(RaspberryPi2)ubuntu@localhost:~$ cat /run/initramfs/resize-writable.log
Re-reading the partition table failed.: Device or resource busy
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 27072511 27070464 12.9G 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.
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.
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: 135627/848640 files (0.0% non-contiguous), 577612/3383808 blocks
resize2fs 1.42.12 (29-Aug-2014)
Resizing the filesystem on /dev/sda1 to 3916544 (4k) blocks.
The filesystem on /dev/sda1 is now 3916544 (4k) blocks long.