4.1. Using CLI Commands

4.1. Using CLI Commands

There are several general features of all LVM CLI commands.

When sizes are required in a command line argument, units can always be specified explicitly. If you do not specify a unit, then a default is assumed, usually KB or MB. LVM CLI commands do not accept fractions.

When specifying units in a command line argument, LVM is case-insensitive; specifying M or m is equivalent, for example, and powers of 2 (multiples of 1024) are used. However, when specifying the --units argument in a command, lower-case indicates that units are in multiples of 1024 while upper-case indicates that units are in multiples of 1000.

Where commands take volume group or logical volume names as arguments, the full path name is optional. A logical volume called lvol0 in a volume group called vg0 can be specified as vg0/lvol0. Where a list of volume groups is required but is left empty, a list of all volume groups will be substituted. Where a list of logical volumes is required but a volume group is given, a list of all the logical volumes in that volume group will be substituted. For example, the lvdisplay vg0 command will display all the logical volumes in volume group vg0.

All LVM commands accept a -v argument, which can be entered multiple times to increase the output verbosity. For example, the following examples shows the default output of the lvcreate command.

# lvcreate -L 50MB new_vg
  Rounding up size to full physical extent 52.00 MB
  Logical volume "lvol0" created

The following command shows the output of the lvcreate command with the -v argument.

# lvcreate -v -L 50MB new_vg
    Finding volume group "new_vg"
  Rounding up size to full physical extent 52.00 MB
    Archiving volume group "new_vg" metadata (seqno 4).
    Creating logical volume lvol0
    Creating volume group backup "/etc/lvm/backup/new_vg" (seqno 5).
    Found volume group "new_vg"
    Creating new_vg-lvol0
    Loading new_vg-lvol0 table
    Resuming new_vg-lvol0 (253:2)
    Clearing start of logical volume "lvol0"
    Creating volume group backup "/etc/lvm/backup/new_vg" (seqno 5).
  Logical volume "lvol0" created

You could also have used the -vv, -vvv or the -vvvv argument to display increasingly more details about the command execution. The -vvvv argument provides the maximum amount of information at this time. The following example shows only the first few lines of output for the lvcreate command with the -vvvv argument specified.

# lvcreate -vvvv -L 50MB new_vg
#lvmcmdline.c:913         Processing: lvcreate -vvvv -L 50MB new_vg
#lvmcmdline.c:916         O_DIRECT will be used
#config/config.c:864       Setting global/locking_type to 1
#locking/locking.c:138       File-based locking selected.
#config/config.c:841       Setting global/locking_dir to /var/lock/lvm
#activate/activate.c:358       Getting target version for linear
#ioctl/libdm-iface.c:1569         dm version   OF   [16384]
#ioctl/libdm-iface.c:1569         dm versions   OF   [16384]
#activate/activate.c:358       Getting target version for striped
#ioctl/libdm-iface.c:1569         dm versions   OF   [16384]
#config/config.c:864       Setting activation/mirror_region_size to 512

You can display help for any of the LVM CLI commands with the --help argument of the command.

commandname --help

To display the man page for a command, execute the man command:

man commandname

The man lvm command provides general online information about LVM.

All LVM objects are referenced internally by a UUID, which is assigned when you create the object. This can be useful in a situation where you remove a physical volume called /dev/sdf which is part of a volume group and, when you plug it back in, you find that it is now /dev/sdk. LVM will still find the physical volume because it identifies the physical volume by its UUID and not its device name. For information on specifying the UUID of a physical volume when creating a physical volume, see see Section 6.4, “Recovering Physical Volume Metadata”.

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