When I run sfdisk -l on my Ubuntu 14.04 machine, it returns the following:Disk /dev/xvda: 36473 cylinders, 255 heads, 63 sectors/trackUnits = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0   Device Boot Start     End   #cyls    #blocks   Id  System/dev/xvda1          0+    522     523-   4200966   83  Linux/dev/xvda2        523     784     262    2104515   82  Linux swap / Solaris/dev/xvda3        785   36473-  35689- 286664983+  8e  Linux LVM                end: (c,h,s) expected (1023,254,63) found (633,35,42)/dev/xvda4          0       -       0          0    0  Empty...I am suprised about the /dev/xvda4 entry: There is no entry for it when listing the /dev/ directory, and other commands such as parted -l and lsblk don't reference that device either.What does sfdisk -l show with that /dev/xvda4 entry?
sfdisk lists an unknown device /dev/xvda4
partition;sfdisk
This disk appears to use the traditional PC partitioning type, also known as MBR. In the MBR format, there are exactly four primary partitions, no more, no less: the partition table in the first sector of the disk has four entries. An entry can be marked with type 0, meaning unused. fdisk -l (like many other tools) omits entries in the primary partition table that are unused. sfdisk -l lists those partitions and indicates that they're empty.