Installation guide

The dmsetup Command
89
device
block device, referenced by the device name in the filesystem or by the major and minor numbers
in the format major:minor
offset
starting offset of the mapping on the device
The following is an example of a crypt target.
0 2097152 crypt aes-plain 0123456789abcdef0123456789abcdef 0 /dev/hda 0
A.2. The dmsetup Command
The dmsetup command is a command line wrapper for communication with the Device Mapper.
For general system information about LVM devices, you may find the info, ls, status, and deps
options of the dmsetup command to be useful, as described in the following subsections.
For information about additional options and capabilities of the dmsetup command, see the
dmsetup(8) man page.
A.2.1. The dmsetup info Command
The dmsetup info device command provides summary information about Device Mapper
devices. If you do not specify a device name, the output is information about all of the currently
configured Device Mapper devices. If you specify a device, then this command yields information for
that device only.
The dmsetup info command provides information in the following categories:
Name
The name of the device. An LVM device is expressed as the volume group name and the logical
volume name separated by a hyphen. A hyphen in the original name is translated to two hyphens.
State
Possible device states are SUSPENDED, ACTIVE, and READ-ONLY. The dmsetup suspend
command sets a device state to SUSPENDED. When a device is suspended, all I/O operations to
that device stop. The dmsetup resume command restores a device state to ACTIVE.
Read Ahead
The number of data blocks that the system reads ahead for any open file on which read operations
are ongoing. By default, the kernel chooses a suitable value automatically. You can change this
value with the --readahead option of the dmsetup command.
Tables present
Possible states for this category are LIVE and INACTIVE. An INACTIVE state indicates that a
table has been loaded which will be swapped in when a dmsetup resume command restores a
device state to ACTIVE, at which point the table's state becomes LIVE. For information, see the
dmsetup man page.
Open count
The open reference count indicates how many times the device is opened. A mount command
opens a device.