Ubuntu Manpage: lvm — LVM2 tools

Provided by: lvm2_2.03.07-1ubuntu1_amd64

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
physical 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 command (for example by using a hard or
soft link) it acts as that command.

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_SUPPRESS_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 substituted. 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 information 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 hardware snapshot).
vgmerge Merge two Volume Groups.
vgmknodes Recreate Volume Group directory and Logical Volume special 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.
vgsplit Split a Volume Group into two, moving any logical volumes from one Volume Group to another
by moving entire Physical Volumes.
lvchange Change attributes of a Logical Volume.
lvconvert Convert a Logical Volume from linear to mirror or snapshot.
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 metadata/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', '_rimage',
'_rmeta', '_tdata', '_tmeta', '_vorigin' or '_vdata'. 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
accessible 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 distributions. Other software and scripts should use the
/dev/VolumeGroupName/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 specified 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 foreign (see lvmsystemid(7).)  In this
       case, the one VG that is not foreign 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 considered.

       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 Logical
       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
       configuration 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 Volume (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 Physical 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
       parameter.

       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 Volumes 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 provisioning (lvmthin(7)) types are
       examples of this.

DIAGNOSTICS

       All tools return a status code of zero on success or non-zero on failure.  The non-zero codes distinguish
       only  between  the  broad  categories  of  unrecognised  commands,  problems  processing the command line
       arguments 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_SUPPRESS_SYSLOG
Suppress contacting syslog.

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_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 debugging.

FILES

       /etc/lvm/lvm.conf
       $HOME/.lvm_history