mount，挂载文件系统。
SYNOPSIS
mount [-l|-h|-V]
mount -a [-fFnrsvw] [-t fstype] [-O optlist]
mount [-fnrsvw] [-o options] device|dir
mount [-fnrsvw] [-t fstype] [-o options] device dir
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:
This tells the kernel to attach the filesystem found on device (which is of type type) at the directory dir. The
previous contents (if any) and owner and mode of dir become invisible, and as long as this filesystem remains
mounted, the pathname dir refers to the root of the filesystem on device.
If only the directory or the device is given, for example:
then mount looks for a mountpoint (and if not found then for a device) in the /etc/fstab file. It’s possible to
use the –target or –source options to avoid ambivalent interpretation of the given argument. For example:
Listing the mounts
The listing mode is maintained for backward compatibility only.
For more robust and customizable output use findmnt(8), especially in your scripts. Note that control characters
in the mountpoint name are replaced with ‘?’.
The following command lists all mounted filesystems (of type type):
The option -l adds labels to this listing. See below.
Indicating the device
Most devices are indicated by a filename (of a block special device), like /dev/sda1, but there are other possibil‐
ities. For example, in the case of an NFS mount, device may look like knuth.cwi.nl:/dir. It is also possible to
indicate a block special device using its filesystem label or UUID (see the -L and -U options below), or its parti‐
tion label or UUID. (Partition identifiers are supported for example for GUID Partition Tables (GPT).)
Don’t forget that there is no guarantee that UUIDs and labels are really unique, especially if you move, share or
copy the device. Use lsblk -o +UUID,PARTUUID to verify that the UUIDs are really unique in your system.
The recommended setup is to use tags (e.g. LABEL=label) rather than /dev/disk/by-{label,uuid,partuuid,partlabel}
udev symlinks in the /etc/fstab file. Tags are more readable, robust and portable. The mount(8) command inter‐
nally uses udev symlinks, so the use of symlinks in /etc/fstab has no advantage over tags. For more details see
libblkid(3).
Note that mount(8) uses UUIDs as strings. The UUIDs from the command line or from fstab(5) are not converted to
internal binary representation. The string representation of the UUID should be based on lower case characters.
The proc filesystem is not associated with a special device, and when mounting it, an arbitrary keyword, such as
proc can be used instead of a device specification. (The customary choice none is less fortunate: the error mes‐
sage `none busy’ from umount can be confusing.)
The files /etc/fstab, /etc/mtab and /proc/mounts
The file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually mounted where, using
which options. The default location of the fstab(5) file can be overridden with the –fstab path command-line
option (see below for more details).
The command
(usually given in a bootscript) causes all filesystems mentioned in fstab (of the proper type and/or having or not
having the proper options) to be mounted as indicated, except for those whose line contains the noauto keyword.
Adding the -F option will make mount fork, so that the filesystems are mounted simultaneously.
When mounting a filesystem mentioned in fstab or mtab, it suffices to specify on the command line only the device,
or only the mount point.
The programs mount and umount traditionally maintained a list of currently mounted filesystems in the file
/etc/mtab. This real mtab file is still supported, but on current Linux systems it is better to make it a symlink
to /proc/mounts instead, because a regular mtab file maintained in userspace cannot reliably work with namespaces,
containers and other advanced Linux features.
If no arguments are given to mount, the list of mounted filesystems is printed.
If you want to override mount options from /etc/fstab you have to use the -o option:
and then the mount options from the command line will be appended to the list of options from /etc/fstab. The
usual behavior is that the last option wins if there are conflicting ones.
The mount program does not read the /etc/fstab file if both device (or LABEL, UUID, PARTUUID or PARTLABEL) and dir
are specified. For example, to mount device foo at /dir:
Non-superuser mounts
Normally, only the superuser can mount filesystems. However, when fstab contains the user option on a line, any‐
body can mount the corresponding filesystem.
Thus, given a line
any user can mount the iso9660 filesystem found on an inserted CDROM using the command:
Note that mount is very strict about non-root users and all paths specified on command line are verified before
fstab is parsed or a helper program is executed. It’s strogly recommended to use a valid mountpoint to specify
filesystem, otherwise mount may fail. For example it’s bad idea to use NFS or CIFS source on command line.
For more details, see fstab(5). Only the user that mounted a filesystem can unmount it again. If any user should
be able to unmount it, then use users instead of user in the fstab line. The owner option is similar to the user
option, with the restriction that the user must be the owner of the special file. This may be useful e.g. for
/dev/fd if a login script makes the console user owner of this device. The group option is similar, with the
restriction that the user must be member of the group of the special file.
绑定挂载（Bind mounts）
Since Linux 2.4.0 it is possible to remount part of the file hierarchy somewhere else. The call is:
or by using this fstab entry:
After this call the same contents are accessible in two places. One can also remount a single file (on a single
file). It’s also possible to use the bind mount to create a mountpoint from a regular directory, for example:
The bind mount call attaches only (part of) a single filesystem, not possible submounts. The entire file hierarchy
including submounts is attached a second place by using:
Note that the filesystem mount options will remain the same as those on the original mount point.
mount(8) since v2.27 allows to change the mount options by passing the relevant options along with –bind. For
example:
This feature is not supported by the Linux kernel; it is implemented in userspace by an additional mount(2)
remounting system call. This solution is not atomic.
The alternative (classic) way to create a read-only bind mount is to use the remount operation, for example:
mount -o remount,bind,ro olddir newdir
Note that a read-only bind will create a read-only mountpoint (VFS entry), but the original filesystem superblock
will still be writable, meaning that the olddir will be writable, but the newdir will be read-only.
It’s also possible to change nosuid, nodev, noexec, noatime, nodiratime and relatime VFS entry flags by
“remount,bind” operation. It’s impossible to change mount options recursively (for example with -o rbind,ro).
注意事项
MacOSX的mount命令是BSD系，不支持绑定挂载，需要使用bindfs。
The move operation
Since Linux 2.5.1 it is possible to atomically move a mounted tree to another place. The call is:
This will cause the contents which previously appeared under olddir to now be accessible under newdir. The physi‐
cal location of the files is not changed. Note that olddir has to be a mountpoint.
Note also that moving a mount residing under a shared mount is invalid and unsupported. Use findmnt -o TAR‐
GET,PROPAGATION to see the current propagation flags.
Shared subtree operations
Since Linux 2.6.15 it is possible to mark a mount and its submounts as shared, private, slave or unbindable. A
shared mount provides the ability to create mirrors of that mount such that mounts and unmounts within any of the
mirrors propagate to the other mirror. A slave mount receives propagation from its master, but not vice versa. A
private mount carries no propagation abilities. An unbindable mount is a private mount which cannot be cloned
through a bind operation. The detailed semantics are documented in Documentation/filesystems/sharedsubtree.txt
file in the kernel source tree.
Supported operations are:
mount –make-slave mountpoint
mount –make-private mountpoint
mount –make-unbindable mountpoint
The following commands allow one to recursively change the type of all the mounts under a given mountpoint.
mount –make-rslave mountpoint
mount –make-rprivate mountpoint
mount –make-runbindable mountpoint
mount(8) does not read fstab(5) when a –make-* operation is requested. All necessary information has to be speci‐
fied on the command line.
Note that the Linux kernel does not allow to change multiple propagation flags with a single mount(2) system call,
and the flags cannot be mixed with other mount options.
Since util-linux 2.23 the mount command allows to use several propagation flags together and also together with
other mount operations. This feature is EXPERIMENTAL. The propagation flags are applied by additional mount(2)
system calls when the preceding mount operations were successful. Note that this use case is not atomic. It is
possible to specify the propagation flags in fstab(5) as mount options (private, slave, shared, unbindable, rpri‐
vate, rslave, rshared, runbindable).
For example:
is the same as:
mount –make-private /foo
mount –make-unbindable /foo
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 apply‐
ing a -r or -w option, when present.
The command mount does not pass all command-line options to the /sbin/mount.suffix mount helpers. The interface
between mount and the mount helpers is described below in the section EXTERNAL HELPERS.
Command-line options available for the mount command are:
-a, –all
noauto keyword). The filesystems are mounted following their order in fstab.
–verify.
-B, –bind
-c, –no-canonicalize
default. This option can be used together with the -f flag for already canonicalized absolute paths. The
option is designed for mount helpers which call mount -i. It is strongly recommended to not use this com‐
mand-line option for normal mount operations.
-F, –fork
mounts on different devices or different NFS servers in parallel. This has the advantage that it is faster;
also NFS timeouts go in parallel. A disadvantage is that the mounts are done in undefined order. Thus, you
cannot use this option if you want to mount both /usr and /usr/spool.
-f, –fake
the filesystem. This option is useful in conjunction with the -v flag to determine what the mount command
is trying to do. It can also be used to add entries for devices that were mounted earlier with the -n
option. The -f option checks for an existing record in /etc/mtab and fails when the record already exists
(with a regular non-fake mount, this check is done by the kernel).
-i, –internal-only
-L, –label label
-l, –show-labels
root) for this to work. One can set such a label for ext2, ext3 or ext4 using the e2label(8) utility, or
for XFS using xfs_admin(8), or for reiserfs using reiserfstune(8).
-M, –move
-n, –no-mtab
-O, –test-opts opts
that -O is useless without -a. For example, the command:
/etc/fstab file.
does not negate the rest.
_netdev option specified.
-o, –options opts
tions.
-R, –rbind
places). See above, the subsection Bind mounts.
-r, –read-only
device. For example, ext3 and ext4 will replay the journal if the filesystem is dirty. To prevent this
kind of write access, you may want to mount an ext3 or ext4 filesystem with the ro,noload mount options or
set the block device itself to read-only mode, see the blockdev(8) command.
-s Tolerate sloppy mount options rather than failing. This will ignore mount options not supported by a
helper only.
–source device
point) or source (device). This option allows to explicitly define that the argument is the mount source.
–target directory
point) or source (device). This option allows to explicitly define that the argument is the mount target.
-T, –fstab path
strverscmp(3); files that start with “.” or without an .fstab extension are ignored. The option can be
specified more than once. This option is mostly designed for initramfs or chroot scripts where additional
configuration is specified beyond standard system configuration.
native fstab files will be invisible for the helpers. This is no problem for normal mounts, but user (non-
root) mounts always require fstab to verify the user’s rights.
-t, –types fstype
rently supported depend on the running kernel. See /proc/filesystems and /lib/modules/$(uname -r)/kernel/fs
for a complete list of the filesystems. The most common are ext2, ext3, ext4, xfs, btrfs, vfat, sysfs,
proc, nfs and cifs.
For example ‘fuse.sshfs’. It’s recommended to use subtype notation rather than add any prefix to the mount
source (for example ‘sshfs#example.com’ is deprecated).
uses the blkid library for guessing the filesystem type; if that does not turn up anything that looks famil‐
iar, mount will try to read the file /etc/filesystems, or, if that does not exist, /proc/filesystems. All
of the filesystem types listed there will be tried, except for those that are labeled “nodev” (e.g. devpts,
proc and nfs). If /etc/filesystems ends in a line with a single *, mount will read /proc/filesystems after‐
wards. While trying, all filesystem types will be mounted with the mount option silent.
change the probe order (e.g., to try vfat before msdos or ext3 before ext2) or if you use a kernel module
autoloader.
entry. The list of filesystem types for option -t can be prefixed with no to specify the filesystem types
on which no action should be taken. The prefix no has no effect when specified in an /etc/fstab entry.
knowledge of the filesystem type is required. For a few types however (like nfs, nfs4, cifs, smbfs, ncpfs)
an ad hoc code is necessary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems have a separate mount pro‐
gram. 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 different versions of the smbmount pro‐
gram have different calling conventions, /sbin/mount.smbfs may have to be a shell script that sets up the
desired call.
-U, –uuid uuid
-v, –verbose
-w, –rw, –read-write
-V, –version
-h, –help
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 an 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 the noatime feature, so the inode access time is controlled by kernel defaults. See also the
noatime
news servers). This works for all inode types (directories too), so it implies nodiratime.
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
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.
option. This means you can use fscontext and defcontext with each other, but neither can be used with con‐
text.
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 permis‐
sion checks, such as during mount or file creation. Individual file labels are still obtained from the xat‐
trs on the files themselves. The context option actually sets the aggregate context that fscontext pro‐
vides, in addition to supplying the same label for individual files.
value set for unlabeled files in the policy and requires a filesystem that supports xattr labeling.
or inode becomes visible to userspace. This was found to be useful for things like stateless linux.
the current context.
wise mount(8) will interpret the comma as a separator between mount options. Don’t forget that the shell
strips off quotes and thus double quoting is required. For example:
‘context=”system_u:object_r:tmp_t:s0:c127,c456″,noexec’
defaults
ning 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
noatime is set.)
nodiratime
set.)
dirsync
calls: creat, link, unlink, symlink, mkdir, rmdir, mknod and rename.
exec Permit execution of binaries.
noexec Do not permit direct execution of any binaries on the mounted filesystem. (Until recently it was possible
2.6.0.)
group Allow an ordinary user to mount the filesystem if one of that user’s groups matches the group of the device.
line group,dev,suid).
iversion
noiversion
mand Allow mandatory locks on this filesystem. See fcntl(2).
nomand Do not allow mandatory locks on this filesystem.
_netdev
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
access time was earlier than the current modify or change time. (Similar to noatime, but it doesn’t break
mutt or other applications that need to know if a file has been read since the last time it was modified.)
fied), and the strictatime option is required to obtain traditional semantics. In addition, since Linux
2.6.30, the file’s last access time is always updated if it is more than 1 day old.
norelatime
strictatime
relatime or noatime but still allow userspace to override it. For more details about the default system
mount options see /proc/mounts.
nostrictatime
lazytime
writes to preallocated files.
nolazytime
suid Allow set-user-ID or set-group-ID bits to take effect.
nosuid Do not allow set-user-ID or set-group-ID bits to take effect.
silent Turn on the silent flag.
loud Turn off the silent flag.
owner Allow an ordinary user to mount the filesystem if that user is the owner of the device. This option implies
owner,dev,suid).
remount
filesystem, especially to make a readonly filesystem writable. It does not change device or mount point.
means that mount does not read fstab (or mtab) only when both device and dir are specified.
except the loop= option which is internally generated and maintained by the mount command.
no mountpoint is found in fstab, then a remount with unspecified source is allowed.
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
sync All I/O to the filesystem should be done synchronously. In the case of media with a limited number of write
user Allow an ordinary user to mount the filesystem. The name of the mounting user is written to the mtab file
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 user to mount the filesystem. This is the default; it does not imply any other options.
users Allow any user to mount and to unmount the filesystem, even when some other ordinary user mounted it. This
option line users,exec,dev,suid).
x-* All options prefixed with “x-” are interpreted as comments or as userspace application-specific options.
call. The suggested format is x-appname.option (e.g. x-systemd.automount).
x-mount.mkdir[=mode]
mode used for mkdir(2) in octal notation. The default mode is 0755. This functionality is supported only
for root users.
FILESYSTEM-SPECIFIC MOUNT OPTIONS
The following options apply only to certain filesystems. We sort them by filesystem. They all follow the -o flag.
What options are supported depends a bit on the running kernel. More info may be found in the kernel source subdi‐
rectory Documentation/filesystems.
Mount options for adfs
uid=value and gid=value
ownmask=value and othmask=value
and 0077, respectively). See also /usr/src/linux/Documentation/filesystems/adfs.txt.
Mount options for affs
uid=value and gid=value
out specified value, the UID and GID of the current process are taken).
setuid=value and setgid=value
mode=value
directories that have read permission. The value is given in octal.
protect
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
verbose
prefix=string
volume=string
reserved=value
root=value
bs=value
grpquota|noquota|quota|usrquota
Mount options for btrfs
Btrfs is a copy-on-write filesystem for Linux aimed at implementing advanced features while focusing on fault tol‐
erance, repair, and easy administration.
alloc_start=bytes
value is specified in bytes, optionally with a K, M, or G suffix, case insensitive. Default is 1MB.
autodefrag
them up for the defrag process. Works best for small files; not well-suited for large database workloads.
check_int|check_int_data|check_int_print_mask=value
config option required).
consistency, at a large memory and CPU cost.
integrity.c, to control the integrity checker module behavior.
commit=seconds
nent storage, with obvious consequences when the system crashes. The upper bound is not forced, but a warn‐
ing is printed if it’s more than 300 seconds (5 minutes).
compress|compress=type|compress-force|compress-force=type
used for remounting). If no type is specified, zlib is used. If compress-force is specified, all files
will be compressed, whether or not they compress well. If compression is enabled, nodatacow and nodatasum
are disabled.
degraded
for example if a stripe member is completely missing.
device=devicepath
trying to mount a multi-device setup as root. May be specified multiple times for multiple devices.
discard
device reclaim space freed by the filesystem. This is useful for SSD devices, thinly provisioned LUNs and
virtual machine images, but may have a significant performance impact. (The fstrim command is also avail‐
able to initiate batch trims from userspace.)
enospc_debug
fatal_errors=action
“panic” – panic() on a fatal error.
flushoncommit
of the current commit. This makes the committed state a fully consistent view of the filesystem from the
application’s perspective (i.e., it includes all completed filesystem operations). This was previously the
behavior only when a snapshot is created.
inode_cache
don’t fit inside a single page.
max_inline=bytes
specified in bytes, optionally with a K, M, or G suffix, case insensitive. In practice, this value is lim‐
ited by the root sector size, with some space unavailable due to leaf headers. For a 4k sectorsize, max
inline data is ~3900 bytes.
metadata_ratio=value
noacl Enable/disable support for Posix Access Control Lists (ACLs). See the acl(5) manual page for more informa‐
nobarrier
through the device cache and are on persistent storage. If disabled on a device with a volatile (non-bat‐
tery-backed) write-back cache, the nobarrier option will lead to filesystem corruption on a system crash or
power loss.
nodatacow
compression.
nodatasum
notreelog
recovery
eral previous tree roots and tries to use the first readable.
rescan_uuid_tree
skip_balance
resume.”
nospace_cache
clear_cache
ssd|nossd|ssd_spread
tics depending on whether a rotational or non-rotational disk is in use. The ssd and nossd options can
override this autodetection.
low-end ssds. ssd_spread implies ssd, enabling all other ssd heuristics as well.
subvol=path
subvolid=ID
umes which are not in the root of the mounted filesystem. You can use “btrfs subvolume list” to see subvol‐
ume ID numbers.
subvolrootid=objectid (deprecated)
which are not in the root of the mounted filesystem. You can use “btrfs subvolume show ” to see the object
ID for a subvolume.
thread_pool=number
whichever is smaller.
user_subvol_rm_allowed
Mount options for cifs
See the options section of the mount.cifs(8) man page (cifs-utils package must be installed).
Mount options for coherent
None.
Mount options for debugfs
The debugfs filesystem is a pseudo filesystem, traditionally mounted on /sys/kernel/debug. As of kernel version
3.4, debugfs has the following options:
uid=n, gid=n
mode=value
Mount options for devpts
The devpts filesystem is a pseudo filesystem, traditionally mounted on /dev/pts. In order to acquire a pseudo ter‐
minal, 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
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
gid=5 makes “mesg y” the default on newly created PTYs.
newinstance
independent of indices created in other instances of devpts.
Each mount of devpts with the newinstance option has a private set of pty indices.
versions starting with 2.6.29. Further, this mount option is valid only if CONFIG_DEVPTS_MULTIPLE_INSTANCES
is enabled in the kernel configuration.
tems/devpts.txt in the linux kernel source tree for details.
ptmxmode=value
vate ptmx node in the root of the devpts filesystem (typically /dev/pts/ptmx).
mode=value specifies a more useful mode for the ptmx node and is highly recommended when the newinstance
option is specified.
valid only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel configuration.
Mount options for ext2
The `ext2′ filesystem is the standard Linux filesystem. Since Linux 2.5.46, for most mount options the default is
determined by the filesystem superblock. Set them with tune2fs(8).
acl|noacl
bsddf|minixdf
total number of blocks of the filesystem, while the bsddf behavior (which is the default) is to subtract the
overhead blocks used by the ext2 filesystem and not available for file storage. Thus
/dev/sda6 2630655 86954 2412169 3% /k
/dev/sda6 2543714 13 2412169 0% /k
check=none or nocheck
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}
neous 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
the directory in which it is created; otherwise (the default) it takes the fsgid of the current process,
unless the directory has the set-group-ID bit set, in which case it takes the GID from the parent directory,
and also gets the set-group-ID bit set if it is a directory itself.
grpquota|noquota|quota|usrquota
group quotas support. You need the quota utilities to actually enable and manage the quota system.
nouid32
16-bit values.
oldalloc or orlov
resgid=n and resuid=n
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.
got thousands of copies on a big filesystem). Since version 1.08, mke2fs has a -s (sparse superblock)
option to reduce the number of backup superblocks, and since version 1.15 this is the default. Note that
this may mean that ext2 filesystems created by a recent mke2fs cannot be mounted r/w under Linux 2.0.*.)
The block number here uses 1 k units. Thus, if you want to use logical block 32768 on a filesystem with 4 k
blocks, use “sb=131072”.
user_xattr|nouser_xattr
Mount options for ext3
The ext3 filesystem is a version of the ext2 filesystem which has been enhanced with journaling. It supports the
same options as ext2 as well as the following additions:
journal=update
journal=inum
which will represent the ext3 filesystem’s journal file; ext3 will create a new journal, overwriting the old
contents of the file whose inode number is inum.
journal_dev=devnum/journal_path=path
the new journal location. The journal device is identified either through its new major/minor numbers
encoded in devnum, or via a path to the device.
norecovery/noload
journal replay will lead to the filesystem containing inconsistencies that can lead to any number of prob‐
lems.
data={journal|ordered|writeback}
on the root filesystem, pass the mode to the kernel as boot parameter, e.g. rootflags=data=journal.
data being committed to the journal.
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.
data_err=ignore
data_err=abort
barrier=0 / barrier=1
(default). This also requires an IO stack which can support barriers, and if jbd gets an error on a barrier
write, it will disable barriers again with a warning. Write barriers enforce proper on-disk ordering of
journal commits, making volatile disk write caches safe to use, at some performance penalty. If your disks
are battery-backed in one way or another, disabling barriers may safely improve performance.
commit=nrsec
user_xattr
acl Enable POSIX Access Control Lists. See the acl(5) manual page.
usrjquota=aquota.user|grpjquota=aquota.group|jqfmt=vfsv0
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
The ext4 filesystem is an advanced level of the ext3 filesystem which incorporates scalability and reliability
enhancements for supporting large filesystem.
The options journal_dev, norecovery, noload, data, commit, orlov, oldalloc, [no]user_xattr [no]acl, bsddf, minixdf,
debug, errors, data_err, grpid, bsdgroups, nogrpid sysvgroups, resgid, resuid, sb, quota, noquota, grpquota,
usrquota usrjquota, grpjquota and jqfmt are backwardly compatible with ext3 or ext2.
journal_checksum
to detect corruption in the kernel. It is a compatible change and will be ignored by older kernels.
journal_async_commit
mount the device. This will enable ‘journal_checksum’ internally.
barrier=0 / barrier=1 / barrier / nobarrier
for consistency with other ext4 mount options.
inode_readahead_blks=n
algorithm will pre-read into the buffer cache. The value must be a power of 2. The default value is 32
blocks.
stripe=n
systems this should be the number of data disks * RAID chunk size in filesystem blocks.
delalloc
nodelalloc
max_batch_time=usec
synchronous write operation. Since a synchronous write operation is going to force a commit and then a wait
for the I/O complete, it doesn’t cost much, and can be a huge throughput win, we wait for a small amount of
time to see if any other transactions can piggyback on the synchronous write. The algorithm used is
designed to automatically tune for the speed of the disk, by measuring the amount of time (on average) that
it takes to finish committing a transaction. Call this time the “commit time”. If the time that the trans‐
action has been running is less than the commit time, ext4 will try sleeping for the commit time to see if
other operations will join the transaction. The commit time is capped by the max_batch_time, which defaults
to 15000 µs (15 ms). This optimization can be turned off entirely by setting max_batch_time to 0.
min_batch_time=usec
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
mitted by kjournald2 during a commit operation. This defaults to 3, which is a slightly higher priority
than the default I/O priority.
abort Simulate the effects of calling ext4_abort() for debugging purposes. This is normally used while remounting
auto_da_alloc|noauto_da_alloc
force that any delayed allocation blocks are allocated such that at the next journal commit, in the default
data=ordered mode, the data blocks of the new file are forced to disk before the rename() operation is com‐
mitted. This provides roughly the same level of guarantees as ext3, and avoids the “zero-length” problem
that can happen when a system crashes before the delayed allocation blocks are forced to disk.
noinit_itable
installation CD’s so that the install process can complete as quickly as possible; the inode table initial‐
ization process would then be deferred until the next time the filesystem is mounted.
init_itable=n
block group’s inode table. This minimizes the impact on system performance while the filesystem’s inode ta‐
ble is being initialized.
discard/nodiscard
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
16-bit values.
block_validity/noblock_validity
within internal data structures. This allows multi-block allocator and other routines to quickly locate
extents which might overlap with filesystem metadata blocks. This option is intended for debugging purposes
and since it negatively affects the performance, it is off by default.
dioread_lock/dioread_nolock
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).
max_dir_size_kb=n
kilobytes will cause an ENOSPC error. This is useful in memory-constrained environments, where a very large
directory can cause severe performance problems or even provoke the Out Of Memory killer. (For example, if
there is only 512 MB memory available, a 176 MB directory may seriously cramp the system’s style.)
i_version
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}
uid=value and gid=value
umask=value
rent process. The value is given in octal.
dmask=value
given in octal.
fmask=value
given in octal.
allow_utime=value
~dmask & 022)
filesystem doesn’t have UID/GID on disk, so normal check is too inflexible. With this option you can relax
it.
check=value
name.foobar becomes verylong.foo), leading and embedded spaces are accepted in each name part (name
and extension).
default.
Linux but are not accepted by MS-DOS (+, =, etc.) are rejected.
codepage=value
437 is used.
conv=mode
The following conversion modes are available:
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).
ruined by this translation. Beware!
obsolete.
cvf_format=module
the kernel supports kmod, the cvf_format=xxx option also controls on-demand CVF module loading. This option
is obsolete.
cvf_option=option
debug Turn on the debug flag. A version string and a list of filesystem parameters will be printed (these data
discard
for SSD devices and sparse/thinly-provisioned LUNs.
dos1xfloppy
static parameters match defaults assumed by DOS 1.x for 160 kiB, 180 kiB, 320 kiB, and 360 kiB floppies and
floppy images.
errors={panic|continue|remount-ro}
read-only mode (default behavior).
fat={12|16|32}
iocharset=value
iso8859-1. Long filenames are stored on disk in Unicode format.
nfs={stale_rw|nostale_ro}
to improve look-ups. Full file operations (read/write) over NFS are supported but with cache eviction at
NFS server, this could result in spurious ESTALE errors.
directory entry. This ensures that ESTALE will not be returned after a file is evicted from the inode
cache. However, it means that operations such as rename, create and unlink could cause file handles that
previously pointed at one file to point at a different file, potentially causing data corruption. For this
reason, this option also mounts the filesystem readonly.
tz=UTC This option disables the conversion of timestamps between local time (as used by Windows on FAT) and UTC
that are set to UTC in order to avoid the pitfalls of local time.
time_offset=minutes
subtracted from each timestamp to convert it to UTC used internally by Linux. This is useful when the time
zone set in the kernel via settimeofday(2) is not the time zone used by the filesystem. Note that this
option still does not provide correct time stamps in all cases in presence of DST – time stamps in a differ‐
ent DST setting will be off by one hour.
quiet Turn on the quiet flag. Attempts to chown or chmod files do not return errors, although they fail. Use
rodir FAT has the ATTR_RO (read-only) attribute. On Windows, the ATTR_RO of the directory will just be ignored,
showexec
.EXE, .COM, or .BAT. Not set by default.
sys_immutable
flush If set, the filesystem will try to flush to disk more early than normal. Not set by default.
usefree
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]
Mount options for hfs
creator=cccc, type=cccc
‘????’.
uid=n, gid=n
dir_umask=n, file_umask=n, umask=n
umask of the current process.
session=n
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 parti‐
quiet Don’t complain about invalid mount options.
Mount options for hpfs
uid=value and gid=value
umask=value
rent process. The value is given in octal.
case={lower|asis}
conv={binary|text|auto}
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
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, provi‐
sion for block/character devices, etc.
Rock Ridge is an extension to iso9660 that provides all of these UNIX-like features. Basically there are exten‐
sions 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
check={r[elaxed]|s[trict]}
only meaningful together with norock and map=normal. (Default: check=strict.)
uid=value and gid=value
in the Rock Ridge extensions. (Default: uid=0,gid=0.)
map={n[ormal]|o[ff]|a[corn]}
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
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
block={512|1024|2048}
conv={a[uto]|b[inary]|m[text]|t[ext]}
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
session=x
sbsector=xxx
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
iso8859-1.
utf8 Convert 16 bit Unicode characters on CD to UTF-8.
Mount options for jfs
iocharset=name
iocharset=utf8 for UTF8 translations. This requires CONFIG_NLS_UTF8 to be set in the kernel .config file.
resize=value
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
ing a volume from backup media. The integrity of the volume is not guaranteed if the system abnormally
ends.
integrity
option was previously specified in order to restore normal behavior.
errors={continue|remount-ro|panic}
neous and continue, or remount the filesystem read-only, or panic and halt the system.)
noquota|quota|usrquota|grpquota
Mount options for minix
None.
Mount options for msdos
See mount options for fat. If the msdos filesystem detects an inconsistency, it reports an error and sets the file
system read-only. The filesystem can be made writable again by remounting it.
Mount options for ncpfs
Just like nfs, the ncpfs implementation expects a binary argument (a struct ncp_mount_data) to the mount system
call. This argument is constructed by ncpmount(8) and the current version of mount (2.12) does not know anything
about ncpfs.
Mount options for nfs and nfs4
See the options section of the nfs(5) man page (the nfs-utils package must be installed).
The nfs and nfs4 implementation expects a binary argument (a struct nfs_mount_data) to the mount system call. This
argument is constructed by mount.nfs(8) and the current version of mount (2.13) does not know anything about nfs
and nfs4.
Mount options for ntfs
iocharset=name
ible characters. Deprecated.
nls=name
utf8 Use UTF-8 for converting file names.
uni_xlate={0|1|2}
`true’) or 2, use vfat-style 4-byte escape sequences starting with “:”. Here 2 give a little-endian encod‐
ing and 1 a byteswapped bigendian encoding.
posix=[0|1]
presented as hard links instead of being suppressed. This option is obsolete.
uid=value, gid=value and umask=value
owned by root and not readable by somebody else.
Mount options for overlay
Since Linux 3.18 the overlay pseudo filesystem implements a union mount for other filesystems.
An overlay filesystem combines two filesystems – an upper filesystem and a lower filesystem. When a name exists in
both filesystems, the object in the upper filesystem is visible while the object in the lower filesystem is either
hidden or, in the case of directories, merged with the upper object.
The lower filesystem can be any filesystem supported by Linux and does not need to be writable. The lower filesys‐
tem can even be another overlayfs. The upper filesystem will normally be writable and if it is it must support the
creation of trusted.* extended attributes, and must provide a valid d_type in readdir responses, so NFS is not
suitable.
A read-only overlay of two read-only filesystems may use any filesystem type. The options lowerdir and upperdir
are combined into a merged directory by using:
lowerdir=directory
upperdir=directory
workdir=directory
Mount options for proc
uid=value and gid=value
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
hash={rupasov|tea|r5|detect}
close file names to close hash values. This option should not be used, as it causes a high probabil‐
ity of hash collisions.
may be used if EHASHCOLLISION errors are experienced with the r5 hash.
of an old format filesystem.
hashed_relocation
no_unhashed_relocation
noborder
ments in some situations.
nolog Disable journaling. This will provide slight performance improvements in some situations at the cost of
journaling operations, save for actual writes into its journaling area. Implementation of nolog is a work
in progress.
notail By default, reiserfs stores small files and `file tails’ directly into its tree. This confuses some utili‐
replayonly
reiserfsck.
resize=number
the device has number blocks. This option is designed for use with devices which are under logical volume
management (LVM). There is a special resizer utility which can be obtained from
ftp://ftp.namesys.com/pub/reiserfsprogs.
user_xattr
acl Enable POSIX Access Control Lists. See the acl(5) manual page.
barrier=none / barrier=flush
rier=flush enables (default). This also requires an IO stack which can support barriers, and if reiserfs
gets an error on a barrier write, it will disable barriers again with a warning. Write barriers enforce
proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some perfor‐
mance penalty. If your disks are battery-backed in one way or another, disabling barriers may safely
improve performance.
Mount options for romfs
None.
Mount options for squashfs
None.
Mount options for smbfs
Just like nfs, the smbfs implementation expects a binary argument (a struct smb_mount_data) to the mount system
call. This argument is constructed by smbmount(8) and the current version of mount (2.12) does not know anything
about smbfs.
Mount options for sysv
None.
Mount options for tmpfs
size=nbytes
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=
nr_inodes=
pages, or (on a machine with highmem) the number of lowmem RAM pages, whichever is the lower.
The tmpfs mount options for sizing (size, nr_blocks, and nr_inodes) accept a suffix k, m or g for Ki, Mi, Gi
(binary kilo (kibi), binary mega (mebi) and binary giga (gibi)) and can be changed on remount.
mode= Set initial permissions of the root directory.
uid= The user id.
gid= The group id.
mpol=[default|prefer:Node|bind:NodeList|interleave|interleave:NodeList]
– which can be adjusted on the fly via ‘mount -o remount …’
minus”-separated decimal numbers, the smallest and largest node numbers in the range. For example,
mpol=bind:0–3,5,7,9–15
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 filesystem 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
Alternative ! separator may be used instead of :.
The following mount options are available:
bulk_read
nal optimization. Some flashes may read faster if the data are read at one go, rather than at several read
requests. For example, OneNAND can do “read-while-load” if it reads more than one NAND page.
no_bulk_read
chk_data_crc
no_chk_data_crc.
data, but it does check it for the internal indexing information. This option only affects reading, not
writing. CRC-32 is always calculated when writing the data.
compr={none|lzo|zlib}
pressed 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
nostrict
iocharset
bs= Set the block size. (May not work unless 2048.)
novrs Skip volume sequence recognition.
session=
anchor=
volume=
partition=
lastblock=
fileset=
rootdir=
Mount options for ufs
ufstype=value
tations. Features of some implementations are undocumented, so its hard to recognize the type of ufs auto‐
matically. That’s why the user must specify the type of ufs by mount option. Possible values are:
Mac OS X.
onerror=value
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. Further‐
more, there are
uni_xlate
names that are created with any Unicode characters. Without this option, a ‘?’ is used when no translation
is possible. The escape character is ‘:’ because it is otherwise invalid on the vfat filesystem. The
escape sequence that gets used, where u is the Unicode character, is: ‘:’, (u & 0x3f), ((u>>6) & 0x3f),
(u>>12).
posix Allow two files with names that only differ in case. This option is obsolete.
nonumtail
utf8 UTF8 is the filesystem safe 8-bit encoding of Unicode that is used by the console. It can be enabled for
UTF8 gets disabled.
shortname=mode
for a file exists, it will always be the preferred one for display. There are four modes:
Mount options for usbfs
devuid=uid and devgid=gid and devmode=mode
mode=0644). The mode is given in octal.
busuid=uid and busgid=gid and busmode=mode
mode=0555). The mode is given in octal.
listuid=uid and listgid=gid and listmode=mode
octal.
Mount options for xenix
None.
Mount options for xfs
See the options section of the xfs(5) man page (the xfsprogs package must be installed).
THE LOOP DEVICE
One further possible type is a mount via the loop device. For example, the command
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
The mount command automatically creates a loop device from a regular file if a filesystem type is not specified or
the filesystem is known for libblkid, for example:
This type of mount knows about three options, namely loop, offset and sizelimit, that are really options to
losetup(8). (These options can be used in addition to those specific to the filesystem type.)
Since Linux 2.6.25 auto-destruction of loop devices is supported, meaning that any loop device allocated by mount
will be freed by umount independently of /etc/mtab.
You can also free a loop device by hand, using losetup -d or umount -d.
Since util-linux v2.29 mount command re-uses the loop device rather than initialize a new device if the same back‐
ing file is already used for some loop device with the same offset and sizelimit. This is necessary to avoid a
filesystem corruption.
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 succeeded), 32 (all failed), or 64 (some failed, some succeeded).
EXTERNAL HELPERS
The syntax of external mount helpers is:
/sbin/mount.suffix spec dir [-sfnv] [-o options] [-t type.subtype]
where the suffix is the filesystem type and the -sfnvo options have the same meaning as the normal mount options.
The -t option is used for filesystems with subtypes support (for example /sbin/mount.fuse -t fuse.sshfs).
The command mount does not pass the mount options unbindable, runbindable, private, rprivate, slave, rslave,
shared, rshared, auto, noauto, comment, x-*, loop, offset and sizelimit to the mount.<suffix> helpers. All other
options are used in a comma-separated list as argument to the -o option.
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>
LIBMOUNT_MTAB=<path>
LIBMOUNT_DEBUG=all
LIBBLKID_DEBUG=all
LOOPDEV_DEBUG=all
简单使用示例（EXAMPLE）
mount –bind /path/to/dir /path/to/ftp/dir
SEE ALSO
mount(2), umount(2), umount(8), fstab(5), nfs(5), xfs(5), e2label(8), findmnt(8), losetup(8), mke2fs(8), mountd(8),
nfsd(8), swapon(8), tune2fs(8), xfs_admin(8)
BUGS
It is possible for a corrupted filesystem to cause a crash.
Some Linux filesystems don’t support -o sync nor -o dirsync (the ext2, ext3, fat and vfat filesystems do support
synchronous updates (a la BSD) when mounted with the sync option).
The -o remount may not be able to change mount parameters (all ext2fs-specific parameters, except sb, are change‐
able with a remount, for example, but you can’t change gid or umask for the fatfs).
It is possible that the files /etc/mtab and /proc/mounts don’t match on systems with a regular mtab file. The
first file is based only on the mount command options, but the content of the second file also depends on the ker‐
nel and others settings (e.g. on a remote NFS server — in certain cases the mount command may report unreliable
information about an NFS mount point and the /proc/mounts file usually contains more reliable information.) This
is another reason to replace the mtab file with a symlink to the /proc/mounts file.
Checking files on NFS filesystems referenced by file descriptors (i.e. the fcntl and ioctl families of functions)
may lead to inconsistent results due to the lack of a consistency check in the kernel even if noac is used.
The loop option with the offset or sizelimit options used may fail when using older kernels if the mount command
can’t confirm that the size of the block device has been configured as requested. This situation can be worked
around by using the losetup command manually before calling mount with the configured loop device.
参考文献
- man 8 mount, version mount from util-linux 2.29.2 (libmount 2.29.2: selinux, btrfs, assert, debug)