partition identifiers are supported for GUID
Partition Table (GPT) and MAC partition tables only).

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.
The tags are more readable, robust and portable. The mount(8) command internally
uses udev symlinks, so use the symlinks in /etc/fstab has no advantage over the
tags. For more details see libblkid(3).

Note that mount(8) uses UUIDs as strings. The UUIDs from command line or 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 could be overridden by --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 indi-
cated, 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 give only the
device, or only the mount point.

The programs mount and umount maintain a list of currently mounted filesystems in
the file /etc/mtab. If no arguments are given to mount, this list is printed.

The mount program does not read the /etc/fstab file if device (or LABEL, UUID, PAR-
TUUID or PARTLABEL) and dir are specified. For example:

mount /dev/foo /dir

If you want to override mount options from /etc/fstab you have to use:

mount device|dir -o <options>

and then the mount options from command line will be appended to the list of
options from /etc/fstab. The usual behaviour is that the last option wins if there
is more duplicated options.

When the proc filesystem is mounted (say at /proc), the files /etc/mtab and
/proc/mounts have very similar contents. The former has somewhat more information,
such as the mount options used, but is not necessarily up-to-date (cf. the -n
option below). It is possible to replace /etc/mtab by a symbolic link to
/proc/mounts, and especially when you have very large numbers of mounts things will
be much faster with that symlink, but some information is lost that way, and in
particular using the "user" option will fail.

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 system.

Thus, given a line

/dev/cdrom /cd iso9660 ro,user,noauto,unhide

any user can mount the iso9660 filesystem found on his CDROM using the command

mount /dev/cdrom

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, 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 shortoption
mount -B olddir newdir
or fstab entry is:
/olddir /newdir none bind

After this call the same contents is 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 sub-
mounts. The entire file hierarchy including submounts is attached a second place
using

mount --rbind olddir newdir

or shortoption

mount -R olddir newdir

Note that the filesystem mount options will remain the same as those on the origi-
nal mount point.

mount(8) since v2.27 (backported to RHEL7.3) allow to change the options by passing
the -o option along with --bind for example:

mount --bind,ro foo foo

This feature is not supported by Linux kernel and it is implemented in userspace by
additional remount mount(2) syscall. This solution is not atomic.

The alternative (classic) way to create a read-only bind mount is to use remount
operation, for example:

mount --bind olddir newdir
mount -o remount,ro,bind olddir newdir

Note that read-only bind will create a read-only mountpoint (VFS entry), but the
original filesystem superblock will still be writable, meaning that the olddir will
be writable, but the newdir will be read-only.

It's impossible to change mount options recursively (for example with -o
rbind,ro).

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
or shortoption
mount -M olddir newdir
This will cause the contents which previously appeared under olddir to be accessed
under newdir. The physical location of the files is not changed. Note that the
olddir has to be a mountpoint.

Note 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 subtrees operations.
Since Linux 2.6.15 it is possible to mark a mount and its submounts as shared, pri-
vate, slave or unbindable. A shared mount provides ability to create mirrors of
that mount such that mounts and umounts within any of the mirrors propagate to the
other mirror. A slave mount receives propagation from its master, but any not vice-
versa. A private mount carries no propagation abilities. A unbindable mount is a
private mount which cannot be cloned through a bind operation. Detailed semantics
is documented in Documentation/filesystems/sharedsubtree.txt file in the kernel
source tree.

Supported operations:
mount --make-shared mountpoint
mount --make-slave mountpoint
mount --make-private mountpoint
mount --make-unbindable mountpoint

The following commands allows 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 --make-* operation is requested. All necessary
information has to be specified on command line.

Note that Linux kernel does not allow to change more propagation flags by one
mount(2) syscall and the flags cannot be mixed with another mount options.

Since util-linux 2.23 mount command allows to use more propagation flags together
and with another mount operations. This feature is EXPERIMENTAL. The propagation
flags are applied by additional mount(2) syscalls after previous successful mount
operation. Note that this use case is not atomic. The propagation flags is possible
to specify in fstab(5) as mount options (private, slave, shared, unbindable, rpri-
vate, rslave, rshared, runbindable).

For example
mount --make-private --make-unbindable /dev/sda1 /A

is the same as
mount /dev/sda1 /A
mount --make-private /A
mount --make-unbindable /A

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.

Command line options available for the mount command:

-V, --version
Output version.

-h, --help
Print a help message.

-v, --verbose
Verbose mode.

-a, --all
Mount all filesystems (of the given types) mentioned 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 paral-
lel. A disadvantage is that the mounts are done in undefined order. Thus, you can-
not 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 obvi-
ous, 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 existing record in /etc/mtab and fails when the record
already exists (with regular non-fake mount, this check is done by 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) and stores canonicalized paths to the /etc/mtab file. This option
can be used together with the -f flag for already canonicalized absolute paths.

-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. This
option exists for support of the Linux autofs-based automounter.

--source src
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 mount source.

-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 or ext4 will replay its journal if
the filesystem is dirty. To prevent this kind of write access, you may want to
mount ext3 or ext4 filesystem with "ro,noload" mount options or set the block
device to read-only mode, see command blockdev(8).

-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 alternative fstab file. If the path is directory then the files in the
directory are sorted by strverscmp(3), files that starts with "." or without .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 outside standard system configuration.

Note that mount(8) does not pass the option --fstab to /sbin/mount.<type> helpers,
it means 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 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, 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, reis-
erfs, 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 '.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#exam-
ple.com' is depreacated).

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) 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
various 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 * only, mount will read /proc/filesystems afterwards. All of the filesystem
types will be mounted with 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 exam-
ple, the command:

mount -a -t nomsdos,ext

mounts all filesystems except those of type msdos and ext.

--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 mount target.

-O, --test-opts opts
Used in conjunction with -a, to limit the set of filesystems to which the -a is
applied. Like -t in this regard except that it is useless except in the context of
-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
Options are specified with a -o flag followed by a comma separated string of
options. For example:

mount LABEL=mydisk -o noatime,nouser

For more details, see 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 effect only for ext2,
ext3, ext4, fat, vfat and ufs):

async All I/O to the filesystem should be done asynchronously. (See also the sync
option.)

atime Do not use noatime feature, then the inode access time is controlled by kernel
defaults. See also the description for 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 or ext4 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:remov-
able_t".

Two other options are fscontext= and defcontext=, both of which are mutually exclu-
sive 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 con-
text that fscontext provides, in addition to supplying the same label for individ-
ual 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 quot-
ing is required. For example:

mount -t tmpfs none /mnt -o 'context="sys-
tem_u:object_r:tmp_t:s0:c127,c456",noexec'

For more details, see selinux(8).

defaults
Use default options: rw, suid, dev, exec, auto, nouser, and async.

Note that the real set of the all default mount options depends on kernel and
filesystem type. See the begin 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 allow 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 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 relatime feature. See also the strictatime mount option.

strictatime
Allows to explicitly requesting full atime updates. This makes it possible for ker-
nel to defaults 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 behaviour 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. (This
seems safe, but is in fact rather unsafe if you have suidperl(1) installed.)

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 how the mount command works with
options from fstab. It means the mount command doesn't read fstab (or mtab) only
when a device and dir are fully 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 options
from 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 case of media with lim-
ited 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 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.

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 applica-
tions specific options. These options are not stored to mtab file, send to
mount.<type> helpers or mount(2) system call. The suggested format is x-<app-
name>.<option> (e.g. x-systemd.automount).

x-mount.mkdir[=<mode>]
Allow to make a target directory (mountpoint). The optional argument <mode> speci-
fies the file system 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/Docu-
mentation/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 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 imple-
mented 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 configu-
ration.

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 (typi-
cally /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. Fur-
ther 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 behaviour for the statfs system call. The minixdf behaviour is to return in
the f_blocks field the total number of blocks of the filesystem, while the bsddf
behaviour (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 behaviour 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 speci-
fied 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 1k units.
Thus, if you want to use logical block 32768 on a filesystem with 4k 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 jour-
naling. 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
When the external journal device's major/minor numbers have changed, this option
allows the user to specify the new journal location. The journal device is identi-
fied through its new major/minor numbers encoded in devnum.

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 incon-
sistencies 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 filesys-
tem 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.

barrier=0 / barrier=1
This enables/disables barriers. barrier=0 disables it, barrier=1 enables it.
Write barriers enforce proper on-disk ordering of journal commits, making volatile
disk write caches safe to use, at some performance penalty. The ext3 filesystem
does not enable write barriers by default. Be sure to enable barriers unless your
disks are battery-backed one way or another. Otherwise you risk filesystem corrup-
tion in case of power failure.

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 scala-
bility and reliability enhancements for supporting large filesystem.

The options journal_dev, 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 back-
wardly 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
This enables/disables the use of write barriers in the jbd code. barrier=0 dis-
ables, barrier=1 enables. This also requires an IO stack which can support barri-
ers, and if jbd gets an error on a barrier write, it will disable 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. The mount options "barrier" and "nobarrier" can also be used to
enable or disable barriers, 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 opera-
tion 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 15000us (15ms). 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 nor-
mally 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 pat-
terns 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 commit-
ted. 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.

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.

resize Allows to resize filesystem to the end of the last existing block group, further
resize has to be done with resize2fs either online, or offline. It can be used only
with conjunction with remount.

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).

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 cur-
rent 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 pickyness can be chosen:

r[elaxed]
Upper and lower case are accepted and equivalent, long name parts are trun-
cated (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 may not contain long parts and special characters
that are sometimes used on Linux, but are not accepted by MS-DOS are
rejected. (+, =, spaces, etc.)

codepage=value
Sets the codepage for converting to shortname characters on FAT and VFAT filesys-
tems. By default, codepage 437 is used.

conv={b[inary]|t[ext]|a[uto]}
The fat filesystem can perform CRLF<-->NL (MS-DOS text format to UNIX text format)
conversion in the kernel. The following conversion modes are available:

binary no translation is performed. This is the default.

text CRLF<-->NL translation is performed on all files.

auto 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 avail-
able. 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 con-
trols 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 inconsis-
tent).

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 exten-
sion 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 direc-
tories. 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 overrid-
ing 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 per-
mission 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 inacces-
sible.)

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 16MB.

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 char-
acters. 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 CON-
FIG_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 shrink-
ing 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.

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 charac-
ters. 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 bigen-
dian 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 compat-
ible 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 colli-
sions.

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 EHASH-
COLLISION 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 filesys-
tem.

hashed_relocation
Tunes the block allocator. This may provide performance improvements in some situa-
tions.

no_unhashed_relocation
Tunes the block allocator. This may provide performance improvements in some situa-
tions.

noborder
Disable the border allocator algorithm invented by Yury Yu. Rupasov. This may pro-
vide performance improvements in some situations.

nolog Disable journaling. This will provide slight performance improvements in some situ-
ations 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 pack-
ing 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 spe-
cial resizer utility which can be obtained from ftp://ftp.namesys.com/pub/reiserf-
sprogs.

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 enables/disables the use of write barriers in the journaling code. bar-
rier=none disables it, barrier=flush enables it. Write barriers enforce proper on-
disk ordering of journal commits, making volatile disk write caches safe to use, at
some performance penalty. The reiserfs filesystem does not enable write barriers by
default. Be sure to enable barriers unless your disks are battery-backed one way or
another. Otherwise you risk filesystem corruption in case of power failure.

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, mega and giga) 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-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 ker-
nel 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 auto-
matic 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 informa-
tion. 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 undocu-
mented, 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 behaviour 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 encoun-
tered 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 illegal 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={lower|win95|winnt|mixed}

Defines the behaviour for creation and display of filenames which fit into 8.3
characters. If a long name for a file exists, it will always be preferred 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 shortname 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 behaviour is for dynamic end-of-file preallocation size, which uses a
set of heuristics to optimise the preallocation size based on the current alloca-
tion patterns within the file and the access patterns to the file. Specifying a
fixed allocsize value turns off the dynamic behaviour.

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 behaviour is determined by the on-disk feature bit indicating that
attr2 behaviour 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.

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 applica-
tions, 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/mod-
ify/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 behaviour 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 relevent to this case.

logbsize=value
Set the size of each in-memory log buffer. The size may be specified in bytes, or
in kilobytes with a "k" suffix. Valid sizes for version 1 and version 2 logs are
16384 (16k) and 32768 (32k). Valid sizes for version 2 logs also include 65536
(64k), 131072 (128k) and 262144 (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=deviceandrtdev=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 rele-
vant 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. Filesys-
tems 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 "norecov-
ery" 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 dur-
ing or after a failover event.

Mount options for xiafs
None. Although nothing is wrong with xiafs, it is not used much, and is not maintained.
Probably one shouldn't use it. Since Linux version 2.1.21 xiafs is no longer part of the
kernel source.

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/loop

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 ext4 /tmp/disk.img /mnt

This type of mount knows about four 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 is supported auto-destruction of loop devices and then any loop device
allocated by mount will be freed by umount independently on /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 success), 32 (all failed) or 64 (some failed, some
success).

NOTES
The syntax of external mount helpers is:

/sbin/mount.<suffix> spec dir [-sfnv] [-o options] [-t type.subtype]

where the <type> is filesystem type and -sfnvo options have same meaning like standard
mount options. The -t option is used for filesystems with subtypes support (for example
/sbin/mount.fuse -t fuse.sshfs).

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, ext4, fat and
vfat filesystems do support synchronous updates (a la BSD) when mounted with the sync
option).

The -o remount may not be able to change mount parameters (all ext2fs-specific parameters,
except sb, are changeable with a remount, for example, but you can't change gid or umask
for the fatfs).

It is possible that files /etc/mtab and /proc/mounts don't match. 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 usu-
ally contains more reliable information.)

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 ker-
nels if the mount command can't confirm that the size of the block device has been config-
ured as requested. This situation can be worked around by using the losetup command manu-
ally before calling mount with the configured loop device.

HISTORY
A mount command existed in Version 5 AT&T UNIX.

AUTHORS
Karel Zak <kzak AT redhat.com>

AVAILABILITY
The mount command is part of the util-linux package and is available from ftp://ftp.ker-
nel.org/pub/linux/utils/util-linux/.

util-linux January 2012 MOUNT(8)

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