Resize partition size

root@server:/home/server# lsblk
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda    254:0    0  20G  0 disk
└─vda1 254:1    0  20G  0 part /

root@server:/home/server# df -ah
Filesystem      Size  Used Avail Use% Mounted on
rootfs          9.9G  3.7G  5.8G  39% /
sysfs              0     0     0    - /sys
proc               0     0     0    - /proc
udev             10M     0   10M   0% /dev
devpts             0     0     0    - /dev/pts
tmpfs           388M  136K  388M   1% /run
/dev/vda1       9.9G  3.7G  5.8G  39% /
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           775M     0  775M   0% /run/shm

Block device size = 20GB
Current partition size= 10GB

Auto resize partition will expand it same block device size

root@server:/home/server# resize2fs /dev/vda1
resize2fs 1.42.5 (29-Jul-2012)
Filesystem at /dev/vda1 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
Performing an on-line resize of /dev/vda1 to 5242624 (4k) blocks.
The filesystem on /dev/vda1 is now 5242624 blocks long.

root@serer:/home/server# df -ah
Filesystem      Size  Used Avail Use% Mounted on
rootfs           20G  3.7G   16G  20% /
sysfs              0     0     0    - /sys
proc               0     0     0    - /proc
udev             10M     0   10M   0% /dev
devpts             0     0     0    - /dev/pts
tmpfs           388M  136K  388M   1% /run
/dev/vda1        20G  3.7G   16G  20% /
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           775M     0  775M   0% /run/shm