mount
MOUNT(8) Linux Programmer’s Manual MOUNT(8)
NAME
mount - mount a file system
SYNOPSIS
mount [-lhV]
mount -a [-fFnrsvw] [-t vfstype] [-O optlist]
mount [-fnrsvw] [-o options [,...]] 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 file system
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 file system 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 file
system remains mounted, the pathname dir refers to the root of the
file system on device.
Three forms of invocation do not actually mount anything:
mount -h
prints a help message;
mount -V
prints a version string; and just
mount [-l] [-t type]
lists all mounted file systems (of type type). The option -l adds the
(ext2, ext3 and XFS) labels in this listing. See below.
Since Linux 2.4.0 it is possible to remount part of the file hierarchy
somewhere else. The call is
mount --bind olddir newdir
After this call the same contents is accessible in two places.
This call attaches only (part of) a single filesystem, not possible
submounts. The entire file hierarchy including submounts is attached a
second place using
mount --rbind olddir newdir
The mount options are not changed.
Note the filesystem mount options will remain the same as those on the
original mount point, and cannot be changed by passing the -o option
along with --bind/--rbind.
Since Linux 2.5.1 it is possible to atomically move a subtree to
another place. The call is
mount --move olddir newdir
The proc file system 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.)
Most devices are indicated by a file name (of a block special device),
like /dev/sda1, but there are other possibilities. For example, in the
case of an NFS mount, device may look like knuth.cwi.nl:/dir. It is
possible to indicate a block special device using its volume label or
UUID (see the -L and -U options below).
The file /etc/fstab (see fstab(5)), may contain lines describing what
devices are usually mounted where, using which options. This file is
used in three ways:
(i) The command
mount -a [-t type] [-O optlist]
(usually given in a bootscript) causes all file systems 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.
(ii) When mounting a file system mentioned in fstab, it suffices to
give only the device, or only the mount point.
(iii) Normally, only the superuser can mount file systems. However,
when fstab contains the user option on a line, then anybody can mount
the corresponding system.
Thus, given a line
/dev/cdrom /cd iso9660 ro,user,noauto,unhide
any user can mount the iso9660 file system found on his CDROM using
the command
mount /dev/cdrom
or
mount /cd
For more details, see fstab(5). Only the user that mounted a filesys-
tem can unmount it again. If any user should be able to unmount, then
use users instead of user in the fstab line. The owner option is sim-
ilar 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 programs mount and umount maintain a list of currently mounted
file systems in the file /etc/mtab. If no arguments are given to
mount, this list is printed.
When the proc filesystem is mounted (say at /proc), the files
/etc/mtab and /proc/mounts have very similar contents. The former has
somewhat more information, such as the mount options used, but is not
necessarily up-to-date (cf. the -n option below). It is possible to
replace /etc/mtab by a symbolic link to /proc/mounts, but some infor-
mation is lost that way, and in particular working with the loop
device will be less convenient, and using the "user" option will fail.
OPTIONS
The full set of options used by an invocation of mount is determined
by first extracting the options for the file system from the fstab ta-
ble, then applying any options specified by the -o argument, and
finally applying a -r or -w option, when present.
Options available for the mount command:
-V Output version.
-h Print a help message.
-v Verbose mode.
-a Mount all filesystems (of the given types) mentioned in fstab.
-F (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 Causes everything to be done except for the actual system call;
if it’s not obvious, this ‘‘fakes’’ mounting the file system.
This option is useful in conjunction with the -v flag to deter-
mine what the mount command is trying to do. It can also be
used to add entries for devices that were mounted earlier with
the -n option.
-i Don’t call the /sbin/mount.<filesystem> helper even if it
exists.
-l Add the ext2, ext3 and XFS 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 or
ext3 using the e2label(8) utility, or for XFS using
xfs_admin(8).
-n Mount without writing in /etc/mtab. This is necessary for
example when /etc is on a read-only file system.
-p num In case of a loop mount with encryption, read the passphrase
from file descriptor num instead of from the terminal.
-s Tolerate sloppy mount options rather than failing. This will
ignore mount options not supported by a filesystem type. Not
all filesystems support this option. This option exists for
support of the Linux autofs-based automounter.
-r Mount the file system read-only. A synonym is -o ro.
-w Mount the file system read/write. This is the default. A syn-
onym is -o rw.
-L label
Mount the partition that has the specified label.
-U uuid
Mount the partition that has the specified uuid. These two
options require the file /proc/partitions (present since Linux
2.1.116) to exist.
-t vfstype
The argument following the -t is used to indicate the file sys-
tem type. The file system types which are currently supported
are: adfs, affs, autofs, coda, coherent, cramfs, devpts, efs,
ext, ext2, ext3, hfs, hpfs, iso9660, jfs, minix, msdos, ncpfs,
nfs, nfs4, ntfs, proc, qnx4, ramfs, reiserfs, romfs, smbfs,
sysv, tmpfs, udf, ufs, umsdos, usbfs, vfat, xenix, xfs, xiafs.
Note that coherent, sysv and xenix are equivalent and that
xenix and coherent will be removed at some point in the future
— use sysv instead. Since kernel version 2.1.21 the types ext
and xiafs do not exist anymore. Earlier, usbfs was known as
usbdevfs.
For most types all the mount program has to do is issue a sim-
ple mount(2) system call, and no detailed knowledge of the
filesystem type is required. For a few types however (like
nfs, nfs4, smbfs, ncpfs, cifs) ad hoc code is necessary. The
nfs ad hoc code is built in, but smbfs, ncpfs and cifs 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.
The type iso9660 is the default. If no -t option is given, or
if the auto type is specified, the superblock is probed for the
filesystem type (adfs, bfs, cramfs, ext, ext2, ext3, hfs, hpfs,
iso9660, jfs, minix, ntfs, qnx4, reiserfs, romfs, udf, ufs,
vxfs, xfs, xiafs are supported). If this probe fails, 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, nfs, and nfs4). If /etc/filesys-
tems ends in a line with a single * only, mount will read
/proc/filesystems afterwards.
The auto type may be useful for user-mounted floppies. Creat-
ing a file /etc/filesystems can be useful to change the probe
order (e.g., to try vfat before msdos) or if you use a kernel
module autoloader. Warning: the probing uses a heuristic (the
presence of appropriate ‘magic’), and could recognize the wrong
filesystem type, possibly with catastrophic consequences. If
your data is valuable, don’t ask mount to guess.
More than one type may be specified in a comma separated list.
The list of file system types can be prefixed with no to spec-
ify the file system 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 file systems except those of type msdos and ext.
-O Used in conjunction with -a, to limit the set of filesystems to
which the -a is applied. Like -t in this regard except that it
is useless except in the context of -a. For example, the com-
mand:
mount -a -O no_netdev
mounts all file systems 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 are specified with a -o flag followed by a comma sepa-
rated string of options. Some of these options are only useful
when they appear in the /etc/fstab file. The following options
apply to any file system that is being mounted (but not every
file system 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 file system should be done asyn-
chronously.
atime Update inode access time for each access. This is the
default.
auto Can be mounted with the -a option.
defaults
Use default options: rw, suid, dev, exec, auto, nouser,
and async.
dev Interpret character or block special devices on the file
system.
exec Permit execution of binaries.
mand Allow mandatory locks on this filesystem. See fcntl(2).
_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).
noatime
Do not update inode access times on this file system
(e.g, for faster access on the news spool to speed up
news servers).
noauto Can only be mounted explicitly (i.e., the -a option will
not cause the file system to be mounted).
nodev Do not interpret character or block special devices on
the file system.
noexec Do not allow execution of any binaries on the mounted
file system. This option might be useful for a server
that has file systems containing binaries for architec-
tures other than its own.
nomand Do not allow mandatory locks on this filesystem.
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.)
nouser Forbid an ordinary (i.e., non-root) user to mount the
file system. This is the default.
remount
Attempt to remount an already-mounted file system. This
is commonly used to change the mount flags for a file
system, especially to make a readonly file system write-
able. It does not change device or mount point.
ro Mount the file system read-only.
rw Mount the file system read-write.
suid Allow set-user-identifier or set-group-identifier bits
to take effect.
sync All I/O to the file system 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.
dirsync
All directory updates within the file system should be
done synchronously. This affects the following system
calls: creat, link, unlink, symlink, mkdir, rmdir, mknod
and rename.
user Allow an ordinary user to mount the file system. The
name of the mounting user is written to mtab so that he
can unmount the file system again. This option implies
the options noexec, nosuid, and nodev (unless overridden
by subsequent options, as in the option line
user,exec,dev,suid).
users Allow every user to mount and unmount the file system.
This option implies the options noexec, nosuid, and
nodev (unless overridden by subsequent options, as in
the option line users,exec,dev,suid).
--bind Remount a subtree somewhere else (so that its contents are
available in both places). See above.
--move Move a subtree to some other place. See above.
FILESYSTEM SPECIFIC MOUNT OPTIONS
The following options apply only to certain file systems. We sort
them by file system. They all follow the -o flag.
Mount options for adfs
uid=value and gid=value
Set the owner and group of the files in the file system
(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/filesys-
tems/adfs.txt.
Mount options for affs
uid=value and gid=value
Set the owner and group of the root of the file system
(default: uid=gid=0, but with option uid or gid without speci-
fied 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 file
system.
usemp Set uid and gid of the root of the file system to the uid and
gid of the mount point upon the first sync or umount, and then
clear this option. Strange...
verbose
Print an informational message for each successful mount.
prefix=string
Prefix used before volume name, when following a link.
volume=string
Prefix (of length at most 30) used before ’/’ when following a
symbolic link.
reserved=value
(Default: 2.) Number of unused blocks at the start of the
device.
root=value
Give explicitly the location of the root block.
bs=value
Give blocksize. Allowed values are 512, 1024, 2048, 4096.
grpquota / noquota / quota / usrquota
These options are accepted but ignored. (However, quota utili-
ties may react to such strings in /etc/fstab.)
Mount options for cifs
Just like nfs or smbfs implementation expects a binary argument to the
mount system call. This argument is constructed by mount.cifs(8) and
the current version of mount (2.12) does not know anything about cifs.
Mount options for coherent
None.
Mount options for devpts
The devpts file system is a pseudo file system, traditionally mounted
on /dev/pts. In order to acquire a pseudo terminal, a process opens
/dev/ptmx; the number of the pseudo terminal is then made available to
the process and the pseudo terminal slave can be accessed as
/dev/pts/<number>.
uid=value and gid=value
This sets the owner or the group of newly created PTYs to the
specified values. When nothing is specified, they will be set
to the UID and GID of the creating process. For example, if
there is a tty group with GID 5, then gid=5 will cause newly
created PTYs to belong to the tty group.
mode=value
Set the mode of newly created PTYs to the specified value. The
default is 0600. A value of mode=620 and gid=5 makes "mesg y"
the default on newly created PTYs.
Mount options for ext
None. Note that the ‘ext’ file system 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’ file system is the standard Linux file system. Due to a
kernel bug, it may be mounted with random mount options (fixed in
Linux 2.0.4).
acl / noacl
Support POSIX Access Control Lists (or not).
bsddf / minixdf
Set the behaviour for the statfs system call. The minixdf
behaviour is to return in the f_blocks field the total number
of blocks of the file system, while the bsddf behaviour (which
is the default) is to subtract the overhead blocks used by the
ext2 file system 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 / check=normal / check=strict
Set checking level. When at least one of these options is set
(and check=normal is set by default) the inodes and blocks
bitmaps are checked upon mount (which can take half a minute or
so on a big disk, and is rather useless). With strict check-
ing, block deallocation checks that the block to free is in the
data zone.
check=none / nocheck
No checking is done. This is fast. Recent kernels do not have a
check option anymore - checking with e2fsck(8) is more meaning-
ful.
debug Print debugging info upon each (re)mount.
errors=continue / errors=remount-ro / errors=panic
Define the behaviour when an error is encountered. (Either
ignore errors and just mark the file system erroneous and con-
tinue, or remount the file system read-only, or panic and halt
the system.) The default is set in the filesystem superblock,
and can be changed using tune2fs(8).
grpid or bsdgroups / nogrpid or 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.
resgid=n and resuid=n
The ext2 file system reserves a certain percentage of the
available space (by default 5%, see mke2fs(8) and tune2fs(8)).
These options determine who can use the reserved blocks.
(Roughly: whoever has the specified uid, or belongs to the
specified group.)
sb=n Instead of block 1, use block n as superblock. This could be
useful when the filesystem has been damaged. (Earlier, copies
of the superblock would be made every 8192 blocks: in block 1,
8193, 16385, ... (and one got hundreds or even 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".
grpquota / noquota / quota / usrquota
These options are accepted but ignored.
nouid32
Disables 32-bit UIDs and GIDs. This is for interoperability
with older kernels which only store and expect 16-bit values.
Mount options for ext3
The ‘ext3’ file system is version of the ext2 file system which has
been enhanced with journalling. It supports the same options as ext2
as well as the following additions:
journal=update
Update the ext3 file system’s journal to the current format.
journal=inum
When a journal already exists, this option is ignored. Other-
wise, it specifies the number of the inode which will represent
the ext3 file system’s journal file; ext3 will create a new
journal, overwriting the old contents of the file whose inode
number is inum.
noload Do not load the ext3 file system’s journal on mounting.
data=journal / data=ordered / data=writeback
Specifies the journalling mode for file data. Metadata is
always journaled.
journal
All data is committed into the journal prior to being
written into the main file system.
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 file system after its metadata has been
committed to the journal. This is rumoured to be the
highest-throughput option. It guarantees internal file
system integrity, however it can allow old data to
appear in files after a crash and journal recovery.
Mount options for fat
(Note: fat is not a separate filesystem, but a common part of the
msdos, umsdos and vfat filesystems.)
blocksize=512 / blocksize=1024 / blocksize=2048
Set blocksize (default 512).
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.
Present since 2.5.43.
fmask=value
Set the umask applied to regular files only. The default is
the umask of the current process. The value is given in octal.
Present since 2.5.43.
check=value
Three different levels of pickyness can be chosen:
r[elaxed]
Upper and lower case are accepted and equivalent, long
name parts are truncated (e.g. verylongname.foobar
becomes verylong.foo), leading and embedded spaces are
accepted in each name part (name and extension).
n[ormal]
Like "relaxed", but many special characters (*, ?, <,
spaces, etc.) are rejected. This is the default.
s[trict]
Like "normal", but names may not contain long parts and
special characters that are sometimes used on Linux, but
are not accepted by MS-DOS are rejected. (+, =, spaces,
etc.)
codepage=value
Sets the codepage for converting to shortname characters on FAT
and VFAT filesystems. By default, codepage 437 is used.
conv=b[inary] / conv=t[ext] / conv=a[uto]
The fat file system can perform CRLF<-->NL (MS-DOS text format
to UNIX text format) conversion in the kernel. The following
conversion modes are available:
binary no translation is performed. This is the default.
text CRLF<-->NL translation is performed on all files.
auto CRLF<-->NL translation is performed on all files that
don’t have a "well-known binary" extension. The list of
known extensions can be found at the beginning of
fs/fat/misc.c (as of 2.0, the list is: exe, com, bin,
app, sys, drv, ovl, ovr, obj, lib, dll, pif, arc, zip,
lha, lzh, zoo, tar, z, arj, tz, taz, tzp, tpz, gz, tgz,
deb, gif, bmp, tif, gl, jpg, pcx, tfm, vf, gf, pk, pxl,
dvi).
Programs that do computed lseeks won’t like in-kernel text con-
version. Several people have had their data ruined by this
translation. Beware!
For file systems mounted in binary mode, a conversion tool
(fromdos/todos) is available.
cvf_format=module
Forces the driver to use the CVF (Compressed Volume File) mod-
ule cvf_module instead of auto-detection. If the kernel sup-
ports kmod, the cvf_format=xxx option also controls on-demand
CVF module loading.
cvf_option=option
Option passed to the CVF module.
debug Turn on the debug flag. A version string and a list of file
system parameters will be printed (these data are also printed
if the parameters appear to be inconsistent).
fat=12 / fat=16 / fat=32
Specify a 12, 16 or 32 bit fat. This overrides the automatic
FAT type detection routine. Use with caution!
iocharset=value
Character set to use for converting between 8 bit characters
and 16 bit Unicode characters. The default is iso8859-1. Long
filenames are stored on disk in Unicode format.
quiet Turn on the quiet flag. Attempts to chown or chmod files do
not return errors, although they fail. Use with caution!
sys_immutable, showexec, dots, nodots, dotsOK=[yes|no]
Various misguided attempts to force Unix or DOS conventions
onto a FAT file system.
Mount options for hpfs
uid=value and gid=value
Set the owner and group of all files. (Default: the uid and gid
of the current process.)
umask=value
Set the umask (the bitmask of the permissions that are not
present). The default is the umask of the current process. The
value is given in octal.
case=lower / case=asis
Convert all files names to lower case, or leave them.
(Default: case=lower.)
conv=binary / conv=text / conv=auto
For conv=text, delete some random CRs (in particular, all fol-
lowed by NL) when reading a file. For conv=auto, choose more
or less at random between conv=binary and conv=text. For
conv=binary, just read what is in the file. This is the
default.
nocheck
Do not abort mounting when certain consistency checks fail.
Mount options for iso9660
ISO 9660 is a standard describing a filesystem structure to be used on
CD-ROMs. (This filesystem type is also seen on some DVDs. See also the
udf filesystem.)
Normal iso9660 filenames appear in a 8.3 format (i.e., DOS-like
restrictions on filename length), and in addition all characters are
in upper case. Also there is no field for file ownership, protection,
number of links, provision for block/character devices, etc.
Rock Ridge is an extension to iso9660 that provides all of these unix
like features. Basically there are extensions to each directory
record that supply all of the additional information, and when Rock
Ridge is in use, the filesystem is indistinguishable from a normal
UNIX file system (except that it is read-only, of course).
norock Disable the use of Rock Ridge extensions, even if available.
Cf. map.
nojoliet
Disable the use of Microsoft Joliet extensions, even if avail-
able. Cf. map.
check=r[elaxed] / check=s[trict]
With check=relaxed, a filename is first converted to lower case
before doing the lookup. This is probably only meaningful
together with norock and map=normal. (Default: check=strict.)
uid=value and gid=value
Give all files in the file system the indicated user or group
id, possibly overriding the information found in the Rock Ridge
extensions. (Default: uid=0,gid=0.)
map=n[ormal] / map=o[ff] / map=a[corn]
For non-Rock Ridge volumes, normal name translation maps upper
to lower case ASCII, drops a trailing ‘;1’, and converts ‘;’ to
‘.’. With map=off no name translation is done. See norock.
(Default: map=normal.) map=acorn is like map=normal but also
apply Acorn extensions if present.
mode=value
For non-Rock Ridge volumes, give all files the indicated mode.
(Default: read permission for everybody.) Since Linux 2.1.37
one no longer needs to specify the mode in decimal. (Octal is
indicated by a leading 0.)
unhide Also show hidden and associated files. (If the ordinary files
and the associated or hidden files have the same filenames,
this may make the ordinary files inaccessible.)
block=[512|1024|2048]
Set the block size to the indicated value. (Default:
block=1024.)
conv=a[uto] / conv=b[inary] / conv=m[text] / conv=t[ext]
(Default: conv=binary.) Since Linux 1.3.54 this option has no
effect anymore. (And non-binary settings used to be very dan-
gerous, possibly leading to silent data corruption.)
cruft If the high byte of the file length contains other garbage, set
this mount option to ignore the high order bits of the file
length. This implies that a file cannot be larger than 16MB.
The ‘cruft’ option is set automatically if the entire CDROM has
a weird size (negative, or more than 800MB). It is also set
when volume sequence numbers other than 0 or 1 are seen.
session=x
Select number of session on multisession CD. (Since 2.3.4.)
sbsector=xxx
Session begins from sector xxx. (Since 2.3.4.)
The following options are the same as for vfat and specifying them
only makes sense when using discs encoded using Microsoft’s Joliet
extensions.
iocharset=value
Character set to use for converting 16 bit Unicode characters
on CD to 8 bit characters. The default is iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for minix
None.
Mount options for msdos
See mount options for fat. If the msdos file system detects an incon-
sistency, it reports an error and sets the file system read-only. The
file system can be made writeable again by remounting it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument (a
struct ncp_mount_data) to the mount system call. This argument is con-
structed by ncpmount(8) and the current version of mount (2.12) does
not know anything about ncpfs.
Mount options for nfs
Instead of a textual option string, parsed by the kernel, the nfs file
system expects a binary argument of type struct nfs_mount_data. The
program mount itself parses the following options of the form
‘tag=value’, and puts them in the structure mentioned: rsize=n,
wsize=n, timeo=n, retrans=n, acregmin=n, acregmax=n, acdirmin=n,
acdirmax=n, actimeo=n, retry=n, port=n, mountport=n, mounthost=name,
mountprog=n, mountvers=n, nfsprog=n, nfsvers=n, namlen=n. The option
addr=n is accepted but ignored. Also the following Boolean options,
possibly preceded by no are recognized: bg, fg, soft, hard, intr,
posix, cto, ac, tcp, udp, lock. For details, see nfs(5).
Especially useful options include
rsize=32768,wsize=32768
This causes the NFS client to try to negotiate a buffer size up
to the size specified. A large buffer size does improve per-
formance, but both the server and client have to support it.
In the case where one of these does not support the size speci-
fied, the size negotiated will be the largest that both sup-
port.
intr This will allow NFS operations (on hard mounts) to be inter-
rupted while waiting for a response from the server.
nolock Do not use locking. Do not start lockd.
Mount options for nfs4
Instead of a textual option string, parsed by the kernel, the nfs4
file system expects a binary argument of type struct nfs4_mount_data.
The program mount itself parses the following options of the form
‘tag=value’, and puts them in the structure mentioned: rsize=n,
wsize=n, timeo=n, retrans=n, acregmin=n, acregmax=n, acdirmin=n,
acdirmax=n, actimeo=n, retry=n, port=n, proto=n, clientaddr=n, sec=n.
The option addr=n is accepted but ignored. Also the following Boolean
options, possibly preceded by no are recognized: bg, fg, soft, hard,
intr, cto, ac, For details, see nfs(5).
Especially useful options include
rsize=32768,wsize=32768
This causes the NFS4 client to try to negotiate a buffer size
up to the size specified. A large buffer size does improve
performance, but both the server and client have to support it.
In the case where one of these does not support the size speci-
fied, the size negotiated will be the largest that both sup-
port.
intr This will allow NFS4 operations (on hard mounts) to be inter-
rupted while waiting for a response from the server.
Mount options for ntfs
iocharset=name
Character set to use when returning file names. Unlike VFAT,
NTFS suppresses names that contain unconvertible characters.
utf8 Use UTF-8 for converting file names.
uni_xlate=[0|1|2]
For 0 (or ‘no’ or ‘false’), do not use escape sequences for
unknown Unicode characters. For 1 (or ‘yes’ or ‘true’) or 2,
use vfat-style 4-byte escape sequences starting with ":". Here
2 give a little-endian encoding and 1 a byteswapped bigendian
encoding.
posix=[0|1]
If enabled (posix=1), the file system distinguishes between
upper and lower case. The 8.3 alias names are presented as hard
links instead of being suppressed.
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. The reiserfs mount options are
more fully described at http://www.namesys.com/mount-options.html.
conv Instructs version 3.6 reiserfs software to mount a version 3.5
file system, using the 3.6 format for newly created objects.
This file system will no longer be compatible with reiserfs 3.5
tools.
hash=rupasov / hash=tea / hash=r5 / hash=detect
Choose which hash function reiserfs will use to find files
within directories.
rupasov
A hash invented by Yury Yu. Rupasov. It is fast and
preserves locality, mapping lexicographically close file
names to close hash values. This option should not be
used, as it causes a high probability of hash colli-
sions.
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 come 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 file system
has huge directories and unusual file-name patterns.
detect Instructs mount to detect which hash function is in use
by examining the file system being mounted, and to
write this information into the reiserfs superblock.
This is only useful on the first mount of an old format
file system.
hashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
no_unhashed_relocation
Tunes the block allocator. This may provide performance
improvements in some situations.
noborder
Disable the border allocator algorithm invented by Yury Yu.
Rupasov. This may provide performance improvements in some
situations.
nolog Disable journalling. This will provide slight performance
improvements in some situations at the cost of losing reis-
erfs’s fast recovery from crashes. Even with this option
turned on, reiserfs still performs all journalling operations,
save for actual writes into its journalling area. Implementa-
tion of nolog is a work in progress.
notail By default, reiserfs stores small files and ‘file tails’
directly into its tree. This confuses some utilities such as
LILO(8). This option is used to disable packing of files into
the tree.
replayonly
Replay the transactions which are in the journal, but do not
actually mount the file system. Mainly used by reiserfsck.
resize=number
A remount option which permits online expansion of reiserfs
partitions. Instructs reiserfs to assume that the device has
number blocks. This option is designed for use with devices
which are under logical volume management (LVM). There is a
special resizer utility which can be obtained from
ftp://ftp.namesys.com/pub/reiserfsprogs.
Mount options for romfs
None.
Mount options for smbfs
Just like nfs, the smbfs implementation expects a binary argument (a
struct smb_mount_data) to the mount system call. This argument is con-
structed by smbmount(8) and the current version of mount (2.12) does
not know anything about smbfs.
Mount options for sysv
None.
Mount options for tmpfs
The following parameters accept a suffix k, m or g for Ki, Mi, Gi
(binary kilo, mega and giga) and can be changed on remount.
size=nbytes
Override default size of the filesystem. The size is given in
bytes, and rounded down to entire pages. The default is half
of the memory.
nr_blocks=
Set number of blocks.
nr_inodes=
Set number of inodes.
mode= Set initial permissions of the root directory.
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.
strict Set strict conformance (unused).
utf8 (unused).
iocharset
(unused).
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 file system widely used in different operating sys-
tems. The problem are differences among implementations. Fea-
tures of some implementations are undocumented, so its hard to
recognize the type of ufs automatically. That’s why the user
must specify the type of ufs by mount option. Possible values
are:
old Old format of ufs, this is the default, read only.
(Don’t forget to give the -r option.)
44bsd For filesystems created by a BSD-like system
(NetBSD,FreeBSD,OpenBSD).
sun For filesystems created by SunOS or Solaris on Sparc.
sunx86 For filesystems created by Solaris on x86.
hp For filesystems created by HP-UX, read-only.
nextstep
For filesystems created by NeXTStep (on NeXT station)
(currently read only).
nextstep-cd
For NextStep CDROMs (block_size == 2048), read-only.
openstep
For filesystems created by OpenStep (currently read
only). The same filesystem type is also used by Mac OS
X.
onerror=value
Set behaviour on error:
panic If an error is encountered, cause a kernel panic.
[lock|umount|repair]
These mount options don’t do anything at present; when
an error is encountered only a console message is
printed.
Mount options for umsdos
See mount options for msdos. The dotsOK option is explicitly killed
by umsdos.
Mount options for vfat
First of all, the mount options for fat are recognized. The dotsOK
option is explicitly killed by vfat. Furthermore, there are
uni_xlate
Translate unhandled Unicode characters to special escaped
sequences. This lets you backup and restore filenames that are
created with any Unicode characters. Without this option, a ’?’
is used when no translation is possible. The escape character
is ’:’ because it is otherwise illegal on the vfat filesystem.
The escape sequence that gets used, where u is the unicode
character, is: ’:’, (u & 0x3f), ((u>>6) & 0x3f), (u>>12).
posix Allow two files with names that only differ in case.
nonumtail
First try to make a short name without sequence number, before
trying name~num.ext.
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is
used by the console. It can be be enabled for the filesystem
with this option. If ‘uni_xlate’ gets set, UTF8 gets disabled.
shortname=[lower|win95|winnt|mixed]
Defines the behaviour for creation and display of filenames
which fit into 8.3 characters. If a long name for a file
exists, it will always be preferred display. There are four
modes:
lower Force the short name to lower case upon display; store a
long name when the short name is not all upper case.
win95 Force the short name to upper case upon display; store a
long name when the short name is not all upper case.
winnt Display the shortname as is; store a long name when the
short name is not all lower case or all upper case.
mixed Display the short name as is; store a long name when the
short name is not all upper case.
The default is "lower".
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 file system (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 file system (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
biosize=size
Sets the preferred buffered I/O size (default size is 64K).
size must be expressed as the logarithm (base2) of the desired
I/O size. Valid values for this option are 14 through 16,
inclusive (i.e. 16K, 32K, and 64K bytes). On machines with a
4K pagesize, 13 (8K bytes) is also a valid size. The preferred
buffered I/O size can also be altered on an individual file
basis using the ioctl(2) system call.
dmapi / xdsm
Enable the DMAPI (Data Management API) event callouts.
logbufs=value
Set the number of in-memory log buffers. Valid numbers range
from 2-8 inclusive. The default value is 8 buffers for
filesystems with a blocksize of 64K, 4 buffers for filesystems
with a blocksize of 32K, 3 buffers for filesystems with a
blocksize of 16K, and 2 buffers for all other configurations.
Increasing the number of buffers may increase performance on
some workloads at the cost of the memory used for the addi-
tional log buffers and their associated control structures.
logbsize=value
Set the size of each in-memory log buffer. Valid sizes are
16384 (16K) and 32768 (32K). The default value for machines
with more than 32MB of memory is 32768, machines with less mem-
ory use 16384 by default.
logdev=device and rtdev=device
Use an external log (metadata journal) and/or real-time device.
An XFS filesystem has up to three parts: a data section, a log
section, and a real-time section. The real-time section is
optional, and the log section can be separate from the data
section or contained within it. Refer to xfs(5).
noalign
Data allocations will not be aligned at stripe unit boundaries.
noatime
Access timestamps are not updated when a file is read.
norecovery
The filesystem will be mounted without running log recovery.
If the filesystem was not cleanly unmounted, it is likely to be
inconsistent when mounted in norecovery mode. Some files or
directories may not be accessible because of this. Filesystems
mounted norecovery must be mounted read-only or the mount will
fail.
osyncisdsync
Make writes to files opened with the O_SYNC flag set behave as
if the O_DSYNC flag had been used instead. This can result in
better performance without compromising data safety. However
if this option is in effect, timestamp updates from O_SYNC
writes can be lost if the system crashes.
quota / usrquota / uqnoenforce
User disk quota accounting enabled, and limits (optionally)
enforced.
grpquota / gqnoenforce
Group disk quota accounting enabled and limits (optionally)
enforced.
sunit=value and swidth=value
Used to specify the stripe unit and width for a RAID device or
a stripe volume. value must be specified in 512-byte block
units. If this option is not specified and the filesystem was
made on a stripe volume or the stripe width or unit were speci-
fied for the RAID device at mkfs time, then the mount system
call will restore the value from the superblock. For filesys-
tems that are made directly on RAID devices, these options can
be used to override the information in the superblock if the
underlying disk layout changes after the filesystem has been
created. The swidth option is required if the sunit option has
been specified, and must be a multiple of the sunit value.
Mount options for xiafs
None. Although nothing is wrong with xiafs, it is not used much, and
is not maintained. Probably one shouldn’t use it. Since Linux version
2.1.21 xiafs is no longer part of the kernel source.
THE LOOP DEVICE
One further possible type is a mount via the loop device. For example,
the command
mount /tmp/fdimage /mnt -t msdos -o loop=/dev/loop3,blocksize=1024
will set up the loop device /dev/loop3 to correspond to the file
/tmp/fdimage, and then mount this device on /mnt. This type of mount
knows about three options, namely loop, offset and encryption, that
are really options to losetup(8). If no explicit loop device is men-
tioned (but just an option ‘-o loop’ is given), then mount will try to
find some unused loop device and use that. If you are not so unwise
as to make /etc/mtab a symbolic link to /proc/mounts then any loop
device allocated by mount will be freed by umount. You can also free
a loop device by hand, using ‘losetup -d’, see losetup(8).
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 or missing nfs support in mount
8 user interrupt
16 problems writing or locking /etc/mtab
32 mount failure
64 some mount succeeded
DUPLICATE LABELS
mount includes support for systems where same partition is shared
between different devices (e.g. multipath kernel drivers). In particu-
lar case when mounting device by LABEL, mount command reports problem
with duplicate labels.
You can define priority of devices in file /etc/fstab.order as simple
list of devices (with full pathname for the devices). The devices
listed in this file have greater priority than other devices. Devices
in configuration file have descending priority.
FILES
/etc/fstab file system table
/etc/fstab.order for multipath device priority
/etc/mtab table of mounted file systems
/etc/mtab~ lock file
/etc/mtab.tmp temporary file
SEE ALSO
mount(2), umount(2), fstab(5), umount(8), swapon(8), nfs(5), xfs(5),
e2label(8), xfs_admin(8), mountd(8), nfsd(8), mke2fs(8), tune2fs(8),
losetup(8)
BUGS
It is possible for a corrupted file system to cause a crash.
Some Linux file systems don’t support -o sync and -o dirsync (the
ext2, ext3, fat and vfat file systems do support synchronous updates
(a la BSD) when mounted with the sync option).
The -o remount may not be able to change mount parameters (all ext2fs-
specific parameters, except sb, are changeable with a remount, for
example, but you can’t change gid or umask for the fatfs).
It is possible that files /etc/mtab and /proc/mounts don’t match. The
first file is based only on the mount command options, but the content
of the second file also depends on the kernel and others settings
(e.g. remote NFS server. In particular case the mount command may
reports unreliable information about a NFS mount point and the
/proc/mounts file usually contains more reliable information.)
Checking files on NFS filesystem referenced by file descriptors (i.e.
the fcntl and ioctl families of functions) may lead to inconsistent
result due to the lack of consistency check in kernel even if noac is
used.
HISTORY
A mount command existed in Version 5 AT&T UNIX.
Linux 2.0 14 September 1997 MOUNT(8)
