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zfs.8
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zfs.8
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.\"
.\" CDDL HEADER START
.\"
.\" The contents of this file are subject to the terms of the
.\" Common Development and Distribution License (the "License").
.\" You may not use this file except in compliance with the License.
.\"
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
.\" or http://www.opensolaris.org/os/licensing.
.\" See the License for the specific language governing permissions
.\" and limitations under the License.
.\"
.\" When distributing Covered Code, include this CDDL HEADER in each
.\" file and include the License file at usr/src/OPENSOLARIS.LICENSE.
.\" If applicable, add the following below this CDDL HEADER, with the
.\" fields enclosed by brackets "[]" replaced with your own identifying
.\" information: Portions Copyright [yyyy] [name of copyright owner]
.\"
.\" CDDL HEADER END
.\"
.\"
.\" Copyright (c) 2009 Sun Microsystems, Inc. All Rights Reserved.
.\" Copyright 2011 Joshua M. Clulow <josh@sysmgr.org>
.\" Copyright (c) 2011, 2019 by Delphix. All rights reserved.
.\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
.\" Copyright (c) 2014, Joyent, Inc. All rights reserved.
.\" Copyright (c) 2014 by Adam Stevko. All rights reserved.
.\" Copyright (c) 2014 Integros [integros.com]
.\" Copyright 2019 Richard Laager. All rights reserved.
.\" Copyright 2018 Nexenta Systems, Inc.
.\" Copyright 2018 Joyent, Inc.
.\"
.Dd April 30, 2019
.Dt ZFS 8 SMM
.Os Linux
.Sh NAME
.Nm zfs
.Nd configures ZFS file systems
.Sh SYNOPSIS
.Nm
.Fl ?V
.Nm
.Cm create
.Op Fl p
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Ar filesystem
.Nm
.Cm create
.Op Fl ps
.Op Fl b Ar blocksize
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Fl V Ar size Ar volume
.Nm
.Cm destroy
.Op Fl Rfnprv
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm destroy
.Op Fl Rdnprv
.Ar filesystem Ns | Ns Ar volume Ns @ Ns Ar snap Ns
.Oo % Ns Ar snap Ns Oo , Ns Ar snap Ns Oo % Ns Ar snap Oc Oc Oc Ns ...
.Nm
.Cm destroy
.Ar filesystem Ns | Ns Ar volume Ns # Ns Ar bookmark
.Nm
.Cm snapshot
.Op Fl r
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Ar filesystem Ns @ Ns Ar snapname Ns | Ns Ar volume Ns @ Ns Ar snapname Ns ...
.Nm
.Cm rollback
.Op Fl Rfr
.Ar snapshot
.Nm
.Cm clone
.Op Fl p
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Ar snapshot Ar filesystem Ns | Ns Ar volume
.Nm
.Cm promote
.Ar clone-filesystem
.Nm
.Cm rename
.Op Fl f
.Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot
.Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot
.Nm
.Cm rename
.Op Fl fp
.Ar filesystem Ns | Ns Ar volume
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm rename
.Fl r
.Ar snapshot Ar snapshot
.Nm
.Cm list
.Op Fl r Ns | Ns Fl d Ar depth
.Op Fl Hp
.Oo Fl o Ar property Ns Oo , Ns Ar property Oc Ns ... Oc
.Oo Fl s Ar property Oc Ns ...
.Oo Fl S Ar property Oc Ns ...
.Oo Fl t Ar type Ns Oo , Ns Ar type Oc Ns ... Oc
.Oo Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot Oc Ns ...
.Nm
.Cm set
.Ar property Ns = Ns Ar value Oo Ar property Ns = Ns Ar value Oc Ns ...
.Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot Ns ...
.Nm
.Cm get
.Op Fl r Ns | Ns Fl d Ar depth
.Op Fl Hp
.Oo Fl o Ar field Ns Oo , Ns Ar field Oc Ns ... Oc
.Oo Fl s Ar source Ns Oo , Ns Ar source Oc Ns ... Oc
.Oo Fl t Ar type Ns Oo , Ns Ar type Oc Ns ... Oc
.Cm all | Ar property Ns Oo , Ns Ar property Oc Ns ...
.Oo Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot Ns | Ns Ar bookmark Oc Ns ...
.Nm
.Cm inherit
.Op Fl rS
.Ar property Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot Ns ...
.Nm
.Cm upgrade
.Nm
.Cm upgrade
.Fl v
.Nm
.Cm upgrade
.Op Fl r
.Op Fl V Ar version
.Fl a | Ar filesystem
.Nm
.Cm userspace
.Op Fl Hinp
.Oo Fl o Ar field Ns Oo , Ns Ar field Oc Ns ... Oc
.Oo Fl s Ar field Oc Ns ...
.Oo Fl S Ar field Oc Ns ...
.Oo Fl t Ar type Ns Oo , Ns Ar type Oc Ns ... Oc
.Ar filesystem Ns | Ns Ar snapshot
.Nm
.Cm groupspace
.Op Fl Hinp
.Oo Fl o Ar field Ns Oo , Ns Ar field Oc Ns ... Oc
.Oo Fl s Ar field Oc Ns ...
.Oo Fl S Ar field Oc Ns ...
.Oo Fl t Ar type Ns Oo , Ns Ar type Oc Ns ... Oc
.Ar filesystem Ns | Ns Ar snapshot
.Nm
.Cm projectspace
.Op Fl Hp
.Oo Fl o Ar field Ns Oo , Ns Ar field Oc Ns ... Oc
.Oo Fl s Ar field Oc Ns ...
.Oo Fl S Ar field Oc Ns ...
.Ar filesystem Ns | Ns Ar snapshot
.Nm
.Cm project
.Oo Fl d Ns | Ns Fl r Ns Oc
.Ar file Ns | Ns Ar directory Ns ...
.Nm
.Cm project
.Fl C
.Oo Fl kr Ns Oc
.Ar file Ns | Ns Ar directory Ns ...
.Nm
.Cm project
.Fl c
.Oo Fl 0 Ns Oc
.Oo Fl d Ns | Ns Fl r Ns Oc
.Op Fl p Ar id
.Ar file Ns | Ns Ar directory Ns ...
.Nm
.Cm project
.Op Fl p Ar id
.Oo Fl rs Ns Oc
.Ar file Ns | Ns Ar directory Ns ...
.Nm
.Cm mount
.Nm
.Cm mount
.Op Fl Olv
.Op Fl o Ar options
.Fl a | Ar filesystem
.Nm
.Cm unmount
.Op Fl f
.Fl a | Ar filesystem Ns | Ns Ar mountpoint
.Nm
.Cm share
.Fl a | Ar filesystem
.Nm
.Cm unshare
.Fl a | Ar filesystem Ns | Ns Ar mountpoint
.Nm
.Cm bookmark
.Ar snapshot bookmark
.Nm
.Cm send
.Op Fl DLPRbcehnpvw
.Op Oo Fl I Ns | Ns Fl i Oc Ar snapshot
.Ar snapshot
.Nm
.Cm send
.Op Fl LPcenvw
.Op Fl i Ar snapshot Ns | Ns Ar bookmark
.Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot
.Nm
.Cm send
.Op Fl Penv
.Fl t Ar receive_resume_token
.Nm
.Cm receive
.Op Fl Fhnsuv
.Op Fl o Sy origin Ns = Ns Ar snapshot
.Op Fl o Ar property Ns = Ns Ar value
.Op Fl x Ar property
.Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot
.Nm
.Cm receive
.Op Fl Fhnsuv
.Op Fl d Ns | Ns Fl e
.Op Fl o Sy origin Ns = Ns Ar snapshot
.Op Fl o Ar property Ns = Ns Ar value
.Op Fl x Ar property
.Ar filesystem
.Nm
.Cm receive
.Fl A
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm allow
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm allow
.Op Fl dglu
.Ar user Ns | Ns Ar group Ns Oo , Ns Ar user Ns | Ns Ar group Oc Ns ...
.Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ...
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm allow
.Op Fl dl
.Fl e Ns | Ns Sy everyone
.Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ...
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm allow
.Fl c
.Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ...
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm allow
.Fl s No @ Ns Ar setname
.Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ...
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm unallow
.Op Fl dglru
.Ar user Ns | Ns Ar group Ns Oo , Ns Ar user Ns | Ns Ar group Oc Ns ...
.Oo Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ... Oc
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm unallow
.Op Fl dlr
.Fl e Ns | Ns Sy everyone
.Oo Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ... Oc
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm unallow
.Op Fl r
.Fl c
.Oo Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ... Oc
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm unallow
.Op Fl r
.Fl s @ Ns Ar setname
.Oo Ar perm Ns | Ns @ Ns Ar setname Ns Oo , Ns Ar perm Ns | Ns @ Ns
.Ar setname Oc Ns ... Oc
.Ar filesystem Ns | Ns Ar volume
.Nm
.Cm hold
.Op Fl r
.Ar tag Ar snapshot Ns ...
.Nm
.Cm holds
.Op Fl rH
.Ar snapshot Ns ...
.Nm
.Cm release
.Op Fl r
.Ar tag Ar snapshot Ns ...
.Nm
.Cm diff
.Op Fl FHt
.Ar snapshot Ar snapshot Ns | Ns Ar filesystem
.Nm
.Cm program
.Op Fl jn
.Op Fl t Ar instruction-limit
.Op Fl m Ar memory-limit
.Ar pool script
.Op --
.Ar arg1 No ...
.Nm
.Cm load-key
.Op Fl nr
.Op Fl L Ar keylocation
.Fl a | Ar filesystem
.Nm
.Cm unload-key
.Op Fl r
.Fl a | Ar filesystem
.Nm
.Cm change-key
.Op Fl l
.Op Fl o Ar keylocation Ns = Ns Ar value
.Op Fl o Ar keyformat Ns = Ns Ar value
.Op Fl o Ar pbkdf2iters Ns = Ns Ar value
.Ar filesystem
.Nm
.Cm change-key
.Fl i
.Op Fl l
.Ar filesystem
.Nm
.Cm version
.Sh DESCRIPTION
The
.Nm
command configures ZFS datasets within a ZFS storage pool, as described in
.Xr zpool 8 .
A dataset is identified by a unique path within the ZFS namespace.
For example:
.Bd -literal
pool/{filesystem,volume,snapshot}
.Ed
.Pp
where the maximum length of a dataset name is
.Dv MAXNAMELEN
.Pq 256 bytes
and the maximum amount of nesting allowed in a path is 50 levels deep.
.Pp
A dataset can be one of the following:
.Bl -tag -width "file system"
.It Sy file system
A ZFS dataset of type
.Sy filesystem
can be mounted within the standard system namespace and behaves like other file
systems.
While ZFS file systems are designed to be POSIX compliant, known issues exist
that prevent compliance in some cases.
Applications that depend on standards conformance might fail due to non-standard
behavior when checking file system free space.
.It Sy volume
A logical volume exported as a raw or block device.
This type of dataset should only be used when a block device is required.
File systems are typically used in most environments.
.It Sy snapshot
A read-only version of a file system or volume at a given point in time.
It is specified as
.Ar filesystem Ns @ Ns Ar name
or
.Ar volume Ns @ Ns Ar name .
.It Sy bookmark
Much like a
.Sy snapshot ,
but without the hold on on-disk data. It can be used as the source of a send
(but not for a receive). It is specified as
.Ar filesystem Ns # Ns Ar name
or
.Ar volume Ns # Ns Ar name .
.El
.Ss ZFS File System Hierarchy
A ZFS storage pool is a logical collection of devices that provide space for
datasets.
A storage pool is also the root of the ZFS file system hierarchy.
.Pp
The root of the pool can be accessed as a file system, such as mounting and
unmounting, taking snapshots, and setting properties.
The physical storage characteristics, however, are managed by the
.Xr zpool 8
command.
.Pp
See
.Xr zpool 8
for more information on creating and administering pools.
.Ss Snapshots
A snapshot is a read-only copy of a file system or volume.
Snapshots can be created extremely quickly, and initially consume no additional
space within the pool.
As data within the active dataset changes, the snapshot consumes more data than
would otherwise be shared with the active dataset.
.Pp
Snapshots can have arbitrary names.
Snapshots of volumes can be cloned or rolled back, visibility is determined
by the
.Sy snapdev
property of the parent volume.
.Pp
File system snapshots can be accessed under the
.Pa .zfs/snapshot
directory in the root of the file system.
Snapshots are automatically mounted on demand and may be unmounted at regular
intervals.
The visibility of the
.Pa .zfs
directory can be controlled by the
.Sy snapdir
property.
.Ss Bookmarks
A bookmark is like a snapshot, a read-only copy of a file system or volume.
Bookmarks can be created extremely quickly, compared to snapshots, and they
consume no additional space within the pool. Bookmarks can also have arbitrary
names, much like snapshots.
.Pp
Unlike snapshots, bookmarks can not be accessed through the filesystem in any
way. From a storage standpoint a bookmark just provides a way to reference
when a snapshot was created as a distinct object. Bookmarks are initially
tied to a snapshot, not the filesystem or volume, and they will survive if the
snapshot itself is destroyed. Since they are very light weight there's little
incentive to destroy them.
.Ss Clones
A clone is a writable volume or file system whose initial contents are the same
as another dataset.
As with snapshots, creating a clone is nearly instantaneous, and initially
consumes no additional space.
.Pp
Clones can only be created from a snapshot.
When a snapshot is cloned, it creates an implicit dependency between the parent
and child.
Even though the clone is created somewhere else in the dataset hierarchy, the
original snapshot cannot be destroyed as long as a clone exists.
The
.Sy origin
property exposes this dependency, and the
.Cm destroy
command lists any such dependencies, if they exist.
.Pp
The clone parent-child dependency relationship can be reversed by using the
.Cm promote
subcommand.
This causes the
.Qq origin
file system to become a clone of the specified file system, which makes it
possible to destroy the file system that the clone was created from.
.Ss "Mount Points"
Creating a ZFS file system is a simple operation, so the number of file systems
per system is likely to be numerous.
To cope with this, ZFS automatically manages mounting and unmounting file
systems without the need to edit the
.Pa /etc/fstab
file.
All automatically managed file systems are mounted by ZFS at boot time.
.Pp
By default, file systems are mounted under
.Pa /path ,
where
.Ar path
is the name of the file system in the ZFS namespace.
Directories are created and destroyed as needed.
.Pp
A file system can also have a mount point set in the
.Sy mountpoint
property.
This directory is created as needed, and ZFS automatically mounts the file
system when the
.Nm zfs Cm mount Fl a
command is invoked
.Po without editing
.Pa /etc/fstab
.Pc .
The
.Sy mountpoint
property can be inherited, so if
.Em pool/home
has a mount point of
.Pa /export/stuff ,
then
.Em pool/home/user
automatically inherits a mount point of
.Pa /export/stuff/user .
.Pp
A file system
.Sy mountpoint
property of
.Sy none
prevents the file system from being mounted.
.Pp
If needed, ZFS file systems can also be managed with traditional tools
.Po
.Nm mount ,
.Nm umount ,
.Pa /etc/fstab
.Pc .
If a file system's mount point is set to
.Sy legacy ,
ZFS makes no attempt to manage the file system, and the administrator is
responsible for mounting and unmounting the file system. Because pools must
be imported before a legacy mount can succeed, administrators should ensure
that legacy mounts are only attempted after the zpool import process
finishes at boot time. For example, on machines using systemd, the mount
option
.Pp
.Nm x-systemd.requires=zfs-import.target
.Pp
will ensure that the zfs-import completes before systemd attempts mounting
the filesystem. See systemd.mount(5) for details.
.Ss Deduplication
Deduplication is the process for removing redundant data at the block level,
reducing the total amount of data stored. If a file system has the
.Sy dedup
property enabled, duplicate data blocks are removed synchronously. The result
is that only unique data is stored and common components are shared among files.
.Pp
Deduplicating data is a very resource-intensive operation. It is generally
recommended that you have at least 1.25 GiB of RAM per 1 TiB of storage when
you enable deduplication. Calculating the exact requirement depends heavily
on the type of data stored in the pool.
.Pp
Enabling deduplication on an improperly-designed system can result in
performance issues (slow IO and administrative operations). It can potentially
lead to problems importing a pool due to memory exhaustion. Deduplication
can consume significant processing power (CPU) and memory as well as generate
additional disk IO.
.Pp
Before creating a pool with deduplication enabled, ensure that you have planned
your hardware requirements appropriately and implemented appropriate recovery
practices, such as regular backups. As an alternative to deduplication
consider using
.Sy compression=on ,
as a less resource-intensive alternative.
.Ss Native Properties
Properties are divided into two types, native properties and user-defined
.Po or
.Qq user
.Pc
properties.
Native properties either export internal statistics or control ZFS behavior.
In addition, native properties are either editable or read-only.
User properties have no effect on ZFS behavior, but you can use them to annotate
datasets in a way that is meaningful in your environment.
For more information about user properties, see the
.Sx User Properties
section, below.
.Pp
Every dataset has a set of properties that export statistics about the dataset
as well as control various behaviors.
Properties are inherited from the parent unless overridden by the child.
Some properties apply only to certain types of datasets
.Pq file systems, volumes, or snapshots .
.Pp
The values of numeric properties can be specified using human-readable suffixes
.Po for example,
.Sy k ,
.Sy KB ,
.Sy M ,
.Sy Gb ,
and so forth, up to
.Sy Z
for zettabyte
.Pc .
The following are all valid
.Pq and equal
specifications:
.Li 1536M, 1.5g, 1.50GB .
.Pp
The values of non-numeric properties are case sensitive and must be lowercase,
except for
.Sy mountpoint ,
.Sy sharenfs ,
and
.Sy sharesmb .
.Pp
The following native properties consist of read-only statistics about the
dataset.
These properties can be neither set, nor inherited.
Native properties apply to all dataset types unless otherwise noted.
.Bl -tag -width "usedbyrefreservation"
.It Sy available
The amount of space available to the dataset and all its children, assuming that
there is no other activity in the pool.
Because space is shared within a pool, availability can be limited by any number
of factors, including physical pool size, quotas, reservations, or other
datasets within the pool.
.Pp
This property can also be referred to by its shortened column name,
.Sy avail .
.It Sy compressratio
For non-snapshots, the compression ratio achieved for the
.Sy used
space of this dataset, expressed as a multiplier.
The
.Sy used
property includes descendant datasets, and, for clones, does not include the
space shared with the origin snapshot.
For snapshots, the
.Sy compressratio
is the same as the
.Sy refcompressratio
property.
Compression can be turned on by running:
.Nm zfs Cm set Sy compression Ns = Ns Sy on Ar dataset .
The default value is
.Sy off .
.It Sy createtxg
The transaction group (txg) in which the dataset was created. Bookmarks have
the same
.Sy createtxg
as the snapshot they are initially tied to. This property is suitable for
ordering a list of snapshots, e.g. for incremental send and receive.
.It Sy creation
The time this dataset was created.
.It Sy clones
For snapshots, this property is a comma-separated list of filesystems or volumes
which are clones of this snapshot.
The clones'
.Sy origin
property is this snapshot.
If the
.Sy clones
property is not empty, then this snapshot can not be destroyed
.Po even with the
.Fl r
or
.Fl f
options
.Pc .
The roles of origin and clone can be swapped by promoting the clone with the
.Nm zfs Cm promote
command.
.It Sy defer_destroy
This property is
.Sy on
if the snapshot has been marked for deferred destroy by using the
.Nm zfs Cm destroy Fl d
command.
Otherwise, the property is
.Sy off .
.It Sy encryptionroot
For encrypted datasets, indicates where the dataset is currently inheriting its
encryption key from. Loading or unloading a key for the
.Sy encryptionroot
will implicitly load / unload the key for any inheriting datasets (see
.Nm zfs Cm load-key
and
.Nm zfs Cm unload-key
for details).
Clones will always share an
encryption key with their origin. See the
.Sx Encryption
section for details.
.It Sy filesystem_count
The total number of filesystems and volumes that exist under this location in
the dataset tree.
This value is only available when a
.Sy filesystem_limit
has been set somewhere in the tree under which the dataset resides.
.It Sy keystatus
Indicates if an encryption key is currently loaded into ZFS. The possible
values are
.Sy none ,
.Sy available ,
and
.Sy unavailable .
See
.Nm zfs Cm load-key
and
.Nm zfs Cm unload-key .
.It Sy guid
The 64 bit GUID of this dataset or bookmark which does not change over its
entire lifetime. When a snapshot is sent to another pool, the received
snapshot has the same GUID. Thus, the
.Sy guid
is suitable to identify a snapshot across pools.
.It Sy logicalreferenced
The amount of space that is
.Qq logically
accessible by this dataset.
See the
.Sy referenced
property.
The logical space ignores the effect of the
.Sy compression
and
.Sy copies
properties, giving a quantity closer to the amount of data that applications
see.
However, it does include space consumed by metadata.
.Pp
This property can also be referred to by its shortened column name,
.Sy lrefer .
.It Sy logicalused
The amount of space that is
.Qq logically
consumed by this dataset and all its descendents.
See the
.Sy used
property.
The logical space ignores the effect of the
.Sy compression
and
.Sy copies
properties, giving a quantity closer to the amount of data that applications
see.
However, it does include space consumed by metadata.
.Pp
This property can also be referred to by its shortened column name,
.Sy lused .
.It Sy mounted
For file systems, indicates whether the file system is currently mounted.
This property can be either
.Sy yes
or
.Sy no .
.It Sy objsetid
A unique identifier for this dataset within the pool. Unlike the dataset's
.Sy guid
, the
.Sy objsetid
of a dataset is not transferred to other pools when the snapshot is copied
with a send/receive operation.
The
.Sy objsetid
can be reused (for a new datatset) after the dataset is deleted.
.It Sy origin
For cloned file systems or volumes, the snapshot from which the clone was
created.
See also the
.Sy clones
property.
.It Sy receive_resume_token
For filesystems or volumes which have saved partially-completed state from
.Sy zfs receive -s ,
this opaque token can be provided to
.Sy zfs send -t
to resume and complete the
.Sy zfs receive .
.It Sy referenced
The amount of data that is accessible by this dataset, which may or may not be
shared with other datasets in the pool.
When a snapshot or clone is created, it initially references the same amount of
space as the file system or snapshot it was created from, since its contents are
identical.
.Pp
This property can also be referred to by its shortened column name,
.Sy refer .
.It Sy refcompressratio
The compression ratio achieved for the
.Sy referenced
space of this dataset, expressed as a multiplier.
See also the
.Sy compressratio
property.
.It Sy snapshot_count
The total number of snapshots that exist under this location in the dataset
tree.
This value is only available when a
.Sy snapshot_limit
has been set somewhere in the tree under which the dataset resides.
.It Sy type
The type of dataset:
.Sy filesystem ,
.Sy volume ,
or
.Sy snapshot .
.It Sy used
The amount of space consumed by this dataset and all its descendents.
This is the value that is checked against this dataset's quota and reservation.
The space used does not include this dataset's reservation, but does take into
account the reservations of any descendent datasets.
The amount of space that a dataset consumes from its parent, as well as the
amount of space that is freed if this dataset is recursively destroyed, is the
greater of its space used and its reservation.
.Pp
The used space of a snapshot
.Po see the
.Sx Snapshots
section
.Pc
is space that is referenced exclusively by this snapshot.
If this snapshot is destroyed, the amount of
.Sy used
space will be freed.
Space that is shared by multiple snapshots isn't accounted for in this metric.
When a snapshot is destroyed, space that was previously shared with this
snapshot can become unique to snapshots adjacent to it, thus changing the used
space of those snapshots.
The used space of the latest snapshot can also be affected by changes in the
file system.
Note that the
.Sy used
space of a snapshot is a subset of the
.Sy written
space of the snapshot.
.Pp
The amount of space used, available, or referenced does not take into account
pending changes.
Pending changes are generally accounted for within a few seconds.
Committing a change to a disk using
.Xr fsync 2
or
.Dv O_SYNC
does not necessarily guarantee that the space usage information is updated
immediately.
.It Sy usedby*
The
.Sy usedby*
properties decompose the
.Sy used
properties into the various reasons that space is used.
Specifically,
.Sy used No =
.Sy usedbychildren No +
.Sy usedbydataset No +
.Sy usedbyrefreservation No +
.Sy usedbysnapshots .
These properties are only available for datasets created on
.Nm zpool
.Qo version 13 Qc
pools.
.It Sy usedbychildren
The amount of space used by children of this dataset, which would be freed if
all the dataset's children were destroyed.
.It Sy usedbydataset
The amount of space used by this dataset itself, which would be freed if the
dataset were destroyed
.Po after first removing any
.Sy refreservation
and destroying any necessary snapshots or descendents
.Pc .
.It Sy usedbyrefreservation
The amount of space used by a
.Sy refreservation
set on this dataset, which would be freed if the
.Sy refreservation
was removed.
.It Sy usedbysnapshots
The amount of space consumed by snapshots of this dataset.
In particular, it is the amount of space that would be freed if all of this
dataset's snapshots were destroyed.
Note that this is not simply the sum of the snapshots'
.Sy used
properties because space can be shared by multiple snapshots.
.It Sy userused Ns @ Ns Em user
The amount of space consumed by the specified user in this dataset.
Space is charged to the owner of each file, as displayed by
.Nm ls Fl l .
The amount of space charged is displayed by
.Nm du
and
.Nm ls Fl s .
See the
.Nm zfs Cm userspace
subcommand for more information.
.Pp
Unprivileged users can access only their own space usage.
The root user, or a user who has been granted the
.Sy userused
privilege with
.Nm zfs Cm allow ,
can access everyone's usage.
.Pp
The
.Sy userused Ns @ Ns Em ...
properties are not displayed by
.Nm zfs Cm get Sy all .
The user's name must be appended after the @ symbol, using one of the following
forms:
.Bl -bullet -width ""
.It
.Em POSIX name
.Po for example,
.Sy joe
.Pc
.It
.Em POSIX numeric ID
.Po for example,
.Sy 789
.Pc
.It
.Em SID name
.Po for example,
.Sy joe.smith@mydomain
.Pc
.It
.Em SID numeric ID
.Po for example,
.Sy S-1-123-456-789
.Pc
.El
.Pp
Files created on Linux always have POSIX owners.
.It Sy userobjused Ns @ Ns Em user
The
.Sy userobjused
property is similar to
.Sy userused
but instead it counts the number of objects consumed by a user. This property
counts all objects allocated on behalf of the user, it may differ from the
results of system tools such as
.Nm df Fl i .
.Pp
When the property
.Sy xattr=on
is set on a file system additional objects will be created per-file to store
extended attributes. These additional objects are reflected in the
.Sy userobjused
value and are counted against the user's
.Sy userobjquota .
When a file system is configured to use
.Sy xattr=sa
no additional internal objects are normally required.
.It Sy userrefs
This property is set to the number of user holds on this snapshot.
User holds are set by using the
.Nm zfs Cm hold
command.
.It Sy groupused Ns @ Ns Em group
The amount of space consumed by the specified group in this dataset.
Space is charged to the group of each file, as displayed by
.Nm ls Fl l .
See the
.Sy userused Ns @ Ns Em user
property for more information.
.Pp
Unprivileged users can only access their own groups' space usage.
The root user, or a user who has been granted the
.Sy groupused
privilege with
.Nm zfs Cm allow ,
can access all groups' usage.
.It Sy groupobjused Ns @ Ns Em group
The number of objects consumed by the specified group in this dataset.
Multiple objects may be charged to the group for each file when extended
attributes are in use. See the
.Sy userobjused Ns @ Ns Em user
property for more information.
.Pp
Unprivileged users can only access their own groups' space usage.
The root user, or a user who has been granted the
.Sy groupobjused
privilege with
.Nm zfs Cm allow ,
can access all groups' usage.
.It Sy projectused Ns @ Ns Em project
The amount of space consumed by the specified project in this dataset. Project
is identified via the project identifier (ID) that is object-based numeral
attribute. An object can inherit the project ID from its parent object (if the
parent has the flag of inherit project ID that can be set and changed via
.Nm chattr Fl /+P
or
.Nm zfs project Fl s )
when being created. The privileged user can set and change object's project
ID via
.Nm chattr Fl p
or
.Nm zfs project Fl s
anytime. Space is charged to the project of each file, as displayed by
.Nm lsattr Fl p
or
.Nm zfs project .
See the
.Sy userused Ns @ Ns Em user
property for more information.
.Pp
The root user, or a user who has been granted the
.Sy projectused
privilege with
.Nm zfs allow ,
can access all projects' usage.
.It Sy projectobjused Ns @ Ns Em project
The
.Sy projectobjused
is similar to
.Sy projectused
but instead it counts the number of objects consumed by project. When the
property
.Sy xattr=on
is set on a fileset, ZFS will create additional objects per-file to store
extended attributes. These additional objects are reflected in the
.Sy projectobjused
value and are counted against the project's
.Sy projectobjquota .
When a filesystem is configured to use
.Sy xattr=sa
no additional internal objects are required. See the
.Sy userobjused Ns @ Ns Em user
property for more information.
.Pp
The root user, or a user who has been granted the
.Sy projectobjused
privilege with
.Nm zfs allow ,
can access all projects' objects usage.