mount — mount a filesystem
mount [ −l | −h | −V ]
mount \-a [−fFnrsvw] [ −t fstype ] [ −O optlist ]
mount [−fnrsvw] [ −o options ] device | dir
mount [−fnrsvw] [ −t fstype ] [ −o options ] device dir
All files accessible in a Unix system are arranged in one
big tree, the file hierarchy, rooted at /. These files can be spread out over
several devices. The mount command serves to
attach the filesystem found on some device to the big file
tree. Conversely, the umount(8) command will
detach it again.
The standard form of the mount command is:
mount −t type device dir
This tells the kernel to attach the filesystem found on
device (which is of
type type) at the directory
dir. The previous
contents (if any) and owner and mode of dir become invisible, and as
long as this filesystem remains mounted, the pathname
dir refers to the
root of the filesystem on device.
If only the directory or the device is given, for example:
mount /dir
then mount
looks for a mountpoint (and if not found then for a device)
in the /etc/fstab file. It's
possible to use the −−target or −−source options to avoid
ambivalent interpretation of the given argument. For
example:
mount −−target /mountpoint
The listing mode is maintained for backward compatibility only.
For more robust and customizable output use findmnt(8), especially in your scripts. Note that control characters in the mountpoint name are replaced with '?'.
The following command lists all mounted filesystems (of
type type):
mount [ −l ] [ −t
type/]
The option −l adds
labels to this listing. See below.
Most devices are indicated by a filename (of a block
special device), like /dev/sda1, but there are other
possibilities. For example, in the case of an NFS mount,
device may look
like knuth.cwi.nl:/dir. It is
also possible to indicate a block special device using its
filesystem label or UUID (see the −L and −U options below), or its partition
label or UUID. (Partition identifiers are supported for
example for GUID Partition Tables (GPT).)
Don't forget that there is no guarantee that UUIDs and labels are really unique, especially if you move, share or copy the device. Use lsblk −o +UUID,PARTUUID to verify that the UUIDs are really unique in your system.
The recommended setup is to use tags (e.g. LABEL=label) rather than /dev/disk/by-{label,uuid,partuuid,partlabel}
udev symlinks in the /etc/fstab file. Tags are more
readable, robust and portable. The mount(8) command
internally uses udev symlinks, so the use of symlinks in
/etc/fstab has no advantage over tags. For more details see
libblkid(3).
Note that mount(8) uses UUIDs as strings. The UUIDs from the command line or from fstab(5) are not converted to internal binary representation. The string representation of the UUID should be based on lower case characters.
The proc filesystem is not
associated with a special device, and when mounting it, an
arbitrary keyword, such as proc can be used instead of a device
specification. (The customary choice none is less fortunate: the error message
`none busy' from umount can be
confusing.)
The file /etc/fstab (see
fstab(5)), may contain
lines describing what devices are usually mounted where,
using which options. The default location of the fstab(5) file can be
overridden with the −−fstab path command-line option (see
below for more details).
The command
mount −a [
−ttype] [−Ooptlist]
(usually given in a bootscript) causes all filesystems
mentioned in fstab (of the
proper type and/or having or not having the proper options)
to be mounted as indicated, except for those whose line
contains the noauto keyword.
Adding the −F option will
make mount
fork, so that the filesystems are mounted
simultaneously.
When mounting a filesystem mentioned in fstab or mtab, it suffices to specify on the
command line only the device, or only the mount point.
The programs mount and umount traditionally
maintained a list of currently mounted filesystems in the
file /etc/mtab. This real
mtab file is still supported, but on current Linux systems
it is better to make it a symlink to /proc/mounts instead, because a regular
mtab file maintained in userspace cannot reliably work with
namespaces, containers and other advanced Linux
features.
If no arguments are given to mount, the list of mounted filesystems is printed.
If you want to override mount options from /etc/fstab you have to use the
−o option:
mount device | dir −o options
and then the mount options from the command line will be
appended to the list of options from /etc/fstab. The usual behavior is that
the last option wins if there are conflicting ones.
The mount
program does not read the /etc/fstab file if both device (or LABEL, UUID,
PARTUUID or PARTLABEL) and dir are specified. For
example, to mount device foo
at /dir:
mount /dev/foo /dir
Normally, only the superuser can mount filesystems.
However, when fstab contains
the user option on a line,
anybody can mount the corresponding filesystem.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 filesystem found on an inserted CDROM using the command:
mount /dev/cdrom
or
mount /cd
For more details, see fstab(5). Only the user
that mounted a filesystem can unmount it again. If any user
should be able to unmount it, then use users instead of user in the fstab line. The owner option is similar to the
user option, with the
restriction that the user must be the owner of the special
file. This may be useful e.g. for /dev/fd if a login script makes the
console user owner of this device. The group option is similar, with the
restriction that the user must be member of the group of
the special file.
Since Linux 2.4.0 it is possible to remount part of the file hierarchy somewhere else. The call is:
mount −−bind olddir newdir
or by using this fstab entry:
/
olddir/newdirnone bind
After this call the same contents are accessible in two places. One can also remount a single file (on a single file). It's also possible to use the bind mount to create a mountpoint from a regular directory, for example:
mount −−bind foo foo
The bind mount call attaches only (part of) a single filesystem, not possible submounts. The entire file hierarchy including submounts is attached a second place by using:
mount −−rbind olddir newdir
Note that the filesystem mount options will remain the same as those on the original mount point.
mount(8) since v2.27
allows to change the mount options by passing the relevant
options along with −−bind. For example:
mount −−bind,ro foo foo
This feature is not supported by the Linux kernel; it is implemented in userspace by an additional mount(2) remounting syscall. This solution is not atomic.
The alternative (classic) way to create a read-only bind mount is to use the remount operation, for example:
mount −−bind olddir newdir
mount −o remount,ro,bind olddir newdir
Note that a 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).
Since Linux 2.5.1 it is possible to atomically move a mounted tree to another place. The call is:
mount −−move olddir newdir
This will cause the contents which previously appeared
under olddir to now be
accessible under newdir. The
physical location of the files is not changed. Note that
olddir has to be a
mountpoint.
Note also that moving a mount residing under a shared mount is invalid and unsupported. Use findmnt −o TARGET,PROPAGATION to see the current propagation flags.
Since Linux 2.6.15 it is possible to mark a mount and
its submounts as shared, private, slave or unbindable. A
shared mount provides the ability to create mirrors of that
mount such that mounts and unmounts within any of the
mirrors propagate to the other mirror. A slave mount
receives propagation from its master, but not vice versa. A
private mount carries no propagation abilities. An
unbindable mount is a private mount which cannot be cloned
through a bind operation. The detailed semantics are
documented in Documentation/filesystems/sharedsubtree.txt
file in the kernel source tree.
Supported operations are:
mount −−make−sharedmountpointmount −−make−slavemountpointmount −−make−privatemountpointmount −−make−unbindablemountpoint
The following commands allow one to recursively change the type of all the mounts under a given mountpoint.
mount −−make−rsharedmountpointmount −−make−rslavemountpointmount −−make−rprivatemountpointmount −−make−runbindablemountpoint
mount(8) does not read fstab(5) when a
−−make−*
operation is requested. All necessary information has to be
specified on the command line.
Note that the Linux kernel does not allow to change multiple propagation flags with a single mount(2) syscall, and the flags cannot be mixed with other mount options.
Since util-linux 2.23 the mount command allows to
use several propagation flags together and also together
with other mount operations. This feature is EXPERIMENTAL.
The propagation flags are applied by additional mount(2) syscalls when
the preceding mount operations were successful. Note that
this use case is not atomic. It is possible to specify the
propagation flags in fstab(5) as mount options
(private, slave, shared, unbindable, rprivate, rslave, rshared, runbindable).
For example:
mount −−make−private −−make−unbindable /dev/sda1 /foo
is the same as:
mount /dev/sda1 /foo mount −−make−private /foo mount −−make−unbindable /foo
The full set of mount options used by an invocation of
mount is
determined by first extracting the mount options for the
filesystem from the fstab
table, then applying any options specified by the
−o argument, and finally
applying a −r or
−w option, when
present.
The command mount does not pass all
command-line options to the /sbin/mount.suffix mount helpers. The interface between
mount and the
mount helpers is described below in the section EXTERNAL HELPERS.
Command-line options available for the mount command are:
−a,
−−allMount all filesystems (of the given types) mentioned
in fstab (except for
those whose line contains the noauto keyword). The filesystems are
mounted following their order in fstab.
−B,
−−bindRemount a subtree somewhere else (so that its contents are available in both places). See above, under Bind mounts.
−c,
−−no−canonicalizeDon't canonicalize paths. The mount command
canonicalizes all paths (from command line or fstab) by
default. This option can be used together with the
−f flag for already
canonicalized absolute paths. The option is designed
for mount helpers which call mount -i. It is strongly
recommended to not use this command-line option for
normal mount operations.
Note that mount(8) does not
pass this option to the /sbin/mount.type helpers.
−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,
−−fakeCauses everything to be done except for the actual
system call; if it's not obvious, this ``fakes''
mounting the filesystem. This option is useful in
conjunction with the −v flag to determine what the
mount
command is trying to do. It can also be used to add
entries for devices that were mounted earlier with the
−n option. The
−f option checks for
an existing record in /etc/mtab and fails when the
record already exists (with a regular non-fake mount,
this check is done by the kernel).
−i,
−−internal−onlyDon't call the /sbin/mount.filesystem helper even if it
exists.
−L,
−−label labelMount the partition that has the specified
label.
−l,
−−show−labelsAdd the labels in the mount output. mount must have permission to read the disk device (e.g. be suid root) for this to work. One can set such a label for ext2, ext3 or ext4 using the e2label(8) utility, or for XFS using xfs_admin(8), or for reiserfs using reiserfstune(8).
−M,
−−moveMove a subtree to some other place. See above, the subsection The move operation.
−n,
−−no−mtabMount without writing in /etc/mtab. This is necessary for
example when /etc is on a
read-only filesystem.
−O,
−−test−opts optsLimit the set of filesystems to which the
−a option applies. In
this regard it is like the −t option except that
−O is useless without
−a. For example, the
command:
mount −a −O no_netdevmounts all filesystems except those which have the option
_netdevspecified in the options field in the/etc/fstabfile.It is different from
−tin that each option is matched exactly; a leadingnoat the beginning of one option does not negate the rest.The
−tand−Ooptions are cumulative in effect; that is, the commandmount −a −t ext2 −O _netdevmounts all ext2 filesystems with the _netdev option, not all filesystems that are either ext2 or have the _netdev option specified.
−o,
−−options optsUse the specified mount options. The opts argument is a comma-separated
list. For example:
mount LABEL=mydisk −o noatime,nodev,nosuidFor more details, see the FILESYSTEM-INDEPENDENT MOUNT OPTIONS and FILESYSTEM-SPECIFIC MOUNT OPTIONS sections.
−R,
−−rbindRemount a subtree and all possible submounts somewhere else (so that its contents are available in both places). See above, the subsection Bind mounts.
−r,
−−read−onlyMount the filesystem read-only. A synonym is
−o ro.
Note that, depending on the filesystem type, state
and kernel behavior, the system may still write to the
device. For example, ext3 and ext4 will replay the
journal if the filesystem is dirty. To prevent this
kind of write access, you may want to mount an ext3 or
ext4 filesystem with the ro,noload mount options
or set the block device itself to read-only mode, see
the blockdev(8)
command.
−sTolerate sloppy mount options rather than failing.
This will ignore mount options not supported by a
filesystem type. Not all filesystems support this
option. Currently it's supported by the mount.nfs mount helper
only.
−−source deviceIf only one argument for the mount command is given then the argument might be interpreted as target (mountpoint) or source (device). This option allows to explicitly define that the argument is the mount source.
−−target
directoryIf only one argument for the mount command is given then the argument might be interpreted as target (mountpoint) or source (device). This option allows to explicitly define that the argument is the mount target.
−T,
−−fstab pathSpecifies an alternative fstab file. If path is a directory then the files in
the directory are sorted by strverscmp(3); files
that start with "." or without an .fstab extension are
ignored. The option can be specified more than once.
This option is mostly designed for initramfs or chroot
scripts where additional configuration is specified
beyond standard system configuration.
Note that mount(8) does not
pass the option −−fstab to the /sbin/mount.type helpers, meaning that the
alternative fstab files will be invisible for the
helpers. This is no problem for normal mounts, but user
(non-root) mounts always require fstab to verify the
user's rights.
−t,
−−types fstypeThe argument following the −t is used to indicate the
filesystem type. The filesystem types which are
currently supported depend on the running kernel. See
/proc/filesystems and
/lib/modules/$(uname
-r)/kernel/fs for a complete list of the
filesystems. The most common are ext2, ext3, ext4, xfs,
btrfs, vfat, sysfs, proc, nfs and cifs.
The programs mount and umount support filesystem subtypes. The subtype is defined by a '.subtype' suffix. For example 'fuse.sshfs'. It's recommended to use subtype notation rather than add any prefix to the mount source (for example 'sshfs#example.com' is deprecated).
If no −t option is
given, or if the auto type
is specified, mount will try to guess the desired type.
Mount uses the blkid library for guessing the
filesystem type; if that does not turn up anything that
looks familiar, mount will try to read the file
/etc/filesystems, or, if
that does not exist, /proc/filesystems. All of the
filesystem types listed there will be tried, except for
those that are labeled "nodev" (e.g. devpts, proc and nfs). If /etc/filesystems ends in a line with
a single *, mount will read /proc/filesystems afterwards. While
trying, all filesystem types will be mounted with the
mount option silent.
The auto type may be
useful for user-mounted floppies. Creating a file
/etc/filesystems can be
useful to change the probe order (e.g., to try vfat
before msdos or ext3 before ext2) or if you use a
kernel module autoloader.
More than one type may be specified in a
comma-separated list, for option −t as well as in an /etc/fstab entry. The list of
filesystem types for option −t can be prefixed with
no to specify the
filesystem types on which no action should be taken.
The prefix no has no
effect when specified in an /etc/fstab entry.
The prefix no can be
meaningful with the −a option. For example, the
command
mount −a −t nomsdos,smbfsmounts all filesystems except those of type
msdosandsmbfs.For most types all the mount program has to do is issue a simple mount(2) system call, and no detailed knowledge of the filesystem type is required. For a few types however (like nfs, nfs4, cifs, smbfs, ncpfs) an ad hoc code is necessary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems have a separate mount program. In order to make it possible to treat all types in a uniform way, mount will execute the program
/sbin/mount.type(if that exists) when called with typetype. Since different versions of the smbmount program have different calling conventions,/sbin/mount.smbfsmay have to be a shell script that sets up the desired call.
−U,
−−uuid uuidMount the partition that has the specified
uuid.
−v,
−−verboseVerbose mode.
−w,
−−rw,
−−read−writeMount the filesystem read/write. This is the
default. A synonym is −o
rw.
−V,
−−versionDisplay version information and exit.
−h,
−−helpDisplay help text and exit.
Some of these options are only useful when they appear in
the /etc/fstab file.
Some of these options could be enabled or disabled by default in the system kernel. To check the current setting see the options in /proc/mounts. Note that filesystems also have per-filesystem specific default mount options (see for example tune2fs −l output for extN filesystems).
The following options apply to any filesystem that is
being mounted (but not every filesystem actually honors them
– e.g., the sync option
today has an effect only for ext2, ext3, fat, vfat and
ufs):
asyncAll I/O to the filesystem should be done
asynchronously. (See also the sync option.)
atimeDo not use the noatime
feature, so the inode access time is controlled by
kernel defaults. See also the descriptions of the
relatime and strictatime mount options.
noatimeDo not update inode access times on this filesystem
(e.g. for faster access on the news spool to speed up
news servers). This works for all inode types
(directories too), so it implies nodiratime.
autoCan be mounted with the −a option.
noautoCan 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=contextThe context= option is
useful when mounting filesystems that do not support
extended attributes, such as a floppy or hard disk
formatted with VFAT, or systems that are not normally
running under SELinux, such as an ext3 formatted disk
from a non-SELinux workstation. You can also use
context= on
filesystems you do not trust, such as a floppy. It also
helps in compatibility with xattr-supporting
filesystems on earlier 2.4.<x> kernel versions.
Even where xattrs are supported, you can save time not
having to label every file by assigning the entire disk
one security context.
A commonly used option for removable media is
context="system_u:object_r:removable_t".
Two other options are fscontext= and
defcontext=,
both of which are mutually exclusive of the context
option. This means you can use fscontext and defcontext
with each other, but neither can be used with
context.
The fscontext= option works
for all filesystems, regardless of their xattr support.
The fscontext option sets the overarching filesystem
label to a specific security context. This filesystem
label is separate from the individual labels on the
files. It represents the entire filesystem for certain
kinds of permission checks, such as during mount or
file creation. Individual file labels are still
obtained from the xattrs on the files themselves. The
context option actually sets the aggregate context that
fscontext provides, in addition to supplying the same
label for individual files.
You can set the default security context for
unlabeled files using defcontext= option.
This overrides the value set for unlabeled files in the
policy and requires a filesystem that supports xattr
labeling.
The rootcontext= option
allows you to explicitly label the root inode of a FS
being mounted before that FS or inode becomes visible
to userspace. This was found to be useful for things
like stateless linux.
Note that the kernel rejects any remount request
that includes the context option, even when unchanged from the current
context.
Warning: the context value might contain
commas, in which case the value has to be
properly quoted, otherwise mount(8) will
interpret the comma as a separator between mount
options. Don't forget that the shell strips off quotes
and thus double quoting is
required. For example:
mount −t tmpfs none /mnt −o \ 'context="system_u:object_r:tmp_t:s0:c127,c456",noexec'For more details, see selinux(8).
defaultsUse the default options: rw, suid,
dev, exec, auto, nouser, and async.
Note that the real set of all default mount options depends on kernel and filesystem type. See the beginning of this section for more details.
devInterpret character or block special devices on the filesystem.
nodevDo not interpret character or block special devices on the file system.
diratimeUpdate directory inode access times on this
filesystem. This is the default. (This option is
ignored when noatime is
set.)
nodiratimeDo not update directory inode access times on this
filesystem. (This option is implied when noatime is set.)
dirsyncAll directory updates within the filesystem should be done synchronously. This affects the following system calls: creat, link, unlink, symlink, mkdir, rmdir, mknod and rename.
execPermit execution of binaries.
noexecDo not permit direct execution of any binaries on the mounted filesystem. (Until recently it was possible to run binaries anyway using a command like /lib/ld*.so /mnt/binary. This trick fails since Linux 2.4.25 / 2.6.0.)
groupAllow an ordinary user to mount the filesystem if
one of that user's 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).
iversionEvery time the inode is modified, the i_version field will be incremented.
noiversionDo not increment the i_version inode field.
mandAllow mandatory locks on this filesystem. See fcntl(2).
nomandDo not allow mandatory locks on this filesystem.
_netdevThe 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).
nofailDo not report errors for this device if it does not exist.
relatimeUpdate inode access times relative to modify or
change time. Access time is only updated if the
previous access time was earlier than the current
modify or change time. (Similar to noatime, but it doesn't break
mutt or other applications
that need to know if a file has been read since the
last time it was modified.)
Since Linux 2.6.30, the kernel defaults to the
behavior provided by this option (unless noatime was specified), and the
strictatime option is
required to obtain traditional semantics. In addition,
since Linux 2.6.30, the file's last access time is
always updated if it is more than 1 day old.
norelatimeDo not use the relatime
feature. See also the strictatime mount option.
strictatimeAllows to explicitly request full atime updates.
This makes it possible for the kernel to default to
relatime or noatime but still allow userspace to
override it. For more details about the default system
mount options see /proc/mounts.
nostrictatimeUse the kernel's default behavior for inode access time updates.
lazytimeOnly update times (atime, mtime, ctime) on the in-memory version of the file inode.
This mount option significantly reduces writes to the inode table for workloads that perform frequent random writes to preallocated files.
The on-disk timestamps are updated only when:
nolazytimeDo not use the lazytime feature.
suidAllow set-user-identifier or set-group-identifier bits to take effect.
nosuidDo not allow set-user-identifier or set-group-identifier bits to take effect.
silentTurn on the silent flag.
loudTurn off the silent flag.
wnerAllow an ordinary user to mount the filesystem if
that user 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).
remountAttempt to remount an already-mounted filesystem. This is commonly used to change the mount flags for a filesystem, especially to make a readonly filesystem writable. It does not change device or mount point.
The remount functionality follows the standard way
the mount command works with options from fstab. This
means that mount does not read
fstab (or mtab) only when both device and dir are specified.
mount −o remount,rw /dev/foo /dir
After this call all old mount options are replaced and arbitrary stuff from fstab (or mtab) 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 and merges these
options with the options from the command line
(−o). If no
mountpoint is found in fstab, then a remount with
unspecified source is allowed.
roMount the filesystem read-only.
rwMount the filesystem read-write.
syncAll I/O to the filesystem should be done
synchronously. In the case of media with a limited
number of write cycles (e.g. some flash drives),
sync may cause life-cycle
shortening.
userAllow an ordinary user to mount the filesystem. The
name of the mounting user is written to the mtab file
(or to the private libmount file in /run/mount on
systems without a regular mtab) so that this same user
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).
nouserForbid an ordinary user to mount the filesystem. This is the default; it does not imply any other options.
usersAllow any user to mount and to unmount the
filesystem, even when some other ordinary user mounted
it. This option implies the options noexec, nosuid, and nodev (unless overridden by subsequent
options, as in the option line users,exec,dev,suid).
All options prefixed with "x-" are interpreted as
comments or as userspace application-specific options.
These options are not stored in the mtab file, nor sent
to the mount.type helpers
nor to the mount(2) system call.
The suggested format is x-appname.option (e.g. x-systemd.automount).
x-mount.mkdir[=mode]Allow to make a target directory (mountpoint). The
optional argument mode specifies the
filesystem access mode used for mkdir(2) in octal
notation. The default mode is 0755. This functionality
is supported only for root users.
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.
uid=value and gid=valueSet the owner and group of the files in the filesystem (default: uid=gid=0).
ownmask=value and othmask=valueSet 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.
uid=value and gid=valueSet 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=valueSet the owner and group of all files.
mode=valueSet 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.
protectDo not allow any changes to the protection bits on the filesystem.
usempSet 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...
verbosePrint an informational message for each successful mount.
prefix=stringPrefix used before volume name, when following a link.
volume=stringPrefix (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=valueGive explicitly the location of the root block.
bs=valueGive blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota|noquota|quota|usrquotaThese options are accepted but ignored. (However,
quota utilities may react to such strings in
/etc/fstab.)
Btrfs is a copy-on-write filesystem for Linux aimed at implementing advanced features while focusing on fault tolerance, repair, and easy administration.
alloc_start=bytesDebugging option to force all block allocations above a certain byte threshold on each block device. The value is specified in bytes, optionally with a K, M, or G suffix, case insensitive. Default is 1MB.
autodefragDisable/enable auto defragmentation. Auto defragmentation detects small random writes into files and queues them up for the defrag process. Works best for small files; not well-suited for large database workloads.
check_int|check_int_data|check_int_print_mask=valueThese debugging options control the behavior of the integrity checking module(the BTRFS_FS_CHECK_INTEGRITY config option required).
check_int enables the
integrity checker module, which examines all
block-write requests to ensure on-disk consistency,
at a large memory and CPU cost.
check_int_data
includes extent data in the integrity checks, and
implies the check_int option.
check_int_print_mask
takes a bitmask of BTRFSIC_PRINT_MASK_* values as
defined in fs/btrfs/check-integrity.c, to control the
integrity checker module behavior.
See comments at the top of fs/btrfs/check-integrity.c for more
info.
commit=secondsSet the interval of periodic commit, 30 seconds by default. Higher values defer data being synced to permanent storage, with obvious consequences when the system crashes. The upper bound is not forced, but a warning is printed if it's more than 300 seconds (5 minutes).
compress|compress=type|Control BTRFS file data compression. Type may be
specified as "zlib" "lzo" or "no" (for no
compression, used for remounting). If no type is
specified, zlib is used. If compress-force is
specified, all files will be compressed, whether or
not they compress well. If compression is enabled,
nodatacow and
nodatasum are
disabled.
degradedAllow mounts to continue with missing devices. A read-write mount may fail with too many devices missing, for example if a stripe member is completely missing.
device=devicepathSpecify a device during mount so that ioctls on the control device can be avoided. Especially useful when trying to mount a multi-device setup as root. May be specified multiple times for multiple devices.
discardDisable/enable the discard mount option. The
discard function issues frequent commands to let the
block device reclaim space freed by the filesystem.
This is useful for SSD devices, thinly provisioned
LUNs and virtual machine images, but may have a
significant performance impact. (The fstrim command is also available to
initiate batch trims from userspace.)
enospc_debugDisable/enable debugging option to be more verbose in some ENOSPC conditions.
fatal_errors=actionAction to take when encountering a fatal error: "bug" - BUG() on a fatal error. This is the default. "panic" - panic() on a fatal error.
flushoncommitThe flushoncommit
mount option forces any data dirtied by a write in a
prior transaction to commit as part of the current
commit. This makes the committed state a fully
consistent view of the filesystem from the
application's perspective (i.e., it includes all
completed filesystem operations). This was previously
the behavior only when a snapshot is created.
inode_cacheEnable free inode number caching. Defaults to off due to an overflow problem when the free space CRCs don't fit inside a single page.
max_inline=bytesSpecify the maximum amount of space, in bytes, that can be inlined in a metadata B-tree leaf. The value is specified in bytes, optionally with a K, M, or G suffix, case insensitive. In practice, this value is limited by the root sector size, with some space unavailable due to leaf headers. For a 4k sectorsize, max inline data is ~3900 bytes.
metadata_ratio=valueSpecify that 1 metadata chunk should be allocated
after every value data chunks.
Off by default.
noaclEnable/disable support for Posix Access Control Lists (ACLs). See the acl(5) manual page for more information about ACLs.
nobarrierEnable/disable the use of block-layer write
barriers. Write barriers ensure that certain IOs make
it through the device cache and are on persistent
storage. If disabled on a device with a volatile
(non-battery-backed) write-back cache, the
nobarrier option will
lead to filesystem corruption on a system crash or
power loss.
nodatacowEnable/disable data copy-on-write for newly
created files. This option implies nodatasum, and disables all
compression.
nodatasumEnable/disable data checksumming for newly created
files. This option implies datacow.
notreelogEnable/disable the tree logging used for fsync and O_SYNC writes.
recoveryEnable autorecovery attempts if a bad tree root is found at mount time. Currently this scans a list of several previous tree roots and tries to use the first readable.
rescan_uuid_treeForce check and rebuild procedure of the UUID tree. This should not normally be needed.
skip_balanceSkip automatic resume of an interrupted balance operation after mount. May be resumed with "btrfs balance resume."
nospace_cacheDisable freespace cache loading without clearing the cache.
clear_cacheForce clearing and rebuilding of the disk space cache if something has gone wrong.
ssd|nossd|ssd_spreadOptions to control ssd allocation schemes. By
default, BTRFS will enable or disable ssd allocation
heuristics depending on whether a rotational or
nonrotational disk is in use. The ssd and nossd options can override this
autodetection.
The ssd_spread mount
option attempts to allocate into big chunks of unused
space, and may perform better on low-end ssds.
ssd_spread implies
ssd, enabling all other
ssd heuristics as well.
subvol=pathMount subvolume at path rather than the root subvolume.
The path is relative to
the top level subvolume.
subvolid=IDMount subvolume specified by an ID number rather than the root subvolume. This allows mounting of subvolumes which are not in the root of the mounted filesystem. You can use "btrfs subvolume list" to see subvolume ID numbers.
subvolrootid=objectid(deprecated)Mount subvolume specified by objectid rather than the root
subvolume. This allows mounting of subvolumes which
are not in the root of the mounted filesystem. You
can use "btrfs subvolume show " to see the object ID
for a subvolume.
thread_pool=numberThe number of worker threads to allocate. The default number is equal to the number of CPUs + 2, or 8, whichever is smaller.
user_subvol_rm_allowedAllow subvolumes to be deleted by a non-root user. Use with caution.
See the options section of the mount.cifs(8) man page (cifs-utils package must be installed).
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=nSet the owner and group of the mountpoint.
mode=valueSets the mode of the mountpoint.
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=valueThis 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=valueSet 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.
newinstanceCreate 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=valueSet 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.
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|noaclSupport POSIX Access Control Lists (or not).
bsddf|minixdfSet the behavior for the statfs system call. The
minixdf behavior is to
return in the f_blocks
field the total number of blocks of the filesystem,
while the bsddf behavior
(which is the default) is to subtract the overhead
blocks used by the ext2 filesystem and not available
for file storage. Thus
% mount /k −o minixdf; df /k; umount /k
| Filesystem | 1024-blocks | Used | Available | Capacity | Mounted on |
| /dev/sda6 | 2630655 | 86954 | 2412169 | 3% | /k |
% mount /k −o bsddf; df /k; umount /k
| Filesystem | 1024-blocks | Used | Available | Capacity | Mounted on |
| /dev/sda6 | 2543714 | 13 | 2412169 | 0% | /k |
(Note that this example shows that one can add
command-line options to the options given in /etc/fstab.)
check=none or
nocheckNo checking is done at mount time. This is the default. This is fast. It is wise to invoke e2fsck(8) every now and then, e.g. at boot time. The non-default behavior is unsupported (check=normal and check=strict options have been removed). Note that these mount options don't have to be supported if ext4 kernel driver is used for ext2 and ext3 filesystems.
debugPrint debugging info upon each (re)mount.
errors={continue|remount-ro|panic}Define the behavior when an error is encountered. (Either ignore errors and just mark the filesystem erroneous and continue, or remount the filesystem read-only, or panic and halt the system.) The default is set in the filesystem superblock, and can be changed using tune2fs(8).
grpid|bsdgroups and nogrpid|sysvgroupsThese 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|usrquotaThe usrquota (same as quota) mount option enables user quota support on the filesystem. grpquota enables group quotas support. You need the quota utilities to actually enable and manage the quota system.
nouid32Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values.
oldalloc or orlovUse old allocator or Orlov allocator for new inodes. Orlov is default.
resgid=n and resuid=nThe 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=nInstead of block 1, use block n as superblock. This could be
useful when the filesystem has been damaged.
(Earlier, copies of the superblock would be made
every 8192 blocks: in block 1, 8193, 16385, ... (and
one got thousands of copies on a big filesystem).
Since version 1.08, mke2fs has a
−s (sparse superblock) option to reduce the
number of backup superblocks, and since version 1.15
this is the default. Note that this may mean that
ext2 filesystems created by a recent mke2fs cannot be
mounted r/w under Linux 2.0.*.) The block number here
uses 1 k units. Thus, if you want to use logical
block 32768 on a filesystem with 4 k blocks, use
"sb=131072".
user_xattr|nouser_xattrSupport "user." extended attributes (or not).
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:
Update the ext3 filesystem's journal to the current format.
When a journal already exists, this option is
ignored. Otherwise, it specifies the number of the
inode which will represent the ext3 filesystem's
journal file; ext3 will create a new journal,
overwriting the old contents of the file whose inode
number is inum.
journal_dev=devnum/journal_path=pathWhen the external journal device's major/minor numbers have changed, these options allow the user to specify the new journal location. The journal device is identified either through its new major/minor numbers encoded in devnum, or via a path to the device.
norecovery/noloadDon't load the journal on mounting. Note that if the filesystem was not unmounted cleanly, skipping the journal replay will lead to the filesystem containing inconsistencies that can lead to any number of problems.
data={journal|ordered|writeback}Specifies the journaling mode for file data.
Metadata is always journaled. To use modes other than
ordered on the root
filesystem, pass the mode to the kernel as boot
parameter, e.g. rootflags=data=journal.
journalAll data is committed into the journal prior to being written into the main filesystem.
rderedThis is the default mode. All data is forced directly out to the main file system prior to its metadata being committed to the journal.
writebackData 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.
Just print an error message if an error occurs in a file data buffer in ordered mode.
Abort the journal if an error occurs in a file data buffer in ordered mode.
barrier=0 / barrier=1This disables / enables the use of write barriers in the jbd code. barrier=0 disables, barrier=1 enables (default). This also requires an IO stack which can support barriers, and if jbd gets an error on a barrier write, it will disable barriers again with a warning. Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance penalty. If your disks are battery-backed in one way or another, disabling barriers may safely improve performance.
commit=nrsecSync all data and metadata every nrsec seconds. The
default value is 5 seconds. Zero means default.
user_xattrEnable Extended User Attributes. See the attr(5) manual page.
aclEnable POSIX Access Control Lists. See the acl(5) manual page.
usrjquota=aquota.user|grpjquota=aquota.group|jqfmt=vfsv0Apart from the old quota system (as in ext2, jqfmt=vfsold aka version 1 quota) ext3 also supports journaled quotas (version 2 quota). jqfmt=vfsv0 enables journaled quotas. For journaled quotas the mount options usrjquota=aquota.user and grpjquota=aquota.group are required to tell the quota system which quota database files to use. Journaled quotas have the advantage that even after a crash no quota check is required.
The ext4 filesystem is an advanced level of the ext3 filesystem which incorporates scalability and reliability enhancements for supporting large filesystem.
The options journal_dev, norecovery, noload, data, commit, orlov, oldalloc, [no]user_xattr [no]acl, bsddf, minixdf, debug, errors, data_err, grpid, bsdgroups, nogrpid sysvgroups, resgid, resuid, sb, quota, noquota, grpquota, usrquota usrjquota, grpjquota and jqfmt are backwardly compatible with ext3 or ext2.
journal_checksumEnable 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_commitCommit block can be written to disk without waiting for descriptor blocks. If enabled, older kernels cannot mount the device. This will enable 'journal_checksum' internally.
barrier=0 / barrier=1 /
barrier / nobarrierThese mount options have the same effect as in ext3. The mount options "barrier" and "nobarrier" are added for consistency with other ext4 mount options.
The ext4 filesystem enables write barriers by default.
inode_readahead_blks=nThis 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=nNumber 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.
delallocDeferring block allocation until write-out time.
nodelallocDisable delayed allocation. Blocks are allocated when data is copied from user to page cache.
max_batch_time=usecMaximum amount of time ext4 should wait for additional filesystem operations to be batch together with a synchronous write operation. Since a synchronous write operation is going to force a commit and then a wait for the I/O complete, it doesn't cost much, and can be a huge throughput win, we wait for a small amount of time to see if any other transactions can piggyback on the synchronous write. The algorithm used is designed to automatically tune for the speed of the disk, by measuring the amount of time (on average) that it takes to finish committing a transaction. Call this time the "commit time". If the time that the transaction has been running is less than the commit time, ext4 will try sleeping for the commit time to see if other operations will join the transaction. The commit time is capped by the max_batch_time, which defaults to 15000 [mc]s (15 ms). This optimization can be turned off entirely by setting max_batch_time to 0.
min_batch_time=usecThis 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=prioThe 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.
abortSimulate 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_allocMany broken applications don't use fsync() when replacing existing files via patterns such as
fd = open("foo.new")/write(fd,...)/close(fd)/ rename("foo.new", "foo")
or worse yet
fd = open("foo", O_TRUNC)/write(fd,...)/close(fd).
If auto_da_alloc is enabled, ext4 will detect the replace-via-rename and replace-via-truncate patterns and force that any delayed allocation blocks are allocated such that at the next journal commit, in the default data=ordered mode, the data blocks of the new file are forced to disk before the rename() operation is committed. This provides roughly the same level of guarantees as ext3, and avoids the "zero-length" problem that can happen when a system crashes before the delayed allocation blocks are forced to disk.
noinit_itableDo not initialize any uninitialized inode table blocks in the background. This feature may be used by installation CD's so that the install process can complete as quickly as possible; the inode table initialization process would then be deferred until the next time the filesystem is mounted.
The lazy itable init code will wait n times the number of milliseconds it took to zero out the previous block group's inode table. This minimizes the impact on system performance while the filesystem's inode table is being initialized.
discard/nodiscardControls 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.
nouid32Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values.
block_validity/noblock_validityThis 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_nolockControls 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).
This limits the size of the directories so that any attempt to expand them beyond the specified limit in kilobytes will cause an ENOSPC error. This is useful in memory-constrained environments, where a very large directory can cause severe performance problems or even provoke the Out Of Memory killer. (For example, if there is only 512 MB memory available, a 176 MB directory may seriously cramp the system's style.)
i_versionEnable 64-bit inode version support. This option is off by default.
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blocksize={512|1024|2048}Set blocksize (default 512). This option is obsolete.
uid=value and gid=valueSet the owner and group of all files. (Default: the uid and gid of the current process.)
umask=valueSet 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=valueSet the umask applied to directories only. The default is the umask of the current process. The value is given in octal.
fmask=valueSet the umask applied to regular files only. The default is the umask of the current process. The value is given in octal.
allow_utime=valueThis option controls the permission check of mtime/atime.
20If current process is in group of file's group ID, you can change timestamp.
2Other 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=valueThree different levels of pickiness can be chosen:
r[elaxed]Upper and lower case are accepted and equivalent, long name parts are truncated (e.g.
verylongname.foobarbecomesverylong.foo), leading and embedded spaces are accepted in each name part (name and extension).n[ormal]Like "relaxed", but many special characters (*, ?, <, spaces, etc.) are rejected. This is the default.
s[trict]Like "normal", but names that contain long parts or special characters that are sometimes used on Linux but are not accepted by MS-DOS (+, =, etc.) are rejected.
codepage=valueSets the codepage for converting to shortname characters on FAT and VFAT filesystems. By default, codepage 437 is used.
conv=modeThe fat filesystem
can perform CRLF<-->NL conversion (MS-DOS text
format to UNIX text format) in the kernel. The
following conversion modes are
available:
b[inary]No translation is performed. This is the default.
t[ext]CRLF<-->NL translation is performed on all files.
a[uto]CRLF<-->NL translation is performed on all files that don't have a "well-known binary" extension. The list of known extensions can be found at the beginning of
fs/fat/misc.c(as of 2.0, the list is: exe, com, bin, app, sys, drv, ovl, ovr, obj, lib, dll, pif, arc, zip, lha, lzh, zoo, tar, z, arj, tz, taz, tzp, tpz, gz, tgz, deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk, pxl, dvi).Programs that do computed lseeks won't like in-kernel text conversion. Several people have had their data ruined by this translation. Beware!
For filesystems mounted in binary mode, a conversion tool (fromdos/todos) is available. This option is obsolete.
cvf_format=moduleForces 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=optionOption passed to the CVF module. This option is obsolete.
debugTurn 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).
discardIf 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.
dos1xfloppyIf set, use a fallback default BIOS Parameter Block configuration, determined by backing device size. These static parameters match defaults assumed by DOS 1.x for 160 kiB, 180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
errors={panic|continue|remount-ro}Specify FAT behavior on critical errors: panic, continue without doing anything, or remount the partition in read-only mode (default behavior).
fat={12|16|32}Specify a 12, 16 or 32 bit fat. This overrides the automatic FAT type detection routine. Use with caution!
iocharset=valueCharacter set to use for converting between 8 bit characters and 16 bit Unicode characters. The default is iso8859-1. Long filenames are stored on disk in Unicode format.
nfs={stale_rw|nostale_ro}Enable this only if you want to export the FAT filesystem over NFS.
stale_rw: This option
maintains an index (cache) of directory inodes which
is used by the nfs-related code to improve look-ups.
Full file operations (read/write) over NFS are
supported but with cache eviction at NFS server, this
could result in spurious ESTALE errors.
nostale_ro: This
option bases the inode number and filehandle on the
on-disk location of a file in the FAT directory
entry. This ensures that ESTALE will not be returned after
a file is evicted from the inode cache. However, it
means that operations such as rename, create and
unlink could cause filehandles that previously
pointed at one file to point at a different file,
potentially causing data corruption. For this reason,
this option also mounts the filesystem readonly.
To maintain backward compatibility, '-o nfs' is
also accepted, defaulting to stale_rw.
tz=UTCThis 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.
time_offset=minutesSet offset for conversion of timestamps from local
time used by FAT to UTC. I.e., minutes minutes will be subtracted
from each timestamp to convert it to UTC used
internally by Linux. This is useful when the time
zone set in the kernel via settimeofday(2) is
not the time zone used by the filesystem. Note that
this option still does not provide correct time
stamps in all cases in presence of DST - time stamps
in a different DST setting will be off by one
hour.
quietTurn on the quiet
flag. Attempts to chown or chmod files do not return
errors, although they fail. Use with caution!
rodirFAT has the ATTR_RO (read-only) attribute. On Windows, the ATTR_RO of the directory will just be ignored, and is used only by applications as a flag (e.g. it's set for the customized folder).
If you want to use ATTR_RO as read-only flag even for the directory, set this option.
showexecIf 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_immutableIf set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag on Linux. Not set by default.
flushIf set, the filesystem will try to flush to disk more early than normal. Not set by default.
usefreeUse 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.
creator=cccc,
type=ccccSet the creator/type values as shown by the MacOS finder used for creating new files. Default values: '????'.
uid=n,
gid=nSet the owner and group of all files. (Default: the uid and gid of the current process.)
dir_umask=n,
file_umask=n,
umask=nSet the umask used for all directories, all regular files, or all files and directories. Defaults to the umask of the current process.
session=nSelect 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=nSelect partition number n from the device. Only makes sense for CDROMs. Defaults to not parsing the partition table at all.
quietDon't complain about invalid mount options.
uid=value and gid=valueSet the owner and group of all files. (Default: the uid and gid of the current process.)
umask=valueSet 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.
nocheckDo not abort mounting when certain consistency checks fail.
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).
norockDisable the use of Rock Ridge extensions, even if
available. Cf. map.
nojolietDisable 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=valueGive 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=valueFor non-Rock Ridge volumes, give all files the indicated mode. (Default: read and execute permission for everybody.) Since Linux 2.1.37 one no longer needs to specify the mode in decimal. (Octal is indicated by a leading 0.)
unhideAlso 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.)
cruftIf the high byte of the file length contains other garbage, set this mount option to ignore the high order bits of the file length. This implies that a file cannot be larger than 16 MB.
session=xSelect number of session on multisession CD. (Since 2.3.4.)
sbsector=xxxSession 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=valueCharacter set to use for converting 16 bit Unicode characters on CD to 8 bit characters. The default is iso8859-1.
utf8Convert 16 bit Unicode characters on CD to UTF-8.
iocharset=nameCharacter 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=valueResize 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.
nointegrityDo 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.
integrityDefault. Commit metadata changes to the journal.
Use this option to remount a volume where the
nointegrity option was
previously specified in order to restore normal
behavior.
errors={continue|remount-ro|panic}Define the behavior when an error is encountered. (Either ignore errors and just mark the filesystem erroneous and continue, or remount the filesystem read-only, or panic and halt the system.)
noquota|quota|usrquota|grpquotaThese options are accepted but ignored.
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.
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.
See the options section of the nfs(5) man page (the 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.
iocharset=nameCharacter set to use when returning file names. Unlike VFAT, NTFS suppresses names that contain nonconvertible characters. Deprecated.
nls=nameNew name for the option earlier called
iocharset.
utf8Use 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.
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=valueSet 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.
Since Linux 3.18 the overlay pseudo filesystem implements a union mount for other filesystems.
An overlay filesystem combines two filesystems - an
upper filesystem and a
lower filesystem. When a name
exists in both filesystems, the object in the upper
filesystem is visible while the object in the lower
filesystem is either hidden or, in the case of directories,
merged with the upper object.
The lower filesystem can be any filesystem supported by Linux and does not need to be writable. The lower filesystem can even be another overlayfs. The upper filesystem will normally be writable and if it is it must support the creation of trusted.* extended attributes, and must provide a valid d_type in readdir responses, so NFS is not suitable.
A read-only overlay of two read-only filesystems may use
any filesystem type. The options lowerdir and upperdir are combined into a merged
directory by using:
mount −t overlay overlay \ −olowerdir=/lower,upperdir=/upper,workdir=/work /merged
lowerdir=directoryAny filesystem, does not need to be on a writable filesystem.
upperdir=directoryThe upperdir is normally on a writable filesystem.
workdir=directoryThe workdir needs to be an empty directory on the same filesystem as upperdir.
uid=value and gid=valueThese options are recognized, but have no effect as far as I can see.
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.
Reiserfs is a journaling filesystem.
convInstructs 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.
rupasovA 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.
teaA 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.
r5A 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.
detectInstructs 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_relocationTunes the block allocator. This may provide performance improvements in some situations.
no_unhashed_relocationTunes the block allocator. This may provide performance improvements in some situations.
noborderDisable the border allocator algorithm invented by Yury Yu. Rupasov. This may provide performance improvements in some situations.
nologDisable 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.
notailBy 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.
replayonlyReplay the transactions which are in the journal,
but do not actually mount the filesystem. Mainly used
by reiserfsck.
resize=numberA 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_xattrEnable Extended User Attributes. See the attr(5) manual page.
aclEnable POSIX Access Control Lists. See the acl(5) manual page.
barrier=none /
barrier=flushThis disables / enables the use of write barriers in the journaling code. barrier=none disables, barrier=flush enables (default). This also requires an IO stack which can support barriers, and if reiserfs gets an error on a barrier write, it will disable barriers again with a warning. Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance penalty. If your disks are battery-backed in one way or another, disabling barriers may safely improve performance.
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.
size=nbytesOverride 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%
The same as size, but in blocks of PAGE_CACHE_SIZE
The maximum number of inodes for this instance. The default is half of the number of your physical RAM pages, or (on a machine with highmem) the number of lowmem RAM pages, whichever is the lower.
The tmpfs mount options for sizing (size, nr_blocks, and nr_inodes) accept a suffix k, m or
g for Ki, Mi, Gi (binary kilo
(kibi), binary mega (mebi) and binary giga (gibi)) and can
be changed on remount.
Set initial permissions of the root directory.
The user id.
The group id.
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 ...'
defaultprefers 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
interleaveprefers to allocate from each node in turn
- interleave:NodeList
allocates from each node of NodeList in turn.
The NodeList format is a comma-separated list of decimal numbers and ranges, a range being two "hyphen-minus"-separated decimal numbers, the smallest and largest node numbers in the range. For example, mpol=bind:0–3,5,7,9–15
Note that trying to mount a tmpfs with an mpol option will fail if the running kernel does not support NUMA; and will fail if its nodelist specifies a node which is not online. If your system relies on that tmpfs being mounted, but from time to time runs a kernel built without NUMA capability (perhaps a safe recovery kernel), or with fewer nodes online, then it is advisable to omit the mpol option from automatic mount options. It can be added later, when the tmpfs is already mounted on MountPoint, by 'mount −o remount,mpol=Policy:NodeList MountPoint'.
UBIFS is a flash filesystem which works on top of UBI
volumes. Note that atime is
not supported and is always turned off.
ubiX_YUBI device numberX, volume numberY
ubiYUBI device number
0, volume numberY- ubiX:NAME
UBI device number
X, volume with nameNAME- ubi:NAME
UBI device number
0, volume with nameNAME
Alternative !
separator may be used instead of :.
bulk_readEnable 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_readDo not bulk-read. This is the default.
chk_data_crcCheck 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.
udf is the "Universal Disk Format" filesystem defined by
the Optical Storage Technology Association, and is often
used for DVD-ROM. See also iso9660.
Set the default group.
Set the default umask. The value is given in octal.
Set the default user.
unhideShow otherwise hidden files.
undeleteShow deleted files in lists.
nostrictUnset strict conformance.
iocharsetSet the NLS character set.
Set the block size. (May not work unless 2048.)
novrsSkip volume sequence recognition.
Set the CDROM session counting from 0. Default: last session.
Override standard anchor location. Default: 256.
Override the VolumeDesc location. (unused)
Override the PartitionDesc location. (unused)
Set the last block of the filesystem.
Override the fileset block location. (unused)
Override the root directory location. (unused)
ufstype=valueUFS 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:
ldOld format of ufs, this is the default, read only. (Don't forget to give the −r option.)
44bsdFor filesystems created by a BSD-like system (NetBSD, FreeBSD, OpenBSD).
ufs2Used in FreeBSD 5.x supported as read-write.
5xbsdSynonym for ufs2.
sunFor filesystems created by SunOS or Solaris on Sparc.
sunx86For filesystems created by Solaris on x86.
hpFor filesystems created by HP-UX, read-only.
nextstepFor filesystems created by NeXTStep (on NeXT station) (currently read only).
- nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
penstepFor filesystems created by OpenStep (currently read only). The same filesystem type is also used by Mac OS X.
onerror=valueSet behavior on error:
panicIf 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.
See mount options for msdos. The dotsOK option is explicitly killed by
umsdos.
First of all, the mount options for fat are recognized. The dotsOK option is explicitly killed by
vfat. Furthermore, there
are
uni_xlateTranslate unhandled Unicode characters to special escaped sequences. This lets you backup and restore filenames that are created with any Unicode characters. Without this option, a '?' is used when no translation is possible. The escape character is ':' because it is otherwise invalid on the vfat filesystem. The escape sequence that gets used, where u is the Unicode character, is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12).
posixAllow two files with names that only differ in case. This option is obsolete.
nonumtailFirst try to make a short name without sequence
number, before trying name~num.ext.
utf8UTF8 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=modeDefines the behavior for creation and display of
filenames which fit into 8.3 characters. If a long
name for a file exists, it will always be the
preferred one for display. There are four modes:
lowerForce the short name to lower case upon display; store a long name when the short name is not all upper case.
win95Force the short name to upper case upon display; store a long name when the short name is not all upper case.
winntDisplay the short name as is; store a long name when the short name is not all lower case or all upper case.
mixedDisplay 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.
devuid=uid and devgid=gid and devmode=modeSet 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=modeSet 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=modeSet the owner and group and mode of the file
devices (default:
uid=gid=0, mode=0444). The mode is given in
octal.
One further possible type is a mount via the loop device. For example, the command
mount /tmp/disk.img /mnt −t vfat −o loop=/dev/loop3
will set up the loop device /dev/loop3 to correspond to the file
/tmp/disk.img, and then mount
this device on /mnt.
If no explicit loop device is mentioned (but just an
option `−o loop' is given),
then mount will
try to find some unused loop device and use that, for
example
mount /tmp/disk.img /mnt −o loop
The mount command automatically creates a loop device from a
regular file if a filesystem type is not specified or the
filesystem is known for libblkid, for example:
mount /tmp/disk.img /mnt mount −t ext3 /tmp/disk.img /mnt
This type of mount knows about three options, namely
loop, offset and sizelimit, that are really options to
losetup(8). (These options
can be used in addition to those specific to the filesystem
type.)
Since Linux 2.6.25 auto-destruction of loop devices is
supported, meaning that any loop device allocated by
mount will be
freed by umount
independently of /etc/mtab.
You can also free a loop device by hand, using losetup −dor umount −d.
mount has the following return codes (the bits can be ORed):
0success
1incorrect invocation or permissions
2system error (out of memory, cannot fork, no more loop devices)
4internal mount bug
8user interrupt
16problems writing or locking /etc/mtab
32mount failure
64some mount succeeded
The command mount −a returns 0 (all succeeded), 32 (all failed), or 64 (some failed, some succeeded).
The syntax of external mount helpers is:
/sbin/mount.suffixspec dir [−sfnv] [−ooptions] [−ttype.subtype]
where the suffix is the
filesystem type and the −sfnvo options have the same meaning as
the normal mount options. The −t option is used for filesystems with
subtypes support (for example /sbin/mount.fuse −t fuse.sshfs).
The command mount does not pass the
mount options unbindable,
runbindable, private, rprivate, slave, rslave,
shared, rshared, auto,
noauto, comment, x-*, loop, offset
and sizelimit to the
mount.<suffix> helpers. All other options are used in a
comma-separated list as argument to the −o option.
/etc/fstabfilesystem table
/etc/mtabtable of mounted filesystems
/etc/mtab~lock file
/etc/mtab.tmptemporary file
/etc/filesystemsa list of filesystem types to try
LIBMOUNT_FSTAB=<path>overrides the default location of the fstab file (ignored for suid)
LIBMOUNT_MTAB=<path>overrides the default location of the mtab file (ignored for suid)
LIBMOUNT_DEBUG=allenables libmount debug output
LIBBLKID_DEBUG=allenables libblkid debug output
LOOPDEV_DEBUG=allenables loop device setup debug output
mount(2), umount(2), umount(8), fstab(5), findmnt(8), nfs(5), nfsd(8), xfs(5), xfs_admin(8), mountd(8), mke2fs(8), tune2fs(8), e2label(8), swapon(8), losetup(8)
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don't support −o syncnor −o dirsync (the ext2, ext3,
fat and vfat filesystems do
support synchronous updates (a la BSD) when mounted with the
sync option).
The −o remount may not
be able to change mount parameters (all ext2fs-specific parameters, except
sb, are changeable with a
remount, for example, but you can't change gid or umask for the fatfs).
It is possible that the files /etc/mtab and /proc/mounts don't match on systems with a
regular mtab file. The first file is based only on the mount
command options, but the content of the second file also
depends on the kernel and others settings (e.g. on a remote
NFS server -- in certain cases the mount command may report
unreliable information about an NFS mount point and the
/proc/mounts file usually contains more reliable
information.) This is another reason to replace the mtab file
with a symlink to the /proc/mounts file.
Checking files on NFS filesystems referenced by file
descriptors (i.e. the fcntl and
ioctl families of functions) may
lead to inconsistent results due to the lack of a consistency
check in the 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.
The mount command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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Copyright (c) 1996-2004 Andries Brouwer Copyright (C) 2006-2012 Karel Zak <kzakredhat.com> This page is somewhat derived from a page that was (c) 1980, 1989, 1991 The Regents of the University of California and had been heavily modified by Rik Faith and myself. (Probably no BSD text remains.) Fragments of text were written by Werner Almesberger, Remy Card, Stephen Tweedie and Eric Youngdale. This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |