MOUNT(8) System Administration MOUNT(8)
NAME
mount - mount a filesystem
SYNOPSIS
mount [-lhV]
mount -a [-fFnrsvw] [-t vfstype] [-O optlist]
mount [-fnrsvw] [-o option[,option]...] device|dir
mount [-fnrsvw] [-t vfstype] [-o options] device dir
DESCRIPTION
All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /. These
files can be spread out over several devices. The mount command serves to attach the filesystem found on some
device to the big file tree. Conversely, the umount(8) command will detach it again.
The standard form of the mount command, is
mount -t type device dir
This tells the kernel to attach the filesystem found on device (which is of type type) at the directory dir.
The previous contents (if any) and owner and mode of dir become 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 Parti‐
tion 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,partu‐
uid,partlabel} udev symlinks in the /etc/fstab file. The tags are more readable, robust and portable.
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 con‐
tains the noauto keyword. Adding the -F option will make mount fork, so that the filesystems are
mounted simultaneously.
When mounting a filesystem mentioned in fstab or mtab, it suffices to give only the device, or only the
mount point.
The programs mount and umount maintain a list of currently mounted filesystems in the file /etc/mtab.
If no arguments are given to mount, this list is printed.
The mount program does not read the /etc/fstab file if device (or LABEL, UUID, 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 sim‐
ilar contents. The former has somewhat more information, such as the mount options used, but is not
necessarily up-to-date (cf. the -n option below). It is possible to replace /etc/mtab by a symbolic
link to /proc/mounts, and especially when you have very large numbers of mounts things will be much
faster with that symlink, but some information is lost that way, and in particular using the "user"
option will fail.
The non-superuser mounts.
Normally, only the superuser can mount filesystems. However, when fstab contains the user option on a
line, anybody can mount the corresponding system.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 filesystem found on his CDROM using the command
mount /dev/cdrom
or
mount /cd
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 direc‐
tory, for example:
mount --bind foo foo
The bind mount call attaches only (part of) a single filesystem, not possible submounts. The entire
file hierarchy including submounts is attached a second place using
mount --rbind olddir newdir
or shortoption
mount -R olddir newdir
Note that the filesystem mount options will remain the same as those on the original mount point.
mount(8) since v2.27 (backported to RHEL7.3) allow to change the options by passing the -o option along
with --bind for example:
mount --bind,ro foo foo
This feature is not supported by Linux kernel and it is implemented in userspace by additional remount
mount(2) syscall. This solution is not atomic.
The alternative (classic) way to create a read-only bind mount is to use remount operation, for exam‐
ple:
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 TAR‐
GET,PROPAGATION to see the current propagation flags.
The shared subtrees operations.
The following commands allows one to recursively change the type of all the mounts under a given mount‐
point.
mount --make-rshared mountpoint
mount --make-rslave mountpoint
mount --make-rprivate mountpoint
mount --make-runbindable mountpoint
mount(8) does not read fstab(5) when --make-* operation is requested. All necessary information has to
be specified on command line.
Note that Linux kernel does not allow to change more propagation flags by one mount(2) syscall and the
flags cannot be mixed with another mount options.
Since util-linux 2.23 mount command allows to use more propagation flags together and with another
mount operations. This feature is EXPERIMENTAL. The propagation flags are applied by additional
mount(2) syscalls after previous successful mount operation. Note that this use case is not atomic. The
propagation flags is possible to specify in fstab(5) as mount options (private, slave, shared, unbind‐
able, 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 determined by first extracting the mount
options for the filesystem from the fstab table, then applying any options specified by the -o argument, and
finally applying a -r or -w option, when present.
Command line options available for the mount command:
-V, --version
Output version.
-h, --help
Print a help message.
-v, --verbose
Verbose mode.
-a, --all
Mount all filesystems (of the given types) mentioned in fstab.
-F, --fork
(Used in conjunction with -a.) Fork off a new incarnation of mount for each device. This will do the
mounts on different devices or different NFS servers in parallel. This has the advantage that it is
faster; also NFS timeouts go in parallel. A disadvantage is that the mounts are done in undefined
order. Thus, you cannot use this option if you want to mount both /usr and /usr/spool.
Add the labels in the mount output. Mount must have permission to read the disk device (e.g. be suid
root) for this to work. One can set such a label for ext2, ext3 or ext4 using the e2label(8) utility,
or for XFS using xfs_admin(8), or for reiserfs using reiserfstune(8).
-n, --no-mtab
Mount without writing in /etc/mtab. This is necessary for example when /etc is on a read-only filesys‐
tem.
-c, --no-canonicalize
Don't canonicalize paths. The mount command canonicalizes all paths (from command line or fstab) and
stores canonicalized paths to the /etc/mtab file. This option can be used together with the -f flag for
already canonicalized absolute paths.
-s Tolerate sloppy mount options rather than failing. This will ignore mount options not supported by a
filesystem type. Not all filesystems support this option. This option exists for support of the Linux
autofs-based automounter.
--source src
If only one argument for the mount command is given then the argument might be interpreted as target
(mountpoint) or source (device). This option allows to explicitly define that the argument is mount
source.
-r, --read-only
Mount the filesystem read-only. A synonym is -o ro.
Note that, depending on the filesystem type, state and kernel behavior, the system may still write to
the device. For example, Ext3 or ext4 will replay its journal if the filesystem is dirty. To prevent
this kind of write access, you may want to mount ext3 or ext4 filesystem with "ro,noload" mount options
or set the block device to read-only mode, see command blockdev(8).
-w, --rw, --read-write
Mount the filesystem read/write. This is the default. A synonym is -o rw.
-L, --label label
Mount the partition that has the specified label.
-U, --uuid uuid
Mount the partition that has the specified uuid. These two options require the file /proc/partitions
(present since Linux 2.1.116) to exist.
-T, --fstab path
Specifies alternative fstab file. If the path is directory then the files in the directory are sorted
by strverscmp(3), files that starts with "." or without .fstab extension are ignored. The option can be
specified more than once. This option is mostly designed for initramfs or chroot scripts where addi‐
tional configuration is specified outside standard system configuration.
Note that mount(8) does not pass the option --fstab to /sbin/mount.<type> helpers, it means that the
alternative fstab files will be invisible for the helpers. This is no problem for normal mounts, but
user (non-root) mounts always require fstab to verify user's rights.
-t, --types vfstype
The argument following the -t is used to indicate the filesystem type. The filesystem types which are
currently supported include: adfs, affs, autofs, cifs, coda, coherent, cramfs, debugfs, devpts, efs,
ext, ext2, ext3, ext4, hfs, hfsplus, hpfs, iso9660, jfs, minix, msdos, ncpfs, nfs, nfs4, ntfs, proc,
ncpfs) ad hoc code is necessary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems have a separate
mount program. In order to make it possible to treat all types in a uniform way, mount will execute the
program /sbin/mount.TYPE (if that exists) when called with type TYPE. Since various versions of the
smbmount program have different calling conventions, /sbin/mount.smbfs may have to be a shell script
that sets up the desired call.
If no -t option is given, or if the auto type is specified, mount will try to guess the desired type.
Mount uses the blkid library for guessing the filesystem type; if that does not turn up anything that
looks familiar, mount will try to read the file /etc/filesystems, or, if that does not exist,
/proc/filesystems. All of the filesystem types listed there will be tried, except for those that are
labeled "nodev" (e.g., devpts, proc and nfs). If /etc/filesystems ends in a line with a single * only,
mount will read /proc/filesystems afterwards. All of the filesystem types will be mounted with mount
option "silent".
The auto type may be useful for user-mounted floppies. Creating a file /etc/filesystems can be useful
to change the probe order (e.g., to try vfat before msdos or ext3 before ext2) or if you use a kernel
module autoloader.
More than one type may be specified in a comma separated list. The list of filesystem types can be
prefixed with no to specify the filesystem types on which no action should be taken. (This can be
meaningful with the -a option.) For 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 argument is mount
target.
-O, --test-opts opts
Used in conjunction with -a, to limit the set of filesystems to which the -a is applied. Like -t in
this regard except that it is useless except in the context of -a. For example, the command:
mount -a -O no_netdev
mounts all filesystems except those which have the option _netdev specified in the options field in the
/etc/fstab file.
It is different from -t in that each option is matched exactly; a leading no at the beginning of one
option does not negate the rest.
The -t and -O options are cumulative in effect; that is, the command
mount -a -t ext2 -O _netdev
mounts all ext2 filesystems with the _netdev option, not all filesystems that are either ext2 or have
the _netdev option specified.
-o, --options opts
Options are specified with a -o flag followed by a comma separated string of options. For example:
mount LABEL=mydisk -o noatime,nouser
-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, fat, vfat and ufs):
async All I/O to the filesystem should be done asynchronously. (See also the sync option.)
atime Do not use noatime feature, then the inode access time is controlled by kernel defaults. See also the
description for strictatime and relatime mount options.
noatime
Do not update inode access times on this filesystem (e.g., for faster access on the news spool to speed
up news servers).
auto Can be mounted with the -a option.
noauto Can only be mounted explicitly (i.e., the -a option will not cause the filesystem to be mounted).
context=context, fscontext=context, defcontext=context and rootcontext=context
The context= option is useful when mounting filesystems that do not support extended attributes, such
as a floppy or hard disk formatted with VFAT, or systems that are not normally running under SELinux,
such as an ext3 formatted disk from a non-SELinux workstation. You can also use context= on filesystems
you do not trust, such as a floppy. It also helps in compatibility with xattr-supporting filesystems on
earlier 2.4.<x> kernel versions. Even where xattrs are supported, you can save time not having to label
every file by assigning the entire disk one security context.
A commonly used option for removable media is context="system_u:object_r:removable_t".
Two other options are fscontext= and defcontext=, both of which are mutually exclusive of the context
option. This means you can use fscontext and defcontext with each other, but neither can be used with
context.
The fscontext= option works for all filesystems, regardless of their xattr support. The fscontext
option sets the overarching filesystem label to a specific security context. This filesystem label is
separate from the individual labels on the files. It represents the entire filesystem for certain kinds
of permission checks, such as during mount or file creation. Individual file labels are still obtained
from the xattrs on the files themselves. The context option actually sets the aggregate context that
fscontext provides, in addition to supplying the same label for individual files.
You can set the default security context for unlabeled files using defcontext= option. This overrides
the value set for unlabeled files in the policy and requires a filesystem that supports xattr labeling.
The rootcontext= option allows you to explicitly label the root inode of a FS being mounted before that
FS or inode becomes visible to userspace. This was found to be useful for things like stateless linux.
defaults
Use default options: rw, suid, dev, exec, auto, nouser, and async.
Note that the real set of the all default mount options depends on kernel and filesystem type. See the
begin of this section for more details.
dev Interpret character or block special devices on the filesystem.
nodev Do not interpret character or block special devices on the file system.
diratime
Update directory inode access times on this filesystem. This is the default.
nodiratime
Do not update directory inode access times on this filesystem.
dirsync
All directory updates within the filesystem should be done synchronously. This affects the following
system calls: creat, link, unlink, symlink, mkdir, rmdir, mknod and rename.
exec Permit execution of binaries.
noexec Do not allow direct execution of any binaries on the mounted filesystem. (Until recently it was possi‐
ble 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 previ‐
ous access time was earlier than the current modify or change time. (Similar to noatime, but doesn't
break mutt or other applications that need to know if a file has been read since the last time it was
modified.)
Since Linux 2.6.30, the kernel defaults to the behavior provided by this option (unless noatime was
Use the kernel's default behaviour for inode access time updates.
suid Allow set-user-identifier or set-group-identifier bits to take effect.
nosuid Do not allow set-user-identifier or set-group-identifier bits to take effect. (This seems safe, but is
in fact rather unsafe if you have suidperl(1) installed.)
silent Turn on the silent flag.
loud Turn off the silent flag.
owner Allow an ordinary (i.e., non-root) user to mount the filesystem if he is the owner of the device. This
option implies the options nosuid and nodev (unless overridden by subsequent options, as in the option
line owner,dev,suid).
remount
Attempt to remount an already-mounted filesystem. This is commonly used to change the mount flags for
a filesystem, especially to make a readonly filesystem writable. It does not change device or mount
point.
The remount functionality follows the standard way how the mount command works with options from fstab.
It means the mount command doesn't read fstab (or mtab) only when a device and dir are fully specified.
mount -o remount,rw /dev/foo /dir
After this call all old mount options are replaced and arbitrary stuff from fstab is ignored, except
the loop= option which is internally generated and maintained by the mount command.
mount -o remount,rw /dir
After this call mount reads fstab (or mtab) and merges these options with options from command line (
-o ).
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
sync All I/O to the filesystem should be done synchronously. In case of media with limited number of write
cycles (e.g. some flash drives) "sync" may cause life-cycle shortening.
user Allow an ordinary user to mount the filesystem. The name of the mounting user is written to mtab so
that he can unmount the filesystem again. This option implies the options noexec, nosuid, and nodev
(unless overridden by subsequent options, as in the option line user,exec,dev,suid).
nouser Forbid an ordinary (i.e., non-root) user to mount the filesystem. This is the default.
users Allow every user to mount and unmount the filesystem. This option implies the options noexec, nosuid,
and nodev (unless overridden by subsequent options, as in the option line users,exec,dev,suid).
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>]
Mount options for adfs
uid=value and gid=value
Set the owner and group of the files in the filesystem (default: uid=gid=0).
ownmask=value and othmask=value
Set the permission mask for ADFS 'owner' permissions and 'other' permissions, respectively (default:
0700 and 0077, respectively). See also /usr/src/linux/Documentation/filesystems/adfs.txt.
Mount options for affs
uid=value and gid=value
Set the owner and group of the root of the filesystem (default: uid=gid=0, but with option uid or gid
without specified value, the uid and gid of the current process are taken).
setuid=value and setgid=value
Set the owner and group of all files.
mode=value
Set the mode of all files to value & 0777 disregarding the original permissions. Add search permission
to directories that have read permission. The value is given in octal.
protect
Do not allow any changes to the protection bits on the filesystem.
usemp Set uid and gid of the root of the filesystem to the uid and gid of the mount point upon the first sync
or umount, and then clear this option. Strange...
verbose
Print an informational message for each successful mount.
prefix=string
Prefix used before volume name, when following a link.
volume=string
Prefix (of length at most 30) used before '/' when following a symbolic link.
reserved=value
(Default: 2.) Number of unused blocks at the start of the device.
root=value
Give explicitly the location of the root block.
bs=value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota|noquota|quota|usrquota
These options are accepted but ignored. (However, quota utilities may react to such strings in
/etc/fstab.)
Mount options for cifs
See the options section of the mount.cifs(8) man page (cifs-utils package must be installed).
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 speci‐
fied, they will be set to the UID and GID of the creating process. For example, if there is a tty
group with GID 5, then gid=5 will cause newly created PTYs to belong to the tty group.
mode=value
Set the mode of newly created PTYs to the specified value. The default is 0600. A value of mode=620
and gid=5 makes "mesg y" the default on newly created PTYs.
newinstance
Create a private instance of devpts filesystem, such that indices of ptys allocated in this new
instance are independent of indices created in other instances of devpts.
All mounts of devpts without this newinstance option share the same set of pty indices (i.e legacy
mode). Each mount of devpts with the newinstance option has a private set of pty indices.
This option is mainly used to support containers in the linux kernel. It is implemented in linux kernel
versions starting with 2.6.29. Further, this mount option is valid only if CONFIG_DEVPTS_MULTI‐
PLE_INSTANCES is enabled in the kernel configuration.
To use this option effectively, /dev/ptmx must be a symbolic link to pts/ptmx. See Documenta‐
tion/filesystems/devpts.txt in the linux kernel source tree for details.
ptmxmode=value
Set the mode for the new ptmx device node in the devpts filesystem.
With the support for multiple instances of devpts (see newinstance option above), each instance has a
private ptmx node in the root of the devpts filesystem (typically /dev/pts/ptmx).
For compatibility with older versions of the kernel, the default mode of the new ptmx node is 0000.
ptmxmode=value specifies a more useful mode for the ptmx node and is highly recommended when the newin‐
stance option is specified.
This option is only implemented in linux kernel versions starting with 2.6.29. Further this option is
valid only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configuration.
Mount options for ext
None. Note that the `ext' filesystem is obsolete. Don't use it. Since Linux version 2.1.21 extfs is no
longer part of the kernel source.
Mount options for ext2
The `ext2' filesystem is the standard Linux filesystem. Since Linux 2.5.46, for most mount options the
default is determined by the filesystem superblock. Set them with tune2fs(8).
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/sda6 2543714 13 2412169 0% /k
(Note that this example shows that one can add command line options to the options given in
/etc/fstab.)
check=none or nocheck
No checking is done at mount time. This is the default. This is fast. It is wise to invoke e2fsck(8)
every now and then, e.g. at boot time. The non-default behavior is unsupported (check=normal and
check=strict options have been removed). Note that these mount options don't have to be supported if
ext4 kernel driver is used for ext2 and ext3 filesystems.
debug Print debugging info upon each (re)mount.
errors={continue|remount-ro|panic}
Define the behaviour when an error is encountered. (Either ignore errors and just mark the filesystem
erroneous and continue, or remount the filesystem read-only, or panic and halt the system.) The
default is set in the filesystem superblock, and can be changed using tune2fs(8).
grpid|bsdgroups and nogrpid|sysvgroups
These options define what group id a newly created file gets. When grpid is set, it takes the group id
of the directory in which it is created; otherwise (the default) it takes the fsgid of the current
process, unless the directory has the setgid bit set, in which case it takes the gid from the parent
directory, and also gets the setgid bit set if it is a directory itself.
grpquota|noquota|quota|usrquota
The usrquota (same as quota) mount option enables user quota support on the filesystem. grpquota
enables group quotas support. You need the quota utilities to actually enable and manage the quota sys‐
tem.
nouid32
Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and
expect 16-bit values.
oldalloc or orlov
Use old allocator or Orlov allocator for new inodes. Orlov is default.
resgid=n and resuid=n
The ext2 filesystem reserves a certain percentage of the available space (by default 5%, see mke2fs(8)
and tune2fs(8)). These options determine who can use the reserved blocks. (Roughly: whoever has the
specified uid, or belongs to the specified group.)
sb=n Instead of block 1, use block n as superblock. This could be useful when the filesystem has been dam‐
aged. (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).
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 filesystem, 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, barrier=1 enables it. Write barriers enforce
proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some per‐
formance penalty. The ext3 filesystem does not enable write barriers by default. Be sure to enable
barriers unless your disks are battery-backed one way or another. Otherwise you risk filesystem cor‐
ruption in case of power failure.
commit=nrsec
Sync all data and metadata every nrsec seconds. The default value is 5 seconds. Zero means default.
user_xattr
Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual page.
usrjquota=aquota.user|grpjquota=aquota.group|jqfmt=vfsv0
Apart from the old quota system (as in ext2, jqfmt=vfsold aka version 1 quota) ext3 also supports jour‐
naled quotas (version 2 quota). jqfmt=vfsv0 enables journaled quotas. For journaled quotas the mount
options usrjquota=aquota.user and grpjquota=aquota.group are required to tell the quota system which
quota database files to use. Journaled quotas have the advantage that even after a crash no quota check
is required.
Mount options for ext4
journal_async_commit
Commit block can be written to disk without waiting for descriptor blocks. If enabled older kernels
cannot mount the device. This will enable 'journal_checksum' internally.
barrier=0 / barrier=1 / barrier / nobarrier
This enables/disables the use of write barriers in the jbd code. barrier=0 disables, barrier=1
enables. This also requires an IO stack which can support barriers, and if jbd gets an error on a bar‐
rier write, it will disable again with a warning. Write barriers enforce proper on-disk ordering of
journal commits, making volatile disk write caches safe to use, at some performance penalty. If your
disks are battery-backed in one way or another, disabling barriers may safely improve performance. The
mount options "barrier" and "nobarrier" can also be used to enable or disable barriers, for consistency
with other ext4 mount options.
The ext4 filesystem enables write barriers by default.
inode_readahead_blks=n
This tuning parameter controls the maximum number of inode table blocks that ext4's inode table reada‐
head algorithm will pre-read into the buffer cache. The value must be a power of 2. The default value
is 32 blocks.
stripe=n
Number of filesystem blocks that mballoc will try to use for allocation size and alignment. For RAID5/6
systems this should be the number of data disks * RAID chunk size in filesystem blocks.
delalloc
Deferring block allocation until write-out time.
nodelalloc
Disable delayed allocation. Blocks are allocated when data is copied from user to page cache.
max_batch_time=usec
Maximum amount of time ext4 should wait for additional filesystem operations to be batch together with
a synchronous write operation. Since a synchronous write 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 algo‐
rithm used is designed to automatically tune for the speed of the disk, by measuring the amount of time
(on average) that it takes to finish committing a transaction. Call this time the "commit time". If
the time that the transaction has been running is less than the commit time, ext4 will try sleeping for
the commit time to see if other operations will join the transaction. The commit time is capped by the
max_batch_time, which defaults to 15000us (15ms). This optimization can be turned off entirely by set‐
ting 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 pri‐
ority than the default I/O priority.
abort Simulate the effects of calling ext4_abort() for debugging purposes. This is normally used while
remounting a filesystem which is already mounted.
default data=ordered mode, the data blocks of the new file are forced to disk before the rename() oper‐
ation is committed. This provides roughly the same level of guarantees as ext3, and avoids the "zero-
length" problem that can happen when a system crashes before the delayed allocation blocks are forced
to disk.
discard/nodiscard
Controls whether ext4 should issue discard/TRIM commands to the underlying block device when blocks are
freed. This is useful for SSD devices and sparse/thinly-provisioned LUNs, but it is off by default
until sufficient testing has been done.
nouid32
Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and
expect 16-bit values.
resize Allows to resize filesystem to the end of the last existing block group, further resize has to be done
with resize2fs either online, or offline. It can be used only with conjunction with remount.
block_validity/noblock_validity
This options allows to enables/disables the in-kernel facility for tracking filesystem metadata blocks
within internal data structures. This allows multi- block allocator and other routines to quickly
locate extents which might overlap with filesystem metadata blocks. This option is intended for 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 uninitialized extent before buffer write and convert the extent to initialized after
IO completes. This approach allows ext4 code to avoid using inode mutex, which improves scalability on
high speed storages. However this does not work with data journaling and dioread_nolock option will be
ignored with kernel warning. Note that dioread_nolock code path is only used for extent-based files.
Because of the restrictions this options comprises it is off by default (e.g. dioread_lock).
i_version
Enable 64-bit inode version support. This option is off by default.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the msdos, umsdos and vfat filesystems.)
blocksize={512|1024|2048}
Set blocksize (default 512). This option is obsolete.
uid=value and gid=value
Set the owner and group of all files. (Default: the uid and gid of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not present). The default is the umask of the
current process. The value is given in octal.
dmask=value
Set the umask applied to directories only. The default is the umask of the current process. The value
is given in octal.
fmask=value
Set the umask applied to regular files only. The default is the umask of the current process. The
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. verylong‐
name.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, code‐
page 437 is used.
conv={b[inary]|t[ext]|a[uto]}
The fat filesystem can perform CRLF<-->NL (MS-DOS text format to UNIX text format) conversion in the
kernel. The following conversion modes are available:
binary no translation is performed. This is the default.
text CRLF<-->NL translation is performed on all files.
auto CRLF<-->NL translation is performed on all files that don't have a "well-known binary" exten‐
sion. The list of known extensions can be found at the beginning of fs/fat/misc.c (as of 2.0,
the list is: exe, com, bin, app, sys, drv, ovl, ovr, obj, lib, dll, pif, arc, zip, lha, lzh,
zoo, tar, z, arj, tz, taz, tzp, tpz, gz, tgz, deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk,
pxl, dvi).
Programs that do computed lseeks won't like in-kernel text conversion. Several people have had their
data ruined by this translation. Beware!
For filesystems mounted in binary mode, a conversion tool (fromdos/todos) is available. This option is
obsolete.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File) module cvf_module instead of auto-detection.
If the kernel supports kmod, the cvf_format=xxx option also controls on-demand CVF module loading.
This option is obsolete.
cvf_option=option
Option passed to the CVF module. This option is obsolete.
debug Turn on the debug flag. A version string and a list of filesystem parameters will be printed (these
data are also printed if the parameters appear to be inconsistent).
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 anything but a CDROM as underlying device.
part=n Select partition number n from the device. Only makes sense for CDROMs. Defaults to not parsing the
partition table at all.
quiet Don't complain about invalid mount options.
Mount options for hpfs
uid=value and gid=value
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 addi‐
tion all characters are in upper case. Also there is no field for file ownership, protection, number of
links, provision for block/character devices, etc.
Rock Ridge is an extension to iso9660 that provides all of these UNIX-like features. Basically there are
extensions to each directory record that supply all of the additional information, and when Rock Ridge is in
use, the filesystem is indistinguishable from a normal UNIX filesystem (except that it is read-only, of
course).
norock Disable the use of Rock Ridge extensions, even if available. Cf. map.
nojoliet
Disable the use of Microsoft Joliet extensions, even if available. Cf. map.
check={r[elaxed]|s[trict]}
With check=relaxed, a filename is first converted to lower case before doing the lookup. This is prob‐
ably 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 every‐
body.) 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 set‐
tings used to be very dangerous, possibly leading to silent data corruption.)
cruft If the high byte of the file length contains other garbage, set this mount option to ignore the high
order bits of the file length. This implies that a file cannot be larger than 16MB.
iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for jfs
iocharset=name
Character set to use for converting from Unicode to ASCII. The default is to do no conversion. Use
iocharset=utf8 for UTF8 translations. This requires CONFIG_NLS_UTF8 to be set in the kernel .config
file.
resize=value
Resize the volume to value blocks. JFS only supports growing a volume, not shrinking it. This option is
only valid during a remount, when the volume is mounted read-write. The resize keyword with no value
will grow the volume to the full size of the partition.
nointegrity
Do not write to the journal. The primary use of this option is to allow for higher performance when
restoring a volume from backup media. The integrity of the volume is not guaranteed if the system
abnormally ends.
integrity
Default. Commit metadata changes to the journal. Use this option to remount a volume where the noin‐
tegrity option was previously specified in order to restore normal behavior.
errors={continue|remount-ro|panic}
Define the behaviour when an error is encountered. (Either ignore errors and just mark the filesystem
erroneous and continue, or remount the filesystem read-only, or panic and halt the system.)
noquota|quota|usrquota|grpquota
These options are accepted but ignored.
Mount options for minix
None.
Mount options for msdos
See mount options for fat. If the msdos filesystem detects an inconsistency, it reports an error and sets the
file system read-only. The filesystem can be made writable again by remounting it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument (a struct ncp_mount_data) to the mount sys‐
tem call. This argument is constructed by ncpmount(8) and the current version of mount (2.12) does not know
anything about ncpfs.
Mount options for nfs and nfs4
See the options section of the nfs(5) man page (nfs-utils package must be installed).
The nfs and nfs4 implementation expects a binary argument (a struct nfs_mount_data) to the mount system call.
This argument is constructed by mount.nfs(8) and the current version of mount (2.13) does not know anything
about nfs and nfs4.
uni_xlate={0|1|2}
For 0 (or `no' or `false'), do not use escape sequences for unknown Unicode characters. For 1 (or
`yes' or `true') or 2, use vfat-style 4-byte escape sequences starting with ":". Here 2 give a little-
endian encoding and 1 a byteswapped bigendian encoding.
posix=[0|1]
If enabled (posix=1), the filesystem distinguishes between upper and lower case. The 8.3 alias names
are presented as hard links instead of being suppressed. This option is obsolete.
uid=value, gid=value and umask=value
Set the file permission on the filesystem. The umask value is given in octal. By default, the files
are owned by root and not readable by somebody else.
Mount options for proc
uid=value and gid=value
These options are recognized, but have no effect as far as I can see.
Mount options for ramfs
Ramfs is a memory based filesystem. Mount it and you have it. Unmount it and it is gone. Present since Linux
2.3.99pre4. There are no mount options.
Mount options for reiserfs
Reiserfs is a journaling filesystem.
conv Instructs version 3.6 reiserfs software to mount a version 3.5 filesystem, using the 3.6 format for
newly created objects. This filesystem will no longer be compatible with reiserfs 3.5 tools.
hash={rupasov|tea|r5|detect}
Choose which hash function reiserfs will use to find files within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast and preserves locality, mapping lexicographi‐
cally close file names to close hash values. This option should not be used, as it causes a
high probability of hash collisions.
tea A Davis-Meyer function implemented by Jeremy Fitzhardinge. It uses hash permuting bits in the
name. It gets high randomness and, therefore, low probability of hash collisions at some CPU
cost. This may be used if EHASHCOLLISION errors are experienced with the r5 hash.
r5 A modified version of the rupasov hash. It is used by default and is the best choice unless the
filesystem has huge directories and unusual file-name patterns.
detect Instructs mount to detect which hash function is in use by examining the filesystem being
mounted, and to write this information into the reiserfs superblock. This is only useful on the
first mount of an old format filesystem.
hashed_relocation
Tunes the block allocator. This may provide performance improvements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance improvements in some situations.
replayonly
Replay the transactions which are in the journal, but do not actually mount the filesystem. Mainly used
by reiserfsck.
resize=number
A remount option which permits online expansion of reiserfs partitions. Instructs reiserfs to assume
that the device has number blocks. This option is designed for use with devices which are under logi‐
cal volume management (LVM). There is a special resizer utility which can be obtained from
ftp://ftp.namesys.com/pub/reiserfsprogs.
user_xattr
Enable Extended User Attributes. See the attr(5) manual page.
acl Enable POSIX Access Control Lists. See the acl(5) manual page.
barrier=none / barrier=flush
This enables/disables the use of write barriers in the journaling code. barrier=none disables it, bar‐
rier=flush enables it. Write barriers enforce proper on-disk ordering of journal commits, making
volatile disk write caches safe to use, at some performance penalty. The reiserfs filesystem does not
enable write barriers by default. Be sure to enable barriers unless your disks are battery-backed one
way or another. Otherwise you risk filesystem corruption in case of power failure.
Mount options for romfs
None.
Mount options for squashfs
None.
Mount options for smbfs
Just like nfs, the smbfs implementation expects a binary argument (a struct smb_mount_data) to the mount sys‐
tem call. This argument is constructed by smbmount(8) and the current version of mount (2.12) does not know
anything about smbfs.
Mount options for sysv
None.
Mount options for tmpfs
size=nbytes
Override default maximum size of the filesystem. The size is given in bytes, and rounded up to entire
pages. The default is half of the memory. The size parameter also accepts a suffix % to limit this
tmpfs instance to that percentage of your physical RAM: the default, when neither size nor nr_blocks is
specified, is size=50%
nr_blocks=
The same as size, but in blocks of PAGE_CACHE_SIZE
nr_inodes=
The maximum number of inodes for this instance. The default is half of the number of your physical RAM
mpol=[default|prefer:Node|bind:NodeList|interleave|interleave:NodeList]
Set the NUMA memory allocation policy for all files in that instance (if the kernel CONFIG_NUMA is
enabled) - which can be adjusted on the fly via 'mount -o remount ...'
default
prefers to allocate memory from the local node
prefer:Node
prefers to allocate memory from the given Node
bind:NodeList
allocates memory only from nodes in NodeList
interleave
prefers to allocate from each node in turn
interleave:NodeList
allocates from each node of NodeList in turn.
The NodeList format is a comma-separated list of decimal numbers and ranges, a range being two hyphen-
separated decimal numbers, the smallest and largest node numbers in the range. For example,
mpol=bind:0-3,5,7,9-15
Note that trying to mount a tmpfs with an mpol option will fail if the running kernel does not support
NUMA; and will fail if its nodelist specifies a node which is not online. If your system relies on
that tmpfs being mounted, but from time to time runs a kernel built without NUMA capability (perhaps a
safe recovery kernel), or with fewer nodes online, then it is advisable to omit the mpol option from
automatic mount options. It can be added later, when the tmpfs is already mounted on MountPoint, by
'mount -o remount,mpol=Policy:NodeList MountPoint'.
Mount options for ubifs
UBIFS is a flash file system which works on top of UBI volumes. Note that atime is not supported and is always
turned off.
The device name may be specified as
ubiX_Y UBI device number X, volume number Y
ubiY UBI device number 0, volume number Y
ubiX:NAME
UBI device number X, volume with name NAME
ubi:NAME
UBI device number 0, volume with name NAME
Alternative ! separator may be used instead of :.
The following mount options are available:
bulk_read
Enable bulk-read. VFS read-ahead is disabled because it slows down the file system. Bulk-Read is an
internal optimization. Some flashes may read faster if the data are read at one go, rather than at sev‐
eral read requests. For example, OneNAND can do "read-while-load" if it reads more than one NAND page.
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
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. Fur‐
thermore, there are
uni_xlate
Translate unhandled Unicode characters to special escaped sequences. This lets you backup and restore
filenames that are created with any Unicode characters. Without this option, a '?' is used when no
translation is possible. The escape character is ':' because it is otherwise illegal on the vfat
filesystem. The escape sequence that gets used, where u is the unicode character, is: ':', (u & 0x3f),
((u>>6) & 0x3f), (u>>12).
posix Allow two files with names that only differ in case. This option is obsolete.
nonumtail
First try to make a short name without sequence number, before trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is used by the console. It can be enabled
for the filesystem with this option or disabled with utf8=0, utf8=no or utf8=false. If `uni_xlate' gets
set, UTF8 gets disabled.
shortname={lower|win95|winnt|mixed}
Defines the behaviour for creation and display of filenames which fit into 8.3 characters. If a long
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 val‐
ues for this option are page size (typically 4KiB) through to 1GiB, inclusive, in power-of-2 incre‐
ments.
The default behaviour is for dynamic end-of-file preallocation size, which uses a set of heuristics to
optimise the preallocation size based on the current 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 sup‐
port 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 per‐
formance impact.
When ikeep is specified, XFS does not delete empty inode
clusters and keeps them around on disk. When noikeep is specified, empty inode clusters are returned
to the free space pool.
inode32|inode64
When inode32 is specified, it indicates that XFS limits inode creation to locations which will not
result in inode numbers with more than 32 bits of significance.
When inode64 is specified, it indicates that XFS is allowed to create inodes at any location in the
filesystem, including those which will result in inode numbers occupying more than 32 bits of signifi‐
cance.
inode32 is provided for backwards compatibility with older systems 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 specified.
largeio|nolargeio
If "nolargeio" is specified, the optimal I/O reported in st_blksize by stat(2) will be as small as pos‐
sible 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 granularity of the page cache.
If "largeio" specified, a filesystem that was created with a "swidth" specified will return the
"swidth" value (in bytes) in st_blksize. If the filesystem does not have a "swidth" specified but does
specify an "allocsize" then "allocsize" (in bytes) will be returned instead. Otherwise the behaviour is
the same as if "nolargeio" was specified.
logbufs=value
Set the number of in-memory log buffers. Valid numbers range from 2-8 inclusive.
The default value is 8 buffers.
If the memory cost of 8 log buffers is too high on small systems, then it may be reduced at some cost
to performance on metadata intensive workloads. The logbsize option below controls the size of each
buffer and so is also relevent to this case.
logbsize=value
Set the size of each in-memory log buffer. The size may be specified in bytes, or in kilobytes with a
"k" suffix. Valid sizes for version 1 and version 2 logs are 16384 (16k) and 32768 (32k). Valid sizes
for version 2 logs also include 65536 (64k), 131072 (128k) and 262144 (256k). The logbsize must be an
integer multiple of the log stripe unit configured at mkfs time.
The default value for version 1 logs is 32768, while the default value for version 2 logs is MAX(32768,
log_sunit).
logdev=deviceandrtdev=device
Use an external log (metadata journal) and/or real-time device. An XFS filesystem has up to three
parts: a data section, a log section, and a real-time section. The real-time section is optional, and
the log section can be separate from the data section or contained within it.
noalign
Data allocations will not be aligned at stripe unit boundaries. This is only relevant to filesystems
created with non-zero data alignment parameters (sunit, swidth) by mkfs.
uquota/usrquota/uqnoenforce/quota
User disk quota accounting enabled, and limits (optionally) enforced. Refer to xfs_quota(8) for fur‐
ther details.
gquota/grpquota/gqnoenforce
Group disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for fur‐
ther details.
pquota/prjquota/pqnoenforce
Project disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for fur‐
ther 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 speci‐
fied in 512-byte block units. These options are only relevant to filesystems that were created with
non-zero data alignment parameters.
The sunit and swidth parameters specified must be compatible with the existing filesystem alignment
characteristics. In general, that means the only valid changes to sunit are increasing it by a power-
of-2 multiple. Valid swidth values are any integer multiple of a valid sunit value.
Typically the only time these mount options are necessary if after an underlying RAID device has had
it's geometry modified, such as adding a new disk to a RAID5 lun and reshaping it.
swalloc
Data allocations will be rounded up to stripe width boundaries when the current end of file is being
extended and the file size is larger than the stripe width size.
wsync When specified, all filesystem namespace operations are executed synchronously. This ensures that when
the namespace operation (create, unlink, etc) completes, the change to the namespace is on stable stor‐
age. This is useful in HA setups where failover must not result in clients seeing inconsistent names‐
pace presentation 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 speci‐
You can also free a loop device by hand, using `losetup -d' or `umount -d`.
RETURN CODES
mount has the following return codes (the bits can be ORed):
0 success
1 incorrect invocation or permissions
2 system error (out of memory, cannot fork, no more loop devices)
4 internal mount bug
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
The command mount -a returns 0 (all success), 32 (all failed) or 64 (some failed, some success).
NOTES
The syntax of external mount helpers is:
/sbin/mount.<suffix> spec dir [-sfnv] [-o options] [-t type.subtype]
where the <type> is filesystem type and -sfnvo options have same meaning like standard mount options. The -t
option is used for filesystems with subtypes support (for example /sbin/mount.fuse -t fuse.sshfs).
FILES
/etc/fstab filesystem table
/etc/mtab table of mounted filesystems
/etc/mtab~ lock file
/etc/mtab.tmp temporary file
/etc/filesystems a list of filesystem types to try
ENVIRONMENT
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file
LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file
LIBMOUNT_DEBUG=0xffff
enables debug output
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 func‐
tions) 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 com‐
mand 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 <[email protected]>
AVAILABILITY
The mount command is part of the util-linux package and is available from ftp://ftp.ker‐
nel.org/pub/linux/utils/util-linux/.
util-linux January 2012 MOUNT(8)
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