mount - Cheap VPS LLC

MOUNT


Section: Linux Programmer’s Manual (8)
Updated: 2004-12-16
Index
Return to Main Contents

 

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.


The listing and help.


Three forms of invocation do not actually mount anything:

mount -h


prints a help message
mount -V


prints a version string
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
volume
LABEL

or
UUID

(see the -L and -U options below).


The recommended setup is to use LABEL=<label> or UUID=<uuid> tags rather than
/dev/disk/by-{label,uuid}

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 is not advantage over LABEL=/UUID=.
For more details see libblkid(3).


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 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 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) 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


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, 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).


This call attaches only (part of) a single filesystem, not possible
submounts. 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 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



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.


The shared subtrees 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 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 cloned through a bind
operation. Detailed semantics is documented in Documentation/sharedsubtree.txt
file in the kernel source tree.




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


 

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
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
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

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.

–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 absolut paths.

-p, –pass-fd num

In case of a loop mount with encryption, read the passphrase from
file descriptor
num

instead of from the terminal.

-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.
-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

Mount the filesystem read/write. This is the default. A synonym is
-o rw.

-L label

Mount the partition that has the specified
label.

-U 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, –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,

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 ‘.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
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 or volume_id 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.


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.
Warning: the probing uses a heuristic (the presence of appropriate `magic’),
and could recognize the wrong filesystem type, possibly with catastrophic
consequences. If your data is valuable, don’t ask
mount

to guess.


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

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.


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, 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 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 because visable to userspace. This was found to be
useful for things like stateless linux.


For more details, see
selinux(8)


defaults


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

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 kernel 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.)
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 writeable. 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.
_rnetdev


Like _netdev, except "fsck -a" checks this filesystem during rc.sysinit.
rw


Mount the filesystem read-write.
sync


All I/O to the filesystem should be done synchronously. In case of media with 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 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).



 

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 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.

There are no mount options.


 

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 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|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.

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


These options are accepted but ignored.
nobh


Do not attach buffer_heads to file pagecache. (Since 2.5.49.)
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 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 journalling. 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
identified 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 inconsistencies that can
lead to any number of problems.
data={journal|ordered|writeback}


Specifies the journalling 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.

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 enables 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.
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.



 

Mount options for ext4

The ext4 filesystem is an an advanced level of the ext3 filesystem which
incorporates scalability 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

and
[no]bh

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=update


Update the ext4 filesystem’s journal to the current format.
barrier=0 / barrier=1 / barrier / nobarrier


This enables/disables the use of write barriers in the jbd code. barrier=0
disables, barrier=1 enables. This also requires an IO stack which can support
barriers, 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 allocation 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 transactoin 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 priorty) 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 noauto_da_alloc
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 commited. 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 nobh option
and the mount will fail. Nor does it 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 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 unflexible. 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
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 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 filesystems. 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 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).

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.
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 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 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 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 abends.
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 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.)
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 writeable 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
unconvertible 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 journalling. 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 journalling
operations, save for actual writes into its journalling 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 enables/disables the use of write barriers in the journaling code.
barrier=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 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).
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 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 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 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. This mode is the default.
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.




 

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 (default size is 64KiB).
Valid values for this option are page size (typically 4KiB)
through to 1GiB, inclusive, in power-of-2 increments.
attr2|noattr2


The options enable/disable (default is enabled) 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 (by setting or
removing extended attributes) the on-disk superblock feature
bit field will be updated to reflect this format being in use.
barrier


Enables the use of block layer write barriers for writes into
the journal and unwritten extent conversion. This allows for
drive level write caching to be enabled, for devices that
support write barriers.
dmapi


Enable the DMAPI (Data Management API) event callouts.
Use with the
mtpt

option.

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.
ihashsize=value


Sets the number of hash buckets available for hashing the
in-memory inodes of the specified mount point. If a value
of zero is used, the value selected by the default algorithm
will be displayed in
/proc/mounts.

ikeep|noikeep


When inode clusters are emptied of inodes, keep them around
on the disk (ikeep) – this is the traditional XFS behaviour
and is still the default for now. Using the noikeep option,
inode clusters are returned to the free space pool.
inode64


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. This is
provided for backwards compatibility, but causes problems for
backup applications that cannot handle large inode numbers.
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.
If
largeio

is specified, a filesystem that has 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.
If neither of these two options are specified, then filesystem
will behave 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 for filesystems with a
blocksize of 64KiB, 4 buffers for filesystems with a blocksize
of 32KiB, 3 buffers for filesystems with a blocksize of 16KiB
and 2 buffers for all other configurations. Increasing the
number of buffers may increase performance on some workloads
at the cost of the memory used for the additional log buffers
and their associated control structures.
logbsize=value


Set the size of each in-memory log buffer.
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 default value for machines with more than 32MiB of memory
is 32768, machines with less memory use 16384 by default.
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.
Refer to
xfs(5).

mtpt=mountpoint


Use with the
dmapi

option. The value specified here will be
included in the DMAPI mount event, and should be the path of
the actual mountpoint that is used.

noalign


Data allocations will not be aligned at stripe unit boundaries.
noatime


Access timestamps are not updated when a file is read.
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 filesystems using the filesystem uuid.
This is useful to mount LVM snapshot volumes.
osyncisosync


Make O_SYNC writes implement true O_SYNC. WITHOUT this option,
Linux XFS behaves as if an
osyncisdsync

option is used,
which will make writes to files opened with the O_SYNC flag set
behave as if the O_DSYNC flag had been used instead.
This can result in better performance without compromising
data safety.
However if this option is not in effect, timestamp updates from
O_SYNC writes can be lost if the system crashes.
If timestamp updates are critical, use the
osyncisosync

option.

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.
If this option is not specified and the filesystem was made on a stripe
volume or the stripe width or unit were specified for the RAID device at
mkfs time, then the mount system call will restore the value from the
superblock.
For filesystems that are made directly on RAID devices, these options can be
used to override the information in the superblock if the underlying disk
layout changes after the filesystem has been created.
The
swidth

option is required if the
sunit

option has been specified,
and must be a multiple of the
sunit

value.

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.



 

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/fdimage /mnt -t vfat -o loop=/dev/loop3


will set up the loop device
/dev/loop3

to correspond to the file
/tmp/fdimage,

and then mount this device on
/mnt.


This type of mount knows about four options, namely
loop, offset, sizelimit and encryption,

that are really options to
losetup(8).

(These options can be used in addition to those specific
to the filesystem type.)


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.


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



 

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



 

SEE ALSO

mount(2),

umount(2),

fstab(5),

umount(8),

swapon(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).

Mount by label or uuid will work only if your devices have the names listed in
/proc/partitions.

In particular, it may well fail if the kernel was compiled with devfs
but devfs is not mounted.

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 usually 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.
 

HISTORY

A
mount

command existed in Version 5 AT&T UNIX.
 

AVAILABILITY

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




 

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 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

Mount options for xiafs

THE LOOP DEVICE

RETURN CODES

NOTES

FILES

SEE ALSO

BUGS

HISTORY

AVAILABILITY



Back to Top

PayPal Logo┬ęCheap VPS LLC - Leader of affordable VPS Hosting Services