MOUNT(8) System Administration December 2004

mount - mount a filesystem

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

.IB 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 " typedevicedir"


This tells the kernel to attach the filesystem found on

device

(which is of type

type)

at the directory

dir.

The previous contents (if any) and owner and mode of

dir

become invisible, and as long as this filesystem remains mounted, the pathname

dir

refers to the root of the filesystem on

device.

If only 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.

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 the use symlinks in /etc/fstab has no advantage over LABEL=/UUID=. 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 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). It's also possible to use the bind mount to create a mountpoint from a regular directory, for example:


mount --bind

foo foo

The bind mount call attaches only (part of) a single filesystem, not possible submounts. The entire file hierarchy including submounts is attached a second place 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

Note that behavior of the remount operation depends on the /etc/mtab file. The first command stores the 'bind' flag to the /etc/mtab file and the second command reads the flag from the file. If you have a system without the /etc/mtab file or if you explicitly define source and target for the remount command (then mount(8) does not read /etc/mtab), then you have to use bind flag (or option) for the remount command too. For example:


mount --bind

olddir newdir


mount -o remount,ro,bind

olddir 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. Note that the

olddir

has to be a mountpoint.

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 be cloned through a bind operation. Detailed semantics is documented in Documentation/filesystems/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:

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

reatime

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.

Note that kernel rejects any remount request that includes the context option even if unchanged from the current context.

For more details, see

selinux(8)

defaults
Use default options:

rw, suid , dev , exec , auto , nouser , and async.

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).

encryption
Specifies an encryption algorithm to use. Used in conjunction with the

loop option.

keybits
Specifies the key size to use for an encryption algorithm. Used in conjunction with the

loop and encryption options.

nofail

Do not report errors for this device if it does not exist.

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.)
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 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 (smbfs 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.
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 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.
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 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 and usrquota

are backwardly compatible with ext3 or ext2.
journal_checksum
Enable checksumming of the journal transactions. This will allow the recovery code in e2fsck and the kernel to detect corruption in the kernel. It is a compatible change and will be ignored by older kernels.
journal_async_commit
Commit block can be written to disk without waiting for descriptor blocks. If enabled older kernels cannot mount the device. This will enable 'journal_checksum' internally.
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=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 default value is 32 blocks.
stripe=n
Number of filesystem blocks that mballoc will try to use for allocation size and alignment. For RAID5/6 systems this should be the number of data disks * RAID chunk size in filesystem blocks.
delalloc
Deferring block allocation until write-out time.
nodelalloc
Disable delayed allocation. Blocks are allocated when data is copied from user to page cache.
max_batch_time=usec
Maximum amount of time ext4 should wait for additional filesystem operations to be batch together with a synchronous write operation. Since a synchronous write operation is going to force a commit and then a wait for the I/O complete, it doesn't cost much, and can be a huge throughput win, we wait for a small amount of time to see if any other transactions can piggyback on the synchronous write. The algorithm used is designed to automatically tune for the speed of the disk, by measuring the amount of time (on average) that it takes to finish committing a transaction. Call this time the "commit time". If the time that the transaction has been running is less than the commit time, ext4 will try sleeping for the commit time to see if other operations will join the transaction. The commit time is capped by the max_batch_time, which defaults to 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 replacing existing files via patterns such as

fd = open("foo.new")/write(fd,..)/close(fd)/ rename("foo.new", "foo")

or worse yet

fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).

If auto_da_alloc is enabled, ext4 will detect the replace-via-rename and replace-via-truncate patterns and force that any delayed allocation blocks are allocated such that at the next journal commit, in the default data=ordered mode, the data blocks of the new file are forced to disk before the rename() operation is committed. This provides roughly the same level of guarantees as ext3, and avoids the "zero-length" problem that can happen when a system crashes before the delayed allocation blocks are forced to disk.

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 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 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-common package must be installed).

The

nfs and nfs4

implementation expects a binary argument (a

struct nfs_mount_data )

to the mount system call. This argument is constructed by

mount.nfs(8)

and the current version of

mount

(2.13) does not know anything about nfs and nfs4.

Mount options for ntfs

iocharset=name
Character set to use when returning file names. Unlike VFAT, NTFS suppresses names that contain nonconvertible characters. Deprecated.
nls=name
New name for the option earlier called

iocharset.

utf8
Use UTF-8 for converting file names.
uni_xlate={0|1|2}
For 0 (or `no' or `false'), do not use escape sequences for unknown Unicode characters. For 1 (or `yes' or `true') or 2, use vfat-style 4-byte escape sequences starting with ":". Here 2 give a little-endian encoding and 1 a byteswapped bigendian encoding.
posix=[0|1]
If enabled (posix=1), the filesystem distinguishes between upper and lower case. The 8.3 alias names are presented as hard links instead of being suppressed. This option is obsolete.
uid=value, gid=value and umask=value
Set the file permission on the filesystem. The umask value is given in octal. By default, the files are owned by root and not readable by somebody else.

Mount options for proc

uid=value and gid=value
These options are recognized, but have no effect as far as I can see.

Mount options for ramfs

Ramfs is a memory based filesystem. Mount it and you have it. Unmount it and it is gone. Present since Linux 2.3.99pre4. There are no mount options.

Mount options for reiserfs

Reiserfs is a journaling filesystem.
conv
Instructs version 3.6 reiserfs software to mount a version 3.5 filesystem, using the 3.6 format for newly created objects. This filesystem will no longer be compatible with reiserfs 3.5 tools.
hash={rupasov|tea|r5|detect}
Choose which hash function reiserfs will use to find files within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast and preserves locality, mapping lexicographically close file names to close hash values. This option should not be used, as it causes a high probability of hash collisions.
tea
A Davis-Meyer function implemented by Jeremy Fitzhardinge. It uses hash permuting bits in the name. It gets high randomness and, therefore, low probability of hash collisions at some CPU cost. This may be used if EHASHCOLLISION errors are experienced with the r5 hash.
r5
A modified version of the rupasov hash. It is used by default and is the best choice unless the filesystem has huge directories and unusual file-name patterns.
detect
Instructs

mount

to detect which hash function is in use by examining the filesystem being mounted, and to write this information into the reiserfs superblock. This is only useful on the first mount of an old format filesystem.
hashed_relocation
Tunes the block allocator. This may provide performance improvements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance improvements in some situations.
noborder
Disable the border allocator algorithm invented by Yury Yu. Rupasov. This may provide performance improvements in some situations.
nolog
Disable 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

.B

atime is not supported and is always turned off.
The device name may be specified as

ubiX_Y

UBI device number

X,

volume number

Y

ubiY
UBI device number

0,

volume number

Y

ubiX:NAME
UBI device number

X,

volume with name

NAME

ubi:NAME
UBI device number

0,

volume with name

NAME

Alternative

!

separator may be used instead of

:.

The following mount options are available:
bulk_read
Enable bulk-read. VFS read-ahead is disabled because it slows down the file system. Bulk-Read is an internal optimization. Some flashes may read faster if the data are read at one go, rather than at several read requests. For example, OneNAND can do "read-while-load" if it reads more than one NAND page.
no_bulk_read
Do not bulk-read. This is the default.
chk_data_crc
Check data CRC-32 checksums. This is the default.
no_chk_data_crc.
Do not check data CRC-32 checksums. With this option, the filesystem does not check CRC-32 checksum for data, but it does check it for the internal indexing information. This option only affects reading, not writing. CRC-32 is always calculated when writing the data.
compr={none|lzo|zlib}
Select the default compressor which is used when new files are written. It is still possible to read compressed files if mounted with the

none

option.

Mount options for udf

udf is the "Universal Disk Format" filesystem defined by the Optical Storage Technology Association, and is often used for DVD-ROM. See also

iso9660.

gid=
Set the default group.
umask=
Set the default umask. The value is given in octal.
uid=
Set the default user.
unhide
Show otherwise hidden files.
undelete
Show deleted files in lists.
nostrict
Unset strict conformance.
iocharset
Set the NLS character set.
bs=
Set the block size. (May not work unless 2048.)
novrs
Skip volume sequence recognition.
session=
Set the CDROM session counting from 0. Default: last session.
anchor=
Override standard anchor location. Default: 256.
volume=
Override the VolumeDesc location. (unused)
partition=
Override the PartitionDesc location. (unused)
lastblock=
Set the last block of the filesystem.
fileset=
Override the fileset block location. (unused)
rootdir=
Override the root directory location. (unused)

Mount options for ufs

ufstype=value
UFS is a filesystem widely used in different operating systems. The problem are differences among implementations. Features of some implementations are undocumented, so its hard to recognize the type of ufs automatically. That's why the user must specify the type of ufs by mount option. Possible values are:
old
Old format of ufs, this is the default, read only. (Don't forget to give the -r option.)
44bsd
For filesystems created by a BSD-like system (NetBSD,FreeBSD,OpenBSD).
ufs2
Used in FreeBSD 5.x supported as read-write.
5xbsd
Synonym for ufs2.
sun
For filesystems created by SunOS or Solaris on Sparc.
sunx86
For filesystems created by Solaris on x86.
hp
For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT station) (currently read only).
nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
openstep
For filesystems created by OpenStep (currently read only). The same filesystem type is also used by Mac OS X.

onerror=value
Set 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 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 (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 any recent kernel.
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 any recent kernel is 32768.
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/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 ext3 /tmp/disk.img /mnt"



This type of mount knows about four options, namely

loop, offset , sizelimit and encryption ,

that are really options to

%losetup(8).

If the mount requires a passphrase, you will be prompted for one unless you specify a file descriptor to read from instead with the

--pass-fd

option. (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

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 package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.