LVM(8) System Manager's Manual LVM(8)
NAME
lvm -- LVM2 tools
SYNOPSIS
lvm [command|file]
DESCRIPTION
The Logical Volume Manager (LVM) provides tools to create virtual block
devices from physical devices. Virtual devices may be easier to manage
than physical devices, and can have capabilities beyond what the physi-
cal devices provide themselves. A Volume Group (VG) is a collection of
one or more physical devices, each called a Physical Volume (PV). A
Logical Volume (LV) is a virtual block device that can be used by the
system or applications. Each block of data in an LV is stored on one
or more PV in the VG, according to algorithms implemented by Device
Mapper (DM) in the kernel.
The lvm command, and other commands listed below, are the command-line
tools for LVM. A separate manual page describes each command in
detail.
If lvm is invoked with no arguments it presents a readline prompt
(assuming it was compiled with readline support). LVM commands may be
entered interactively at this prompt with readline facilities including
history and command name and option completion. Refer to readline(3)
for details.
If lvm is invoked with argv[0] set to the name of a specific LVM com-
mand (for example by using a hard or soft link) it acts as that com-
mand.
On invocation, lvm requires that only the standard file descriptors
stdin, stdout and stderr are available. If others are found, they get
closed and messages are issued warning about the leak. This warning
can be suppressed by setting the environment variable LVM_SUP-
PRESS_FD_WARNINGS.
Where commands take VG or LV names as arguments, the full path name is
optional. An LV called "lvol0" in a VG called "vg0" can be specified
as "vg0/lvol0". Where a list of VGs is required but is left empty, a
list of all VGs will be substituted. Where a list of LVs is required
but a VG is given, a list of all the LVs in that VG will be substi-
tuted. So lvdisplay vg0 will display all the LVs in "vg0". Tags can
also be used - see --addtag below.
One advantage of using the built-in shell is that configuration infor-
mation gets cached internally between commands.
A file containing a simple script with one command per line can also be
given on the command line. The script can also be executed directly if
the first line is #! followed by the absolute path of lvm.
Additional hyphens within option names are ignored. For example,
--readonly and --read-only are both accepted.
BUILT-IN COMMANDS
The following commands are built into lvm without links normally being
created in the filesystem for them.
config The same as lvmconfig(8) below.
devtypes Display the recognised built-in block device types.
dumpconfig The same as lvmconfig(8) below.
formats Display recognised metadata formats.
fullreport Report information about PVs, PV segments, VGs, LVs and
LV segments, all at once.
help Display the help text.
lastlog Display log report of last command run in LVM shell if
command log reporting is enabled.
lvpoll Complete lvmpolld operations (Internal command).
segtypes Display recognised Logical Volume segment types.
systemid Display any system ID currently set on this host.
tags Display any tags defined on this host.
version Display version information.
COMMANDS
The following commands implement the core LVM functionality.
pvchange Change attributes of a Physical Volume.
pvck Check Physical Volume metadata.
pvcreate Initialize a disk or partition for use by LVM.
pvdisplay Display attributes of a Physical Volume.
pvmove Move Physical Extents.
pvremove Remove a Physical Volume.
pvresize Resize a disk or partition in use by LVM2.
pvs Report information about Physical Volumes.
pvscan Scan all disks for Physical Volumes.
vgcfgbackup Backup Volume Group descriptor area.
vgcfgrestore Restore Volume Group descriptor area.
vgchange Change attributes of a Volume Group.
vgck Check Volume Group metadata.
vgconvert Convert Volume Group metadata format.
vgcreate Create a Volume Group.
vgdisplay Display attributes of Volume Groups.
vgexport Make volume Groups unknown to the system.
vgextend Add Physical Volumes to a Volume Group.
vgimport Make exported Volume Groups known to the system.
vgimportclone Import and rename duplicated Volume Group (e.g. a hard-
ware snapshot).
vgmerge Merge two Volume Groups.
vgmknodes Recreate Volume Group directory and Logical Volume spe-
cial files
vgreduce Reduce a Volume Group by removing one or more Physical
Volumes.
vgremove Remove a Volume Group.
vgrename Rename a Volume Group.
vgs Report information about Volume Groups.
vgscan Scan all disks for Volume Groups and rebuild caches.
vgsplit Split a Volume Group into two, moving any logical volumes
from one Volume Group to another by moving entire Physi-
cal Volumes.
lvchange Change attributes of a Logical Volume.
lvconvert Convert a Logical Volume from linear to mirror or snap-
shot.
lvcreate Create a Logical Volume in an existing Volume Group.
lvdisplay Display attributes of a Logical Volume.
lvextend Extend the size of a Logical Volume.
lvmconfig Display the configuration information after loading
lvm.conf(5) and any other configuration files.
lvmdiskscan Scan for all devices visible to LVM2.
lvmdump Create lvm2 information dumps for diagnostic purposes.
lvreduce Reduce the size of a Logical Volume.
lvremove Remove a Logical Volume.
lvrename Rename a Logical Volume.
lvresize Resize a Logical Volume.
lvs Report information about Logical Volumes.
lvscan Scan (all disks) for Logical Volumes.
The following LVM1 commands are not implemented in LVM2: lvmchange,
lvmsadc, lvmsar, pvdata. For performance metrics, use dmstats(8) or to
manipulate the kernel device-mapper driver used by LVM2 directly, use
dmsetup(8).
VALID NAMES
The valid characters for VG and LV names are: a-z A-Z 0-9 + _ . -
VG names cannot begin with a hyphen. The name of a new LV also cannot
begin with a hyphen. However, if the configuration setting meta-
data/record_lvs_history is enabled then an LV name with a hyphen as a
prefix indicates that, although the LV was removed, it is still being
tracked because it forms part of the history of at least one LV that is
still present. This helps to record the ancestry of thin snapshots
even after some links in the chain have been removed. A reference to
the historical LV 'lvol1' in VG 'vg00' would be 'vg00/\-lvol1' or just
'-lvol1' if the VG is already set. (The latter form must be preceded
by '--' to terminate command line option processing before reaching
this argument.)
There are also various reserved names that are used internally by lvm
that can not be used as LV or VG names. A VG cannot be called anything
that exists in /dev/ at the time of creation, nor can it be called '.'
or '..'. An LV cannot be called '.', '..', 'snapshot' or 'pvmove'.
The LV name may also not contain any of the following strings:
'_cdata', '_cmeta', '_corig', '_mlog', '_mimage', '_pmspare', '_rim-
age', '_rmeta', '_tdata', '_tmeta' or '_vorigin'. A directory bearing
the name of each Volume Group is created under /dev when any of its
Logical Volumes are activated. Each active Logical Volume is accessi-
ble from this directory as a symbolic link leading to a device node.
Links or nodes in /dev/mapper are intended only for internal use and
the precise format and escaping might change between releases and dis-
tributions. Other software and scripts should use the /dev/Vol-
umeGroupName/LogicalVolumeName format to reduce the chance of needing
amendment when the software is updated. Should you need to process the
node names in /dev/mapper, you may use dmsetup splitname to separate
out the original VG, LV and internal layer names.
UNIQUE NAMES
VG names should be unique. vgcreate will produce an error if the spec-
ified VG name matches an existing VG name. However, there are cases
where different VGs with the same name can appear to LVM, e.g. after
moving disks or changing filters.
When VGs with the same name exist, commands operating on all VGs will
include all of the VGs with the same name. If the ambiguous VG name is
specified on the command line, the command will produce an error. The
error states that multiple VGs exist with the specified name. To
process one of the VGs specifically, the --select option should be used
with the UUID of the intended VG: '--select vg_uuid=<uuid>'.
An exception is if all but one of the VGs with the shared name is for-
eign (see lvmsystemid(7).) In this case, the one VG that is not for-
eign is assumed to be the intended VG and is processed.
LV names are unique within a VG. The name of an historical LV cannot
be reused until the historical LV has itself been removed or renamed.
ALLOCATION
When an operation needs to allocate Physical Extents for one or more
Logical Volumes, the tools proceed as follows:
First of all, they generate the complete set of unallocated Physical
Extents in the Volume Group. If any ranges of Physical Extents are
supplied at the end of the command line, only unallocated Physical
Extents within those ranges on the specified Physical Volumes are con-
sidered.
Then they try each allocation policy in turn, starting with the
strictest policy (contiguous) and ending with the allocation policy
specified using --alloc or set as the default for the particular Logi-
cal Volume or Volume Group concerned. For each policy, working from
the lowest-numbered Logical Extent of the empty Logical Volume space
that needs to be filled, they allocate as much space as possible
according to the restrictions imposed by the policy. If more space is
needed, they move on to the next policy.
The restrictions are as follows:
Contiguous requires that the physical location of any Logical Extent
that is not the first Logical Extent of a Logical Volume is adjacent to
the physical location of the Logical Extent immediately preceding it.
Cling requires that the Physical Volume used for any Logical Extent to
be added to an existing Logical Volume is already in use by at least
one Logical Extent earlier in that Logical Volume. If the configura-
tion parameter allocation/cling_tag_list is defined, then two Physical
Volumes are considered to match if any of the listed tags is present on
both Physical Volumes. This allows groups of Physical Volumes with
similar properties (such as their physical location) to be tagged and
treated as equivalent for allocation purposes.
When a Logical Volume is striped or mirrored, the above restrictions
are applied independently to each stripe or mirror image (leg) that
needs space.
Normal will not choose a Physical Extent that shares the same Physical
Volume as a Logical Extent already allocated to a parallel Logical Vol-
ume (i.e. a different stripe or mirror image/leg) at the same offset
within that parallel Logical Volume.
When allocating a mirror log at the same time as Logical Volumes to
hold the mirror data, Normal will first try to select different Physi-
cal Volumes for the log and the data. If that's not possible and the
allocation/mirror_logs_require_separate_pvs configuration parameter is
set to 0, it will then allow the log to share Physical Volume(s) with
part of the data.
When allocating thin pool metadata, similar considerations to those of
a mirror log in the last paragraph apply based on the value of the
allocation/thin_pool_metadata_require_separate_pvs configuration param-
eter.
If you rely upon any layout behaviour beyond that documented here, be
aware that it might change in future versions of the code.
For example, if you supply on the command line two empty Physical Vol-
umes that have an identical number of free Physical Extents available
for allocation, the current code considers using each of them in the
order they are listed, but there is no guarantee that future releases
will maintain that property. If it is important to obtain a specific
layout for a particular Logical Volume, then you should build it up
through a sequence of lvcreate(8) and lvconvert(8) steps such that the
restrictions described above applied to each step leave the tools no
discretion over the layout.
To view the way the allocation process currently works in any specific
case, read the debug logging output, for example by adding -vvvv to a
command.
LOGICAL VOLUME TYPES
Some logical volume types are simple to create and can be done with a
single lvcreate(8) command. The linear and striped logical volume
types are an example of this. Other logical volume types may require
more than one command to create. The cache (lvmcache(7)) and thin pro-
visioning (lvmthin(7)) types are examples of this.
DIAGNOSTICS
All tools return a status code of zero on success or non-zero on fail-
ure. The non-zero codes distinguish only between the broad categories
of unrecognised commands, problems processing the command line argu-
ments and any other failures. As LVM remains under active development,
the code used in a specific case occasionally changes between releases.
Message text may also change.
ENVIRONMENT VARIABLES
HOME Directory containing .lvm_history if the internal readline shell
is invoked.
LVM_OUT_FD
File descriptor to use for common output from LVM commands.
LVM_ERR_FD
File descriptor to use for error output from LVM commands.
LVM_REPORT_FD
File descriptor to use for report output from LVM commands.
LVM_COMMAND_PROFILE
Name of default command profile to use for LVM commands. This
profile is overriden by direct use of --commandprofile command
line option.
LVM_RUN_BY_DMEVENTD
This variable is normally set by dmeventd plugin to inform lvm2
command it is running from dmeventd plugin so lvm2 takes some
extra action to avoid comunication and deadlocks with dmeventd.
LVM_SYSTEM_DIR
Directory containing lvm.conf(5) and other LVM system files.
Defaults to "/etc/lvm".
LVM_SUPPRESS_FD_WARNINGS
Suppress warnings about unexpected file descriptors passed into
LVM.
LVM_VG_NAME
The Volume Group name that is assumed for any reference to a
Logical Volume that doesn't specify a path. Not set by default.
LVM_LVMETAD_PIDFILE
Path to the file that stores the lvmetad process ID.
LVM_LVMETAD_SOCKET
Path to the socket used to communicate with lvmetad.
LVM_LVMPOLLD_PIDFILE
Path to the file that stores the lvmpolld process ID.
LVM_LVMPOLLD_SOCKET
Path to the socket used to communicate with lvmpolld..
LVM_LOG_FILE_EPOCH
A string of up to 32 letters appended to the log filename and
followed by the process ID and a startup timestamp using this
format string "_%s_%d_%llu". When set, each process logs to a
separate file.
LVM_LOG_FILE_MAX_LINES
If more than this number of lines are sent to the log file, the
command gets aborted. Automated tests use this to terminate
looping commands.
LVM_EXPECTED_EXIT_STATUS
The status anticipated when the process exits. Use ">N" to
match any status greater than N. If the actual exit status
matches and a log file got produced, it is deleted.
LVM_LOG_FILE_EPOCH and LVM_EXPECTED_EXIT_STATUS together allow
automated test scripts to discard uninteresting log data.
LVM_SUPPRESS_LOCKING_FAILURE_MESSAGES
Used to suppress warning messages when the configured locking is
known to be unavailable.
DM_ABORT_ON_INTERNAL_ERRORS
Abort processing if the code detects a non-fatal internal error.
DM_DISABLE_UDEV
Avoid interaction with udev. LVM will manage the relevant nodes
in /dev directly.
DM_DEBUG_WITH_LINE_NUMBERS
Prepends source file name and code line number with libdm debug-
ging.
FILES
/etc/lvm/lvm.conf
$HOME/.lvm_history
SEE ALSO
lvm(8) lvm.conf(5) lvmconfig(8)
pvchange(8) pvck(8) pvcreate(8) pvdisplay(8) pvmove(8) pvremove(8)
pvresize(8) pvs(8) pvscan(8)
vgcfgbackup(8) vgcfgrestore(8) vgchange(8) vgck(8) vgcreate(8)
vgconvert(8) vgdisplay(8) vgexport(8) vgextend(8) vgimport(8)
vgimportclone(8) vgmerge(8) vgmknodes(8) vgreduce(8) vgremove(8)
vgrename(8) vgs(8) vgscan(8) vgsplit(8)
lvcreate(8) lvchange(8) lvconvert(8) lvdisplay(8) lvextend(8)
lvreduce(8) lvremove(8) lvrename(8) lvresize(8) lvs(8) lvscan(8)
lvm-fullreport(8) lvm-lvpoll(8) lvm2-activation-generator(8)
blkdeactivate(8) lvmdump(8)
dmeventd(8) lvmetad(8) lvmpolld(8) lvmlockd(8) lvmlockctl(8) clvmd(8)
cmirrord(8) lvmdbusd(8)
lvmsystemid(7) lvmreport(7) lvmraid(7) lvmthin(7) lvmcache(7)
dmsetup(8), dmstats(8), readline(3)
Red Hat, Inc. LVM TOOLS 2.02.187(2)-RHEL7 (2020-03-24) LVM(8)
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