MOUNT(8) System Administration MOUNT(8)
NAME
mount - mount a filesystem
SYNOPSIS
mount [-lhV]
mount -a [-fFnrsvw] [-t vfstype] [-O optlist]
mount [-fnrsvw] [-o option[,option]...] device|dir
mount [-fnrsvw] [-t vfstype] [-o options] device dir
DESCRIPTION
All files accessible in a Unix system are arranged in one big tree, the
file hierarchy, rooted at /. These files can be spread out over sev-
eral devices. The mount command serves to attach the filesystem found
on some device to the big file tree. Conversely, the umount(8) command
will detach it again.
The standard form of the mount command, is
mount -t type device dir
This tells the kernel to attach the filesystem found on device (which
is of type type) at the directory dir. The previous contents (if any)
and owner and mode of dir become invisible, and as long as this
filesystem remains mounted, the pathname dir refers to the root of the
filesystem on device.
If only directory or device is given, for example:
mount /dir
then mount looks for a mountpoint and if not found then for a device in
the /etc/fstab file. It's possible to use --target or --source options
to avoid ambivalent interpretation of the given argument. For example
mount --target /mountpoint
The listing and help.
The listing mode is maintained for backward compatibility only.
For more robust and definable output use findmnt(8), especially
in your scripts. Note that control characters in the mountpoint
name are replaced with '?'.
mount [-l] [-t type]
lists all mounted filesystems (of type type). The option
-l adds the labels in this listing. See below.
The device indication.
Most devices are indicated by a file name (of a block special
device), like /dev/sda1, but there are other possibilities. For
example, in the case of an NFS mount, device may look like
knuth.cwi.nl:/dir. It is possible to indicate a block special
device using its filesystem LABEL or UUID (see the -L and -U
options below) and partition PARTUUID or PARTLABEL (partition
identifiers are supported for GUID Partition Table (GPT) and MAC
partition tables only).
The recommended setup is to use tags (e.g. LABEL=<label>) rather
than /dev/disk/by-{label,uuid,partuuid,partlabel} udev symlinks
in the /etc/fstab file. The tags are more readable, robust and
portable. The mount(8) command internally uses udev symlinks, so
use the symlinks in /etc/fstab has no advantage over the tags.
For more details see libblkid(3).
Note that mount(8) uses UUIDs as strings. The UUIDs from command
line or fstab(5) are not converted to internal binary represen-
tation. The string representation of the UUID should be based on
lower case characters.
The proc filesystem is not associated with a special device, and
when mounting it, an arbitrary keyword, such as proc can be used
instead of a device specification. (The customary choice none
is less fortunate: the error message `none busy' from umount can
be confusing.)
The /etc/fstab, /etc/mtab and /proc/mounts files.
The file /etc/fstab (see fstab(5)), may contain lines describing
what devices are usually mounted where, using which options. The
default location of the fstab(5) file could be overridden by
--fstab <path> command line option (see below for more details).
The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all filesystems mentioned
in fstab (of the proper type and/or having or not having the
proper options) to be mounted as indicated, except for those
whose line contains the noauto keyword. Adding the -F option
will make mount fork, so that the filesystems are mounted simul-
taneously.
When mounting a filesystem mentioned in fstab or mtab, it suf-
fices 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, PARTUUID or PARTLABEL) and dir are specified.
For example:
mount /dev/foo /dir
If you want to override mount options from /etc/fstab you have
to use:
mount device|dir -o <options>
and then the mount options from command line will be appended to
the list of options from /etc/fstab. The usual behaviour is
that the last option wins if there is more duplicated options.
When the proc filesystem is mounted (say at /proc), the files
/etc/mtab and /proc/mounts have very similar contents. The for-
mer 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 sub-
mounts 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.
mount(8) since v2.27 (backported to RHEL7.3) allow to change the
options by passing the -o option along with --bind for example:
mount --bind,ro foo foo
This feature is not supported by Linux kernel and it is imple-
mented in userspace by additional remount mount(2) syscall. This
solution is not atomic.
The alternative (classic) way to create a read-only bind mount
is to use remount operation, for example:
mount --bind olddir newdir
mount -o remount,ro,bind olddir newdir
Note that read-only bind will create a read-only mountpoint (VFS
entry), but the original filesystem superblock will still be
writable, meaning that the olddir will be writable, but the
newdir will be read-only.
It's impossible to change mount options recursively (for example
with -o rbind,ro).
The move operation.
Since Linux 2.5.1 it is possible to atomically move a mounted
tree to another place. The call is
mount --move olddir newdir
or shortoption
mount -M olddir newdir
This will cause the contents which previously appeared under
olddir to be accessed under newdir. The physical location of
the files is not changed. Note that the olddir has to be a
mountpoint.
Note that moving a mount residing under a shared mount is
invalid and unsupported. Use findmnt -o TARGET,PROPAGATION to
see the current propagation flags.
The shared subtrees operations.
Since Linux 2.6.15 it is possible to mark a mount and its sub-
mounts 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 mas-
ter, but any not vice-versa. A private mount carries no propa-
gation abilities. A unbindable mount is a private mount which
cannot be cloned through a bind operation. Detailed semantics is
documented in Documentation/filesystems/sharedsubtree.txt file
in the kernel source tree.
Supported operations:
mount --make-shared mountpoint
mount --make-slave mountpoint
mount --make-private mountpoint
mount --make-unbindable mountpoint
The following commands allows one to recursively change the type
of all the mounts under a given mountpoint.
mount --make-rshared mountpoint
mount --make-rslave mountpoint
mount --make-rprivate mountpoint
mount --make-runbindable mountpoint
mount(8) does not read fstab(5) when --make-* operation is
requested. All necessary information has to be specified on com-
mand line.
Note that Linux kernel does not allow to change more propagation
flags by one mount(2) syscall and the flags cannot be mixed with
another mount options.
Since util-linux 2.23 mount command allows to use more propaga-
tion flags together and with another mount operations. This fea-
ture is EXPERIMENTAL. The propagation flags are applied by
additional mount(2) syscalls after previous successful mount
operation. Note that this use case is not atomic. The propaga-
tion flags is possible to specify in fstab(5) as mount options
(private, slave, shared, unbindable, rprivate, rslave, rshared,
runbindable).
For example
mount --make-private --make-unbindable /dev/sda1 /A
is the same as
mount /dev/sda1 /A
mount --make-private /A
mount --make-unbindable /A
COMMAND LINE OPTIONS
The full set of mount options used by an invocation of mount is deter-
mined 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 deter-
mine what the mount command is trying to do. It can also be used
to add entries for devices that were mounted earlier with the -n
option. The -f option checks for existing record in /etc/mtab
and fails when the record already exists (with regular non-fake
mount, this check is done by kernel).
-i, --internal-only
Don't call the /sbin/mount.<filesystem> helper even if it
exists.
-l, --show-labels
Add the labels in the mount output. Mount must have permission
to read the disk device (e.g. be suid root) for this to work.
One can set such a label for ext2, ext3 or ext4 using the
e2label(8) utility, or for XFS using xfs_admin(8), or for reis-
erfs using reiserfstune(8).
-n, --no-mtab
Mount without writing in /etc/mtab. This is necessary for exam-
ple when /etc is on a read-only filesystem.
-c, --no-canonicalize
Don't canonicalize paths. The mount command canonicalizes all
paths (from command line or fstab) and stores canonicalized
paths to the /etc/mtab file. This option can be used together
with the -f flag for already canonicalized absolute paths.
-s Tolerate sloppy mount options rather than failing. This will
ignore mount options not supported by a filesystem type. Not all
filesystems support this option. This option exists for support
of the Linux autofs-based automounter.
--source src
If only one argument for the mount command is given then the
argument might be interpreted as target (mountpoint) or source
(device). This option allows to explicitly define that the argu-
ment is mount source.
-r, --read-only
Mount the filesystem read-only. A synonym is -o ro.
Note that, depending on the filesystem type, state and kernel
behavior, the system may still write to the device. For example,
Ext3 or ext4 will replay its journal if the filesystem is dirty.
To prevent this kind of write access, you may want to mount ext3
or ext4 filesystem with "ro,noload" mount options or set the
block device to read-only mode, see command blockdev(8).
-w, --rw, --read-write
Mount the filesystem read/write. This is the default. A synonym
is -o rw.
-L, --label label
Mount the partition that has the specified label.
-U, --uuid uuid
Mount the partition that has the specified uuid. These two
options require the file /proc/partitions (present since Linux
2.1.116) to exist.
-T, --fstab path
Specifies alternative fstab file. If the path is directory then
the files in the directory are sorted by strverscmp(3), files
that starts with "." or without .fstab extension are ignored.
The option can be specified more than once. This option is
mostly designed for initramfs or chroot scripts where additional
configuration is specified outside standard system configura-
tion.
Note that mount(8) does not pass the option --fstab to
/sbin/mount.<type> helpers, it means that the alternative fstab
files will be invisible for the helpers. This is no problem for
normal mounts, but user (non-root) mounts always require fstab
to verify user's rights.
-t, --types vfstype
The argument following the -t is used to indicate the filesystem
type. The filesystem types which are currently supported
include: adfs, affs, autofs, cifs, coda, coherent, cramfs,
debugfs, devpts, efs, ext, ext2, ext3, ext4, hfs, hfsplus, hpfs,
iso9660, jfs, minix, msdos, ncpfs, nfs, nfs4, ntfs, proc, qnx4,
ramfs, 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 ker-
nel.
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 filesys-
tem 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 pro-
gram. In order to make it possible to treat all types in a uni-
form way, mount will execute the program /sbin/mount.TYPE (if
that exists) when called with type TYPE. Since various versions
of the smbmount program have different calling conventions,
/sbin/mount.smbfs may have to be a shell script that sets up the
desired call.
If no -t option is given, or if the auto type is specified,
mount will try to guess the desired type. Mount uses the blkid
library for guessing the filesystem type; if that does not turn
up anything that looks familiar, mount will try to read the file
/etc/filesystems, or, if that does not exist, /proc/filesystems.
All of the filesystem types listed there will be tried, except
for those that are labeled "nodev" (e.g., devpts, proc and nfs).
If /etc/filesystems ends in a line with a single * only, mount
will read /proc/filesystems afterwards. All of the filesystem
types will be mounted with mount option "silent".
The auto type may be useful for user-mounted floppies. Creating
a file /etc/filesystems can be useful to change the probe order
(e.g., to try vfat before msdos or ext3 before ext2) or if you
use a kernel module autoloader.
More than one type may be specified in a comma separated list.
The list of filesystem types can be prefixed with no to specify
the filesystem types on which no action should be taken. (This
can be meaningful with the -a option.) For example, the command:
mount -a -t nomsdos,ext
mounts all filesystems except those of type msdos and ext.
--target dir
If only one argument for the mount command is given then the
argument might be interpreted as target (mountpoint) or source
(device). This option allows to explicitly define that the argu-
ment is mount target.
-O, --test-opts opts
Used in conjunction with -a, to limit the set of filesystems to
which the -a is applied. Like -t in this regard except that it
is useless except in the context of -a. For example, the com-
mand:
mount -a -O no_netdev
mounts all filesystems except those which have the option _net-
dev 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 sepa-
rated string of options. For example:
mount LABEL=mydisk -o noatime,nouser
For more details, see FILESYSTEM INDEPENDENT MOUNT OPTIONS and
FILESYSTEM SPECIFIC MOUNT OPTIONS sections.
-B, --bind
Remount a subtree somewhere else (so that its contents are
available in both places). See above.
-R, --rbind
Remount a subtree and all possible submounts somewhere else (so
that its contents are available in both places). See above.
-M, --move
Move a subtree to some other place. See above.
FILESYSTEM INDEPENDENT MOUNT OPTIONS
Some of these options are only useful when they appear in the
/etc/fstab file.
Some of these options could be enabled or disabled by default in the
system kernel. To check the current setting see the options in
/proc/mounts. Note that filesystems also have per-filesystem specific
default mount options (see for example tune2fs -l output for extN
filesystems).
The following options apply to any filesystem that is being mounted
(but not every filesystem actually honors them - e.g., the sync option
today has effect only for ext2, ext3, ext4, fat, vfat and ufs):
async All I/O to the filesystem should be done asynchronously. (See
also the sync option.)
atime Do not use noatime feature, then the inode access time is con-
trolled by kernel defaults. See also the description for stric-
tatime 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 rootcon-
text=context
The context= option is useful when mounting filesystems that do
not support extended attributes, such as a floppy or hard disk
formatted with VFAT, or systems that are not normally running
under SELinux, such as an ext3 or ext4 formatted disk from a
non-SELinux workstation. You can also use context= on filesys-
tems you do not trust, such as a floppy. It also helps in com-
patibility 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="sys-
tem_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 them-
selves. 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 unla-
beled files in the policy and requires a filesystem that sup-
ports xattr labeling.
The rootcontext= option allows you to explicitly label the root
inode of a FS being mounted before that FS or inode becomes vis-
ible to userspace. This was found to be useful for things like
stateless linux.
Note that the kernel rejects any remount request that includes
the context option, even when unchanged from the current con-
text.
Warning: the context value might contain commas, in which case
the value has to be properly quoted, otherwise mount(8) will
interpret the comma as a separator between mount options. Don't
forget that the shell strips off quotes and thus double quoting
is required. For example:
mount -t tmpfs none /mnt -o 'context="sys-
tem_u:object_r:tmp_t:s0:c127,c456",noexec'
For more details, see selinux(8).
defaults
Use default options: rw, suid, dev, exec, auto, nouser, and
async.
Note that the real set of the all default mount options depends
on kernel and filesystem type. See the begin of this section for
more details.
dev Interpret character or block special devices on the filesystem.
nodev Do not interpret character or block special devices on the file
system.
diratime
Update directory inode access times on this filesystem. This is
the default.
nodiratime
Do not update directory inode access times on this filesystem.
dirsync
All directory updates within the filesystem should be done syn-
chronously. 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 ear-
lier than the current modify or change time. (Similar to noat-
ime, but doesn't break mutt or other applications that need to
know if a file has been read since the last time it was modi-
fied.)
Since Linux 2.6.30, the kernel defaults to the behavior provided
by this option (unless noatime was specified), and the stricta-
time 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 com-
monly used to change the mount flags for a filesystem, espe-
cially 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 com-
mand 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 filesys-
tem. This is the default.
users Allow every user to mount and unmount the filesystem. This
option implies the options noexec, nosuid, and nodev (unless
overridden by subsequent options, as in the option line
users,exec,dev,suid).
x-* All options prefixed with "x-" are interpreted as comments or
userspace applications specific options. These options are not
stored to mtab file, send to mount.<type> helpers or mount(2)
system call. The suggested format is x-<appname>.<option> (e.g.
x-systemd.automount).
x-mount.mkdir[=<mode>]
Allow to make a target directory (mountpoint). The optional
argument <mode> specifies the file system access mode used for
mkdir (2) in octal notation. The default mode is 0755. This
functionality is supported only for root users.
FILESYSTEM SPECIFIC MOUNT OPTIONS
The following options apply only to certain filesystems. We sort them
by filesystem. They all follow the -o flag.
What options are supported depends a bit on the running kernel. More
info may be found in the kernel source subdirectory Documenta-
tion/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, respec-
tively). See also /usr/src/linux/Documentation/filesys-
tems/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 orig-
inal 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 filesys-
tem.
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 utili-
ties 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 pack-
age must be installed).
Mount options for coherent
None.
Mount options for debugfs
The debugfs filesystem is a pseudo filesystem, traditionally mounted on
/sys/kernel/debug. As of kernel version 3.4, debugfs has the following
options:
uid=n, gid=n
Set the owner and group of the mountpoint.
mode=value
Sets the mode of the mountpoint.
Mount options for devpts
The devpts filesystem is a pseudo filesystem, traditionally mounted on
/dev/pts. In order to acquire a pseudo terminal, a process opens
/dev/ptmx; the number of the pseudo terminal is then made available to
the process and the pseudo terminal slave can be accessed as
/dev/pts/<number>.
uid=value and gid=value
This sets the owner or the group of newly created PTYs to the
specified values. When nothing is specified, they will be set to
the UID and GID of the creating process. For example, if there
is a tty group with GID 5, then gid=5 will cause newly created
PTYs to belong to the tty group.
mode=value
Set the mode of newly created PTYs to the specified value. The
default is 0600. A value of mode=620 and gid=5 makes "mesg y"
the default on newly created PTYs.
newinstance
Create a private instance of devpts filesystem, such that
indices of ptys allocated in this new instance are independent
of indices created in other instances of devpts.
All mounts of devpts without this newinstance option share the
same set of pty indices (i.e legacy mode). Each mount of devpts
with the newinstance option has a private set of pty indices.
This option is mainly used to support containers in the linux
kernel. It is implemented in linux kernel versions starting with
2.6.29. Further, this mount option is valid only if CON-
FIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configu-
ration.
To use this option effectively, /dev/ptmx must be a symbolic
link to pts/ptmx. See Documentation/filesystems/devpts.txt in
the linux kernel source tree for details.
ptmxmode=value
Set the mode for the new ptmx device node in the devpts filesys-
tem.
With the support for multiple instances of devpts (see newin-
stance 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 start-
ing with 2.6.29. Further this option is valid only if CON-
FIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configu-
ration.
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 behav-
iour is to return in the f_blocks field the total number of
blocks of the filesystem, while the bsddf behaviour (which is
the default) is to subtract the overhead blocks used by the ext2
filesystem and not available for file storage. Thus
% mount /k -o minixdf; df /k; umount /k
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/sda6 2630655 86954 2412169 3% /k
% mount /k -o bsddf; df /k; umount /k
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/sda6 2543714 13 2412169 0% /k
(Note that this example shows that one can add command line
options to the options given in /etc/fstab.)
check=none or nocheck
No checking is done at mount time. This is the default. This is
fast. It is wise to invoke e2fsck(8) every now and then, e.g.
at boot time. The non-default behavior is unsupported
(check=normal and check=strict options have been removed). Note
that these mount options don't have to be supported if ext4 ker-
nel driver is used for ext2 and ext3 filesystems.
debug Print debugging info upon each (re)mount.
errors={continue|remount-ro|panic}
Define the behaviour when an error is encountered. (Either
ignore errors and just mark the filesystem erroneous and con-
tinue, or remount the filesystem read-only, or panic and halt
the system.) The default is set in the filesystem superblock,
and can be changed using tune2fs(8).
grpid|bsdgroups and nogrpid|sysvgroups
These options define what group id a newly created file gets.
When grpid is set, it takes the group id of the directory in
which it is created; otherwise (the default) it takes the fsgid
of the current process, unless the directory has the setgid bit
set, in which case it takes the gid from the parent directory,
and also gets the setgid bit set if it is a directory itself.
grpquota|noquota|quota|usrquota
The usrquota (same as quota) mount option enables user quota
support on the filesystem. grpquota enables group quotas sup-
port. You need the quota utilities to actually enable and manage
the quota system.
nouid32
Disables 32-bit UIDs and GIDs. This is for interoperability
with older kernels which only store and expect 16-bit values.
oldalloc or orlov
Use old allocator or Orlov allocator for new inodes. Orlov is
default.
resgid=n and resuid=n
The ext2 filesystem reserves a certain percentage of the avail-
able 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 journaling. It supports the same options as ext2 as well
as the following additions:
journal=update
Update the ext3 filesystem's journal to the current format.
journal=inum
When a journal already exists, this option is ignored. Other-
wise, 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 journaling mode for file data. Metadata is always
journaled. To use modes other than ordered on the root filesys-
tem, pass the mode to the kernel as boot parameter, e.g. root-
flags=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, bar-
rier=1 enables it. Write barriers enforce proper on-disk order-
ing 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 barri-
ers unless your disks are battery-backed one way or another.
Otherwise you risk filesystem corruption in case of power fail-
ure.
commit=nrsec
Sync all data and metadata every nrsec seconds. The default
value is 5 seconds. Zero means default.
user_xattr
Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual page.
usrjquota=aquota.user|grpjquota=aquota.group|jqfmt=vfsv0
Apart from the old quota system (as in ext2, jqfmt=vfsold aka
version 1 quota) ext3 also supports journaled quotas (version 2
quota). jqfmt=vfsv0 enables journaled quotas. For journaled quo-
tas the mount options usrjquota=aquota.user and
grpjquota=aquota.group are required to tell the quota system
which quota database files to use. Journaled quotas have the
advantage that even after a crash no quota check is required.
Mount options for ext4
The ext4 filesystem is an advanced level of the ext3 filesystem which
incorporates scalability and reliability enhancements for supporting
large filesystem.
The options journal_dev, noload, data, commit, orlov, oldalloc,
[no]user_xattr [no]acl, bsddf, minixdf, debug, errors, data_err, grpid,
bsdgroups, nogrpid sysvgroups, resgid, resuid, sb, quota, noquota,
grpquota, usrquota usrjquota, grpjquota and jqfmt are backwardly com-
patible 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 cor-
ruption 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 descrip-
tor blocks. If enabled older kernels cannot mount the device.
This will enable 'journal_checksum' internally.
barrier=0 / barrier=1 / barrier / nobarrier
This enables/disables the use of write barriers in the jbd code.
barrier=0 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 bar-
riers enforce proper on-disk ordering of journal commits, making
volatile disk write caches safe to use, at some performance
penalty. If your disks are battery-backed in one way or
another, disabling barriers may safely improve performance. The
mount options "barrier" and "nobarrier" can also be used to
enable or disable barriers, for consistency with other ext4
mount options.
The ext4 filesystem enables write barriers by default.
inode_readahead_blks=n
This tuning parameter controls the maximum number of inode table
blocks that ext4's inode table readahead algorithm will pre-read
into the buffer cache. The value must be a power of 2. The
default value is 32 blocks.
stripe=n
Number of filesystem blocks that mballoc will try to use for
allocation size and alignment. For RAID5/6 systems this should
be the number of data disks * RAID chunk size in filesystem
blocks.
delalloc
Deferring block allocation until write-out time.
nodelalloc
Disable delayed allocation. Blocks are allocated when data is
copied from user to page cache.
max_batch_time=usec
Maximum amount of time ext4 should wait for additional filesys-
tem 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 auto-
matically 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 oper-
ations will join the transaction. The commit time is capped by
the max_batch_time, which defaults to 15000us (15ms). This opti-
mization can be turned off entirely by setting max_batch_time to
0.
min_batch_time=usec
This parameter sets the commit time (as described above) to be
at least min_batch_time. It defaults to zero microseconds.
Increasing this parameter may improve the throughput of multi-
threaded, synchronous workloads on very fast disks, at the cost
of increasing latency.
journal_ioprio=prio
The I/O priority (from 0 to 7, where 0 is the highest priority)
which should be used for I/O operations submitted by kjournald2
during a commit operation. This defaults to 3, which is a
slightly higher priority than the default I/O priority.
abort Simulate the effects of calling ext4_abort() for debugging pur-
poses. 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 exist-
ing 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 rou-
tines to quickly locate extents which might overlap with
filesystem metadata blocks. This option is intended for debug-
ging 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 unini-
tialized 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 inflexible. With
this option you can relax it.
check=value
Three different levels of pickyness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent, long
name parts are 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 con-
version 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 con-
version. Several people have had their data ruined by this
translation. Beware!
For filesystems mounted in binary mode, a conversion tool (from-
dos/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 mod-
ule 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 filesys-
tem parameters will be printed (these data are also printed if
the parameters appear to be inconsistent).
discard
If set, causes discard/TRIM commands to be issued to the block
device when blocks are freed. This is useful for SSD devices and
sparse/thinly-provisioned LUNs.
fat={12|16|32}
Specify a 12, 16 or 32 bit fat. This overrides the automatic
FAT type detection routine. Use with caution!
iocharset=value
Character set to use for converting between 8 bit characters and
16 bit Unicode characters. The default is iso8859-1. Long file-
names are stored on disk in Unicode format.
nfs If set, enables in-memory indexing of directory inodes to reduce
the frequency of ESTALE errors in NFS client operations. Useful
only when the filesystem is exported via NFS.
tz=UTC This option disables the conversion of timestamps between local
time (as used by Windows on FAT) and UTC (which Linux uses
internally). This is particularly useful when mounting devices
(like digital cameras) that are set to UTC in order to avoid the
pitfalls of local time.
quiet Turn on the quiet flag. Attempts to chown or chmod files do not
return errors, although they fail. Use with caution!
showexec
If set, the execute permission bits of the file will be allowed
only if the extension part of the name is .EXE, .COM, or .BAT.
Not set by default.
sys_immutable
If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag
on Linux. Not set by default.
flush If set, the filesystem will try to flush to disk more early than
normal. Not set by default.
usefree
Use the "free clusters" value stored on FSINFO. It'll be used to
determine number of free clusters without scanning disk. But
it's not used by default, because recent Windows don't update it
correctly in some case. If you are sure the "free clusters" on
FSINFO is correct, by this option you can avoid scanning disk.
dots, nodots, dotsOK=[yes|no]
Various misguided attempts to force Unix or DOS conventions onto
a FAT filesystem.
Mount options for hfs
creator=cccc, type=cccc
Set the creator/type values as shown by the MacOS finder used
for creating new files. Default values: '????'.
uid=n, gid=n
Set the owner and group of all files. (Default: the uid and gid
of the current process.)
dir_umask=n, file_umask=n, umask=n
Set the umask used for all directories, all regular files, or
all files and directories. Defaults to the umask of the current
process.
session=n
Select the CDROM session to mount. Defaults to leaving that
decision to the CDROM driver. This option will fail with any-
thing 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 fol-
lowed 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 filesys-
tem (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 avail-
able. 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 dan-
gerous, 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 exten-
sions.
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 key-
word with no value will grow the volume to the full size of the
partition.
nointegrity
Do not write to the journal. The primary use of this option is
to allow for higher performance when restoring a volume from
backup media. The integrity of the volume is not guaranteed if
the system abnormally ends.
integrity
Default. Commit metadata changes to the journal. Use this
option to remount a volume where the nointegrity option was pre-
viously 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 con-
tinue, 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 incon-
sistency, 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 con-
structed by ncpmount(8) and the current version of mount (2.12) does
not know anything about ncpfs.
Mount options for nfs and nfs4
See the options section of the nfs(5) man page (nfs-utils package must
be installed).
The nfs and nfs4 implementation expects a binary argument (a struct
nfs_mount_data) to the mount system call. This argument is constructed
by mount.nfs(8) and the current version of mount (2.13) does not know
anything about nfs and nfs4.
Mount options for ntfs
iocharset=name
Character set to use when returning file names. Unlike VFAT,
NTFS suppresses names that contain nonconvertible characters.
Deprecated.
nls=name
New name for the option earlier called iocharset.
utf8 Use UTF-8 for converting file names.
uni_xlate={0|1|2}
For 0 (or `no' or `false'), do not use escape sequences for
unknown Unicode characters. For 1 (or `yes' or `true') or 2,
use vfat-style 4-byte escape sequences starting with ":". Here 2
give a little-endian encoding and 1 a byteswapped bigendian
encoding.
posix=[0|1]
If enabled (posix=1), the filesystem distinguishes between upper
and lower case. The 8.3 alias names are presented as hard links
instead of being suppressed. This option is obsolete.
uid=value, gid=value and umask=value
Set the file permission on the filesystem. The umask value is
given in octal. By default, the files are owned by root and not
readable by somebody else.
Mount options for proc
uid=value and gid=value
These options are recognized, but have no effect as far as I can
see.
Mount options for ramfs
Ramfs is a memory based filesystem. Mount it and you have it. Unmount
it and it is gone. Present since Linux 2.3.99pre4. There are no mount
options.
Mount options for reiserfs
Reiserfs is a journaling filesystem.
conv Instructs version 3.6 reiserfs software to mount a version 3.5
filesystem, using the 3.6 format for newly created objects. This
filesystem will no longer be compatible with reiserfs 3.5 tools.
hash={rupasov|tea|r5|detect}
Choose which hash function reiserfs will use to find files
within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast and pre-
serves 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 filesys-
tem.
hashed_relocation
Tunes the block allocator. This may provide performance improve-
ments in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance improve-
ments in some situations.
noborder
Disable the border allocator algorithm invented by Yury Yu.
Rupasov. This may provide performance improvements in some sit-
uations.
nolog Disable journaling. This will provide slight performance
improvements in some situations at the cost of losing reiserfs's
fast recovery from crashes. Even with this option turned on,
reiserfs still performs all journaling operations, save for
actual writes into its journaling area. Implementation of nolog
is a work in progress.
notail By default, reiserfs stores small files and `file tails'
directly into its tree. This confuses some utilities such as
LILO(8). This option is used to disable packing of files into
the tree.
replayonly
Replay the transactions which are in the journal, but do not
actually mount the filesystem. Mainly used by reiserfsck.
resize=number
A remount option which permits online expansion of reiserfs par-
titions. Instructs reiserfs to assume that the device has num-
ber 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 journal-
ing code. barrier=none disables it, barrier=flush enables it.
Write barriers enforce proper on-disk ordering of journal com-
mits, 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 con-
structed 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 exam-
ple, 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 sys-
tem 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 advis-
able to omit the mpol option from automatic mount options. It
can be added later, when the tmpfs is already mounted on Mount-
Point, 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 (Net-
BSD,FreeBSD,OpenBSD).
ufs2 Used in FreeBSD 5.x supported as read-write.
5xbsd Synonym for ufs2.
sun For filesystems created by SunOS or Solaris on Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT 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 charac-
ter, is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).
posix Allow two files with names that only differ in case. This
option is obsolete.
nonumtail
First try to make a short name without sequence number, before
trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is
used by the console. It can be enabled for the filesystem with
this option or disabled with utf8=0, utf8=no or utf8=false. If
`uni_xlate' gets set, UTF8 gets disabled.
shortname={lower|win95|winnt|mixed}
Defines the behaviour for creation and display of filenames
which fit into 8.3 characters. If a long name for a file exists,
it will always be preferred display. There are four modes: :
lower Force the short name to lower case upon display; store a
long name when the short name is not all upper case.
win95 Force the short name to upper case upon display; store a
long name when the short name is not all upper case.
winnt Display the shortname as is; store a long name when the
short name is not all lower case or all upper case.
mixed Display the short name as is; store a long name when the
short name is not all upper case. This mode is the
default since Linux 2.6.32.
Mount options for usbfs
devuid=uid and devgid=gid and devmode=mode
Set the owner and group and mode of the device files in the
usbfs filesystem (default: uid=gid=0, mode=0644). The mode is
given in octal.
busuid=uid and busgid=gid and busmode=mode
Set the owner and group and mode of the bus directories in the
usbfs filesystem (default: uid=gid=0, mode=0555). The mode is
given in octal.
listuid=uid and listgid=gid and listmode=mode
Set the owner and group and mode of the file devices (default:
uid=gid=0, mode=0444). The mode is given in octal.
Mount options for xenix
None.
Mount options for xfs
allocsize=size
Sets the buffered I/O end-of-file preallocation size when doing
delayed allocation writeout. Valid values for this option are
page size (typically 4KiB) through to 1GiB, inclusive, in power-
of-2 increments.
The default behaviour is for dynamic end-of-file preallocation
size, which uses a set of heuristics to optimise the prealloca-
tion size based on the current allocation patterns within the
file and the access patterns to the file. Specifying a fixed
allocsize value turns off the dynamic behaviour.
attr2|noattr2
The options enable/disable an "opportunistic" improvement to be
made in the way inline extended attributes are stored on-disk.
When the new form is used for the first time when attr2 is
selected (either when setting or removing extended attributes)
the on-disk superblock feature bit field will be updated to
reflect this format being in use.
The default behaviour is determined by the on-disk feature bit
indicating that attr2 behaviour is active. If either mount
option it set, then that becomes the new default used by the
filesystem.
CRC enabled filesystems always use the attr2 format, and so will
reject the noattr2 mount option if it is set.
barrier|nobarrier
Enables/disables the use of block layer write barriers for
writes into the journal and for data integrity operations. This
allows for drive level write caching to be enabled, for devices
that support write barriers.
discard|nodiscard
Enable/disable the issuing of commands to let the block device
reclaim space freed by the filesystem. This is useful for SSD
devices, thinly provisioned LUNs and virtual machine images, but
may have a performance impact.
Note: It is currently recommended that you use the fstrim appli-
cation to discard unused blocks rather than the discard mount
option because the performance impact of this option is quite
severe.
grpid|bsdgroups|nogrpid|sysvgroups
These options define what group ID a newly created file gets.
When grpid is set, it takes the group ID of the directory in
which it is created; otherwise it takes the fsgid of the current
process, unless the directory has the setgid bit set, in which
case it takes the gid from the parent directory, and also gets
the setgid bit set if it is a directory itself.
filestreams
Make the data allocator use the filestreams allocation mode
across the entire filesystem rather than just on directories
configured to use it.
When ikeep is specified, XFS does not delete empty inode
clusters and keeps them around on disk. When noikeep is speci-
fied, empty inode clusters are returned to the free space pool.
inode32|inode64
When inode32 is specified, it indicates that XFS limits inode
creation to locations which will not result in inode numbers
with more than 32 bits of significance.
When inode64 is specified, it indicates that XFS is allowed to
create inodes at any location in the filesystem, including those
which will result in inode numbers occupying more than 32 bits
of significance.
inode32 is provided for backwards compatibility with older sys-
tems and applications, since 64 bits inode numbers might cause
problems for some applications that cannot handle large inode
numbers. If applications are in use which do not handle inode
numbers bigger than 32 bits, the inode32 option should be speci-
fied.
largeio|nolargeio
If "nolargeio" is specified, the optimal I/O reported in st_blk-
size by stat(2) will be as small as possible to allow user
applications to avoid inefficient read/modify/write I/O. This
is typically the page size of the machine, as this is the granu-
larity of the page cache.
If "largeio" specified, a filesystem that was created with a
"swidth" specified will return the "swidth" value (in bytes) in
st_blksize. If the filesystem does not have a "swidth" specified
but does specify an "allocsize" then "allocsize" (in bytes) will
be returned instead. Otherwise the behaviour is the same as if
"nolargeio" was specified.
logbufs=value
Set the number of in-memory log buffers. Valid numbers range
from 2-8 inclusive.
The default value is 8 buffers.
If the memory cost of 8 log buffers is too high on small sys-
tems, then it may be reduced at some cost to performance on
metadata intensive workloads. The logbsize option below controls
the size of each buffer and so is also relevent to this case.
logbsize=value
Set the size of each in-memory log buffer. The size may be
specified in bytes, or in kilobytes with a "k" suffix. Valid
sizes for version 1 and version 2 logs are 16384 (16k) and 32768
(32k). Valid sizes for version 2 logs also include 65536 (64k),
131072 (128k) and 262144 (256k). The logbsize must be an integer
multiple of the log stripe unit configured at mkfs time.
The default value for version 1 logs is 32768, while the default
value for version 2 logs is MAX(32768, log_sunit).
logdev=deviceandrtdev=device
Use an external log (metadata journal) and/or real-time device.
An XFS filesystem has up to three parts: a data section, a log
section, and a real-time section. The real-time section is
optional, and the log section can be separate from the data sec-
tion or contained within it.
noalign
Data allocations will not be aligned at stripe unit boundaries.
This is only relevant to filesystems created with non-zero data
alignment parameters (sunit, swidth) by mkfs.
norecovery
The filesystem will be mounted without running log recovery. If
the filesystem was not cleanly unmounted, it is likely to be
inconsistent when mounted in "norecovery" mode. Some files or
directories may not be accessible because of this. Filesystems
mounted "norecovery" must be mounted read-only or the mount will
fail.
nouuid Don't check for double mounted file systems using the file sys-
tem uuid. This is useful to mount LVM snapshot volumes, and
often used in combination with "norecovery" for mounting read-
only snapshots.
noquota
Forcibly turns off all quota accounting and enforcement within
the filesystem.
uquota/usrquota/uqnoenforce/quota
User disk quota accounting enabled, and limits (optionally)
enforced. Refer to xfs_quota(8) for further details.
gquota/grpquota/gqnoenforce
Group disk quota accounting enabled and limits (optionally)
enforced. Refer to xfs_quota(8) for further details.
pquota/prjquota/pqnoenforce
Project disk quota accounting enabled and limits (optionally)
enforced. Refer to xfs_quota(8) for further details.
sunit=value and swidth=value
Used to specify the stripe unit and width for a RAID device or a
stripe volume. "value" must be specified in 512-byte block
units. These options are only relevant to filesystems that were
created with non-zero data alignment parameters.
The sunit and swidth parameters specified must be compatible
with the existing filesystem alignment characteristics. In gen-
eral, that means the only valid changes to sunit are increasing
it by a power-of-2 multiple. Valid swidth values are any integer
multiple of a valid sunit value.
Typically the only time these mount options are necessary if
after an underlying RAID device has had it's geometry modified,
such as adding a new disk to a RAID5 lun and reshaping it.
swalloc
Data allocations will be rounded up to stripe width boundaries
when the current end of file is being extended and the file size
is larger than the stripe width size.
wsync When specified, all filesystem namespace operations are executed
synchronously. This ensures that when the namespace operation
(create, unlink, etc) completes, the change to the namespace is
on stable storage. This is useful in HA setups where failover
must not result in clients seeing inconsistent namespace presen-
tation during or after a failover event.
Mount options for xiafs
None. Although nothing is wrong with xiafs, it is not used much, and is
not maintained. Probably one shouldn't use it. Since Linux version
2.1.21 xiafs is no longer part of the kernel source.
THE LOOP DEVICE
One further possible type is a mount via the loop device. For example,
the command
mount /tmp/disk.img /mnt -t vfat -o loop=/dev/loop
will set up the loop device /dev/loop3 to correspond to the file
/tmp/disk.img, and then mount this device on /mnt.
If no explicit loop device is mentioned (but just an option `-o loop'
is given), then mount will try to find some unused loop device and use
that, for example
mount /tmp/disk.img /mnt -o loop
The mount command automatically creates a loop device from a regular
file if a filesystem type is not specified or the filesystem is known
for libblkid, for example:
mount /tmp/disk.img /mnt
mount -t ext4 /tmp/disk.img /mnt
This type of mount knows about four options, namely loop, offset and
sizelimit , that are really options to losetup(8). (These options can
be used in addition to those specific to the filesystem type.)
Since Linux 2.6.25 is supported auto-destruction of loop devices and
then any loop device allocated by mount will be freed by umount inde-
pendently on /etc/mtab.
You can also free a loop device by hand, using `losetup -d' or `umount
-d`.
RETURN CODES
mount has the following return codes (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
The command mount -a returns 0 (all success), 32 (all failed) or 64
(some failed, some success).
NOTES
The syntax of external mount helpers is:
/sbin/mount.<suffix> spec dir [-sfnv] [-o options] [-t type.sub-
type]
where the <type> is filesystem type and -sfnvo options have same mean-
ing like standard mount options. The -t option is used for filesystems
with subtypes support (for example /sbin/mount.fuse -t fuse.sshfs).
FILES
/etc/fstab filesystem table
/etc/mtab table of mounted filesystems
/etc/mtab~ lock file
/etc/mtab.tmp temporary file
/etc/filesystems a list of filesystem types to try
ENVIRONMENT
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file
LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file
LIBMOUNT_DEBUG=0xffff
enables debug output
SEE ALSO
mount(2), umount(2), fstab(5), umount(8), swapon(8), findmnt(8),
nfs(5), xfs(5), e2label(8), xfs_admin(8), mountd(8), nfsd(8),
mke2fs(8), tune2fs(8), losetup(8)
BUGS
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don't support -o sync and -o dirsync (the ext2,
ext3, ext4, fat and vfat filesystems do support synchronous updates (a
la BSD) when mounted with the sync option).
The -o remount may not be able to change mount parameters (all ext2fs-
specific parameters, except sb, are changeable with a remount, for
example, but you can't change gid or umask for the fatfs).
It is possible that files /etc/mtab and /proc/mounts don't match. The
first file is based only on the mount command options, but the content
of the second file also depends on the kernel and others settings (e.g.
remote NFS server. In particular case the mount command may reports
unreliable information about a NFS mount point and the /proc/mounts
file 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.
The loop option with the offset or sizelimit options used may fail when
using older kernels if the mount command can't confirm that the size of
the block device has been configured as requested. This situation can
be worked around by using the losetup command manually before calling
mount with the configured loop device.
HISTORY
A mount command existed in Version 5 AT&T UNIX.
AUTHORS
Karel Zak <kzak AT redhat.com>
AVAILABILITY
The mount command is part of the util-linux package and is available
from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
util-linux January 2012 MOUNT(8)
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