Resize root partition of CentOS running on EC2

resize-centos-ec2.sh

# df -h  <<1>>

Filesystem      Size  Used Avail Use% Mounted on
/dev/xvda1      6.0G  2.0G  3.7G  35% / 
tmpfs            15G     0   15G   0% /dev/shm

# fdisk -l  <<2>>

Disk /dev/xvda: 21.5 GB, 21474836480 bytes
97 heads, 17 sectors/track, 25435 cylinders
Units = cylinders of 1649 * 512 = 844288 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0003b587

    Device Boot      Start         End      Blocks   Id  System
/dev/xvda1   *           2        7632     6291456   83  Linux

# fdisk /dev/xvda  <<3>>

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): u  <<4>>
Changing display/entry units to sectors

Command (m for help): p  <<5>>

Disk /dev/xvda: 21.5 GB, 21474836480 bytes
97 heads, 17 sectors/track, 25435 cylinders, total 41943040 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: 0x0003b587

    Device Boot      Start         End      Blocks   Id  System
/dev/xvda1   *        2048    12584959     6291456   83  Linux

Command (m for help): d  <<6>>
Selected partition 1

Command (m for help): n  <<7>>
Command action
   e   extended
   p   primary partition (1-4)
p  <<8>>
Partition number (1-4): 1  <<9>>
First sector (17-41943039, default 17): 2048  <<10>>
Last sector, +sectors or +size{K,M,G} (2048-41943039, default 41943039): <<11>>
Using default value 41943039

Command (m for help): p <<12>>

Disk /dev/xvda: 21.5 GB, 21474836480 bytes
97 heads, 17 sectors/track, 25435 cylinders, total 41943040 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: 0x0003b587

    Device Boot      Start         End      Blocks   Id  System
/dev/xvda1            2048    41943039    20970496   83  Linux

Command (m for help): a  <<13>>
Partition number (1-4): 1  <<14>>


Command (m for help): w  <<15>>
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

# reboot  <<16>>

<wait>

# df -h  <<17>>
Filesystem      Size  Used Avail Use% Mounted on
/dev/xvda1       20G  2.0G   17G  11% / 
tmpfs            15G     0   15G   0% /dev/shm

# resize2fs /dev/xvda1  <<18>>
resize2fs 1.41.12 (17-May-2010)
The filesystem is already 5242624 blocks long.  Nothing to do!