vgdisplay and lvdisplay No volume groups found

root@ubuntu-server:~# pvdisplay
root@ubuntu-server:~# vgdisplay
  No volume groups found
root@ubuntu-server:~# lvdisplay
  No volume groups found
root@ubuntu-server:~#

what to do. I can't find solutions on google or somewhere else?

i try:

pvcreate /dev/sdb5
  Device /dev/sdb5 not found (or ignored by filtering).

and this is my fdisk:

 fdisk -l

Disk /dev/sdb: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00050ccb

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *        2048      499711      248832   83  Linux
/dev/sdb2          501758   488396799   243947521    5  Extended
/dev/sdb5          501760   488396799   243947520   8e  Linux LVM

Disk /dev/sda: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00050ccb

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      499711      248832   fd  Linux raid autodetect
/dev/sda2          501758   488396799   243947521    5  Extended
/dev/sda5          501760   488396799   243947520   fd  Linux raid autodetect

Disk /dev/mapper/ubuntu--server-root: 247.7 GB, 247652679680 bytes
255 heads, 63 sectors/track, 30108 cylinders, total 483696640 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/ubuntu--server-root doesn't contain a valid partition table

Disk /dev/mapper/ubuntu--server-swap_1: 2143 MB, 2143289344 bytes
255 heads, 63 sectors/track, 260 cylinders, total 4186112 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/ubuntu--server-swap_1 doesn't contain a valid partition table

and my df -h

df -h

Filesystem                       Size  Used Avail Use% Mounted on
/dev/mapper/ubuntu--server-root  231G  5,0G  214G   3% /
udev                             993M   12K  993M   1% /dev
tmpfs                            401M  356K  401M   1% /run
none                             5,0M     0  5,0M   0% /run/lock
none                            1002M     0 1002M   0% /run/shm
/dev/sdb1                        228M   25M  192M  12% /boot

Quite often, new users are confused by logical volumes not showing up even after they have been set up correctly. If this is the case for you, did you try the following?

pvscan

This scans for physical volumes. It should show /dev/sdb5 if you made this an LVM physical volume before.

vgscan

Looks for existing volume groups. Should show your volume group if you properly set it up before.

vgchange -a y

Activates all available volume groups (changes their "active" state to "yes"). Now your logical volumes should show up in /dev/mapper/ and as /dev/VGNAME/LVNAME.