Using docker version 1.4.1, build 5bc2ff8-dirty on CoreOS 557.2.0 in EC2

# docker build .
Sending build context to Docker daemon   181 MB
Sending build context to Docker daemon
Step 0 : FROM fedora
INFO[0001] unexpected end of JSON input

This error betrays filesystem corruption, and probably contributed to CoreOS's decision to move away from BTRFS to overlayfs.

The issue is this file should contain a JSON blob for the daemon to read, but in this case it's empty:

# sudo ls -lasp /var/lib/docker/repositories-btrfs
0 -rw------- 1 root root    0 Feb 19 17:35 repositories-btrfs

The fix (to be run as root):

# [[ ! -s  /var/lib/docker/repositories-btrfs ]] && echo '{"Repositories":{}}' > /var/lib/docker/repositories-btrfs

If this is a production system a better solution would be to reallocate the containers to other hosts and tear the server down as there may be further issues with BTRFS - many users have reported strange behaviour.