If only the directory or the device is given, for example:
.RS
.sp
-.BI "mount /dir"
+.B mount /dir
.sp
.RE
then \fBmount\fR looks for a mountpoint (and if not found then for a device) in the
-.IR /etc/fstab
+.I /etc/fstab
file. It's possible to use the
.B \-\-target
or
options to avoid ambivalent interpretation of the given argument. For example:
.RS
.sp
-.BI "mount \-\-target /mountpoint"
+.B mount \-\-target /mountpoint
.sp
.RE
+The same filesystem may be mounted more than once, and in some cases (e.g.,
+network filesystems) the same filesystem may be mounted on the same
+mountpoint more times. The mount command does not implement any policy to
+control this behavior. All behavior is controlled by the kernel and it is usually
+specific to the filesystem driver. The exception is \fB\-\-all\fR, in this case
+already mounted filesystems are ignored (see \fB\-\-all\fR below for more details).
+
.SS Listing the mounts
The listing mode is maintained for backward compatibility only.
or UUID. Partition identifiers are supported for example for GUID Partition
Tables (GPT).
-The device name of disk partitions are unstable; hardware reconfiguration,
-adding or removing a device can cause change in names. This is reason why it's
-strongly recommended to use filesystem or partition identificators like UUID or
+The device names of disk partitions are unstable; hardware reconfiguration,
+adding or removing a device can cause changes in names. This is the reason why it's
+strongly recommended to use filesystem or partition identifiers like UUID or
LABEL.
-The command \fBlsblk --fs\fR provides overview of filesystems, LABELs and UUIDs
-on available block devices. The command \fBblkid -p <device>\fR provides details about
+The command \fBlsblk \-\-fs\fR provides an overview of filesystems, LABELs and UUIDs
+on available block devices. The command \fBblkid \-p <device>\fR provides details about
a filesystem on the specified device.
Don't forget that there is no guarantee that UUIDs and labels are really
more readable, robust and portable. The
.BR mount (8)
command internally uses udev
-symlinks, so the use of symlinks in /etc/fstab has no advantage over tags.
+symlinks, so the use of symlinks in
+.I /etc/fstab
+has no advantage over tags.
For more details see
.BR libblkid (3).
can be used instead of a device specification.
(The customary choice
.I none
-is less fortunate: the error message `none busy' from
-.B umount
+is less fortunate: the error message `none already mounted' from
+.B mount
can be confusing.)
.SS The files /etc/fstab, /etc/mtab and /proc/mounts
.B umount
traditionally maintained a list of currently mounted filesystems in the file
.IR /etc/mtab .
-This real mtab file is still supported, but on current Linux systems it is
-better to make it a symlink to
+The support for regular classic
+.I /etc/mtab
+is completely disabled in compile time by default, because on current Linux
+systems it is better to make it a symlink to
.I /proc/mounts
-instead, because a regular mtab file maintained in userspace cannot reliably
+instead. The regular mtab file maintained in userspace cannot reliably
work with namespaces, containers and other advanced Linux features.
+If the regular mtab support is enabled than it's possible to
+use the file as well as the symlink.
.sp
If no arguments are given to
.BR mount ,
and then the mount options from the command line will be appended to
the list of options from
.IR /etc/fstab .
+This default behaviour is possible to change by command line
+option \fB\-\-options\-mode\fR.
The usual behavior is that the last option wins if there are conflicting
ones.
.sp
.B "mount /dev/foo /dir"
.sp
.RE
+This default behaviour is possible to change by command line option
+\fB\-\-options\-source\-force\fR to always read configuration from
+.IR fstab .
+For non-root users
+.B mount
+always read
+.I fstab
+configuration.
.SS Non-superuser mounts
Normally, only the superuser can mount filesystems.
.sp
.RE
Note that \fBmount\fR is very strict about non-root users and all paths
-specified on command line are verified before fstab is parsed or a helper
+specified on command line are verified before
+.I fstab
+is parsed or a helper
program is executed. It's strongly recommended to use a valid mountpoint to
specify filesystem, otherwise \fBmount\fR may fail. For example it's bad idea
to use NFS or CIFS source on command line.
.PP
+Since version 2.35 \fBmount\fR command does not exit when user permissions are
+inadequate by internal libmount security rules. It drops suid permissions
+and continue as regular non-root user. It allows to support use-cases where
+root permissions are not necessary (e.g., fuse filesystems, user namespaces,
+etc).
+.PP
For more details, see
.BR fstab (5).
Only the user that mounted a filesystem can unmount it again.
option is similar, with the restriction that the user must be
member of the group of the special file.
-.SS Bind mounts
+.SS Bind mount operation
Remount part of the file hierarchy somewhere else. The call is:
.RS
.I olddir newdir
.RE
-or by using this fstab entry:
+or by using this
+.I fstab
+entry:
.RS
.br
.RE
After this call the same contents are accessible in two places.
+
+It is important to understand that "bind" does not to create any second-class
+or special node in the kernel VFS. The "bind" is just another operation to
+attach a filesystem. There is nowhere stored information that the filesystem
+has been attached by "bind" operation. The \fIolddir\fR and \fInewdir\fR are
+independent and the \fIolddir\fR may be umounted.
+
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:
.I olddir newdir
.RE
-Note that the filesystem mount options will remain the same as those
-on the original mount point.
+Note that the filesystem mount options maintained by kernel will remain the same as those
+on the original mount point. The userspace mount options (e.g., _netdev) will not be copied
+by
+.BR mount (8)
+and it's necessary explicitly specify the options on mount command line.
.BR mount (8)
since v2.27 allows to change the mount options by passing the
.RS
.br
-.B mount -o bind,ro foo foo
+.B mount \-o bind,ro foo foo
.RE
This feature is not supported by the Linux kernel; it is implemented in userspace
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 \fB-o rbind,ro\fR).
+relatime VFS entry flags by "remount,bind" operation. The another (for example
+filesystem specific flags) are silently ignored. It's impossible to change mount
+options recursively (for example with \fB\-o rbind,ro\fR).
.BR mount (8)
since v2.31 ignores the \fBbind\fR flag from
.I /etc/fstab
on
.B remount operation
-(if "-o remount" specified on command line). This is necessary to fully control
+(if "\-o remount" specified on command line). This is necessary to fully control
mount options on remount by command line. In the previous versions the bind
flag has been always applied and it was impossible to re-define mount options
without interaction with the bind semantic. This
behavior does not affect situations when "remount,bind" is specified in the
.I /etc/fstab
file.
-.RE
.SS The move operation
Move a
Note that the Linux kernel does not allow to change multiple propagation flags
with a single
.BR mount (2)
-system call, and the flags cannot be mixed with other mount options.
-
-Since util-linux 2.23 the \fBmount\fR 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 \fBmount\fR(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
+system call, and the flags cannot be mixed with other mount options and operations.
+
+Since util-linux 2.23 the \fBmount\fR command allows to do more propagation
+(topology) changes by one mount(8) call and do it also together with other
+mount operations. This feature is EXPERIMENTAL. The propagation flags are applied
+by additional \fBmount\fR(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
.BR fstab (5)
as mount options
.RB ( private ,
.RS
.nf
-.BI "mount \-\-make\-private \-\-make\-unbindable /dev/sda1 /foo"
+.B mount \-\-make\-private \-\-make\-unbindable /dev/sda1 /foo
.fi
.RE
.RS
.nf
-.BI "mount /dev/sda1 /foo"
-.BI "mount \-\-make\-private /foo"
-.BI "mount \-\-make\-unbindable /foo"
+.B mount /dev/sda1 /foo
+.B mount \-\-make\-private /foo
+.B mount \-\-make\-unbindable /foo
.fi
.RE
.B noauto
keyword). The filesystems are mounted following their order in
.IR fstab .
+The mount command compares filesystem source, target (and fs root for bind
+mount or btrfs) to detect already mounted filesystems. The kernel table with
+already mounted filesystems is cached during \fBmount \-\-all\fR. It means
+that all duplicated
+.I fstab
+entries will be mounted.
+.sp
+The option \fB\-\-all\fR is possible to use for remount operation too. In this
+case all filters (\fB\-t\fR and \fB\-O\fR) are applied to the table of already
+mounted filesystems.
+.sp
+Since version 2.35 is possible to use the command line option \fB\-o\fR to
+alter mount options from
+.I fstab
+(see also \fB\-\-options\-mode\fR).
.sp
Note that it is a bad practice to use \fBmount \-a\fR for
-.IR fstab
+.I fstab
checking. The recommended solution is \fBfindmnt \-\-verify\fR.
.TP
.BR \-B , " \-\-bind"
.TP
.BR \-c , " \-\-no\-canonicalize"
Don't canonicalize paths. The mount command canonicalizes all paths
-(from command line or fstab) by default. This option can be used
+(from command line or
+.IR fstab )
+by default. This option can be used
together with the
.B \-f
flag for already canonicalized absolute paths. The option is designed for mount
-helpers which call \fBmount -i\fR. It is strongly recommended to not use this
+helpers which call \fBmount \-i\fR. It is strongly recommended to not use this
command-line option for normal mount operations.
.sp
Note that \fBmount\fR(8) does not pass this option to the
.B mount
command is trying to do. It can also be used to add entries for devices
that were mounted earlier with the \fB\-n\fR option. The \fB\-f\fR option
-checks for an existing record in /etc/mtab and fails when the record already
+checks for an existing record in
+.I /etc/mtab
+and fails when the record already
exists (with a regular non-fake mount, this check is done by the kernel).
.IP "\fB\-i, \-\-internal\-only\fP"
Don't call the \fB/sbin/mount.\fIfilesystem\fR helper even if it exists.
.I /etc
is on a read-only filesystem.
.TP
+.BR \-N , " \-\-namespace " \fIns
+Perform mount in the mount namespace specified by \fIns\fR.
+\fIns\fR is either PID of process running in that namespace
+or special file representing that namespace.
+.sp
+.BR mount (8)
+switches to the mount namespace when it reads
+.IR /etc/fstab ,
+writes
+.I /etc/mtab
+(or writes to
+.IR /run/mount )
+and calls
+.BR mount (2)
+system call, otherwise it runs in the original mount namespace.
+It means that the target namespace does not have
+to contain any libraries or another requirements necessary to execute
+.BR mount (2)
+command.
+.sp
+See \fBmount_namespaces\fR(7) for more information.
+.TP
.BR \-O , " \-\-test\-opts " \fIopts
Limit the set of filesystems to which the
.B \-a
sections.
.RE
+.TP
+.BR "\-\-options\-mode " \fImode
+Controls how to combine options from
+.IR fstab / mtab
+with options from command line.
+\fImode\fR can be one of
+.BR ignore ", " append ", " prepend " or " replace .
+For example \fBappend\fR means that options from
+.I fstab
+are appended to options from command line.
+Default value is \fBprepend\fR -- it means command line options are evaluated after
+.I fstab
+options.
+Note that the last option wins if there are conflicting ones.
+
+.TP
+.BR "\-\-options\-source " \fIsource
+Source of default options.
+\fIsource\fR is comma separated list of
+.BR fstab ", " mtab " and " disable .
+\fBdisable\fR disables
+.BR fstab " and " mtab
+and disables \fB\-\-options\-source\-force\fR.
+Default value is \fBfstab,mtab\fR.
+
+.TP
+.B \-\-options\-source\-force
+Use options from
+.IR fstab / mtab
+even if both \fIdevice\fR and \fIdir\fR are specified.
+
.TP
.BR \-R , " \-\-rbind"
Remount a subtree and all possible submounts somewhere else (so that its
interpreted as target (mountpoint) or source (device). This option allows to
explicitly define that the argument is the mount target.
.TP
+.BI \-\-target\-prefix " directory"
+Prepend specified directory to all mount targets. This option allows to follow
+.IR fstab ,
+but mount operations is done on another place, for example:
+.RS
+.RS
+.sp
+.B "mount \-\-all \-\-target\-prefix /chroot \-o X\-mount.mkdir
+.sp
+.RE
+mounts all from system
+.I fstab
+to
+.IR /chroot ,
+all missing muontpoint are created
+(due to X-mount.mkdir). See also \fB\-\-fstab\fP to use an alternative
+.IR fstab .
+.RE
+.TP
.BR \-T , " \-\-fstab " \fIpath
-Specifies an alternative fstab file. If \fIpath\fP is a directory then the files
+Specifies an alternative
+.I fstab
+file. If \fIpath\fP is a directory then the files
in the directory are sorted by
.BR strverscmp (3);
-files that start with "."\& or without an \&.fstab extension are ignored. The option
+files that start with "."\& or without an
+.I \&.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.
.sp
Note that \fBmount\fR(8) does not pass the option \fB\-\-fstab\fP to the
-\fB/sbin/mount.\fItype\fR helpers, meaning that the alternative fstab files will be
+\fB/sbin/mount.\fItype\fR helpers, meaning that the alternative
+.I 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.
+(non-root) mounts always require
+.I fstab
+to verify the user's rights.
.TP
.BR \-t , " \-\-types " \fIfstype
The argument following the
currently supported depend on the running kernel. See
.I /proc/filesystems
and
-.I /lib/modules/$(uname -r)/kernel/fs
+.I /lib/modules/$(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.
.sp
Verbose mode.
.TP
.BR \-w , " \-\-rw" , " \-\-read\-write"
-Mount the filesystem read/write. The read-write is kernel default. A synonym is
+Mount the filesystem read/write. The read-write is kernel default and
+.BR mount (8)
+default is to try read-only if the previous mount syscall with read-write flags
+on write-protected devices of filesystems failed.
+.sp
+A synonym is
.BR "\-o rw" .
-Note that specify \fB\-w\fR on command line forces \fBmount\fR command
-to never try read-only mount on write-protected devices. The default is
-try read-only if the previous mount syscall with read-write flags failed.
+Note that specify \fB\-w\fR on command line forces \fBmount\fR command to never
+try read-only mount on write-protected devices or already mounted read-only
+filesystems.
.TP
.BR \-V , " \-\-version"
Display version information and exit.
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
+in
+.IR /proc/mounts .
+Note that filesystems also have per-filesystem
specific default mount options (see for example \fBtune2fs \-l\fP
output for extN filesystems).
The following options apply to any filesystem that is being
mounted (but not every filesystem actually honors them \(en e.g.\&, the
.B sync
-option today has an effect only for ext2, ext3, fat, vfat and ufs):
+option today has an effect only for ext2, ext3, ext4, fat, vfat, ufs and xfs):
.TP
.B async
.B context=
option is useful when mounting filesystems that do not support
extended attributes, such as a floppy or hard disk formatted with VFAT, or
-systems that are not normally running under SELinux, such as an ext3 formatted
+systems that are not normally running under SELinux, such as an ext3 or ext4 formatted
+
disk from a non-SELinux workstation. You can also use
.B context=
on filesystems you do not trust, such as a floppy. It also helps in compatibility with
or
.B \%noatime
but still allow userspace to override it. For more details about the default
-system mount options see /proc/mounts.
+system mount options see
+.IR /proc/mounts .
.TP
.B nostrictatime
Use the kernel's default behavior for inode access time updates.
Do not use the lazytime feature.
.TP
.B suid
-Allow set-user-ID or set-group-ID bits to take
-effect.
+Honor set-user-ID and set-group-ID bits or file capabilities when
+executing programs from this filesystem.
.TP
.B nosuid
-Do not allow set-user-ID or set-group-ID bits to take
-effect.
+Do not honor set-user-ID and set-group-ID bits or file capabilities when
+executing programs from this filesystem.
.TP
.B silent
Turn on the silent flag.
flag has special semantic. See above, the subsection \fBBind mounts\fR.
The remount functionality follows the standard way the mount command works
-with options from fstab. This means that \fBmount\fR does not
-read fstab (or mtab) only when both
+with options from
+.IR fstab .
+This means that \fBmount\fR does not read
+.I fstab
+(or
+.IR mtab )
+only when both
.I device
and
.I dir
.in
.sp
After this call all old mount options are replaced and arbitrary stuff from
-fstab (or mtab) is ignored, except the loop= option which is internally
+.I fstab
+(or
+.IR mtab )
+is ignored, except the loop= option which is internally
generated and maintained by the mount command.
.sp
.in +4
.B "mount \-o remount,rw /dir"
.in
.sp
-After this call, mount reads fstab and merges these options with
+After this call, mount reads
+.I fstab
+and merges these options with
the options from the command line (\fB\-o\fR).
-If no mountpoint is found in fstab, then a remount with unspecified source is
+If no mountpoint is found in
+.IR fstab ,
+then a remount with unspecified source is
allowed.
+.sp
+mount(8) allows to use \fB\-\-all\fR to remount all already mounted filesystems
+which match a specified filter (\fB\-O\fR and \fB\-t\fR). For example:
+.sp
+.in +4
+.B "mount \-\-all \-o remount,ro \-t vfat"
+.in
+.sp
+remounts all already mounted vfat filesystems in read-only mode. The each of the
+filesystems is remounted by "mount \-o remount,ro /dir" semantic. It means the
+mount command reads
+.I fstab
+or
+.I mtab
+and merges these options with the options
+from the command line.
.TP
.B ro
Mount the filesystem read-only.
.TP
.B user
Allow an ordinary user to mount the filesystem.
-The name of the mounting user is written to the mtab file (or to the private
-libmount file in /run/mount on systems without a regular mtab) so that this
+The name of the mounting user is written to the
+.I mtab
+file (or to the private
+libmount file in
+.I /run/mount
+on systems without a regular
+.IR mtab )
+so that this
same user can unmount the filesystem again.
This option implies the options
.BR noexec ", " nosuid ", and " nodev
.TP
.B X-*
All options prefixed with "X-" are interpreted as comments or as userspace
-application-specific options. These options are not stored in the user space (e.g. mtab file),
+application-specific options.
+These options are not stored in the user space (e.g.,
+.I mtab
+file),
nor sent to the mount.\fItype\fR helpers nor to the
.BR mount (2)
system call. The suggested format is \fBX-\fIappname\fR.\fIoption\fR.
Note that before util-linux v2.30 the x-* options have not been maintained by
libmount and stored in user space (functionality was the same as have X-* now),
but due to growing number of use-cases (in initrd, systemd etc.) the
-functionality have been extended to keep existing fstab configurations usable
+functionality have been extended to keep existing
+.I fstab
+configurations usable
without a change.
.TP
.BR X-mount.mkdir [ = \fImode\fR ]
-Allow to make a target directory (mountpoint). The optional argument
+Allow to make a target directory (mountpoint) if it does not exit yet.
+The optional argument
.I mode
specifies the filesystem access mode used for
.BR mkdir (2)
in octal notation. The default mode is 0755. This functionality is supported
-only for root users. The option is also supported as x-mount.mkdir, this notation
-is deprecated for mount.mkdir since v2.30.
-
-.SH "FILESYSTEM-SPECIFIC MOUNT OPTIONS"
+only for root users or when mount executed without suid permissions. The option
+is also supported as x-mount.mkdir, this notation is deprecated since v2.30.
+
+.SH FILESYSTEM-SPECIFIC MOUNT OPTIONS
+You should consult the respective man page for the filesystem first.
+If you want to know what options the ext4 filesystem supports, then check the
+.BR ext4 (5)
+man page.
+If that doesn't exist, you can also check the corresponding mount page like
+.BR mount.cifs (8).
+Note that you might have to install the respective userland tools.
+.sp
The following options apply only to certain filesystems.
We sort them by filesystem. They all follow the
.B \-o
Set the permission mask for ADFS 'owner' permissions and 'other' permissions,
respectively (default: 0700 and 0077, respectively).
See also
-.IR /usr/src/linux/Documentation/filesystems/adfs.txt .
+.IR /usr/src/linux/Documentation/filesystems/adfs.rst .
.SS "Mount options for affs"
.TP
(However, quota utilities may react to such strings in
.IR /etc/fstab .)
-.SS "Mount options for btrfs"
-Btrfs is a copy-on-write filesystem for Linux aimed at
-implementing advanced features while focusing on fault tolerance,
-repair, and easy administration.
-.TP
-.BI alloc_start= bytes
-Debugging option to force all block allocations above a certain
-byte threshold on each block device. The value is specified in
-bytes, optionally with a K, M, or G suffix, case insensitive.
-Default is 1MB.
-.TP
-.B autodefrag
-Disable/enable auto defragmentation.
-Auto defragmentation detects small random writes into files and queues
-them up for the defrag process. Works best for small files;
-not well-suited for large database workloads.
-.TP
-.BR check_int | check_int_data | check_int_print_mask =\fIvalue\fR
-These debugging options control the behavior of the integrity checking
-module(the BTRFS_FS_CHECK_INTEGRITY config option required).
-
-.B check_int
-enables the integrity checker module, which examines all
-block-write requests to ensure on-disk consistency, at a large
-memory and CPU cost.
-
-.B check_int_data
-includes extent data in the integrity checks, and
-implies the check_int option.
-
-.B check_int_print_mask
-takes a bitmask of BTRFSIC_PRINT_MASK_* values
-as defined in fs/btrfs/check-integrity.c, to control the integrity
-checker module behavior.
-
-See comments at the top of
-.IR fs/btrfs/check-integrity.c
-for more info.
-.TP
-.BI commit= seconds
-Set the interval of periodic commit, 30 seconds by default. Higher
-values defer data being synced to permanent storage, with obvious
-consequences when the system crashes. The upper bound is not forced,
-but a warning is printed if it's more than 300 seconds (5 minutes).
-.TP
-.BR compress | compress= \fItype\fR| compress-force | compress-force= \fItype\fR
-Control BTRFS file data compression. Type may be specified as "zlib"
-"lzo" or "no" (for no compression, used for remounting). If no type
-is specified, zlib is used. If \fBcompress-force\fR is specified,
-all files will be compressed, whether or not they compress well.
-If compression is enabled, \fBnodatacow\fR and \fBnodatasum\fR are disabled.
-.TP
-.B degraded
-Allow mounts to continue with missing devices. A read-write mount may
-fail with too many devices missing, for example if a stripe member
-is completely missing.
-.TP
-.BI device= devicepath
-Specify a device during mount so that ioctls on the control device
-can be avoided. Especially useful when trying to mount a multi-device
-setup as root. May be specified multiple times for multiple devices.
-.TP
-.B discard
-Disable/enable the discard mount option.
-The discard function issues frequent commands to let the block device
-reclaim space freed by the filesystem.
-This is useful for SSD devices, thinly provisioned
-LUNs and virtual machine images, but may have a significant
-performance impact. (The \fBfstrim\fR command is also available to
-initiate batch trims from userspace.)
-.TP
-.B enospc_debug
-Disable/enable debugging option to be more verbose in some ENOSPC conditions.
-.TP
-.BI fatal_errors= action
-Action to take when encountering a fatal error:
- "bug" - BUG() on a fatal error. This is the default.
- "panic" - panic() on a fatal error.
-.TP
-.B flushoncommit
-The
-.B flushoncommit
-mount option forces any data dirtied by a write in a
-prior transaction to commit as part of the current commit. This makes
-the committed state a fully consistent view of the filesystem from the
-application's perspective (i.e., it includes all completed filesystem
-operations). This was previously the behavior only when a snapshot is
-created.
-.TP
-.B inode_cache
-Enable free inode number caching. Defaults to off due to an overflow
-problem when the free space CRCs don't fit inside a single page.
-.TP
-.BI max_inline= bytes
-Specify the maximum amount of space, in bytes, that can be inlined in
-a metadata B-tree leaf. The value is specified in bytes, optionally
-with a K, M, or G suffix, case insensitive. In practice, this value
-is limited by the root sector size, with some space unavailable due
-to leaf headers. For a 4k sectorsize, max inline data is ~3900 bytes.
-.TP
-.BI metadata_ratio= value
-Specify that 1 metadata chunk should be allocated after every
-.I value
-data chunks. Off by default.
-.TP
-.B noacl
-Enable/disable support for Posix Access Control Lists (ACLs). See the
-.BR acl (5)
-manual page for more information about ACLs.
-.TP
-.B nobarrier
-Enable/disable the use of block-layer write barriers. Write barriers
-ensure that certain IOs make it through the device cache and are on
-persistent storage. If disabled on a device with a volatile
-(non-battery-backed) write-back cache, the \fBnobarrier\fR option will
-lead to filesystem corruption on a system crash or power loss.
-.TP
-.B nodatacow
-Enable/disable data copy-on-write for newly created files.
-This option implies \fBnodatasum\fR, and disables all compression.
-.TP
-.B nodatasum
-Enable/disable data checksumming for newly created files.
-This option implies \fBdatacow\fR.
-.TP
-.B notreelog
-Enable/disable the tree logging used for fsync and O_SYNC writes.
-.TP
-.B recovery
-Enable autorecovery attempts if a bad tree root is found at mount time.
-Currently this scans a list of several previous tree roots and tries to
-use the first readable.
-.TP
-.B rescan_uuid_tree
-Force check and rebuild procedure of the UUID tree. This should not
-normally be needed.
-.TP
-.B skip_balance
-Skip automatic resume of an interrupted balance operation after mount.
-May be resumed with "btrfs balance resume."
-.TP
-.B nospace_cache
-Disable freespace cache loading without clearing the cache.
-.TP
-.B clear_cache
-Force clearing and rebuilding of the disk space cache if something
-has gone wrong.
-.TP
-.BR ssd | nossd | ssd_spread
-Options to control ssd allocation schemes. By default, BTRFS will
-enable or disable ssd allocation heuristics depending on whether a
-rotational or non-rotational disk is in use. The \fBssd\fR and
-\fBnossd\fR options can override this autodetection.
-
-The \fBssd_spread\fR mount option attempts to allocate into big chunks
-of unused space, and may perform better on low-end ssds. \fBssd_spread\fR
-implies \fBssd\fR, enabling all other ssd heuristics as well.
-.TP
-.BI subvol= path
-Mount subvolume at
-.IR path
-rather than the root subvolume. The
-.IR path
-is relative to the top level subvolume.
-.TP
-.BI subvolid= ID
-Mount subvolume specified by an ID number rather than the root subvolume.
-This allows mounting of subvolumes which are not in the root of the mounted
-filesystem.
-You can use "btrfs subvolume list" to see subvolume ID numbers.
-.TP
-.BI subvolrootid= objectid " \fR(deprecated)"
-Mount subvolume specified by
-.IR objectid
-rather than the root subvolume.
-This allows mounting of subvolumes which are not in the root of the mounted
-filesystem.
-You can use "btrfs subvolume show " to see the object ID for a subvolume.
-.TP
-.BI thread_pool= number
-The number of worker threads to allocate. The default number is equal
-to the number of CPUs + 2, or 8, whichever is smaller.
-.TP
-.B user_subvol_rm_allowed
-Allow subvolumes to be deleted by a non-root user. Use with caution.
-
-.SS "Mount options for cifs"
-See the options section of the
-.BR mount.cifs (8)
-man page (cifs-utils package must be installed).
-
-.SS "Mount options for coherent"
-None.
-
.SS "Mount options for debugfs"
The debugfs filesystem is a pseudo filesystem, traditionally mounted on
.IR /sys/kernel/debug .
All mounts of devpts without this
.B newinstance
-option share the same set of pty indices (i.e legacy mode).
+option share the same set of pty indices (i.e., legacy mode).
Each mount of devpts with the
.B newinstance
option has a private set of pty indices.
CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel
configuration.
-.SS "Mount options for ext2, ext3 and ext4"
-See the options section of the ext2(5), ext3(5) or ext4(5) man page (the e2fsprogs package must be installed).
-
.SS "Mount options for fat"
(Note:
.I fat
.RE
.TP
.BI check= value
-Three different levels of pickyness can be chosen:
+Three different levels of pickiness can be chosen:
.RS
.TP
.BR r [ elaxed ]
potentially causing data corruption. For this reason, this
option also mounts the filesystem readonly.
-To maintain backward compatibility, '-o nfs' is also accepted,
+To maintain backward compatibility, '\-o nfs' is also accepted,
defaulting to
.BR stale_rw .
.TP
-.BI tz=UTC
+.B tz=UTC
This option disables the conversion of timestamps
between local time (as used by Windows on FAT) and UTC
(which Linux uses internally). This is particularly
Normal
.I iso9660
-filenames appear in a 8.3 format (i.e., DOS-like restrictions on filename
+filenames appear in an 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.
.BR noquota | quota | usrquota | grpquota
These options are accepted but ignored.
-.SS "Mount options for minix"
-None.
-
.SS "Mount options for msdos"
See mount options for fat.
If the
.B mount
(2.12) does not know anything about ncpfs.
-.SS "Mount options for nfs and nfs4"
-See the options section of the
-.BR nfs (5)
-man page (the nfs-utils package must be installed).
-
-The
-.IR nfs " and " nfs4
-implementation expects a binary argument (a
-.IR "struct nfs_mount_data" )
-to the mount system call. This argument is constructed by
-.BR mount.nfs (8)
-and the current version of
-.B mount
-(2.13) does not know anything about nfs and nfs4.
-
.SS "Mount options for ntfs"
.TP
.BI iocharset= name
.BI workdir= directory
The workdir needs to be an empty directory on the same filesystem as upperdir.
-.SS "Mount options for proc"
-.TP
-\fBuid=\fP\,\fIvalue\fP and \fBgid=\fP\,\fIvalue\fP
-These options are recognized, but have no effect as far as I can see.
-
-.SS "Mount options for ramfs"
-Ramfs is a memory based filesystem. Mount it and you have it. Unmount it
-and it is gone.
-There are no mount options.
-
.SS "Mount options for reiserfs"
Reiserfs is a journaling filesystem.
.TP
.TP
.B user_xattr
Enable Extended User Attributes. See the
-.BR attr (5)
+.BR attr (1)
manual page.
.TP
.B acl
safe to use, at some performance penalty. If your disks are battery-backed in
one way or another, disabling barriers may safely improve performance.
-.SS "Mount options for romfs"
-None.
-
-.SS "Mount options for squashfs"
-None.
-
-.SS "Mount options for smbfs"
-Just like
-.IR nfs ", the " smbfs
-implementation expects a binary argument (a
-.IR "struct smb_mount_data" )
-to the mount system call. This argument is constructed by
-.BR smbmount (8)
-and the current version of
-.B mount
-(2.12) does not know anything about smbfs.
-
-.SS "Mount options for sysv"
-None.
-
-.SS "Mount options for tmpfs"
-.TP
-.BI size= nbytes
-Override default maximum size of the filesystem.
-The size is given in bytes, and rounded up to entire pages.
-The default is half of the memory. The size parameter also accepts a suffix %
-to limit this tmpfs instance to that percentage of your physical RAM:
-the default, when neither size nor nr_blocks is specified, is size=50%
-.TP
-.B nr_blocks=
-The same as size, but in blocks of PAGE_CACHE_SIZE
-.TP
-.B nr_inodes=
-The maximum number of inodes for this instance. The default
-is half of the number of your physical RAM pages, or (on a
-machine with highmem) the number of lowmem RAM pages,
-whichever is the lower.
-.PP
-The tmpfs mount options for sizing (\c
-.BR size ,
-.BR nr_blocks ,
-and
-.BR nr_inodes )
-accept a suffix
-.BR k ,
-.B m
-or
-.B g
-for Ki, Mi, Gi (binary kilo (kibi), binary mega (mebi) and binary giga (gibi)) and can be changed on remount.
-
-.TP
-.B mode=
-Set initial permissions of the root directory.
-.TP
-.B uid=
-The user id.
-.TP
-.B gid=
-The group id.
-.TP
-.B mpol=[default|prefer:Node|bind:NodeList|interleave|interleave:NodeList]
-Set the NUMA memory allocation policy for all files in that
-instance (if the kernel CONFIG_NUMA is enabled) \(en which can be adjusted on the
-fly via 'mount \-o remount \&...'
-.RS
-.TP
-.B default
-prefers to allocate memory from the local node
-.TP
-.B prefer:Node
-prefers to allocate memory from the given Node
-.TP
-.B bind:NodeList
-allocates memory only from nodes in NodeList
-.TP
-.B interleave
-prefers to allocate from each node in turn
-.TP
-.B interleave:NodeList
-allocates from each node of NodeList in turn.
-.PP
-The NodeList format is a comma-separated list of decimal numbers and ranges, a
-range being two "hyphen-minus"-separated decimal numbers, the smallest and largest node
-numbers in the range. For example, mpol=bind:0\(en3,5,7,9\(en15
-
-Note that trying to mount a tmpfs with an mpol option will fail if the
-running kernel does not support NUMA; and will fail if its nodelist
-specifies a node which is not online. If your system relies on that
-tmpfs being mounted, but from time to time runs a kernel built without
-NUMA capability (perhaps a safe recovery kernel), or with fewer nodes
-online, then it is advisable to omit the mpol option from automatic
-mount options. It can be added later, when the tmpfs is already mounted
-on MountPoint, by 'mount \-o remount,mpol=Policy:NodeList MountPoint'.
-
.SS "Mount options for ubifs"
UBIFS is a flash filesystem which works on top of UBI volumes. Note that
\fBatime\fR is not supported and is always turned off.
option.
.SS "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.
+UDF is the "Universal Disk Format" filesystem defined by OSTA, the Optical
+Storage Technology Association, and is often used for DVD-ROM, frequently
+in the form of a hybrid UDF/ISO-9660 filesystem. It is, however,
+perfectly usable by itself on disk drives, flash drives and other block devices.
See also
.IR iso9660 .
.TP
+.B uid=
+Make all files in the filesystem belong to the given user.
+uid=forget can be specified independently of (or usually in
+addition to) uid=<user> and results in UDF
+not storing uids to the media. In fact the recorded uid
+is the 32-bit overflow uid \-1 as defined by the UDF standard.
+The value is given as either <user> which is a valid user name or the corresponding
+decimal user id, or the special string "forget".
+.TP
.B gid=
-Set the default group.
+Make all files in the filesystem belong to the given group.
+gid=forget can be specified independently of (or usually in
+addition to) gid=<group> and results in UDF
+not storing gids to the media. In fact the recorded gid
+is the 32-bit overflow gid \-1 as defined by the UDF standard.
+The value is given as either <group> which is a valid group name or the corresponding
+decimal group id, or the special string "forget".
.TP
.B umask=
-Set the default umask.
+Mask out the given permissions from all inodes read from the filesystem.
The value is given in octal.
.TP
-.B uid=
-Set the default user.
+.B mode=
+If mode= is set the permissions of all non-directory inodes read from the
+filesystem will be set to the given mode. The value is given in octal.
+.TP
+.B dmode=
+If dmode= is set the permissions of all directory inodes read from the
+filesystem will be set to the given dmode. The value is given in octal.
+.TP
+.B bs=
+Set the block size. Default value prior to kernel version 2.6.30 was
+2048. Since 2.6.30 and prior to 4.11 it was logical device block size with
+fallback to 2048. Since 4.11 it is logical block size with fallback to
+any valid block size between logical device block size and 4096.
+
+For other details see the \fBmkudffs\fP(8) 2.0+ manpage, sections
+\fBCOMPATIBILITY\fP and \fBBLOCK SIZE\fP.
.TP
.B unhide
Show otherwise hidden files.
.B undelete
Show deleted files in lists.
.TP
+.B adinicb
+Embed data in the inode. (default)
+.TP
+.B noadinicb
+Don't embed data in the inode.
+.TP
+.B shortad
+Use short UDF address descriptors.
+.TP
+.B longad
+Use long UDF address descriptors. (default)
+.TP
.B nostrict
Unset strict conformance.
-.\" .TP
-.\" .B utf8
-.\" (unused).
.TP
-.B iocharset
-Set the NLS character set.
+.B iocharset=
+Set the NLS character set. This requires kernel compiled with CONFIG_UDF_NLS option.
.TP
-.B bs=
-Set the block size. (May not work unless 2048.)
+.B utf8
+Set the UTF-8 character set.
+.SS Mount options for debugging and disaster recovery
.TP
.B novrs
-Skip volume sequence recognition.
+Ignore the Volume Recognition Sequence and attempt to mount anyway.
.TP
.B session=
-Set the CDROM session counting from 0. Default: last session.
+Select the session number for multi-session recorded optical media. (default= last session)
.TP
.B anchor=
-Override standard anchor location. Default: 256.
+Override standard anchor location. (default= 256)
+.TP
+.B lastblock=
+Set the last block of the filesystem.
+.SS Unused historical mount options that may be encountered and should be removed
+.TP
+.B uid=ignore
+Ignored, use uid=<user> instead.
+.TP
+.B gid=ignore
+Ignored, use gid=<group> instead.
.TP
.B volume=
-Override the VolumeDesc location. (unused)
+Unimplemented and ignored.
.TP
.B partition=
-Override the PartitionDesc location. (unused)
-.TP
-.B lastblock=
-Set the last block of the filesystem.
+Unimplemented and ignored.
.TP
.B fileset=
-Override the fileset block location. (unused)
+Unimplemented and ignored.
.TP
.B rootdir=
-Override the root directory location. (unused)
+Unimplemented and ignored.
.SS "Mount options for ufs"
.TP
.I devices
(default: uid=gid=0, mode=0444). The mode is given in octal.
-.SS "Mount options for xenix"
-None.
-
-.SS "Mount options for xfs"
-See the options section of the
-.BR xfs (5)
-man page (the xfsprogs package must be installed).
+.SH DM-VERITY SUPPORT (experimental)
+The device-mapper verity target provides read-only transparent integrity
+checking of block devices using kernel crypto API. The mount command can open
+the dm-verity device and do the integrity verification before on the device
+filesystem is mounted. Requires libcryptsetup with in libmount. If
+libcryptsetup supports extracting the root hash of an already mounted device,
+existing devices will be automatically reused in case of a match.
+Mount options for dm-verity:
+.TP
+\fBverity.hashdevice=\fP\,\fIpath\fP
+Path to the hash tree device associated with the source volume to pass to dm-verity.
+.TP
+\fBverity.roothash=\fP\,\fIhex\fP
+Hex-encoded hash of the root of
+.I verity.hashdevice
+Mutually exclusive with
+.I verity.roothashfile.
+.TP
+\fBverity.roothashfile=\fP\,\fIpath\fP
+Path to file containing the hex-encoded hash of the root of
+.I verity.hashdevice.
+Mutually exclusive with
+.I verity.roothash.
+.TP
+\fBverity.hashoffset=\fP\,\fIoffset\fP
+If the hash tree device is embedded in the source volume,
+.I offset
+(default: 0) is used by dm-verity to get to the tree.
+.TP
+\fBverity.fecdevice=\fP\,\fIpath\fP
+Path to the Forward Error Correction (FEC) device associated with the source volume to pass to dm-verity.
+Optional. Requires kernel built with CONFIG_DM_VERITY_FEC.
+.TP
+\fBverity.fecoffset=\fP\,\fIoffset\fP
+If the FEC device is embedded in the source volume,
+.I offset
+(default: 0) is used by dm-verity to get to the FEC area. Optional.
+.TP
+\fBverity.fecroots=\fP\,\fIvalue\fP
+Parity bytes for FEC (default: 2). Optional.
+.TP
+\fBverity.roothashsig=\fP\,\fIpath\fP
+Path to pkcs7 signature of root hash hex string. Requires crypt_activate_by_signed_key() from cryptsetup and
+kernel built with CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG. For device reuse, signatures have to be either used by all
+mounts of a device or by none. Optional.
+.PP
+Supported since util-linux v2.35.
+.PP
+For example commands:
+.sp
+.RS
+.nf
+.B mksquashfs /etc /tmp/etc.squashfs
+.B dd if=/dev/zero of=/tmp/etc.hash bs=1M count=10
+.B veritysetup format /tmp/etc.squashfs /tmp/etc.hash
+.B openssl smime \-sign \-in <hash> \-nocerts \-inkey private.key \-signer private.crt \-noattr \-binary \-outform der \-out /tmp/etc.p7
+.B mount \-o verity.hashdevice=/tmp/etc.hash,verity.roothash=<hash>,verity.roothashsig=/tmp/etc.p7 /tmp/etc.squashfs /mnt
+.fi
+.RE
+.sp
+create squashfs image from /etc directory, verity hash device
+and mount verified filesystem image to /mnt.
+The kernel will verify that the root hash is signed by a key from the kernel keyring if roothashsig is used.
-.SH "THE LOOP DEVICE"
+.SH LOOP-DEVICE SUPPORT
One further possible type is a mount via the loop device. For example,
the command
.RS
.sp
.B "mount /tmp/disk.img /mnt"
.sp
-.B "mount \-t ext3 /tmp/disk.img /mnt"
+.B "mount \-t ext4 /tmp/disk.img /mnt"
.sp
.RE
This type of mount knows about three options, namely
device with the same offset and sizelimit. This is necessary to avoid
a filesystem corruption.
-.SH RETURN CODES
+.SH EXIT STATUS
.B mount
-has the following return codes (the bits can be ORed):
+has the following exit status values (the bits can be ORed):
.TP
.B 0
success
.TP
.B 64
some mount succeeded
-.RE
The command \fBmount \-a\fR returns 0 (all succeeded), 32 (all failed), or 64 (some
failed, some succeeded).
-.SH "EXTERNAL HELPERS"
+.SH EXTERNAL HELPERS
The syntax of external mount helpers is:
.sp
.in +4
.BI /sbin/mount. suffix
.I spec dir
.RB [ \-sfnv ]
+.RB [ \-N
+.IR namespace ]
.RB [ \-o
.IR options ]
.RB [ \-t
.IR type \fB. subtype ]
.in
.sp
-where the \fIsuffix\fR is the filesystem type and the \fB\-sfnvo\fR options have
+where the \fIsuffix\fR is the filesystem type and the \fB\-sfnvoN\fR options have
the same meaning as the normal mount options. The \fB\-t\fR option is used for
filesystems with subtypes support (for example
.BR "/sbin/mount.fuse \-t fuse.sshfs" ).
to the mount.<suffix> helpers. All other options are used in a
comma-separated list as argument to the \fB\-o\fR option.
+.SH ENVIRONMENT
+.IP LIBMOUNT_FSTAB=<path>
+overrides the default location of the
+.I fstab
+file (ignored for suid)
+.IP LIBMOUNT_MTAB=<path>
+overrides the default location of the
+.I mtab
+file (ignored for suid)
+.IP LIBMOUNT_DEBUG=all
+enables libmount debug output
+.IP LIBBLKID_DEBUG=all
+enables libblkid debug output
+.IP LOOPDEV_DEBUG=all
+enables loop device setup debug output
.SH FILES
+See also "\fBThe files /etc/fstab, /etc/mtab and /proc/mounts\fR" section above.
.TP 18n
.I /etc/fstab
filesystem table
.TP
+.I /run/mount
+libmount private runtime directory
+.TP
.I /etc/mtab
-table of mounted filesystems
+table of mounted filesystems or symlink to
+.I /proc/mounts
.TP
.I /etc/mtab\s+3~\s0
-lock file
+lock file (unused on systems with mtab symlink)
.TP
.I /etc/mtab.tmp
-temporary file
+temporary file (unused on systems with mtab symlink)
.TP
.I /etc/filesystems
a list of filesystem types to try
-.SH ENVIRONMENT
-.IP LIBMOUNT_FSTAB=<path>
-overrides the default location of the fstab file (ignored for suid)
-.IP LIBMOUNT_MTAB=<path>
-overrides the default location of the mtab file (ignored for suid)
-.IP LIBMOUNT_DEBUG=all
-enables libmount debug output
-.IP LIBBLKID_DEBUG=all
-enables libblkid debug output
-.IP LOOPDEV_DEBUG=all
-enables loop device setup debug output
-.SH "SEE ALSO"
-.na
-.BR mount (2),
-.BR umount (2),
-.BR umount (8),
-.BR fstab (5),
-.BR nfs (5),
-.BR xfs (5),
-.BR e2label (8),
-.BR findmnt (8),
-.BR losetup (8),
-.BR mke2fs (8),
-.BR mountd (8),
-.BR nfsd (8),
-.BR swapon (8),
-.BR tune2fs (8),
-.BR xfs_admin (8)
-.ad
+.SH HISTORY
+A
+.B mount
+command existed in Version 5 AT&T UNIX.
.SH BUGS
It is possible for a corrupted filesystem to cause a crash.
.PP
Some Linux filesystems don't support
.BR "\-o sync " nor " \-o dirsync"
-(the ext2, ext3, fat and vfat filesystems
+(the ext2, ext3, ext4, fat and vfat filesystems
.I do
support synchronous updates (a la BSD) when mounted with the
.B sync
the mount command options, but the content of the second file also depends on
the kernel and others settings (e.g.\& on a remote NFS server -- in certain cases
the mount command may report unreliable information about an NFS mount point
-and the /proc/mounts file usually contains more reliable information.) This is
-another reason to replace the mtab file with a symlink to the
+and the
+.I /proc/mount
+file usually contains more reliable information.) This is
+another reason to replace the
+.I mtab
+file with a symlink to the
.I /proc/mounts
file.
.PP
command manually before calling
.B mount
with the configured loop device.
-.SH HISTORY
-A
-.B mount
-command existed in Version 5 AT&T UNIX.
.SH AUTHORS
.nf
Karel Zak <kzak@redhat.com>
.fi
+.SH SEE ALSO
+.na
+.BR lsblk (1),
+.BR mount (2),
+.BR umount (2),
+.BR fileystems (5),
+.BR fstab (5),
+.BR nfs (5),
+.BR xfs (5),
+.BR mount_namespaces (7)
+.BR xattr (7)
+.BR e2label (8),
+.BR findmnt (8),
+.BR losetup (8),
+.BR mke2fs (8),
+.BR mountd (8),
+.BR nfsd (8),
+.BR swapon (8),
+.BR tune2fs (8),
+.BR umount (8),
+.BR xfs_admin (8)
+.ad
.SH AVAILABILITY
The mount command is part of the util-linux package and is available from
https://www.kernel.org/pub/linux/utils/util-linux/.
projects / thirdparty / util-linux.git / blobdiff