(RaspberryPi2)ubuntu@localhost:~$ cat /run/initramfs/resize-writable.log
Checking that no-one is using this disk right now ... OK

Disk /dev/sda: 15 GiB, 16043212800 bytes, 31334400 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
Disklabel type: dos
Disk identifier: 0x0005e7c3

Old situation:

Device     Boot Start      End  Sectors  Size Id Type
/dev/sda1        2048 25006079 25004032 11.9G 83 Linux

/dev/sda1: 
New situation:

Device     Boot Start      End  Sectors Size Id Type
/dev/sda1        2048 31334399 31332352  15G 83 Linux

The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.
e2fsck 1.42.12 (29-Aug-2014)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
writable: 135627/783360 files (0.0% non-contiguous), 573436/3125504 blocks
/sbin/sfdisk: invalid option -- 'R'

Usage:
 sfdisk [options] <dev> [[-N] <part>]
 sfdisk [options] <command>

Display or manipulate a disk partition table.

Commands:
 -A, --activate <dev> [<part> ...] list or set bootable MBR partitions
 -d, --dump <dev>                  dump partition table (usable for later input)
 -g, --show-geometry [<dev> ...]   list geometry of all or specified devices
 -l, --list [<dev> ...]            list partitions of each device
 -s, --show-size [<dev> ...]       list sizes of all or specified devices
 -T, --list-types                  print the recognized types (see -X)
 -V, --verify                      test whether partitions seem correct

 --part-label <dev> <part> [<str>] print or change partition label
 --part-type <dev> <part> [<type>] print or change partition type
 --part-uuid <dev> <part> [<uuid>] print or change partition uuid
 --part-attrs <dev> <part> [<str>] print or change partition attributes

 <dev>                     device (usually disk) path
 <part>                    partition number
 <type>                    partition type, GUID for GPT, hex for MBR

Options:
 -a, --append              append partitions to existing partition table
 -b, --backup              backup partition table sectors (see -O)
     --bytes               print SIZE in bytes rather than in human readable format
 -f, --force               disable all consistency checking
     --color[=<when>]      colorize output (auto, always or never)
                             colors disabled by default
 -N, --partno <num>        specify partition number
 -n, --no-act              do everything except write to device
     --no-reread           do not check whether the device is in use
 -O, --backup-file <path>  override default backup file name
 -o, --output <list>       output columns
 -q, --quiet               suppress extra info messages
 -X, --label <name>        specify label type (dos, gpt, ...)
 -Y, --label-nested <name> specify nested label type (dos, bsd)

 -L, --Linux               deprecated, only for backward compatibility
 -u, --unit S              deprecated, only sector unit is supported

 -h, --help     display this help and exit
 -v, --version  output version information and exit

Available columns (for -o):
 gpt: Device Start End Sectors Size Type Type-UUID Attrs Name UUID
 dos: Device Start End Sectors Cylinders Size Type Id Attrs Boot End-C/H/S
      Start-C/H/S
 bsd: Slice Start End Sectors Cylinders Size Type Bsize Cpg Fsize
 sgi: Device Start End Sectors Cylinders Size Type Id Attrs
 sun: Device Start End Sectors Cylinders Size Type Id Flags

For more details see sfdisk(8).
resize2fs 1.42.12 (29-Aug-2014)
Please run 'e2fsck -f /dev/sda1' first.