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. During standard LVM operations, you should not use the name of an LVM device in this format to specify an LVM device directly, but instead you should use the vg / lv alternative. 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. Event number The current number of events received. Issuing a dmsetup wait n command allows you to wait for the n'th event, blocking the call until it is received. Major, minor Major and minor device number. Number of targets The number of segments that make up a device. For example, a linear device spanning 3 disks would have 3 targets. A linear device composed of the beginning and end of a disk, but not the middle would have 2 targets. UUID UUID of the device. The following example shows partial output for the dmsetup info command. A.2.2. The dmsetup ls Command You can list the device names of mapped devices with the dmsetup ls command. You can list devices that have at least one target of a specified type with the dmsetup ls --target target_type command. For other options of the dmsetup ls command, see the dmsetup man page. The following example shows the command to list the device names of currently configured mapped devices. The following example shows the command to list the device names of currently configured mirror mappings. LVM configurations that are stacked on multipath or other device mapper devices can be complex to sort out. The dmsetup ls command provides a --tree option that displays dependencies between devices as a tree, as in the following example. A.2.3. The dmsetup status Command The dmsetup status device command provides status information for each target in a specified device. If you do not specify a device name, the output is information about all of the currently configured Device Mapper devices. You can list the status only of devices that have at least one target of a specified type with the dmsetup status --target target_type command. The following example shows the command to list the status of the targets in all currently configured mapped devices. A.2.4. The dmsetup deps Command The dmsetup deps device command provides a list of (major, minor) pairs for devices referenced by the mapping table for the specified device. If you do not specify a device name, the output is information about all of the currently configured Device Mapper devices. The following example shows the command to list the dependencies of all currently configured mapped devices. The following example shows the command to list the dependencies only of the device lock_stress-grant--02.1722 :

Commands:
dmsetup info Name: testgfsvg-testgfslv1 State: ACTIVE Read Ahead: 256 Tables present: LIVE Open count: 0 Event number: 0 Major, minor: 253, 2 Number of targets: 2 UUID: LVM-K528WUGQgPadNXYcFrrf9LnPlUMswgkCkpgPIgYzSvigM7SfeWCypddNSWtNzc2N Name: VolGroup00-LogVol00 State: ACTIVE Read Ahead: 256 Tables present: LIVE Open count: 1 Event number: 0 Major, minor: 253, 0 Number of targets: 1 UUID: LVM-tOcS1kqFV9drb0X1Vr8sxeYP0tqcrpdegyqj5lZxe45JMGlmvtqLmbLpBcenh2L3
dmsetup ls testgfsvg-testgfslv3 (253:4) testgfsvg-testgfslv2 (253:3) testgfsvg-testgfslv1 (253:2) VolGroup00-LogVol01 (253:1) VolGroup00-LogVol00 (253:0)
dmsetup ls --target mirror lock_stress-grant--02.1722 (253, 34) lock_stress-grant--01.1720 (253, 18) lock_stress-grant--03.1718 (253, 52) lock_stress-grant--02.1716 (253, 40) lock_stress-grant--03.1713 (253, 47) lock_stress-grant--02.1709 (253, 23) lock_stress-grant--01.1707 (253, 8) lock_stress-grant--01.1724 (253, 14) lock_stress-grant--03.1711 (253, 27)
dmsetup ls --tree vgtest-lvmir (253:13) ├─vgtest-lvmir_mimage_1 (253:12) │ └─mpathep1 (253:8) │ └─mpathe (253:5) │ ├─ (8:112) │ └─ (8:64) ├─vgtest-lvmir_mimage_0 (253:11) │ └─mpathcp1 (253:3) │ └─mpathc (253:2) │ ├─ (8:32) │ └─ (8:16) └─vgtest-lvmir_mlog (253:4) └─mpathfp1 (253:10) └─mpathf (253:6) ├─ (8:128) └─ (8:80)
dmsetup status testgfsvg-testgfslv3: 0 312352768 linear testgfsvg-testgfslv2: 0 312352768 linear testgfsvg-testgfslv1: 0 312352768 linear testgfsvg-testgfslv1: 312352768 50331648 linear VolGroup00-LogVol01: 0 4063232 linear VolGroup00-LogVol00: 0 151912448 linear
dmsetup deps testgfsvg-testgfslv3: 1 dependencies : (8, 16) testgfsvg-testgfslv2: 1 dependencies : (8, 16) testgfsvg-testgfslv1: 1 dependencies : (8, 16) VolGroup00-LogVol01: 1 dependencies : (8, 2) VolGroup00-LogVol00: 1 dependencies : (8, 2)
dmsetup deps lock_stress-grant--02.1722 3 dependencies : (253, 33) (253, 32) (253, 31)