# fdisk /dev/sda

Command (m for help): d
No partition is defined yet!

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-1021, default 1): 
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-1021, default 1021): 
Using default value 1021

Command (m for help): o
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)