"absolute device name" is not a term that is in common use as far as I know.
Maybe they mean an absolute path to a block device file that corresponds to the LVM logical volume.
Or given that they mention "soft link", which itself is more commonly referred to as "symbolic link" or "symlink", maybe they meant the absolute canonical (i.e. free or any symlink,
.. components and with only one
/ in between each component and at the start and none at the end) path to a device file for that LV.
/dev/VG_name/LV_name is generally an absolute path to the
LV_name LV in the
VG_name volume group.
/dev/mapper/VG_name-LV_name is often another one path to the same device file (though note that
- in the VG/LV names are encoded as
readlink -e <that-path> on both should give you the canonical absolute path of that file (generally something like
Now, you do
cp -a /dev/dm-<number> /root/mydevice, and
/root/mydevice will be another canonical absolute path to a block device file for that LV.
$ ls -l /root/mydevice
brw-rw---- 1 root disk 253, 1 Sep 15 06:17 /dev/dm-1
What identifies the device here are the
b (type: block),
253 (major number) and
1 (minor number) above that identify the device. You can recreate the same with the
On Linux, to find the canonical name for that block device, you can look for
$ grep -xFl 253:1 /sys/class/block/*/dev
Or resolve the
$ readlink -e /sys/dev/block/253:1
dm-1 being the canonical name here.
udev would generally create a corresponding
/dev/dm-1 file when that device is discovered.